Oil coolers and Heat exchangers - how do they compare?

Road-race engines and ancillaries - general discussion
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TomLouwrier
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Oil coolers and Heat exchangers - how do they compare?

Post by TomLouwrier »

hi guys

Many of us find they need to get the engine's oil temperature down. The usual means for that is to fit an oil cooler (oil-air heat exchanger) somewhere in the nose and feed engine oil to it from a sandwich plate-type take off under the filter, and back again.
The capacity for this cooler needs to be chosen for maximum power and less than optimal air flow, so that the oil will not get too hot under any working condition.

In true competition this unit can be ungoverned if the lines and radiator size are chosen well and if the engine will be run on a more or less constant power level. In short: a static situation. We rarely have that.
When not running at full power the oil cooler will have too much capacity, over-cooling the oil so it stays too thick and will not boil off water and petrol that is contaminating the oil.
While the engine is not fully warm yet, the radiator is already taking heat from the oil anyway, making the warming up phase longer than needed.
So in many cases you need a thermostat between the engine and the oil-radiator. It is always necessary to properly size the cooler, too small and you still have the oil temp too high, too large and the oil temp drops too low and/or the thermostat gets 'nervous' (outside it's proper working range).


Personally I'm not the greatest fan of these coolers; I'v seen them get damaged by stones, crack from vibrations, mounted in the wrong place (which is no fault of the cooler of course) because of lack of space, etc. They tend to get dirty and blocked up. If the oil lines get damaged, your engine throws its oil out fast and you may likely lose it.
In the industry (process, oil and chemicals) heat exchangers are a well known way of transferring heat. You cool one medium and heat up the other, depending on what you need. It may be oil-water, water-water, oil-gas (air) or something as exotic as sodium-steam.

Back in the mid eighties VW started adding cute little heat exchangers to their turbo-diesels. Because they built them in very large numbers they needed something compact, cheap, efficient and easily fitted to existing engines and car bodies. They came up with this aluminium device.
It is sandwiched between the block and the oil filter like a remote oil cooler adapter plate. Two water hoses hook it up to the existing cooling system.
VAG water oil heat exchangers.JPG
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VW engine with sandwich type water-oil heat exchanger.jpg
VW engine with sandwich type water-oil heat exchanger.jpg (186.38 KiB) Viewed 18218 times
This one is from a Fiat 1.8 type 183 engine (Coupe, Barchetta, etc). Pretty much the same thing.
fiat 183 oil water heat exchanger.jpg
fiat 183 oil water heat exchanger.jpg (34 KiB) Viewed 18218 times
Fiat type 183 1.8 16v.JPG
Fiat type 183 1.8 16v.JPG (60.72 KiB) Viewed 18218 times
Looking at cars and bikes today I see these devices in practically all engines, all brands.
Part of this will be because engines generate more power while noses have to get lower and grills smaller because of aerodynamics. The excess heat has to be taken out of the engine and out of the engine bay.
Also engines must run hotter for fuel efficiency but not too hot because then the NOx emissions get too high. The thermal working range is smaller. This is the main reason why air cooled engines died out: not enough capacity and not enough control, especially in the cylinder head.
The final big reason is to shorten the warm up cycle, because that is when engines use most fuel and emit most 'unwanted' stuff. The sooner it's warmed up, the better. (Good news for us: almost all wear happens in the first 5-10 minutes of driving, during warm up. The sooner it's warmed up, the better (again).)


Broadly speaking, water-oil heat exchangers come in three sorts:
- integrated; one half of the unit is mounted on/in the engine and the other half is fed by hoses.
This is very car specific and out of scope for us because you can not retro-fit or upgrade it.
- sandwich; like the VAG units above.
These were meant as upgrade / retro-fit and can easily be fitted to any engine that never had originally.
- remote; very much like a regular oil cooler with sandwich pick up (or sometimes direct lines from the block)
These are sold as after-market products by well known companies like Mocal / Laminova and Aeroquip. They need 4 hoses: 2x water and 2x oil.


I would like to find out
- when would you choose a 'classic' oil cooler, and when an oil-water heat exchanger? Why?
- what sort of capacity do these oil-water devices have, and how does that compare to oil-air radiators that are usually measured in rows and cm's length?
- what would be a good position to plumb them in the water circuit, depending on the use of the car?

How are your experiences? Has anyone tried either sort or both?
To start off discussion, I'll set up a list of pro's and con's. This is my view on things, correct me if I'm wrong.


Air-oil ('classic' oil cooler)
Pro's
- easily available, many bolt-on kits
- proven capacities and solutions

Con's
- vulnerable, could be overcome with good materials and installation
- sandwich pick jup may give issues with ground clearance (oil filter sitting lower), may need remote filter
- need own thermostat unless only running at constant high output


Water-oil (heat exchanger)
Pro's
- faster heat up
- just one thermostat in the water circuit
- pretty stable relation between water and oil temperature
- cannot over-cool the oil
- easily installed (sandwich type), or not more difficult than air-oil (remote type)
- clean installation, just 2 extra water hoses (sandwich type)

Con's
- risk of mixing water and oil when seals leak
- risk of failing, mixing water and oil, due to corrosion (must use proper 'anti freeze', not all tracks and racing classes allow that)
- sandwich type makes a nice Christmas tree, could be vulnerable due to vibration
- sandwich type may give issues with ground clearance (oil filter sitting lower), may need remote filter


Position in cooling system
Basically, there are 3 positions where you can fit the water-oil heat exchanger:

- in the bypass circuit
This is placing the unit before the water thermostat, either tee'd parallel to the interior heater of simply instead of it. This is the usual way in road cars.
When warming up, the first warm water to come from the head will help to heat the oil. Shorter warm up times.
When hot, the oil will give off heat to the water, to be taken to the engine, then to the radiator and dumped in the air there.
If the device has too small a capacity, the oil can still get too hot. Fit a larger one.
If the device is too large, the oil will not get cooler than the water temperature because the heat transfer then stops. This is less than ideal, but how many are running with oil temperatures that are often / usually way too low?

- in the main circuit, before the radiator
When thermostat closed:
no water flowing so no cooling effect, no heating either
When thermostat opened:
hot water-hot oil, so less heat transfer from oil to water. need larger exchanger
heat from oil goes to radiator and must be dumped in the air there.

- in the main circuit, after the radiator
When thermostat closed:
no water flowing so no cooling effect, no heating either
When thermostat opened:
cool water-hot oil, so more heat transfer from oil to water. can do with smaller exchanger
heat from oil goes back to engine with the water, then to the radiator and must be dumped in the air there.

Whatever you do, the amount of heat you try to take out of the engine and out of the engine bay stays the same. Energy can not be 'destroyed', only transferred.
So moving heat from the oil to the water will put extra load on your cooling system. The oil temperature may go down only to see the water temperature go up. You may need to increase the capacity of your existing cooling by fitting a larger/better radiator or improving the air flow out of the engine bay.


I intend to fit one of these sandwich type heat exchangers to all my engines that don't have one yet. They will be in the bypass ciruit, parallel to the interior heater. Main reasons are:
- faster heat up, lower maximum temperature
- fixed relation water-oil temperature
- easy retrofit
- clean looks

Your opinions and experiences please?
If possible, add numbers like engine power, water and oil temperatures, before and after, etc etc.

regards
Tom
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Re: Oil coolers and Heat exchangers - how do they compare?

Post by TR-Spider »

Tom

interessting topic and nicely written up.
Just some short comments:
I think the modern car sandwitch heat exchangers serve primarily the purpose to heat up the oil quickly, in order to reduce the emissions during cold running. The oil cooling is most likely a "side effect".
When you look at the oil/water heat exchangers you can buy as oilcoolers, you note that the water pipe diameter and thus water massflow is much bigger.
Heat transfer is (in first aproximation) proportional to the massflow and the temperature difference between hot and cold media (and of course the heat pickup capacity specific to the media).
So probably the sandwitch heat exchangers would be a nice extension to a oil cooling system which only needs a little extra cooling capacity?

Thomas
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Re: Oil coolers and Heat exchangers - how do they compare?

Post by TS131Volumex »

Thanks Tom , woken me up to an interesting issue , think I might be needing to make ( small ? ) changes to my propossed laminova positioning/hossing once forums responses return . If the weather is good I shall post some pics/diagrams over the weekend . Am I right in thinking the fast oil warm up is a possitive for reducing initial engine ware ? If one is controlled on warm up procedure , no load until warm etc , is this as important ?
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Re: Oil coolers and Heat exchangers - how do they compare?

Post by WhizzMan »

TR-Spider wrote:Tom

interessting topic and nicely written up.
Just some short comments:
I think the modern car sandwitch heat exchangers serve primarily the purpose to heat up the oil quickly, in order to reduce the emissions during cold running. The oil cooling is most likely a "side effect".
I doubt it's just a side effect. Bear in mind that flow in the engine bay, and most notably around the block, is much more restricted with the bottom plates and plastic shrouds and enclosures modern cars have. I daily drive the Fiat 183 derived Alfa engines and all need this heat exchanger. I had this itty-bitty 1.4TS I got for scrap that I decided to fix up again. Some previous owner had shorted out the heat exchanger water piping and just omitted the exchanger, possibly after a leak. The result was severe damage to the exhaust cam and I had to clean out the entire engine to get the debris out. This 145 doesn't even come with a tray under the engine bay. This is an almost 20 year old design of the car and engine. Thermal design of modern engines totally relies on the radiator and most sumps don't have large surface area any more.
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Re: Oil coolers and Heat exchangers - how do they compare?

Post by Guy Croft »

Since the topic begins by exploring bolt-on OE type coolers and since this is a race engine website I want to remark that if you want your oil filter housing to look like a 'Xmas tree' they are 'just the job'.

This isn't just aesthetics. Remoting the filter makes it easier to get to and its also easier to check for leaks.



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model of a 'clean' engine bay
model of a 'clean' engine bay
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fine example of a cluttered engine bay
fine example of a cluttered engine bay
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TomLouwrier
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Re: Oil coolers and Heat exchangers - how do they compare?

Post by TomLouwrier »

hi guys, thanks for the responses.

@Guy
Don't get me wrong, I'm not trying to promote second hand OEM parts as "the cheapskate way to a wannabe racing engine". To make this clear, I started this thread in the Road section, mentioned the Laminova and Aeroquip versions, and listed the Xmas-tree aspect as a 'contra'.

It's the difference between the two sorts of heat exchange that is under discussion here, efficiency and effectiveness.
What bothers me is that these oil-water things have been commonplace for 25 years, but when I search the net for information I find nothing much more concrete than "it's a miracle" or "it's poor 'cause it's not a proper racing part". None of which are a great help.
I haven't found much usable information on the 'racing grade' varieties either, neither in the tech docs nor in forums.

About the Xmas tree: I do agree, but it's not worse than a pick up plate for a remote cooler, is it? And of course you can still fit a remote filter and close up with a blanking plate. Now if you would stack a heat exchanger, a pick up for a remote *and* a filter, then you would win the 'bodge of the year' award indeed.

Not everything OEM should be suspected as 'not fit for racing duty', if it's a good part then that matters. All our engines -entire cars actually- once left the factory as a very big assembly of OE components.
Whether I fit a sub-standard part to my engine and wreck it is of course entirely on my head and nobody else's. If that happens I will report back here so that we all learn, and apologize.

@WhizzMan
That confirms some of the anecdotes I came across in VAG-land. They do cool the oil as well as heat it, depending on the temperature of both fluids.

@Matt
Almost all wear takes place in the warm up phase. How you treat the engine may limit that wear or make it unnecessarily worse (I hate people who hammer a cold engine), but the sooner your engine is fully warmed up, the better. Current doctrine is: start it and just drive off with moderate speed and acceleration. Warming up by letting the engine idle for 10 minutes or more just makes it take longer. It also means more petrol getting into the oil.

So you're building with one of the remote water-oil units? Please post your layout and component specs, we may elect you as guinea pig... ;-)

@Thomas
Yep, mass flow, surface area, wall material and thickness, temperature difference between media and of course the coefficient that is specific for exchange between the two media used. Between oil and water is quite a different number than between air and water or air and oil. You get it.

Having a heat exchanger in the bypass circuit (or 'small circuit' in German terms) seems to indicate a main purpose of heating up the oil faster. Still the cooling effect must not be overlooked. See WhizzMan's post.
The hotter the oil, the more energy will be transferred into the water. I have read stories of oil temps between 120-150 Celsius being considered common and not dangerous or bad if you use synthetic. Brrrr!
Putting the exchanger in the main ('big') circuit gives much more flow of the water, and thus more cooling (if that is at all needed). There will be no effect on the heating up phase, since the thermostat will keep water from going out there while still cold.


We could set up a rough calculation of the amount of heat taken out of the oil, if we know
- amount of oil
- amount of water
- temperature before (both oil and water)
- temperature after (both oil and water)
With a given
- engine power
- engine use (it won't be going full out all the time)
it should be quite do-able to get some realistic numbers.

My Coupé doesn't have an oil thermometer, and as far as I know they dropped that with the introduction of the 183 engine (1.8 16v) that has a heat exchanger on board. Does that mean Fiat thought oil temperature is something no longer to be measured separately?
I might just clamp the water hose on it and see what effect that has on the water temp, but right now my only indication would be the dashboard instrument.
And considering it's summer and my engine is starting to get pretty low oil pressure at hot idle, I'd rather avoid the risk of damage.

Guy, would you and/or Keith McMullen be so good to do a small experiment like this when you have an engine on the dyno? Rig it up, run it with a heat exchanger plumbed in, and then with it blocked off? You would certainly notice the difference.
If anyone is in a position to do some valid testing, it would be you two.


I shall try to tackle it another way: by the dimensions of those units and the number of plates it's possible to make a reasonable estimate of the total surface area. The material is alloy. Let's say water is 75 degrees Celsius, oil is 85 degrees.
Now we need to estimate oil and water flow through the unit and we'll have an idea of what is going on.
Oil is full flow, what sort of volume are we speaking?
The water inlets are 12-15 mm. Really, I have no idea what flow or pressure drop we would have.

The same can be done for an air-oil cooler.
Oil temp 85 degrees, full flow.
Air temp 25 (ambient, summer), flow: 75 km/h (average?), surface area and drag to be determined. I'll see if I can dig up some indications of oil cooler size versus nominal engine power from tech docs.


Looking forward to your reactions!


regards
Tom
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Re: Oil coolers and Heat exchangers - how do they compare?

Post by Guy Croft »

OK Tom but don't try and re-invent the wheel.

About the Xmas tree: I do agree, but it's not worse than a pick up plate for a remote cooler, is it? And of course you can still fit a remote filter and close up with a blanking plate. Now if you would stack a heat exchanger, a pick up for a remote *and* a filter, then you would win the 'bodge of the year' award indeed.

I'm sorry but I have no idea what you are talking about here. A take off for a remote cooler (as you call it) will usually be a small and compact thing with merely in and out unions. There are numerous types aval incl my own. A sandwich type cooler will generally never be that as it has the oil filter under it and sites the filter in what is invariably the least accessible location on the engine.

The calculations for determination of cooling capacity on an air/oil system are identical in principle to those for intercoolers and there are plenty of complex examples on the net which cover important things like Reynolds number if you want to try them those which I have examined are correct.

The theoretical issue of whether this or that is better (judged here) is immaterial in my expert view when judged against the proven effectiveness in practice (or otherwise) and careful examination of running conditions temp/power/pressure and post-test strip & examination and considerations of wear and longevity under real conditions are frankly all that counts.

No offence but I have spent years coaching people on race grade oil system layouts and people depend on me for proven advice. I shall not be revamping my concepts because of this thread or any other. I use a well-defined system that is robust and fit-for-duty ie: race proven. I say this because some forums are notorious for building up a 'head of steam' where novices become expert on all things and when my phone rings, people who have never wielded anything heavier than a pencil in their lives tell me how the world works. If I find this thread going that way I shall be forced to lock it.

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RFH & Acc layout dwg only.doc
Simple and robust layout that is used on almost every wet sump race car.
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GC take off plate as used in the above layout.
GC take off plate as used in the above layout.
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Re: Oil coolers and Heat exchangers - how do they compare?

Post by andy wright »

Evening All,
Interesting discussion. Calculating heat transfer rates is a lovely thing to do to wile away these long summer evenings. Heat transfer looks simple enough at one level because, essentially, one is just using Newton's law of cooling; that is, rate of flow of heat is proportional to the temperature gradient, with the constants including area and thermal conductivity. So far then , nothing to make one poorly. Snag is that the heat source (engine) changes its output more rapidly than a coalition governments policies. That means that, in practice, it is almost impossible to calculate the relavant factors to model all conditions.The consequence is that a solution is achieved empirically, ie by experiment, and experiments are usually conducted under realistic conditions. For motor vehicle manufactures, I suspect it is via thousands of miles of road testing, and for competition, via the racetrack.
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Re: Oil coolers and Heat exchangers - how do they compare?

Post by WhizzMan »

From what I've been taught about modern oils, the base oil will not deteriorate at 120-150 degrees Celsius. That being said, the additives that make it multi-grade, will start to break up at about 110 degrees or above. The hotter, the faster the break up. The additives are very long molecules of polymers, also known as "plastic". If those additives fall apart, your nice 10W60 will eventually turn into 10W10. Usually it won't get that degraded, because your engine will have seized before that point. It's hard to tell this has happened by smelling or feeling cold oil. You need to do viscosity tests at working temperature before the problem shows itself.

The 16V twinsparks based on the Fiat 183 actually do have temperature sensors in the 1.8 and 2.0 versions in the Alfa 155. They usually display oil below 70 degrees on the road, but it quickly goes up when the car is being driven in anger. Personally, I'd like to see them get warmer and get there quicker. Accessibility on the 16V twinspark isn't a problem and seeing Toms pictures, I may want to experiment with a larger heat exchanger from a VW.

Regarding the xmas-tree problem. I've heard of a few cases where the heat exchanger came undone on the Alfa engines. Often because mechanics did not bother to re-torque the center part as part of the replacing of the oil filter. That's the only conclusion you could come to, given that almost all occurred shortly after a service. I have been warned by these stories and I always torque it up if I replace an oil filter on those engines.

Guy does have a point here, his setup works and there are almost infinitely more ways to do oil wrong than there are to do it right. If someone here can show examples of racing setups, that have proven themselves that use heat exchangers, I for one would love to see them and learn.
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Re: Oil coolers and Heat exchangers - how do they compare?

Post by Guy Croft »

You have to be careful with high oil temperatures. My dyno tests in the 90s indicated that there was no power gain over 85 deg C and power loss from 65 deg C or lower. An oil will of course not reject unwanted contaminants (water, gasoline) properly if its too cold but 85 deg C is plenty high enough to do that. As the oil temp climbs the oil viscosity drops and the bleed-down rate at the bearings increases ( I explained this at length in my new book BTW) and if the pump delivery is inadequate the oil film will not be sustained and the crank and bearing surfaces will start to deteriorate; under high load the bearings can rupture. Crescent (crank nose driven) and rotor (dry-sump) type pumps have much higher flowrates than old-fashioned TC type gear pumps and thus offer less risk at high oil temperatures.

I remember driving a fast-road VW Scirroco 8V that I had prepped where the oil cooler was too small (or at least ineffective at full power) and the oil pressure halved between 80 deg and 110 deg C. That was quite simply down to the pump being unable to keep up the pressure in the galleries and bearing clearances with the much thinner oil. If it falls below a critical 55psi under any load then you're going to wreck the engine.

As far as heat exchangers external to the engine (what Tom sensibly calls 'remote') I have used and recommended them quite widely.

The effectiveness of any system to control oil temperature depends entirely on underhood airflow and this is as much misunderstood as ever. Most engine bay architectures are poorly-suited to the needs of a more powerful engine (even lightly tuned), they do what they have to satisfactorily with the OE engine and no more than that and who says there is anything wrong with that. Moreover OE engines are deliberately run much hotter than ours (or should I say 'than ours should be'..) for reasons that don't concern us here. I know how alterations should be done and to an extent have been recently coaching Miroslaw on this. It would be heartening to see a site member devote some pen-time to this.

I used a Laminova oil-water heat exchanger from Think Automotive for the first time in the Lotus Lada (though I had previously used other types too) and it worked like a dream. It really did. Mind you I had supervised everything under the engine bay during the build of that car at Hethel all those years ago.

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Re: Oil coolers and Heat exchangers - how do they compare?

Post by turbofiat »

I would like to know if an oil cooler is a must on a turbocharged engine. I ran one on my Spider after turbocharging it in 1998 because I thought it was nessessary. Just like I thought it was nessessary to run Mobil 1 synthetic to protect the turbo. Since adding A/C I have removed my oil cooler and switched back to Castrol 10W30 years ago after engine leaks and recently started using Shell Rotella 15W40.

You might say removing an oil cooler just for the sake of an A/C condensor sounds like sacrifciing engine life for comfort however I have yet to install an oil cooler on my turbocharged Yugo 1500 and have put almost the same amount of miles on it as I have my Spider and have yet to suffer an engine failure.

I did aim one of those heat pen guns at the oil pan immedietly after pulling into my garage and the oil pan temperature measure 230F/110C. I have read 300F/150 is the danger zone.

This is not to say that the oil does not heat up when the engine is under boost for no more than 5 seconds. But the engine coolant temperature never goes up either and both cars have stock cooling systems except for SPAL radiator fans.

I did suffer a turbo failure on my Spider and the jury is still out on that way. I shaft seemed to have stretched causing the shaft to wobble and leak oil into the compressor when the oil was cold. I sent it off to be rebuilt and the shop said something went wrong with the oil and reunied the bearings yet could not say what actually happened to the oil other than it was caused by an additive which I don't add to my engine oil.

I personally think this was caused by years of not running a blow off valve and the constant pressure spikes pushing against the compressor wheel either loosened the nut or caused ths shaft to stretch. I have a BOV on my Yugo. The main reason I installed it was to prevent the float valve from being blown off it's seat from fuel pressure spikes and it has worked well.

I did not think a BOV was nessessary when running 7 lbs of boost but I believe it is a nessessary piece of equiptment on any turbocharged engine.

Sorry to mix oil coolers and blow off valves in the same thread, just thought it was worth mentioning.
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Re: Oil coolers and Heat exchangers - how do they compare?

Post by WhizzMan »

Turbos tend to be cooled by the oil a lot as well, even the "water cooled" ones. That means a lot of heat transfer to the oil and subsequently, very hot oil in the exit pipe of the turbo. If your oil can't take that, it will chemically decompose and leave black carbon debris in the hot parts, especially if you switch the car off with super hot turbo and not let it cool down first. Therefor, you'd be better off with oil that is more resilient to higher temperatures.

Also, since the oil will get heated to high temperatures in the turbo, you will need to replace the oil more often. Sure, in the sump the oil may be as "cool" as 110 degrees C, but most of that oil would not have just traveled through the turbo, so it is very well possible that the oil coming out of the turbo is over 150 degrees C. If the rest of your engine would heat up the oil to 80 degrees C, just the turbo return feed would be the reason it's 30 degrees hotter. Even if the turbo "only" gets 20% of the feed, that's a lot of heat energy coming from such a small part of the flow.

If your engine oil is 110 degrees C, you'd want to be cooling it in some way or form, regardless off the fuel, turbo or NA, two or four stroke. 110 will make it deteriorate much faster than a healthy 70-90 degrees C. I wouldn't want to run more than a few thousand kilometers between oil changes, at max, with temperatures like that.

Wear on your engine may come gradually. Even when you "abuse" it with less care for the oil than possible, it may still last longer than you'd expect if you read all the warnings and horror anecdotes. That doesn't mean those stories are false. It most likely means that your engine would last even longer if you were to get your oil setup done better than you have it now. "I haven't changed oil in three years and my car is still running fine" stories are common. However, once you pull engines that had that sort of treatment apart, you usually find it is much more work to rebuild them properly than engines that had regular maintenance.
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