AP2 S2000 race car German Castrol UOA

[Grant]

GC doesn't look like a good choice for tracked S2000s. The oil in my race car (actually a Miata with a F22C1 swap) sheared down to a 20-weight (9.24 cSt @ 100C) after only 4.5 hours of use. The (stock) shortblock has 5.5 hours on it, with the first hour being on a dino oil. The head has 60k+ miles.

I think I will switch to Redline. I was hoping to be able to stick with an oil I could purchase locally. I'm not sure if I should be using a 40 or 50 weight, so I think I'll email Redline and ask.

Main bearing clearances are listed as 0.0007" to 0.0016", with a limit of 0.0020".

Rod bearing clearances are listed as 0.0012" to 0.0020", with a limit of 0.0024".

With the stock oil cooler the highest oil temp I've seen was 255F. It is most often 245F.

For reference, new GC has a viscosity of 12.1 cst @ 100C (30-weight oils are anywhere from 9.30 to 12.49 cst @ 100C; 5w30 M1 starts at 11.3).

 

[d00df00d]

A new-ish bottom end, race use, and huge temps? Considering that, I'd say GC did pretty well.

Moreover, judging by the flash point in combination with the viscosity, you probably have considerable fuel dilution despite what Blacksone's measurement says.

245º - 255º F is pretty hot. However, considering that the car was made to run on dino, you're probably fine with an xw-30 synthetic. If you do decide to use a thicker oil, don't go thicker than xw-40 IMO.

 

[d00df00d]

Originally Posted By: d00df00d
I'd say GC did pretty well.

Sorry... What I meant to say is that there's no reason to suspect that GC did poorly.

 

[Grant]

Does a new bottom end tend to shear an oil more quickly than an older one? I'd never thought about that.

What else can lower the flash point other than fuel dilution? Mine appears to be down 90F. A friend of mine had a similar UOA with 50wt Redline: low viscosity, 100F lower flash temperature but no indicated dilution.

 

[d00df00d]

Originally Posted By: Grant
Does a new bottom end tend to shear an oil more quickly than an older one? I'd never thought about that.

No, but it will be a bigger source of wear metals until it finishes breaking in. That's what I was talking about: I don't think your wear metal numbers seem particularly high for a new-ish bottom end.


Originally Posted By: Grant
What else can lower the flash point other than fuel dilution? Mine appears to be down 90F. A friend of mine had a similar UOA with 50wt Redline: low viscosity, 100F lower flash temperature but no indicated dilution.

The only thing I've ever seen that will do that is fuel dilution. Maybe someone else can chime in.

Blackstone seems almost never to indicate fuel dilution, even in many cases where it is highly likely to have occurred...

 

[oliveoil]

The oil did well. This engine is still breaking in.

 

[Grant]

Originally Posted By: oliveoil
The oil did well. This engine is still breaking in.

I agree the wear metals look fine. However, if the oil did shear down to a 20wt then it isn't suitable for more than one race weekend or so.

Oddly most S2000 racers I've talked to run 30wt oils, despite the fact that even the owner's manual allows 40wt at higher temps. Given that racing oil temps seem about 40F higher than street temps, to me it would make sense to run at least a 40wt.