Oil Cooling - An In-Depth Look
 

Hey guys, Eric from Verus Engineering here with some more cooling information gained from another lifetime. I hope you find some of this information beneficial and helpful :cheers: . It's a lot of verbiage and not a lot of pictures but if you're interested in cooling your oil, it's a great primer.

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This will be a discussion for oil cooling, in which there are two main ways to cool oil. Engine oil, transmission oil, hydraulic oil, power steering oil, differential oil, and even shock oil can and will need cooling. We will focus on engine oil cooling in this article but the two cooling methods apply to any heat rejection application, each with their positives and negatives. There is not a lot of information regarding either of these methods, the positives, the negatives, or why sometimes they work and other times they do not. We want to help bring light to this somewhat “black art” of cooling the engine oil. The information we are pulling from is gathered from over decades of experience as engineers for the world’s leading cooling system supplier for motorsports. Working with ALMS, to Tudor World Series, to NASCAR, IndyCar, F1 and Trophy Trucks, we have firsthand cooling experience at the pinnacle of multiple motorsports ventures.

Why does Engine oil heat up?
Engine oil serves two functions, to lubricate the engine and to remove heat from components that coolant cannot (IE under the piston, rods, crankshaft, cams, etc). As a result, engine oil heats up from friction and from internal combustion increasing the temperatures of the engine.

Typical Oil Temperatures:
Before diving into how to cool the oil, we feel it necessary to express the large misconception with oil temperature that seems rampant within the aftermarket community and even some race series. Engine oil temperature IS NOT engine coolant temperature. Coolant temperature in passenger cars is generally kept between 180-215 degrees Fahrenheit (85-100 Celsius) with some reaching up to 230 (110 C) safely. Some race series run coolant temperatures up to 260 degrees Fahrenheit (127 C); however, these engines are designed to handle this without distorting the block or cylinder head.
Engine oil, on the other hand, is expected to reach much higher temperatures! Anyone telling you otherwise should be questioned intently. Engine oil needs to reach *at least* 100 degrees C (212 degrees F) to burn off condensation (water) build up within the engine *which is perfectly normal and happens in every single engine*. If oil does not reach this temperature, the oil is unable to do its job to the best of its abilities and increased engine wear will result. It is a wise assumption to believe oil temperature sampling is anywhere between 85-95% of the hottest points in the engine, which means engine oil needs to be 90-100 degrees Celsius minimum to burn off condensation.

So what temperature can you run in your car/engine?
That is quite a loaded question and near impossible to answer without a lot of testing. We can give it our best shot, though. Most passenger cars are perfectly fine with oil temps up to 240-260 degrees F *utilizing the OEM recommended oil weight*, with some being designed to handle temps up to 315 Degrees F and higher! How can this be? Standard oil these days have flash temps well over 200 C (400 degrees F), and as long as there is sufficient oil pressure, the oil does not care what temperature it is at. That being said, utilizing an OEM engine and OEM clearances, we would suggest sticking to the OEM oil weight up to around (240-250 Deg. F). If it makes you feel safer, run a bit thicker oil but with thicker oil, comes increased engine wear at cooler temperatures and increased heat into the oil through more friction and less flow (flow and pressure are inverse, as you increase pressure, you decrease flow). Above this temperature, we would recommend increasing the hot temperature weight to ensure sufficient oil pressure. Due to each engine having different optimum operating conditions, we cannot recommend a pressure/RPM to shoot for.

How can we get rid of this heat?
There are two ways to reduce the heat that is transferred into the oil. Oil to water (or O2W for short) transfers the oil’s heat into the engine’s coolant system through a unit typically called a heat exchanger. Another route is oil to air (or O2A for short), which transfers the oil’s heat through an exchange with airflow through a unit typically called an oil cooler. Both of these systems can be implemented incorrectly and work poorly, both of these systems can be implemented correctly and work great. Individual applications tend to favor a certain method over the other but ultimately that decision should be an end user choice as each person has his or her own goals, objectives, and ideals. Both can and will work great when properly executed.

Air to Oil (A2O) Oil Coolers:
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These are the units you see on the front of cars and are generally square in shape and not that large. These use ambient air to cool the engine oil which flows through small tubes with internal turbulators, working very similar to radiators but with increased cooling directed at the slower flowing, high-pressure oil. These units are easy to implement across a wide range of applications as they only require application specific bracketry and lines. Overall, they are generally quite effective but have some pitfalls. The units are small enough to be placed in various places throughout the cooling stack, be it in front of the radiator, behind the radiator, or in front of the front wheels. Below are listed some positives and negatives for this type of cooler.

Positives:
-Extremely simple design and operating principle
-Easy to implement on a wide range of applications
-Costs are generally reasonable
-Large delta T (change in temperature) for increased heat rejection
-Wide range of possible locations for mounting
Negatives:
-Performance is highly dependent on airflow.
-Airflow is highly dependent on coolant stack pressure differential, which increases from adding another heat exchanger (engine oil cooler) to the stack.
-With higher coolant stack pressure, flow through ALL UNITS is decreased.
-You can see a reduction in radiator performance from adding an oil cooler.
-When placed in front of other heat exchangers (radiator), hotter air is now reaching the radiator, reducing efficiency even further/
-Pinhole leaks from rocks are possible.
-Highly recommended to run a thermostat on the engine oil cooler to reach operating temperatures quicker, increasing costs.
-Very easy to over-cool the engine oil with an improperly setup system.
-Lines are typically long and increase pressure drop of the system.

Oil to Water (O2W) oil coolers:

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These are the units generally found on OE applications where engine oil cooling is necessary. Utilizing the engine’s coolant to heat the oil quickly during initial start and to cool the oil when the engine oil reaches operating temperature, this system is quite ingenious and reduces cold start wear and hot running wear. However, it comes with its own pitfalls of course, just like nearly all designs, compromises are necessary. Typically they utilize a portion of the engine’s coolant flow which surrounds internal turbulated tubes, extremely similar in design to the O2A tubes, which the oil flows through. These can be constructed from stainless steel or aluminum. Through this interaction, engine oil temperature is reduced and coolant temperature is increased. Below are positives and negatives regarding this style of engine oil cooling.

Positives:
-Ability to be packaged in small spaces
-Ability to be packaged without any airflow consideration
-Heats up oil when beneficial and cools oil when beneficial automatically by design
-Does not require a thermostat
-Very low chance of leaking
-Great at regulating an adequate temperate for proper oil operation
-Does NOT add a unit to the cooling stack, thereby decreasing delta P for the cooling stack as compared to O2A
Negatives:
-These systems are generally more expensive as they are typically application specific.
-Inputting more heat into an already taxed coolant system can lead to overheating.
-Due to the lack of delta T, engine oil temperature will likely be higher than O2A counterparts unless airflow is an issue.
-Possibility to leak oil into the coolant system or coolant into the oil system. Extremely rare for this to happen though.

Conclusion:
We have witnessed *both styles* successfully used in nearly every motorsports venue. That being said, if ultimate oil cooling is required, an O2A is still recommended though typically much larger than what is commonplace in the aftermarket community and *behind* the radiator (see below photo). For those that drive their cars on a normal basis, off track, we would strongly urge you to look into O2W units as they offer a lot of positives geared towards daily driving. When airflow is hard to come by, we would also recommend looking into O2W as reducing airflow through the radiator can be very detrimental. Systems have to be looked at as a whole and not just single entities.
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Regardless of which style you utilize, please keep in mind that temperatures below 100 degrees C are not recommended and can actually be detrimental to engine health in the long run.

As always, please let us know if you have any questions and we will do our best to answer.

Thanks,
Eric

Thanks Eric. People like you are a huge asset to a car community. Many props and lots of respect!

Thanks, I appreciate it. Thanks for asking me to write it!

I have one other cooling article regarding high performance vs. low profile fan performance. If there are any other good topics we should look into for blog/forum posts, I'm all ears as well :thumbsup: .

Thanks,
Eric

:thanks:

Every time I read in a forum that someone got an oil cooler and a low temp thermostat I want to smack them :slap:

I wish just this quote was stickied here in this forum somewhere. Hot is good!

Most of these cars are used for daily use and not track only duty, which is the scary thing to me.

:party0030: :cheers:

Thanks,
Eric

Yeh getting a nice oil cooler is great bling but for a DD it's not needed. I've been eying the Subaru O2W system that many on here have used with success. I'll track the car in the sping/summer months a few times a month. To me no need to get a fancy expensive cooler. Waste of time and $$

our main issue on 86\brz seems to be keeping suffient oil pressure at high rpm when oil is hot and its viscosity less.

While the modern synthetic oils are cabable of handling high temps like 290f, our issue seems to be keeping suffient oil pressure once oil temps get past 230f or so especially if your staying with 0w20 oils.

If you not seeing temps over say 220 then 0w20 seems the choice, if your going north of that like 230 then a W30 oil may be better suited, unless your going to keep the temps under controll with a better oil cooler

your thoughts @VeloxEric ?

I use the OEM Forester unit and am quite happy with it.

I wrote the article to encompass all vehicles and to be a good primer for any car/track car owner, not specifically for the FA20. I agree with a lot of your statements though for the FA20.

Thanks,
Eric

Did you use the throttle body method or the actual forester method (with the extra piping and such)?

I started another informative thread on low profile vs. high performance (profile) fans for those interested. Fans are often overlooked but quite crucial to DD performance. http://www.ft86club.com/forums/showthread.php?t=114585

I used a modified Forester method. I accidentally had it hooked up backward and to my surprise, I had 2-3 degrees C hotter oil when it was hooked up backward. I'm sure as you started pushing the system (I only used it for a week that way, very early on in the build), the difference would reduce as the delta between oil and water increased.

I go into a little detail in the shop car build thread in this post on fluid flow: http://www.ft86club.com/forums/showp...0&postcount=43

Basically, routing goes from right after the t-stat (coolest water, coming from the cool side of the radiator), and goes to the oil cooler. From the oil cooler, my routing goes through the turbo. From the turbo, water goes back to the heater hose which used to go to the TB. I capped a TB hose on the top of the engine and the TB no longer sees coolant.

Thanks,
Eric

As a guy who DD his car mostly, and probably hit the track 1-3 times every summer.

Would you say its necessary to get an oil cooler?

Or should i switch just to 30w for my track day? then switch back to oem standard after the track day is finished.

Thanks!

Personally, I think you're the perfect person for the OEM Forester, or similar, oil to water oil cooler. It heats the oil up for daily use (good thing), it cools the oil for track abuse (good thing).

I wouldn't even personally worry about changing your oil. If you keep oil temps under 230-240, I *believe* 20 weight is perfectly acceptable for an NA car. I'm pretty sure I've seen a few guys track above this for seasons without issues. And if you want the added security of a heavier weight, you have an oil heater which heats the oil up to operating temps faster!

Thanks,
Eric

Eric (and many others) know more about this than i do. But to be honest, dont buy an oil cooler till you need one. Next time you hit your AX/HPDE, monitor your oil temps to see if you are very high. As you progress or get faster you may require one. But, dont add one till you need one. If your HPDE keeps getting cut short due to heat soak and high oil temps, then you need an oil cooler. But I dont see the reason to buy one just cause you hit the track a couple of time. Its just another place to check for leaks anyway.

Plus the car wont really let you hurt it. It will start retarding things if the temps go too north of 300*F.

Thanks for the useful input,

Im not that type of hardcore track rat who stay on for 20-30 minutes per session, I usually do 1-2 warm up then 2 hot laps and 1 cool down lap. So i guess i wouldn't even need an oil cooler in my situation, considered the cost, installation labour and potential leaking issue after installed.