Oil Pressure issue (Not the switch)

[JODiE_DLN]

Hi, so have been having a few oil pressure issues on the dash at least, have hooked up a mechanical oil pressure gauge and truck sits between 50-60psi at idle and when left running for over 20mins and oil heats up it only drops to around 45-50, but on the dash it starts at 30 and then gradually drops down to 0 once engine warms up, and then throws the check gauges warning light. Have changed oil just yesterday as well and that hasn't changed what I'm seeing on the dash. I don't think it's the bottom end bearing as there is no engine noise and mechanical gauge states no actual loss in oil pressure. Have also replaced the oil pressure switch behind the dizzy. Any ideas what could be causing the issue? All help appreciated.

 

[c1500deathtrap]

the gauge

 

[JODiE_DLN]

the gauge

So like the gauge on the Dash? I did think that might be the issue, any advice on how to fix that kind of thing?

 

[df2x4]

What year is your truck? From your avatar it looks like a pre-'95 but I can't tell.

My first guess would be the oil pressure sending unit based on the fact that your factory gauge seems to cooperate with the "Check Gauges" light.

 

[JODiE_DLN]

What year is your truck? From your avatar it looks like a pre-'95 but I can't tell.

My first guess would be the oil pressure sending unit based on the fact that your factory gauge seems to cooperate with the "Check Gauges" light.

My trucks a 1988, Do you mean the unit at the back of the engine bay under the distributor? Cause that's been replaced and have only seen a slight increase in pressure shown on the dash, it does still drop to zero after a long period driving though, very stumped as to what it could be.

 

[evilunclegrimace]

If your truck is an 88 the sender is on the side of the block above the oil filter. The switch at the rear of the block under the distributor is a low oil pressure switch only. Later years the two where incorporated in to one unit that is under the distributor.

 

[JODiE_DLN]

If your truck is an 88 the sender is on the side of the block above the oil filter. The switch at the rear of the block under the distributor is a low oil pressure switch only. Later years the two where incorporated in to one unit that is under the distributor.

Thank You! I have a place to look now. This has helped me out a lot. Complicated to replace? Or not so much?

 

[evilunclegrimace]

Thank You! I have a place to look now. This has helped me out a lot. Complicated to replace? Or not so much?

Not so much.

 

[Robert Parzych]

Not so much.

 

[Robert Parzych]

I have a 1990 GMC 1500 ext cab. When I bought it the odometer read 351390 miles. What a worn out 350 TBI engine. One quart per 100 miles. I had a 1972 350 from a Rally Nova and had it machined. Put Scat rods and flat top pistons with 4cc valve reliefs in it with a new TBI camshaft and lifters. New oil pump that came with 3 different strength relief springs. I chose the middle one. This is a 355 TBI engine and it runs stronger than most because of raised compression. The only oil sending unit it has is behind the distributor. It has the 4 gauges and a speedo dash. Oil pressure is high when engine cold and drops down at idle lower than I like. The block that came out of the truck may or may not be original to truck but it has a pipe plug in the oil hole above the oil filter. I plan to put a manual oil pressure gauge in and use that oil hole to feed it. Then I will know for sure what pressure it has. I have had this truck for 10 years now and have only put around 4000 miles on it. Always runs good though.