Weird oil pressure problem
Thread Starter
Junior Member
Joined: Nov 2006
Posts: 27
Likes: 0
From: Lilburn
Car: Modified 91 RS
Engine: 350 (1977 4 bolt main casting)
Transmission: 700R4 salvaged from an 84
Weird oil pressure problem
Hi guys. This one has everyone here scratching their head. This behavior started a few days ago. The basic situation is this: We built up a 350 and installed it in a 91 RS. Still working on the EFI setup. All in all the engine is running pretty smooth. No strange noises or anything. I am using a Summit hi flow oil pump with integrated (welded on) pickup.
Warmed up an at idle, this pump delivers about 20 lbs of pressure. (But with cold oil it delivers over 75 lbs at idle ... which killed the original pressure guage. I rigged a T-Connector to install an Auto-Meter guage and retain the stock oil pressure sending until/switch.)
At 1500 RPM, the new guage always read around 25-30 lbs. At 3000 RPM, it read a shade over 60 ... so I was getting around 20 lbs/ 1000 RPM. (My understanding is a small block Chevy needs at least 10 lbs/1000 RPM, so this is more than adequate.) So far so good.
But starting a few days ago, it began beahving differently. Still over 25lbs at idle, but when revved to 3000 RPM on the road pressure usually dips and then suddenly rises to a shade over 50 and then drops again. Sometimes it just goes up a little. Now, this makes me think bearing clearance issues, which would be tragic in a freshly worn in engine.
Parked in the driveway, when I rev the normal relationship is obtained without hesitation. (About 20 lbs/1000 RPM.) If I am on the road and down shift the engine revs up and I get about 20 lbs/1000 RPM. That would seem to eliminate bearing clearance issues as a cause. But why, then, does oil pressure drop or not rise properly when I am actually accelerating? I began to suspect the guage itself.
So I eliminated the T connector and installed the Auto-Meter sending unit directly. No change. I have checked the wiring and everything looks good. I have wiggled the wires with engine running trying to produce a fluctuation in the guage without effect. So I don't think the problem is with guage wiring.
There's no oil leak that I can find. The engine is running fine. No noises. Engine temperature is nominal.
If anyone has any ideas or thoughts on this, I would really appreciate hearing from them! Thanks.
Rob
Warmed up an at idle, this pump delivers about 20 lbs of pressure. (But with cold oil it delivers over 75 lbs at idle ... which killed the original pressure guage. I rigged a T-Connector to install an Auto-Meter guage and retain the stock oil pressure sending until/switch.)
At 1500 RPM, the new guage always read around 25-30 lbs. At 3000 RPM, it read a shade over 60 ... so I was getting around 20 lbs/ 1000 RPM. (My understanding is a small block Chevy needs at least 10 lbs/1000 RPM, so this is more than adequate.) So far so good.
But starting a few days ago, it began beahving differently. Still over 25lbs at idle, but when revved to 3000 RPM on the road pressure usually dips and then suddenly rises to a shade over 50 and then drops again. Sometimes it just goes up a little. Now, this makes me think bearing clearance issues, which would be tragic in a freshly worn in engine.
Parked in the driveway, when I rev the normal relationship is obtained without hesitation. (About 20 lbs/1000 RPM.) If I am on the road and down shift the engine revs up and I get about 20 lbs/1000 RPM. That would seem to eliminate bearing clearance issues as a cause. But why, then, does oil pressure drop or not rise properly when I am actually accelerating? I began to suspect the guage itself.
So I eliminated the T connector and installed the Auto-Meter sending unit directly. No change. I have checked the wiring and everything looks good. I have wiggled the wires with engine running trying to produce a fluctuation in the guage without effect. So I don't think the problem is with guage wiring.
There's no oil leak that I can find. The engine is running fine. No noises. Engine temperature is nominal.
If anyone has any ideas or thoughts on this, I would really appreciate hearing from them! Thanks.
Rob
Thread
Thread Starter
Forum
Replies
Last Post
ambainb
Camaros for Sale
11
Apr 25, 2016 09:21 PM
