Oil pressure, then there was none

GotWood

GotWood

Sayer of Fact
Joined
Jan 12, 2007
Location
Maiden, NC
Just picked up a 97 TJ 4cyl and took it for a spin around the block last night. Oil pressure was reading 40 and all was well. After 2 miles the gauge dropped to 0 and I pulled over. After I sat there for maybe 2 min I fired it up and the pressure was back to normal. I revved it a couple times, all seems good, I roll back to the house. As I pull in the pressure drops out to 0 again.

This morning I changed the oil and added a little Marvel's to the mix. I left it idle in the garage for 30 min and all looked good so I took off down the road. At about the 2 mile mark I watched the pressure steadily creep down to 0 so I shut it off and pulled over. I sat on the side of the road no more than 5 min and fired it up, 40psi. All was well all the way home (2.5 miles) but as I sat in the garage idling the pressure dropped steadily from 40 to 0 in about 1 min.

I'm heading to go get a sending unit.......
 
Defiantly sounds like the sending unit, wouldn't be surprised if it is leaking either.

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Guess I should have asked, does it sound like it has low oil pressure or just a low/false reading?

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Did the engine start rattling when oil psi dropped?

I think your on track with the sending unit.
 
No noticeable rattle increase. Temp gauge stays around 200.
 
Infamous1 said:
Replace sender or screw a manual gauge in there. How did old oil look?
Click to expand...
Old oil looked fine, still more brown than black.

I changed the sending unit with no improvement, same exact results. It has to be something electrical because I can pull over and shut the engine then restart and everything is normal. I can also reset it driving down the road and cutting the key off.
 
Install an Autometer gauge.
 
Not sure on these engines, but:
Possible that system has some clumps, that will migrate to the oil passage for the gauge.
If it's an electrical problem, find, borrow, or buy a mechanical gauge and test it out with it.

I once had an older Chevy that was doing the same thing, except it was an engine light that would come on(idiot light)
Culprit there was a heater vent hose, that was blowing hot air on the gauge, or the idiot light.

if it's junk you might fit you a hose over a fitting, let it spray into a jug. see if any clumps come out or, if it actually stops spraying oil out.

Just giving some ideas, have nothing concrete!
 
Go buy cheapo mechanical gauge from parts store. Tape it to a wiper blade and run hose to stock sender location and go drive. If mechanical gauge shows good then you definitely have an electric gauge issue. If mechanical gauge does the same thing it's likely sucking sludge or trash against pickup tube. Key off pump quits pulling, shit falls back down in pan, few miles later it's sucked back up. That's a pretty common issue too, especially on engines that aren't well cared for. If this is the case flush may work or could make it worse. The only true fix is to pull the pan and scrape it out.

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Only takes 30 mins to drop the pan.
 
Pull the old sender out and blow some air in that port. See if there is a blockage.

If no change, start with the dielectric grease on all the plug ends in the harness and grounds!
 
<shrug>

I wouldn't drop the main caps.
 
A manual gauge screwed into the port will eliminate speculation. Clean oil isnt usually "clumpy" either. If it isnt noisy its oiling, you will hear the clatter pretty quickly if it running dry.
 
shawn said:
He said he already did that.
Click to expand...

Well then, start looking for poor connection somewhere. When they fail many times the sender will weep oil into the connector. That could be a cause too. @Jeff B already said to check connections and apply dielectric grease where appropriate.
Since the sender is a case ground to the block, I'd be looking at the block grounds near the coil and the firewall ground strap as a start.
 
When oil pressure goes to zero, all other gages staymnormal?
Tach keeps working?
 
Red brakleen will eat oily clumpy deposits.. I pulled a Silverado 5.3 oil pan and time I got through scraping the bulk out and washing the pan out with red brakleen, I had no clumps left in the drain pan to show my customer!!
 
Mechanical gauge, installed. I don't know why @ol'Jeeps and @MarsFab charge so much. Fabrication is easy!
IMG_20170416_124415932_HDR.jpg
 
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