Guys I have got a really friggin weird oil pressure problem.

Some background information.
Melling 10554 standard volume pump w/ white spring
Stock pan and windage tray

Two weeks ago the oil pickup fell off of the pump. It is possible that I had nearly 200 miles and 6 dyno pulls with the pickup off. The pickup was replaced and the engine believe it or no seems fine. I only noted the pressure falling when braking which lit the dash light. Never saw an ill effect accelerating or cruising but I think its safe to say that I might not have seen the idiot light occasionally coming on to indicate split second no oil pressure.

Cold idle oil pressure is 60#.
Cold rev makes 70#.
Hot idle oil pressure is 20#.
Cruising at 2K RPM is 30#.
Cruising at 4K RPM is 50K#.

Here is where it all goes to Hell.
When at WOT, pressure climbs and is consistent with having 10# per thousand RPM until around 5K RPM.

When you hit 5.5K, the pressure drops instantly to around 30# then shoots back up to around 60# at around 6K RPM. I can slowly accelerate and the same thing happens.

I have tested with 1 quart oil under filled, oil level full and 1/2 quart overfilled. The problem remains. I have replaced the filter, problem remains. I have not yet tried thicker oil but I have noticed the pressure drop still occurs with cold oil and a WOT blast.

The oil pump pickup is between 3/8" and 1/2" from the oil pan floor. The relief valve is not seized up. At a glance, the pump showed nothing unusual but I did not look very close at it. Also I can not say for certain that the oil pressure drop issue was occurring prior to the pickup falling off. I do find it difficult to believe that I would never have noticed the gauge behavior when blasting on it for nearly two years.

I am confident in the following:
It is not g-force related
The pan is not being sucked dry
The pickup height is not out of spec
The pickup is still attached because I welded the Hell out of it

I called Melling and they had nothing to contribute other than to say they have never heard of this problem. I don't think its bearing clearance related because if it was, I would have lower oil pressures across the board. Also when I recently drained the oil to replace the pickup, the oil was very clean with no signs of bearing fragment or other junk. I asked the folks at Melling to blame either the pump or the motor. They blamed the pump. Could it have gotten damaged as a result of the pickup being off?

Can someone provide some insight into this problem. I really want this fixed ASAP.

Thanks.
Bill

 

It's funny you asked this because I have my motor apart now for almost the same issue....video in the first thread(takes a couple of mins to load ~30megs).

https://www.camaroz28.com/forums/sho...d.php?t=703486
https://www.camaroz28.com/forums/sho...d.php?t=713070

I have always had a dip at 5000 rpms of around 5-7psi at WOT, but this seems consistent with what I have seen from many stock LT1 oiling concerns over the years(many blamed it on the crank whipping up the oil at high rpm). However the issue I have is now in-between 3500 and 5000. As in your case, by 6000 rpms, my pressure has recovered to 60psi.

I have not been able to narrow down a cause yet.

Before I pulled the engine, I did replace the oil pressure sending unit with a new GM unit. No change to my problem. So the sender is not to blame.

My Dad and numerous people I have spoken with(including some of the boys that build NASCAR engines) have blamed my oil pump. So I am going to change that....and also being so deep into the engine...I'm going to replace the bearings too.

I am going to go back to the standard pressure oil spring. I installed a high pressure spring(white) back when I did the cam and do wonder if it's some how contributing to the strange pressure problem.

 

Thanks for the reply.

My 5K RPM dip is definitely more than your. This morning I saw it dip to 40# and then shoot back up to around 60# or so.

One other thing I forgot to mention above. I did tee in a mechanical pressure gauge and loop it under the wiper blade and it shows the exact same pressure drop as the dash gauge.

I don't see how the crank can whip the oil cause I am running a half quart under for test purposes.

Also I cant see it being the white spring because I dont think it even opens and purges till around 80#. I can get 80# revving the motor on cold oil but during hot operation, it comes nowhere near that. Highest I have seen hot is about 60#.

I think the next step is to drain the new M1 5w30 and try some Standard Penzoil 5w30 and see if there is a difference. I have seen many posts where folks believe the M1 is thinner than dino oil.

As much as I really want to blame the pump. I still cant see in my mind how it could be the problem considering the excellent pressure everywhere in the operating range except for a occasional 5K RPM WOT blast.

 

I agree with the reasoning of everything you are tell me. I've been through the same exact thought process. The difference is where the problem is happening. It will be interesting to see if the issue disappears when I get mine back together. I actually went up in oil weight....the pressure went up, but still the same problem....just at a higher pressure.

Everywhere was fine except for WOT and high load.

Do me a favor. Get your Z on the highway in 6th gear....then floor it in 6th. Watch the oil pressure when you floor it. Does it drop 5 or so PSI and then come back up 5 or so PSI when you let off the throttle? I'm looking to see if you have a pressure drop under high load, low RPM.

Also, how new is bottom end of your short block? How many miles on the bearings?

 

Maybe 8K on the shortblock.
I average 1.5x - 2X the 10# per thousand RPM rule for nearly all operating ranges which is great. Its just this dam 5.5K RPM drop off that is not right.

In 6th and floor it the gauge holds steady. This only happen around 5.5K RPM.

Okay guys, here is a video of the 5.5K RPM pressure drop and 1st, 2nd and third gears:


You can see it drop from 60# to about 30# - 40# in a split second. The dash gauge is very accurate to the mechanical gauge.
Thoughts?

 

Interesting...have a look at this....

http://www.chevyhiperformance.com/te...ems/index.html

"High-performance engines place increased bearing loads on the oiling system (especially during higher rpm), and if it's not up to the task, it can cause very premature engine failure. To combat this, most aftermarket high-performance pumps provide a 20-30 percent increase in both volume and pressure. For most applications, you'll want a good pump that delivers in the neighborhood of 55-65 psi or about 10 psi per every 1,000 rpm; anything more may just add air into the system or labor the engine with the task of turning an oil pump that makes excessive pressure. If you doubt that an oil pump takes power to turn, watch what happens to a drill motor during the initial phase of oil pump priming."

There was some minor wearing on my Melling oil pump drive shaft.....so it was taking some power to turn the pump.

I wonder if our high pressure springs are some how causing air to be pumped into the system. This might explain why there is so much "contact" damage on my mains. I'd be interested to see what your mains look like. If you get the chance, have a look at them.

I'm reaching and guessing I know, but maybe between the two of us we can figure this issue out. I'll keep you up to date on my progress. I expect to have my engine back together sometime in May.

 

Just saw your video......Wow, that is a sudden drop in pressure. Much quicker than I expected.

 

Man, it does drop quick!

 

Sure does. Gives me a heart attack when I see it.

Anyone got any ideas on what is causing this? I dont want my motor to go Kaboom.

 

Update.
I put a brand new 10554 pump and pickup on. The pickup was too high at around 3/4" so now it is set to 1/4". I let the pan push the pickup up up to make it flush with the floor. Then raised in 1/8" and along with the gasket it should be a tad over 1/4" off the floor.

The problem remains and is not better or worse. I dont get it. I hate this car.

I guess next is going to be a bigger oil pan although I am not convinced its a starvation problem. It seems like a momentary bleed off problem.

 

I had a similar problem, I bought a HV oil pump but it worked so well that the oil wasn't returning fast enough to the bottom, therefore it was running dry at high RPM. I bought a moroso oil pan that holds more oil and completely solved that problem.

 

Did your instantly rebound after it dropped like mine is doing in the vid?

Well process of elimination is moving toward a bigger pan and more oil capacity.

Let me ask this. Does a more powerful 355ci motor with OE spec oil pump really suck that much more oil at WOT next to a stock LT1?

 

Did you have a standard pressure spring in the new pump? Did you have a look at bottom half of the mains?

 

I was uncomfortable pulling the caps so no I did not. I took the standard spring out and installed my GM white spring. Idle pressure is now about 23# so it actually went up a tad.

If the pan got sucked dry. Would the low oil light come on or is it delayed somehow?

 

If that pump is the same volume as a stock LT1 pump, I doubt the pan is being sucked dry. Looking on Melling's site, it appears to be a standard volume pump.