OK here is my problem:

The last few days I've been driving my car (Its very hot out) My car normally has about 20psi of oil pressure when its is warm and idling.

BUT

Today I was out and it was at 20 psi when idling warm but when I was driving it keep going up until I hit around 4000 Rpm's.....then my oil pressure started dropping back towards 20psi!!!!!!!

Can anyone explain why my oil pressure would start dropping when my RPM's are around 4000? My idle pressure is still around 20psi when warm


Any suggestions are welcome on why it does this!!!!

CmanZ28

 

What oil weight and type are you using?

I have a crazy story like yours where I used valvoline 10w30 and experienced the oil pressure drop at higher RPMs but maybe not quite as bad as what you have described. Anyway, I broke down and bought some of that 0w40 Mobil1 synthetic since the oil analysis boys where claiming it was good stuff and amazingly enough it cured that pressure drop problem. In fact the thin Mobil1 holds more pressure than that old dino oil in all RPMs at all temps.

 

I use 10W30 Mobil 1 Syn. and a WIX filter


CmanZ28

 

Could be crank windage, or a blockage with the filter.

If you have a pep boys around you try the Proline filter (super cheap)

If no pep boys try a Napa Racing filter. (13 bucks or so)

 

I dont think it could be a blockage in the filter. If there was a block in the filter, the filter would go into by-pass mode. This would let the oil bypass the filter without being filtered.....crank windage? I'm not very familiar to what this would mean.


Could my intake tube on the oil pump have fallen off some how? Would these symptoms corralate with my problem?

CmanZ28

 

No,and the pickup doesn't just fall off,unless it has been installed wrong during a build.

Change your oil to a 20-50 and the filter and see. Get some dino oil to try that way it won't cost so much. Ya can drain your high priced oil in a CLEAN pan and reinstall if the other doesn't work.

 

Crank windage means the crank pretty much whips up the oil when you get spinning more RPMs. The air bubbles in the oil will cause a pressure drop. "Crank Windage" search will get you tons of more info.

As for the filter, the bypass is located in the oil cooler, could be gummed up or any number of things.

On my motor i took off the oil cooler and put on one of the 2500 truck filters (about 1 qt). That worked on the 350.

On the 383 the problem arose again. Thick oil masked the problem (thinking loose bearing clearence) but it happened still. Finally switched to the high flow Napa Race filter and the problem went away.

For me it wasnt so much the filter was clogged, but rather the filter couldnt keep up with the pressure.

 

I think I might try to change the oil weight to a 20W50. But any of these other things I dont know about.....

Would these things just happen for no reason? I ask this because my oil pressure has been "normal" all summer and this stuff just started happening the past few days.

CmanZ28

 

Did ya just change the oil/filter? Did ya change brands or weight?
If the 20/50 and filter don't fix it I would pull it and find out what's going on.

I would put a manual guage on it before pulling.

 

I changed my oil at the beginning of summer. It has been about 1000 miles since an oil change. I just purchased the car in Feb. so I don't know what kind of oil was in there before....but I changed to the factory recommend 10W30...and I went to full synthetic.

I think I should use a manual guage too...but I dont have one nor can I afford to buy one right now.

Thanks
CmanZ28

 

Do the 20/50 dino and filter and see if it improves
I wouldn't pull it until ya put a manual guage on it. If there is something wrong it will be a lot less costly to fix it now rather than later.

 

Thanks 1racerdude

I will prolly change my oil here in the next few days. I'll get back to this post if it does not cure it.

Thanks again,
CmanZ28

 

I have two '94 z-28 m6's both with about 33k miles and on several occasions I have seen some oil pressure fluctuation as the rpm is on the increase. Neither of the cars do this consistantly, both idle at about 20psi hot and have valvoline 10-30. Recently I checked the oil level right after the pressure fluctuated...it was about 1/2 quart low so I topped it off and drove it again and did not see the fluctuation. I do not know if the intermittant problem ceased because I topped off the oil level or if it stopped flucuating due to another variable...oil pump relief valve sticking?? , oil sender, or other?? I find it interesting that I have seen this on both of my low mile LT-1's. I would interested to know if others have also seen this fluctuation on an intermittant basis.

 

Well,

I have another twist.....I havn't had time to change my oil or anything yet. But I decided to take it out and see if it still does it......well


It still does it Right around 4000rpm the oil pressure drops

But

It only does it while the engine is under load....not when I put the clutch in and rev it up to 4000rpms. It only does it when I'm driving it. Could it be just a faulty sensor?

CmanZ28

 

sounding more like crank windage, if it only does it under load(accelerating), the oil sloshes to the rear of the pan, creeps up the back and get aerated by the crank, and , just like brakes, air in the system means you lose measurable pressure(air compresses, liquid does not)