What could cause low oil pressure?

[92Ty#1524]

My pressure is slightly above the half way mark on the dash guage and drops below it when the engine warms. With the drop in pressure comes what I believe is valve train noise (still trying to confirming it). The motor has just been overhauled and was tore down out of concern for the condition of the bearings. All bearings are new and plastigaged within limits. The above mentioned symptoms came back within minutes of being fired up for the first time.

I've read other posts regarding oil pressure and from what I can see, mine seems to be lower than what is considered normal. What would cause the oil pressure to be so low?

 

[Ghostman]

This would seem like the obvious but have you checked your oil level? This was my problem. I checked it one week and the second week I was getting strange oil pressure readings and thought it couldn't be my oil level because I just checked it a week early....to make a long story short it was my oil level.

 

[92Ty#1524]

Level is fine. Primed the oil system before I fired it up. No shortage of oil.

 

[havin-fun]

Did you replace the oil pump, I just puy a new motor in my 99 blazer due to a stuck oil pump bypass

 

[92Ty#1524]

Pump? I didnt. Considered that as well and wish I did. Just figured that if it wasnt working that I'd have no pressure at all. Wasnt till this weekend that I read up on the spring bypasses in the lube system. Ugh....hindsight.

 

[myclone]

Need more info.

What oil pump are you using?
Shimmed bypasses in the block/remote filter?
What weight oil?
Pressure readings hot at idle in gear or hot idle in neutral?
Cam bearings checked when tear down occurred?
Cam bearings replaced when engine was rebuilt before tear down?
Oil gally plugs in block installed correctly at front/rear of cam?
Using stock gauge to get readings or have you verified oil press with a mechanical gauge?

 

[bezerk]

Need more info.


Shimmed bypasses in the block/remote filter

can you explain that to me?
is it for basicly cutting off the Bybass, so it won't work annymore?
is that a good thing?

 

[gmcturbo]

Need more info.

Using stock gauge to get readings or have you verified oil press with a mechanical gauge?

 

[92Ty#1524]

I have yet to verify it with a mechanical guage. Will to today. I can tap into the oil filter housing for an accurate reading?

I didnt look at the cam bearings this time. I had aready found a couple of main bearings worn excessively and just assumed that was the problem and didnt dig any further.

Oil pump is most likely original. I've yet to replace it. It has about 110k miles on it if so.

Im not sure about the oil galley plugs. I do know that when I had the block bored, the small caps on the rear of the block were replaced. They look new anyway.

I havent tampered with any bypass springs. Never noticed them before.

 

[myclone]

So you rebuilt the engine but didnt replace the VERY important $29 oil pump? Oooops.

Without seeing/hearing your engine an educated guess tells me the 110k mile worn out oil pump is prolly the source of your problems.

 

[92Ty#1524]

Oil pressure with guage on filter housing is 54. Tapping starts around 40 psi as the engine warms. Once temp has stablized, oil pressure hunts between 24 and 26. Pressure increases with revs (40 @ 1800rpm).

The tapping is intermittent and is not audible when above idle. Unplugging injector #1 quiets it considerably but then it taps as engine is coasting back to idle from a rev up. This is the only time I've been able to hear it above idle.

 

[myclone]

Those numbers arent too awfully bad for a stock 110k mile oil pump IMO as a matter of fact they are better than my 74k mile engine with 50w synth but then again you have new bearings and I dont. What weight oil do you have in the engine?

Have you verified that the injectors arent seated too deeply in the intake since the engine has been apart? The injector tick is similar to a valve train noise (a well trained ear can tell them apart :wink: ) and fools a LOT of ppl into thinking they have more serious issues than they really do. When I bought my first sy I loosened the inj rails and raised them up as far as they would go. This quieted the motor down a fair amount for me so it might be worth taking a look at on your truck. That really doesnt sound like your prob but it might be worth looking into anyway since the only way to diagnose engine noise over the net is to elliminate possible causes one at a time.

Last thing... If the youre sure its not the injectors then Id go through and adjust the valve lash again just for the heck of it since the engine was rebuilt as you might have a rocker arm thats just a tiny bit on the loose side that quiets down when the rpms come up.

Hope some of that helps