Oil coolers and Heat exchangers - how do they compare?
Posted: June 13th, 2011, 4:59 pm
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. This one is from a Fiat 1.8 type 183 engine (Coupe, Barchetta, etc). Pretty much the same thing. 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
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. This one is from a Fiat 1.8 type 183 engine (Coupe, Barchetta, etc). Pretty much the same thing. 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