Oil, Fluids, and Gauges, Oh My

[ForcedFirebird]

Conventional oil tends to break down at about 250*, synthetic much higher. Down here in FL on a hot summer day, it's not uncommon for guys to see 240* (215* coolant). Biggest factor is your viscosity. Redline is a good oil, and 50w is the minimum we like to run (no oil cooler, 14hr+ races). At ~240* 50w is actually more like 20w. Remember, air cooled VW's would run ~220* on a normal basis with conventional oil back in the day, and do so for hundreds of thousands of miles. We recently switched to Liqui Moly RaceTech 10w60 and saw a ~5psi increase at idle after a hard session on a hot day. If you are below 10psi per 1000rpm, you run into sheer issues.

Sounds like you had another issues going on, sorry to hear :( Bearing babbitt will definitely increase pressure.

[TobyB]

Bearing babbitt will definitely increase pressure.

Hmmm, maybe I'll throw some into the next clunker I'm looking to pawn off on some sucka...

;)

t

[Preyupy]

If you were dropping to 20psi in the corners you have trashed the bearings at least. Remember your "oil pressure" gauge is just a PRESSURE gauge that is reading pressure in the oil galley of the engine. When you slosh the oil away from the oil pump pickup in the pan the pump starts to suck AIR. With the residual oil coating the pump impeller the pump can actually move the enough AIR to still make PRESSURE in the oil galley, or at least pump some percentage of air along with the oil. AIR IS NOT A GOOD LUBRICANT!!! If you have ANY drop in oil pressure that does not correspond to a drop in engine speed you are SUCKING AIR and need to baffle the pan, run more oil, run an Accusump o something to fix the problem or you are going to trash your engine every time you go to the track!

[TobyB]

....that said, in the old days of PRO3, dropping to 20 psi in right handers was pretty common.
And those engines back then ran for seasons between rebuilds.

Not like now...

;)

t

[ak-]

I've been using an aluminum sandwich plate with a temp sensor in it for oil for about 2+ years now on my turbo m20.
The first year I had it sandwiched in the stock location and the year after I had it remotely located up front near my brake duct with my filter.
On both occasions, cruising barely tipped into 200*F and heavy constant loads on the street or canyon roads would nearly touch 240*F but never passed it.
I don't think the plate is a factor and don't believe a reading from the oil pan would be accurate either.

[Digitalwave]

Conventional oil tends to break down at about 250*, synthetic much higher. Down here in FL on a hot summer day, it's not uncommon for guys to see 240* (215* coolant). Biggest factor is your viscosity. Redline is a good oil, and 50w is the minimum we like to run (no oil cooler, 14hr+ races). At ~240* 50w is actually more like 20w. Remember, air cooled VW's would run ~220* on a normal basis with conventional oil back in the day, and do so for hundreds of thousands of miles. We recently switched to Liqui Moly RaceTech 10w60 and saw a ~5psi increase at idle after a hard session on a hot day. If you are below 10psi per 1000rpm, you run into sheer issues.

Sounds like you had another issues going on, sorry to hear :( Bearing babbitt will definitely increase pressure.

Thanks for the info John. (we spoke at Sebring waiting for the parade lap, I was in the black coupe and was having issues with my wideband at the time)

I do think the issue may have been pre-existing with this motor. I've only put about 300 miles on it myself after swapping it out of a parts car I purchased. The plan for now is to refresh this motor if it's not too far gone, and I will run synthetic oil going forward.

If you were dropping to 20psi in the corners you have trashed the bearings at least. Remember your "oil pressure" gauge is just a PRESSURE gauge that is reading pressure in the oil galley of the engine. When you slosh the oil away from the oil pump pickup in the pan the pump starts to suck AIR. With the residual oil coating the pump impeller the pump can actually move the enough AIR to still make PRESSURE in the oil galley, or at least pump some percentage of air along with the oil. AIR IS NOT A GOOD LUBRICANT!!! If you have ANY drop in oil pressure that does not correspond to a drop in engine speed you are SUCKING AIR and need to baffle the pan, run more oil, run an Accusump o something to fix the problem or you are going to trash your engine every time you go to the track!

Are you sure that 20psi = automatic trashed bearings? That seems pretty normal based on what I've read on the SpecE30 forums.

My oil pan is baffled. 20psi was in a longggg left hander, at about 3.5k RPM, while off throttle. It got worse throughout the day (it was about 35-40psi in the same corner in the morning), at which point my oil was probably already cooked and the oil level was about 1/2 quart low from the rear main seal leak. From what I can tell, the 20psi was probably a symptom and not the cause.

Long story short, I think a lot of factors were in play here.

If you consider 20psi to be certain death for rod bearings, what is the minimum pressure you like to see? I definitely don't want a repeat, and I plan to retain the baffled pan, possibly include a crank scraper this time, run synthetic oil, and overfill the oil by 1/2 to 1 quart (rather than being underfilled by 1/2 like I was by the end of the day).

EDIT: also keep in mind if my oil temps were really 280*+ on the dino oil, it had thinned and sheared badly already which would drop the pressure in the corners. Reviewing my GoPro footage, earlier on in each session when the temps were still coming up (indicated around 240*), oil pressure in the same corner stayed at 55+. It got progressively lower as the oil got hotter, and throughout the day as I am sure everything deteriorated more. Makes sense.

....that said, in the old days of PRO3, dropping to 20 psi in right handers was pretty common.
And those engines back then ran for seasons between rebuilds.

Not like now...

;)

t

I seem to notice pressure drops more in left handers than right handers for whatever reason. But yeah, it does seem relatively normal.

I've been using an aluminum sandwich plate with a temp sensor in it for oil for about 2+ years now on my turbo m20.
The first year I had it sandwiched in the stock location and the year after I had it remotely located up front near my brake duct with my filter.
On both occasions, cruising barely tipped into 200*F and heavy constant loads on the street or canyon roads would nearly touch 240*F but never passed it.
I don't think the plate is a factor and don't believe a reading from the oil pan would be accurate either.

Thanks for the data point. I intend to leave the temp thermistor in the sandwich plate with the new motor, at least to compare to what I was seeing with this trashed motor. I expected to see 240-250* on the track, but when I saw those temps driving a leisurely 10 miles home from my warehouse I wrongly assumed the gauge had an issue.

[TobyB]

Whoopsie, yes, left- handers!

Run with your oil about 1/4" over the full mark. That helps a lot.
I have both a baffle and a windage tray, and I think perhaps I need to ditch the windage tray... that oil's sitting up on top of it somewhere...

t