Oil weight for track only car with a lot of cooling?
 

My BRZ is track only and engine oil temps rarely top 235, even in the summer. It just has a lot of cooling.

Factory oil is 0w-20. I'm running 300V X-40 (cold number varies based on what's available but I'm not real concerned about the cold number since it's track only and doesn't see significant time while cold).

Should I drop down to a 20 weight oil? or just a 30 weight? I think I'd like to run Mobil 1 extended performance (basically the regular synthetics with more additives).
I change the oil every 800-1000 miles (roughly, 10 hours).

If you're running 300v in 40 weight and it's working, why are you looking to change?

I see in your signature it's a full track car, caged, aero, etc... so you're probably ragging on it a good bit. 40 weight is probably a good choice. 300V is designed for track use vs street use.

I don't see any issue with what you're running right now.

Looking into what is used in spec 86 series is a good place to start. I recall seeing 60W used over in Australia if I recall correctly

I've run 40 year round, daily and track, in Canadian winters, with 265,000 trouble free kms. If anything, for a track only car, I'd go up to 50 or 60.

Spec rules require M1 5W-30.
However, I'm not sure how hot they are running. They can remove the AC condenser but the only rules for Cooling system is "A protective screen mounted in front of the radiator may be fitted, subject to the satisfaction of the TD and TM. "
So I guess bigger radiators and oil coolers are allowed, but I'd imagine for a spec series, they aren't running as much cooling as me as its wicking out more power. They probably want the oil 30-40 degrees hotter?

IDK, a big part of oil viscosity specification is bearing clearance. Given I'm only running about 20 degrees hotter than an OEM vehicle cruising down the highway, I'm concerned I'm running too thick. Then again, it went about 15-18k track miles on the last engine with 50 weight.

Maybe I'll just drop down to 30 weight for winter and 30 weight + a quart or two of 40 weight for the winter.

If your max oil temp is 235, then a 40w seems a bit thick to me. Personally, I'd look at a viscosity chart and aim to have a similar viscosity at track temps as a street car would on 0w-20.

I had an interesting discussion at PRI with the lead engineer for Driven Racing Oil... he was strongly in favor of keeping viscosity at OEM specs and adding cooling to keep oil temps in check.

FWIW, I run 5w-30 in a similar car. 2017 BRZ track car, full cage, lots of cooling.

Unfortunately, this is often easier said than done. The BRZ is an exception, and I'm not entirely sure why. It's not like it has some sort of massive air inlet.

I can't keep my spec Miata COOLANT temps below 210 on hot days (105 degree ambient). No idea what engine oil temps are, but I bet they're close to 300. And that car makes a ton less power.

My "intuition" agrees with him. Quote frankly, if you look at viscosity charts, whether its 20weight or 50 weight, they all have damn near the same viscosity after about 270 degrees. Almost none.

Ever change your oil when the car is hot? I thought 20 min of sitting around after getting off track in my Miata was good enough. Came out like water (and burned!)

Keeping temps cool is (based on intuition and no actual testing) the way to go. It doesn't appear that heavier oil does much of anything at 140C (~280F). Even at 245 (~120C) there isn't much difference.

https://penriteoil.com.au/assets/wiki_imgs/aSZ9QeGTRj

You know, looking at the chart, I may be wrong. 50weight oil has more viscosity at 140C than 20 weight at about 95 degrees. and 95 degrees C (about 205 F) is pretty unrealistic (and even undesirable) for engine oil.

Back to the BRZ, if you assume 20weight is the "correct" oil for it at 210 degrees (~100C), the closest oil to that viscosity at 115C (240F) is 30 weight oil. I think I'll run 30 weight from now on- which is easy because Mobil 1 makes 5-W30 extended performance (20k mile, more additives for more protection) for $27/5 quarts on amazon.
I think changing a bit more frequently (600 miles? 800 miles?) with this "cheap oil" is the way to go over 1000miles with the race oils and such.

Thoughts?
https://www.amazon.com/Mobil-120766-...27&sr=8-3&th=1

95C is perfectly fine for engine oil. Water does not need to "boil" to evaporate out of solution. That's a myth.

Your oil temps are similar to mine (I run slightly lower), on my turbo BRZ. I ran 5W30 300V with nary an issue.

I also had no issues with longer intervals on race oils. Remember, the good stuff is made for what you are doing, vs the cheaper stuff is made for street use.

Dead on. Water evaporates at temps much lower than boiling, and will evaporate out of oil!

I get it- water evaporates out off my bathroom floor at 70 degrees. It just does it much faster above boiling points. I agree that 95 is probably just fine.

I get it- water evaporates out off my bathroom floor at 70 degrees. It just does it much faster above boiling points. I agree that 95 is probably just fine.

IMO the right answer to the OP's question is used oil analysis. Running too thick would be a worry of mine given the tight bearing tolerances on modern engines, but the only way to know for sure is to analyze the oil to see what the bearing wear looks like.

Anything else is guessing and vibes. Nothing wrong with that, I use a vibes-based methodology for selecting my own motor oil weight (hint, it's the one that makes me stop thinking about motor oil weight). But I also accept it might be suboptimal and I'm prepared to live with the consequences.

What do tight tolerances have to do with anything?