Oil Pressure Drop at WOT

[Greasemonkey]

I tried doing a search on this, but it didn't seem to be working. In the last day or two I've noticed a drop in oil pressure at WOT. At normal cruising, pressure is usually 50-55 psi, but when going to WOT the pressure drops quickly to about 30 psi or so. This seems to have became a problem after getting the alchy setup on the car. The oil is full, and the only thing I can think of is that the sump is being uncovered. The TR's are supposed to have a baffled pan correct? However, the engine was rebuilt previous to our purchase, and it would not have surprised me if that was missing. When it was rebuilt after we purchased it I did not even think to look. Sorry for the length, anyone have any suggestions?

 

[Blown&Injected]

Strange indeed.

Does it do it under load only? I am curious to know if, in neutral, what happens to OP with just about 1/2 inch of throttle or whatever it take to get to about 4,500 RPM's.

Just wondering if the stress at WOT in gear is causing some sort of distortion that is bleeding off pressure

 

[noslo6]

I posted on here about this very same thing happening with my car. I check everything, pulled pan-check bearings, changed pump and spring everything. Mine would do it only when it got to operating temp. I changed the oil sending unit and BOOYA! Maybe something to consider. It worked for me.

 

[wagon]

There is an article in Car Craft this month about Oil levels. It says that if the oil level is too high, then you can have the crank whipping the oil at high rpms, and the air in the oil causes the oil pressure to drop. How is your level? It suggests draining 1/2 quart and watch the oil pressure at high rpms. If the oil pressure improves, and you don't have any issues with losing pressure while braking, then drain another half quart and try again. It warns about going more than 1 to 1 1/2 quarts though. It also says that the gains are less on small block engines, and smaller oil pans. Just a thought.
Oh, and it can also increase horsepower.

 

[Greasemonkey]

The car only seems to do it under load. Had my dad check it at lunch, and sitting in park the oil pressure does rise with RPM without a problem.

I'll check the sending unit and see if I can find any problems with that.

In regards to oil level, I thought that could be a problem, as the car was actually overfilled a bit when I first noticed the problem. I drained oil to get it down to the correct level hoping that would fix the problem, but did not. I may attempt draining another half quart or so to see if that helps alleviate the problem any.

Any other ideas?

 

[turbosam6]

I had that problem once, I could disconnect the wastegate and the oil psi would be fine (eliminates rpm related problem), but as soon as boost came on the oil psi would drop. NO ONE ever figured out why. Bearings looked fine, thrust was fine, oil level didn't matter, gauge was fine, I gave up and bought a new motor. Problems like that are one of the reasons I'm selling mine. It gets frustrating when no one can figure it out.

 

[Razor]

Buddy of mine had the same problem, when driving and the converter locked, oil pressure would drop when the car was accellerated.

A month later pulling from a light, the crank snapped and split the block, cracked the transmission, destroyed everything.

If the guage is a mechanical guage verified accurate, then you have to dig into the motor.

Laz once had a problem on theyre race motor.. it ended up being an issue with the lifter bores.. The fix was to bush the lifters bores.

 

[bruce]

There is an article in Car Craft this month about Oil levels. It says that if the oil level is too high, then you can have the crank whipping the oil at high rpms, and the air in the oil causes the oil pressure to drop.

Yes,
but, reducing the volume of oil, puts alot more heat into the oil. IMO, that's something to be attempted only with monitoring the oil temps., closely.
Very closely.

 

[mweber]

Had the same problem on a car that I have been working on. Oil pressure dropped under WOT with boost and with no boost the oil pressure was over 60 psi at WOT. Pulled the engine, cam bearings were toast and the 1st and 3rd main bearings were showing copper. The main journals were worn but not evenly, my machinist said it looks like it was detonated pretty badly. It has o-ringed head gaskets which is probably why it didn't blow the head gasket first.

On the cam bearings you could see that the cam was being pushed downward by the wear pattern on the first bearing.

Check the main bearings and cam bearings.

Mike

 

[Greasemonkey]

Crap

Thanks for the replies so far guys. This isn't getting any better. Last night I had the car out and after a while the temp quickly rose to 230, and after a bit lowered back down to normal. It did this a second time while taking the car back home.

Checked tonight, very low on coolant. I had just filled it up the other night. No external leaks that can be seen big enough to cause this amount of loss. Oil looks fine, no milky sludge. Started the car up, didn't notice any white smoke. Does the car have to be warmed up for it to smoke? I don't recall it smoking last night.

Will the plugs show any signs of coolant on them if I check them? This is starting to look more like an engine pull job, but I wanted to make sure before I start doing that.

Thanks.

 

[Blown&Injected]

The 3.8 in my Bonneville was using lots of coolant and I could find no signs of any leakage anywhere; it did not show on the plugs either, but it would use a half gallon per day. It was an internal leak in the intake manifold. I would have believed it would have shown somewhere but I guess it is easy for the engine to cover up about a half gallon every 75 miles.

Sorry not much of a solution but just some experience I had with a GM 3.8 V6 using coolant.

 

[ijames]

My Chevy 5.0 v8 cracked between water jacket and lifter valley and was eating over a gallon per 50 miles and the oil on the dipstick looked just fine level-wise and color-wise after two gallons. There was sludge in the lifter valley and on the distributor shaft but under the valve covers still looked normal.

 

[turbosam6]

The 3.8 in my Bonneville was using lots of coolant and I could find no signs of any leakage anywhere; it did not show on the plugs either, but it would use a half gallon per day. It was an internal leak in the intake manifold. I would have believed it would have shown somewhere but I guess it is easy for the engine to cover up about a half gallon every 75 miles.

Sorry not much of a solution but just some experience I had with a GM 3.8 V6 using coolant.

Thats a completely different engine using a completely different intake assembly. Its also common for that engine to do that, its a gasket leak.

Sounds like you might have 2 different problems, as I wouldn't think oil psi and coolant would be related unless you had a blown HG causing low coolant and diluted oil.

 

[Blown&Injected]

Actually it was the EGR that burned a small hole in the plastic near the throttle body that caused the internal leak, but just like ijames, it is evidence of the ability of an engine to deal with lots of water with nearly no sign of trouble except always a low level

 

[Lee Thompson]

Imo

Baffle or no baffle should not make a difference. I would suspect a pickup screen with a lot of head gasket particles on it.

 

[Greasemonkey]

Baffle or no baffle should not make a difference. I would suspect a pickup screen with a lot of head gasket particles on it.

Sounds very plausible. I'm pretty sure I've lost a head gasket, and the two problems showed up about the same time. Now my next question, would it be best just to pull the engine for this? For pulling both heads and the oil pan it may be worth it. How hard is pulling the oil pan? I did the SBC in my Cutlass and it wasn't too bad, is the Buick do-able?

 

[Lee Thompson]

Just me but,

I had rather be beat up and pissed on than work under an eng. dripping oil. Do your self a favor and do it right, pull the eng.
I am only a few minutes away and am willing to loan you an eng. picker and eng. stand and any other tools. Best of luck.

 

[Greasemonkey]

I had rather be beat up and pissed on than work under an eng. dripping oil. Do your self a favor and do it right, pull the eng.
I am only a few minutes away and am willing to loan you an eng. picker and eng. stand and any other tools. Best of luck.

Thanks for the offer Lee. I've got a hoist and stand though. I'm just kind of hesitant to pull the engine as last time it was out it was out for about a year. I'd like to get this thing running again as quickly as possible. Looks like the engine's coming out this weekend.