View Full Version : Wierd Oil Pressure?
Like the tile says, I'm getting some wierd things happening with my oil pressure. First off, my oil pressure ranges from 25psi @ idle to 70psi @ ~6k rpm at operating temperature. Secondly, when I'm accelerating at WOT my oil pressure gets up to about 60psi at ~4k rpm, starts to drop off to ~45-50psi then goes back up between 5k and 6k rpm. I have a melling hi pressure, standard volume pump that I installed when I rebuilt the engine, I believe it is a M55A Has anyone else had a similar problem?
I probably should mention that I am running Mobil Delvac 15w-40.
My95Z
02-06-2009, 06:52 PM
Could be the pickup is too close to the pan, did it just start with this or has it been doing it since the rebuild?
Could be the pickup is too close to the pan, did it just start with this or has it been doing it since the rebuild?
it's been doing it since the rebuild. i didn't actually set the pickup myself, I let the engine builder who did my heads do it because I didn't want to mess it up. So I am not exactly sure how close the pickup is
mike2244
02-06-2009, 08:10 PM
your oil pressure is good, all you need is 5psi for every 1000 RPM's, mine does the same thing.
your oil pressure is good, all you need is 5psi for every 1000 RPM's, mine does the same thing.
Not sure I am getting your wording correctly(to the OP), but oil pressure should never go DOWN while rpms are going UP. If it does it means oil is being squeezed through your bearings and they are going, or the pan is being sucked dry from either incorrect parts or pickup too close to the bottom.
While the pressure itself is good, it should not be dipping down at any point in time at WOT until you let off the throttle.
Edit: Excuse my language, but why the hell are you running such a thick oil, especially in the cold?!? :doh:Thick oil, freezing temps (or so I assume, IL in Feb.)which makes it even thicker at a cold start, PLUS an HP pump is torturing that poor shortblock...
mike2244
02-06-2009, 11:20 PM
sorry i didn't read the part where he is loosing oil pressure. losing oil pressure is not normal.
my bad
the reason for such thick oil is because it was recommended to me by someone who I believe to know a little about engines because he builds some pretty nasty power plants. as far as the cold weather, the car is in a heated garage when it's not running. I tried switching to 10w-30 for the winter, but then I ended up getting a wierd lifter noise. I know it doesn't make sense, but i switched back to the heavier oil as a band-aid until i could replace the lifters. So far, the noise has completely disappeared and I've been running it like that for 3 days now with no sign of the noise returning. I know I'm gonna get flamed for the last sentance, but I needed transportation, and it's all I've got that's legal right now. Once I start making some money again, I'll fix the problem properly.
Not sure I am getting your wording correctly(to the OP), but oil pressure should never go DOWN while rpms are going UP. If it does it means oil is being squeezed through your bearings and they are going, or the pan is being sucked dry from either incorrect parts or pickup too close to the bottom.
While the pressure itself is good, it should not be dipping down at any point in time at WOT until you let off the throttle.
Edit: Excuse my language, but why the hell are you running such a thick oil, especially in the cold?!? :doh:Thick oil, freezing temps (or so I assume, IL in Feb.)which makes it even thicker at a cold start, PLUS an HP pump is torturing that poor shortblock...
As far as the bearings go, I really hope that they are not going, as I just re-built the engine in July and replaced the bearings. The engine only has like 7000 miles on it since the rebuild. I am going to assume that the problem is that the pickup is set too close to the pan. Out of curiousity, how would that work. if the pickup is at the bottom of the pan, wouldn't it always be submerged in oil (assuming the pan isn't being sucked dry)
My95Z
02-06-2009, 11:32 PM
15W-40 isn't that thick?
Next time i'd recomend 10w-40 just because it will start up a little thinner when cold, but the 40 part is fine, I am one of those believers like the guy who told you to run a little thicker oil.
My95Z
02-06-2009, 11:33 PM
As far as the bearings go, I really hope that they are not going, as I just re-built the engine in July and replaced the bearings. The engine only has like 7000 miles on it since the rebuild. I am going to assume that the problem is that the pickup is set too close to the pan. Out of curiousity, how would that work. if the pickup is at the bottom of the pan, wouldn't it always be submerged in oil (assuming the pan isn't being sucked dry)
Next time you take a drink put your straw real close to the bottom of the cup :laugh:
Works the same way only oil is thicker so its even worse. It gets worse with rpm because the speed in which the oil is being sucked up is increasing.
Green96Z
02-07-2009, 12:43 AM
I have a melling hi pressure pump that I installed when I rebuilt the engine, I believe it is a M55?
Is that a high volume pump? Are you running it on a stock pan? A HV pump can suck a stock pan dry.
mtperformance
02-07-2009, 03:45 AM
If you are running the factory oil pressure gauge I would put a mechanical gauge on there just to be sure. I lost 20psi when I changed my sending unit at 900 rpms it went from 40 psi to 20 but as soon as I break 1100 rpms its a little over 40psi.
z rated
02-07-2009, 10:38 AM
i agree with green96z, it will suck the pan dry if its a high volume and a stock pan, what kind of pan do you have
Z28pr0jekt
02-07-2009, 10:40 AM
the melling M55 is a standard volume, standard pressure pump.. that shouldn't be the problem unless like stated, something is messed up with the pickup
The melling M55A is a standard volume, high pressure pump
the M55A is the same pump I'll be using with my canton pan, but even still if I had stock pan I would still be comfortable running it
The M55HV is high volume, high pressure
need to know which one
the melling M55 is a standard volume, standard pressure pump.. that shouldn't be the problem unless like stated, something is messed up with the pickup
The melling M55A is a standard volume, high pressure pump
the M55A is the same pump I'll be using with my canton pan, but even still if I had stock pan I would still be comfortable running it
The M55HV is high volume, high pressure
need to know which one
thanx, I Wasn't sure the exact part number, but now I can tell you it is a M55A
Also isn't the only difference between the M55 and M55A a different pressure spring?
If you are running the factory oil pressure gauge I would put a mechanical gauge on there just to be sure. I lost 20psi when I changed my sending unit at 900 rpms it went from 40 psi to 20 but as soon as I break 1100 rpms its a little over 40psi.
I am running a Autometer mechanical oil pressure guage. I actually broke off my stock oil pressure sending unit when I did my header install. I swear that was the worst place to put it from the factory. (for those who don't know early 94's and 93's had the oil pressure sending unit just above the oil filter on the side of the block)
connexion2005
02-07-2009, 05:05 PM
After reading this, I would suspect that you pickup is not set at the correct height and most likely to high. It sounds like the issue is occuring when rpms go up as the pump is sucking for more oil. But, due to the fact the pump may be set to high, it is slightly gasping a bit.
How high did you set the pickup from the bottom of the pan? I like to get between 1/2 inch - 3/4 inch.
^^I'll have to look at that. It's a little difficult because I don't feel like pulling the motor, but maybe I can take out the oil level sensor and have a peek that way.
When the builder mocked up the pickup, he put the pickup on the pump so that is was a little too low, then placed the pan on over it to push it in place. Then took the pan off and welded the pickup in place. my guess is that somwhere between the engine block and the vice he put it into to weld it the pickup got moved.
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