Faulty oil pressure sender (I hope)

[jjonez]

Today I was driving my 87 pathy down the highway and I noticed my oil pressure light was on. Weirdly though my oil pressure gauge was showing what it normally does.

 

Some backstory: When I bought the truck about 18 months ago the oil pressure gauge wasn't working properly. The light was never on after startup, but oil pressure would read zero at idle and only like 10 on the highway. On cold starts it would climb to about 30 until warmed up then drop back down. I replaced the sending unit and things improved but still not quite spec. Now on cold starts pressure will go to the middle (45 I think?), then when warm at idle it will drop to zero/sometimes slightly above zero, then when cruising at about 3000 rpm it will be at 30.

 

I figured since just changing the sending unit improved the pressure reading, that maybe the old sender or the port that it screws into is partially clogged or there's some issue with the wiring. So I assumed that my actual oil pressure was fine. In any case, kind of weird that the light would come on even though the pressure gauge was "normal". To be on the safe side I had it towed 50 miles back home.

 

My initial plan now is to check the pressure with a mechanical tester and get a new sender on there. But I was hoping to get some insight or suggestions from you guys as well. Clogged oil pickup maybe? It's worth noting that the truck doesn't consume any oil, and the dipstick today showed full and the oil looked pretty clean (I think about 1500 miles since the last change). Also there wasn't much discernible valvetrain noise (this is usually a symptom of low pressure right?)

 

Last thing, I happened to snap a picture of the passenger side valve train the other day when I changed the valve cover gaskets. Besides a little bit of sludge in areas where the oil pools (i.e. bolt heads), I'd say things look pretty good right? I read somewhere that sludge here can indicate a clogged pickup.

 

 

Thanks for all the help guys! She'll stay parked until I can figure this out.

Edited November 4, 2017 by jjonez

[Slartibartfast]

Looks nice and clean under the valve cover. Cleaner than mine, actually. I'd be surprised if gunk in the sender was enough to throw off the reading, seems like more people would have trouble with senders if they were that easy to screw up. Good thinking checking with an external gauge to rule out wiring issues. Hopefully it's something external.

[jjonez]

Update:

 

Tested it with a mechanical gauge from harbor freight and oil pressure is great. I replaced the sender (for the second time), this time with an Airtex/Wells unit and the light is no longer on and the gauge works much better than before.

 

Phew!

[RF600]

That's the reason I don't skimp on certain things.