Failed Engine, Oil Temp Related

#1

Ok guys, hoping you can help shed some light on a engine failure this last weekend at Willow Springs.

Quick Background, 87 325is, 225,000 used engine. 2 hour session (Chump Car)

I ran for 2 hours straight, came in refueled and switched drivers. The second driver at about 10 minutes in went down the front stretch with what sounded like a missing cylinder and a big puff of smoke on decel into turn one, did not even make it to the horseshoe before pulling into the dirt.

When the car came back into the pits, we found the crank seized, oil soaked #3 plug, the engine was so hot it was smoking, the dipstick was melted, and looked like a charred hot dog on a weenie roast. The oil cooler was bone cold.

The oil was pitch black and smelled like freshly laid asphalt. We had no coolant in the oil, but about a quart in the cooling system.

On my driving session I never noticed a problem with oil pressure and engine temp was 1/2 way. The second driver reported coolant temp at 3/4 way at engine failure. After reviewing some in car video it appeared that the second driver did not see the oil warning light come on at least 4 times during his last laps. The warning light is set to 5psi.

We do not have a oil temp gauge in the car, but will have one before the next event. I have also yet to do a tear down as we just ran this Saturday.

On a different note I have never been in a race car, on track, or even a autocross event. I got a golden opportunity and I got a drivers position on a chump car team. I got strapped in and did 30 minute shake down run on Friday evening and 2 hours on Saturday. I went from a initial 2:20 down to a 1:54, I took us from 20th place to 4rth place. Not bad for a rookie who had never been strapped into a race ever before!

I know Ranger has done alot of research on oil systems in these cars and would love to hear his feedback or anyone elses on this situation.

At what point does the oil break down enough for the engine to seize? What is considered normal oil temp, and do you guys remove the oil temp t/stat in the oil filter housing?

Also, one other possible related issue. We removed the secondary oil relief valve and plugged it solid. Oil pressure was in the 80+ psi range. I doubt this had anything to do with engine failure, if anything it kept the pressure higher then normal and probably extended the life of the engine until the oil turned to water from the heat.

Also no skid plate, I know Ranger reported 35* drop in temp when removing the skid plate.

Thanks,
Robert

#2

When was the low pressure light coming on? Left turns perhaps? My oil runs in the 160 to 180 F range.

#3

Hole in the piston would not effect oil pressure and would not seize the crank and cook the engine.

I am also sure the driver would have heard a blown piston, all he commented on was that it just started losing power. I assume as the crank and bearings started welding themselves together.

#4

Agreed! I didn’t catch that the engine actually seized in my first read of his post…

#5

Hi ya Robert/Peerless, good to see you. Sorry it’s under tough circumstances tho.

Since you’re one of the most knowledgeable E30 guys I know, it’s going to be hard to have useful ideas that you’ve not already thought of. But being the national champion of killing M20’s, I’ll give it a try.

99% of this you will have already thought of, so don’t let me patronize you.

I think that what happened “boils down to” a loss of coolant. Everything else is just frosting. The temp sensor won’t indicate a loss of coolant because it’s up at the top of the system in the tstat. So the first thing that happens with a loss of coolant is that the coolant drops away from the sensor. That would be my engine #5.

The loss of power could be from cooked rings. Once the water jacket is empty the cylinder walls and rings get ferociously hot and the rings can metallurgically fail, even if they seem to pass a visual inspection. That would be my engine #6.

A cooked ring would also explain the puff of smoke. Overpressure into the block blowing oil up the overflow pipe to the intake.

I don’t think that failing bearings would cause a noticeable loss of power. If the bearings were creating, for example, 40hp of resistance, IMO the engine would blow rods thru the hood.

Modern oils, especially synthetics, have a very high temp tolerance. I don’t know #'s, but we’re talking closer to 400deg then 300deg before lubricity fails.

The oil cooler being cold means the oil tstat failed or the oil filter failed.

The crank either seized because oil became too thin, or the issue impacting the oil cooler affected the whole oiling system. What were the rpms and g-load of the car when the 5psi light came on? Was there a crankscraper in the car and was it 1qt over full?

5psi is spooky low. Since the OP light was only coming on towards the end, I’m inclined to think that something in the oiling system failed. Unless the driver was allowing rpms to get down to idle while shifting or something.

I’d consider putting in a 20psi OP switch. That will give you more warning that there is a problem.

What the car needs is a 4psi coolant pressure switch. Knowing oil temp is good, but the important thing is knowing you have coolant.

Ok so where are we. The engine failed because of coolant loss. No matter what happened in the oiling system, nothing was going to save that motor. The behavior of the oiling system is a little odd tho. For sure something was blocking oil from the oil cooler. Not ideal, but not a crisis. But the 5psi OP business might be a crisis, depending on what the engine was doing at the time. That might tell us if the crank seized because of thin oil, or because of no oil.

Welcome to the madness Robert.

#6

The over heat condition may by just a red herring. Excessive bearing clearance results in both a loose of oil pressure and damage to the hydrostatic process that keeps the bearing and journal separated. Normally the bearing doesn’t touch the journal but rides on a pressure formed wedge of oil. If something interrupts that process the bearing can quickly fail. On a 225k engine (especially if there’s a history of poor maintenance) excessive bearing clearance is highly likely.

#7

Peerless, when you say you had a “quart in the cooling system” do you mean that you had almost no coolant or do you mean that the coolant system was full but that you had oil in the coolant?

#8

We had a quart of oil in the coolant, and no coolant in the oil. The cooling system did have water in it, but it did seem low so there was definately a loss of coolant in the whole episode. I have a feeling cylinder 3 will tell all.

The engine essentially cooked itself.

#9

peerless wrote:

[quote]We had a quart of oil in the coolant, and no coolant in the oil. The cooling system did have water in it, but it did seem low so there was definately a loss of coolant in the whole episode. I have a feeling cylinder 3 will tell all.

The engine essentially cooked itself.[/quote]

Interesting.
I suppose that coolant could have gotten in the oil but was then boiled out. Not sure I buy that tho. It doesn’t take much coolant to contaminate oil so IMO the oil quality would have indicated the problem. Therefore I’d go along with a face value interpretation. That is to say…coolant never got in the oil.

So what does oil in the coolant but not the reverse tell us? What if enough oil got into the coolant that the car ended up a quart low on oil and starved on left turns. That would explain the crank seizing, but doesn’t explain the over-heat.

Maybe there’s two separate things going on. Maybe loss of coolant at the water pump or a hose created the over-heat, and loss of oil into the coolant at the HG caused the crank to fail.

Re. the overheat may be just and red herring. I dunno. The dip stick melted. That’s pretty damned hot.

#10

I agree with Levie’s assessment. I’ve had a spun bearing failure like this before (in a Honda) right after a driver change.

The spun bearing was probably happening during the first stint. When the car was running slowly during the pit stop, then probably stopped during the driver change, the bearing was super heated, coked the oil in that bearing and ruined the hydrostaic oil film. Then when you went back out that bearing was gummed up with coked oil, wasn’t getting cool oil then catastrphic bearing failure occured. The super heated oil, block, and oil in coolant probably all happened in a matter of a few seconds at the very end.

The fact that the oil t-stat (or something in the system) failed certainly did not help the situation.

An oil temp guage may not have even allerted you. Because when the bad bearing was coking the oil, you are talking a couple ounces of oil amongst 4 quarts. The oil temp guage would have gone up a little but not pegged until the final failure occured.

Syntehtic oil would have helped as it has a much higher coking temperature. But if the bearing clearances were already large, no oil in the world will prevent a failure.

Oil temperature guages can alert the driver that somethng is not right but that is all. In that above mentioned Honda, we had no oil cooler and only a 4 quart sump. We did use synthetic oil. The oil temp would raise to 280F if we were really beating the piss out of it, water temp stayed straight up. Normally if we backed out of it and shifted at red line, the oil temp would come right back down. The day we had the bearing failure oil temp was up but not excessive. I noticed that car was not right and brought it in before it threw a rod. At pit speed it clattered like a diesel.

I bet you’ll find one bearing completely shot and unfortunately probably a scored crank as well. Best of luck.

Don