Odd Sudden Oil Pressure Drop Problem

Really odd thing happened at Mosport this past weekend, trying to narrow down the problem before ripping the whole thing apart.

Some background. I am running a stock 86-88 6port in our Touring GT Championship, sorta a poor mans Speed GT. I am running an RB Baffle plate, the 80 psi pressure regulator, a 2 quart Accusump, new stock cooler and a remote filter.

The scenario. Out for the first time with this motor. Bought it from a kid as a runner, saw it running in the car before I removed it. Compression/ oil pressure were good. Added the above pieces to the motor and installed it all into my car. Fired it up and all pressures were good. 60 lbs oil pressure at 1500 rpm when cold, up to about 80 psi at 5000 rpm. Car starts first ignition spark. Looked good.

Went to Mosport and ran it in Practice. Car ran for 10 mins full out, good power, oil temps about 180 - 200, pressures about 80 psi all through the session. Checked the car over after the session, no leaks, no oil in water, level the same and about 3 teaspoons of oil in the puke tank (less than normal).

Ran it in the first 20 minute race, it was spitting rain, so didn't get to go too hard but got down to within 12 seconds of my best dry time. Power good, pressures normal (80 psi max idle at 30 psi) and oil temp maxed out at 210. Checked the car over and had about half a cup in the puke tank. Another competitor came up to me and told me that the car was puffing blue when shifting. Oil level was about the same as when we started, down 1/4 quart. Looked at the car and found that 1 of the 2 crankcase vent tubes was capped (we normally run both vented to atmosphere) and felt that not having enough ventilation was causing a pressure buildup and less than optimal oil control rings weren't controlling the oil well. We were cool and as long as we added additional venting before the next race weekend and didn't run the oil out we would be fine.

Ran the 40 minute race. Didn't get a chance to open the Accusump on the mock grid. Again it was spitting rain. Couldn't push too hard. Oil pressure remained as per previous 80 max, 30 idle, oil temps were in the 180 to 190 range, water about 170. At the 30 minute mark the oil temps started to slowly drop, down to about 170. After a couple of laps the oil pressure started to drop. Up the back straight at about half throttle it dropped from 80 down to about 40, then 30 at 4000 rpm. Then when I slowed for the pits idle pressure was about 15 - 20 psi but dropping without me revving it up. Oil temps were still at about 160 degrees, water at 160 degrees as well. Crew chief opened the Accusump and pressure went up to about 40 psi. I saw the last lap board and went out for 1 slooow lap. Maintained my position in the race as I was substantially ahead of the next car, but by the time I came across the start finish I had to keep it at about 4000 rpm to keep the pressure above 20 lbs, but the temps were at 150 -155 degrees. Pulled into the pits, shut off the car. Checked the oil level and it was slightly above full (forgot to shut off the accusump), the oil was barely colored, no metallic bits, no burn't smell, etc.... We had about 1/2 a quart in the puke tank (again normal). Let the engine cool off for about an hour and fired it up to put it on the trailer. No weird noises, started very quick, no smoke puffs but oil pressure max about 25 psi, idle about 10 psi but erratic (too chicken to let it idle for too long to get a steady rate).

Don't think I wiped out the bearings as temps did not rise a bit and the oil looks almost new. What is the pump failure mode or a pressure regulator being stuck open with some slag failure mode. Could it be the thermal pellet in the eccentric shaft?

Oh guru's with more rotary experience than I please give me your opinions and trouble shooting tips.

Thanks a bunch in advance.

Well, there can be several reason for the cause of the pressure drop. The first one that comes to mind is the o-ring in the front cover, which is known to blow out causing loss of pressure. The worst case scenario is a sudden large clearance (i.e. spun bearing). I am not sure if high oil mperature always plays a role in spun bearings. I have had it happen either way.

It won't be easy to access "in situ". The only things controlling pressure are the regulator at the back of the engine and the bypass regualtor located in the front cover. I have yet to hear of an oil pump failure, but anything is possible in this world.

Like Paul said the obvious answers are the two regulators and the front cover o-ring. Very odd to me though that the temps would suddenly drop when the low pressure problem occured. The spring in the front regulator can break on ocassion.

The oil pressure will behave erratically if the oil cooler thermostat is not installed correctly - and it goes together different than common sense might say - copper thermostat, then the spring, then the cap.

That being said, if ANY debris gets in the pan, then the pump can suck it up, it will flow into the front regulator, and might hang it open.

You CAN pull the front cover while the engine is in the car, and inspect both the o ring seal and front pressure regulator. Good luck!

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Originally posted by paulydee@Aug 15 2005, 04:14 PM
I have yet to hear of an oil pump failure, but anything is possible in this world.

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Not that this will help with this topic but I have had an oil pump shaft snap in half. Can you guess what the oil pressure did then? :)

:( i think you may have bearing damage or the front cover pressure reg. is stuck. anyway if you drop the oil pan and there is no signs of brass or metallic pieces then it may be the pressure regulator. i would check both of them.good luck.

Thanks a bunch guys. You have confirmed what I was thinking/ dreading. I will pull the oil pan off and the front cover to find out what is wrong. By the way I am not running any thermostat in the cooler, but thanks for the heads up.

Interesting notes, I fired up the car yesterday and it held a steady 15 lbs of oil pressure at idle but would only go up to 25 lbs at 4000 rpm. Checked the oil after running it for about 20 seconds and the oil on the dip stick had air bubbles in it, not foam but bubbles. Let it sit for 15 minutes, checked the oil again and the bubbles were gone. Second point the kid who owned the engine before me has swapped an S5 front cover on to an S4 block. I am really going to look at the o-ring closely.

Another point, had to fly down to Atlanta yesterday on business. I had to go to Oakwood to visit a customer. Took the opportunity to visit Road Atlanta for the first time. Oh my goodness!!!!! That last turn before the pit straight, the drop while turning...... A ton of people say that Turn 2 at Mosport is one of the most difficult corners in racing, but you guys that race hard through there have just as big cojones as we do. My eternal respect.

Just wanted to provide an update to let you know what happened. Pulled the front cover off (in car, motor mounts still bolted, takes bow, thank you, thank you) and was wondering how I would be able to tell if the o-ring had blown. Found a thready, shredded c-shaped rubber thingy inside the front cover gasket at the oil passageway. Looks like a really blown oil ring to me.

Went to the Mazdatrix FAQ's, read the blurb on blown oil rings found that I had the same issues, same diagnostic. Going to clean it all up, wash it all down with alcohol/ oil cleaner, put it all back together and make the ALMS Support Touring GT Race next weekend.

Thanks a bunch for your help and thought you guys would like to see a shot from my last race at Mosport. Just finished passing the Vette, some weird motorcycle engined old-style pickup thing and Camaro on the outside of turn 8. Yes I did finish the race ahead of all of the cars in the shot.

Talked to a an Automotive Engineer friend of mine who is a cooling system specialist. I asked her about the oil temps going cooler while my pressures were dropping and she said the answer was simple.

First, the oil was doing less work, therefore less temp. Second the oil was being aerated from the internal leak. The leak was on the exit of the oil pump. the air would be trapped in the oil as it passed my temp gauge. More than likely my oil temps weren't really going down that fast, but the gauge wasn't reading correctly due to the air in the oil.

Really simple when you think about it.

Thats a common problem with water temp sensors as well. If they are installed near the top of the system, they will often read erratically, as they are the first to be "exposed" and not in full contact with the coolant. The guage will have large swings in temperature.

On one hand, it's not the best place for a sensor for that reason, on the other hand, it is a great place for a sensor, as it winds up doubling as an early warning device for low coolant levels if you know how to read the indications.

as you stated o ring on the front cover is blown. that mean less oil going through the engine,and also aerated oil to lubricate the bearings, that sound to me as very dangerous to the life of the bearings. just my .02 cents worth.

Just fired it up after putting the oil system back together. Looks like I dodged a bullet. Oil pressures okay, 35 lbs at idle and 70 lbs at 3000 rpm (going up as the car got warmer) no crud in oil (metal or silicone). Back to wondering if this junkyard motor will hold together for the whole weekend, but thats a different issue for a different time.

Looking good (well okay, adequate, fine?) for the Touring GT Race this weekend in support of the ALMS and Speed GT/ Touring races at Mosport.

Thanks to everyone for your help.

Eric

Glad to hear, and good luck this weekend.

Don't make the same mistake I made, last time I removed the cover with the engine still in the car: Be sure to use a torque wrench on that front pulley bolt !!!

:D , no fully torqued and bound with Loctite Blue. I am a bit anal about stuff falling off. Will let you guys know how things turn out.

sound like the engine is still good you may have dodged a bullet. good luck at the races.

Started the weekend off with a few issues. Went out for Qualifying and within half a lap oil temps were up in the 220 - 230 range. Came in checked everything over, saw no issues and went out again. Oil temps were up again in 1 lap. Short shifted to get a single lap in and came in. The car had no pull at all, sounded like it was struggling to make power.

Sat in the car thinking, D#@% the engine is hooped.

Did a little diagnostic. First let the car cool off, fired it up again and watched to see how the temps went up. Oil temps seemed to rpm related versus load related.

Left the track bought a stock Mazda oil filter. Came back the next day took off all external oiling stuff, pulled off the Accusump, remote filter and hoses. Decided to check timing again. Found out that I was a few degrees retarded. Adjusted timing added new oil and started the race.

Started 29th out of 30 cars and 24th out of 24 cars in Touring class. Car was still slow in a straight line, down almost 15 mph in a straight line, but it ran the whole hour with no oil system issues. Pressure after the race was 45 lbs idling and 80 lbs at 3000 rpm. Temps were in the 200 degree range. Finished 7th in class and 13th overall. Fastest lap was almost 2 seconds slower than previous norm. May have been a dirty track as there was a ton of oil and dirt on the track from the Speed GT race ( watch the race, the first turn was nuts).

Now to figure out why the engine is down on power as the compression is good and oiling seems to be good, but that is another problem for another day and more than anything related to tuning.

Again thanks to all.