Oil pressure drop?

y'sguy

y'sguy

Senior Member
I recently installed a used 292 in my old pickup. Knowing full well it may have unknown issues. I checked it out by running it first on a stand and it had acceptable oil pressure as well as oil to the rockers. About 25 lbs.
After that I was satisfied with the way it was running, smooth and clean. I never expected it to be like a new one, hence on the cheap.

I then cleaned it all up installed a new rear main seal. New oil pump. water pump. Timing chain. Carb rebuild. And assorted gaskets.
Installed and has been running great, almost ready to do a complete oil change. BUT the oil pressure has dropped to 0. Although the gauge needle seems to quiver when I barely rev it.

I drove it home today after a short errand with no issues, no heat up (about 170) and no valve or rocker noise at all.

I have some ideas where and how to check first but where would you start and what would be your list in order? I am using a new, direct oil pressure line & gauge.

Thanks guys!
 
It sounds like you know what you are doing, but if the oil pressure was zero and you drove it with no noise/heat, I would first double check the 'new' gauge. Then i would suspect the 'new' oil pump or pump drive.

I hope it isn't much wrong. Let us know what you find.
 
I would suspect the gauge, if its an electric I would install a manual gauge to check the electric one, oil pressure comes from the pump, main bearings and cam bearings, maybe the oil pick up screen has come loose, ive had cheap oil filters cause lose of oil pressure
 
The only kind of pressure guage I am familiar with has a fitting that screws into one of the un-used oil ports in the engine block. Semi-transparent plastic tubing runs from that fitting to the back of the pressure guage. If there is no oil in that tubing, the guage won't move.
 
Respectively there is no reason to bleed the air from an oil pressure gauge. It will make no difference in the reading whatsoever as the air will compress and be at the same pressure as the oil and the reading will be the same. Even if you do manage bleed it once the oil drains back when you shut the engine down the line will get air in it again. There is no way to keep air out of a dead ended connection such as an oil pressure gauge.

jb
 
jb's right. Done it both ways and it didn't make a difference. If you drove it any distance it would have froze up. Do what was suggested - get a manual gauge and check the pressure and the electric gauge.
 
y'sguy said:
BUT the oil pressure has dropped to 0. Although the gauge needle seems to quiver when I barely rev it.

I drove it home today after a short errand with no issues, no heat up (about 170) and no valve or rocker noise at all.

I have some ideas where and how to check first but where would you start and what would be your list in order? I am using a new, direct oil pressure line & gauge.

Thanks guys!
Click to expand...

In the past 3 years, I have had TWO! brand new gauges go bad within a few weeks of installation. One was an electric gauge that had a sender and the other was a mechanical gauge from Autometer. Go figure. I would imagine that is your problem. Do what another poster suggested. Unhook your oil line at the gauge, unhook your coil, and then spin your engine over... if there is oil coming out of the oil line you installed, then you have pressure. That gauge is probably faulty.
 
First suspicion the gauge. But I had a motor go to 0 oil pressure once due to a bad grommet at the oil pump pick up tube connection. I don't think I over tightened it, but it failed, leaked air, and oil pressure when to 0
 
If you confirm the gauge is good and it works you have the symptoms of a oil pressure relief valve that is stuck open.

R
 
OK guys, I do have a mech. gauge. Sorry, I thought I mentioned that. And yes I realize air in the line is ok or normal. I'm hoping it is just the gauge (it is a cheapy one). I'm hoping I can get to fiddle with it in a couple of days but not sure when. I also am going to purge that oil line after disconnecting it to make sure it doesn't have any crud in it.
thanks for all the suggestions. I'll update when I know something.
I did consider the oil pump pick up tube connection, but I'm thinking it should be ok as it has been for some time now.
Shouldn't I also be able to check the gauge itself by pressurizing it with an air compressor? just a thought.
I'm also going to remove the rocker cover to see if I do have oil!
 
Until oil pressure is found to be present, do not start your engine. Crank it over with the starter to see if it is pumping oil. Years ago, I was on my way to work and my Y block lost oil pressure. I checked my oil level and determined that it was OK. I drove the rest of the way to work and back home that evening. A total of about 2.5 miles. At home I found that the oil pump drive rod had twisted off when the recently installed new oil pump had become bound up. The oil pump was too tight is why it bound up. I cleaned up the oil pump with emery paper and replaced it's drive rod and I never had another problem after that. No oil pressure? Don't start any engine until you see the oil flow.
 
^^ yes, good advice but I'm hoping I have it the other signals aren't there. Like I said before I'll get to it soon to better diagnose.
 
Well, I finialyy got a chance to take a loo a things.
I discovered that I was low on ooil due to some other brand of dipstick that someone had used. I know better than that so I'll accept the blame. I changed the oil and filter, the oil was black black black!. It wa sthe oil change from the first go around on the engine when I cleaned it up to start it. So, it had a lot of contaminants in it I'm sure and I WAS expecting that.
Fired it up and the oil pressure jumped right up to fifty lbs and settled out to 25lbs. Fine for now.

However, I still don't like that it's smoking as much as it is.

I may do a valve seal install to see if it helps. I've never done a compression check on it but the power seems acceptable for its old condition.
 
If the engine was unknown it might pay to pull the sump and have a good look at the oil pickup.. I swear I had one pin hole left in mine..Pfft!, I have a PCV setup and half my valve seals are gone the rest rock hard and she don't smoke .. runs like a champ
; o )
 
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