Correctly sizing an Oil Cooler core

[cantfindausername]

I've pretty much spec'd out an oil cooler setup for my car (Toyota MR2 Turbo - mk2).

I'm using a take off plate, to a remote filter plate, then to an oil-stat, and on to the cooler core.

I intend on placing the oil cooler in the drivers side vent panel, with a shroud to help air pass through the core. Alternatively I am considering placing the cooler lower in the engine bay, but with a 7.5" spal fan sucking the air through it.

However, one thing that has always been a concern to me is getting the correct size core for the application. With the oil-stat, the cooler won't be used before the temp reaches a certain temp (norm. 80 degrees C). Does the size of the core really just dictate how quick the temp would be normalised? can you fit a core that is too big or too small?

Main times for use would be serious track usage. I would guess that the stock cooler would suffice for road use.

Thanks, Ant

[Guy Croft]

I'd be using a Mocal 235mm long 15 row 1/2bsp there Ant, yes the stat will prevent over-cooling, temperature monitoring will show how effective it is when the stat is open, you want 85 deg C oil temp peak. If the temp climbs higher it can be due to inadequate airflow in or out, obviously the heat rejection depends on the relative temp between oil and surrounding area.

You might be better off with a Laminova oil-water heat exchanger. Here is one (below), you can see a coolant hose at one end (blue pipe) and the oil line coming in at 90 deg to the body. It puts more load on the radiator but it's much more compact and at least you don't need to worry about airflow.

GC

[cantfindausername]

Thanks Guy.

I think the approach I would take (now I know what size is recommended) will be to place the cooler as I initially though, in the side vent. This is the stock intercooler location so it should see good airflow. You can also get vent extensions to help pull air in. I will be measuring the oil temp from the output of the oil stat as this will monitor both stat open and stat closed temps. Beats my original idea of 2 gauges!

If the temps raise above 85degrees C in that location then I would look at the possibility of swapping the system out to an oil/water cooler. I have a feeling that the side vent will suffice though.

Ok, so now my question will move on to oil stat opening temp. You say that 85degrees C is a peak temp. I think I remember reading that I'd want it between 80 and 85 degrees for optimum performance. So would the stat open at 85 to flow the oil at that temp and bring it back below? Or would I want it to open a little sooner to give some flexibility?
I don't know how quickly these thing wil drop the temp.

Sorry for all the questions. Feel like I'm spamming the forum sometimes.

Everyones help is much appreciated,
Thanks
Ant

[Guy Croft]

Ant, hi

No, it's not spamming, it's 'knowledge transfer'! I take the strong view that if people want help they should get it. You should hear some of the phone calls I get. I don't mind helping if folk are polite and respectful - as I hope they find me of course.

My advice is test the stat in hot water and see what it does first of all,

G

[cantfindausername]

I figured this was the best place to ask my questions, and I'm glad I was correct.

Its a Mocal oil-stat that I'm looking at, and apparently you can specify the opening temp when you order it. I'm not sure to what precision this is, wether its every 5 degrees or something or hopefully every 1 degree, but I am going with the train of thought that I would go for around 82 degrees C. My thoughts are that when the temp is on the rise, it will be under the more extreme driving conditions (heavy use), and the turbo will be heating the oil before dumping it back into the sump. So by the time the oil being pumped is at 83 degrees, the cooler has time to start the cooling process. and regulate the temp, hopefully keeping it below 85 degrees.

[Guy Croft]

Yes, but I couldn't remark on the stat response times.

Broadly speaking from my own tests:

Below 75 deg C oil - power loss. Over 85 deg C oil - significant loss of oil pressure due to very high bleed down rate.

The latter varies according to the type of pump, those were done on an old-fashioned gear pump setup not crank driven internal-external crescent type. However no power gain noted over 85 deg C oil, so pretty sensitive results if you want optimum performance.

GC

[cantfindausername]

Looking into the stats a bit more, I think I would go for a normal "off the shelf" 80 degree stat.

I'm glad I have a spec now that I can work from down the road. I've already got a colder thermostat for the water system, and a big allyy sump, so I will monitor the temps from my remote filter plate for a while before fitting the oil cooler. I think if I'm running over 85degrees during fast road driving then I will need to add these additions to the set up.