Unusually high oil pressure

[PistonPopper]

Hello, my rig is a 90' C1500 with a 5.7

Truck ran normally all week, starting and running this morning the oil pressure is running much higher than usual. Usually runs around 25-40 psi between warm idle and driving in town and highway driving. I let the truck warm a little more and psi is about 40 at warm idle. I'm going to change the oil today as it needs it soon. I'm hoping it's not a clog or a relief valve but I'll find out. Any ideas on what the cause is? Any help is appreciated, thanks

 

[PistonPopper]

Update, oil pressure is around normal psi at idle after town and highway driving, but jumps rapidly when driving.

 

[DerekTheGreat]

Probably a flakey sending unit. You'd need to pop an actual gauge on it to verify.

 

[Jroctizzle]

Did you change out the PCV valve?

 

[PistonPopper]

Did you change out the PCV valve?

I have not, no.

 

[PistonPopper]

Probably a flakey sending unit. You'd need to pop an actual gauge on it to verify.

I'll give it a go as soon as I can. Thanks

 

[Road Trip]

I'll give it a go as soon as I can. Thanks

Hello PistonPopper,

Elsewhere we were having a similar discussion trying to figure out if the engine was alright
and was a victim of a truth-bending vintage electrical oil pressure gauge in the dash...or was
the engine actually goofed up?

For me, the gauge in the dash helps to confirm that the engine is still quiet...but if I need to
make an informed decision whether or not to spend actual money in the engine bay, then my
go-to is a mechanical oil pressure gauge. There is a huge range in cost vs accuracy, but over
the years I've found this to be the most affordable gauge that I can trust: (AutoGauge 0-100psi gauge)

FWIW, I agree with DerekTheGreat on this. But it could also be the gauge itself, or (a bit more far-fetched)
the wiring between the two.

At any rate, once you figure out/fix this issue, please be sure to return here and
share what you found.

Best of luck. Happy Hunting --

 

[Schurkey]

Does the '90 model year 5.7L still use the same fist-sized, green-stripe oil pressure sending unit down by the oil filter as the '88--'89?

They've got a known-high failure rate. They can read too low, they can read too high, and they can just read whatever they damn well please at any given moment.

If so, many parts-store computers list the WRONG sending unit for that application. What they list is too big, doesn't fit, and the heat shield has to be forced over the thing.

Left: Correct "green stripe" sending unit with heat shield. Right: Incorrect, too-big unit specified by NAPA and others.

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Correct P/Ns are
BWD S4320 It has a silver case, and green paint around the end with the electrical connector.

http://weblink.carquest.com/acl/?mfg...rtNumber=S4320

The NAPA / Echlin crossover from that number is OP6729. AutoZone sells it as PS150.

Best I can tell, they're all sourced from the same manufacturer.

If this is what you have, consider moving the wire up to the distributor area. Buy a 3-wire sensor, and the 3-wire pigtail. Take the two existing wires by the distributor, add the third one from the original sending unit, and use the more-reliable 3-wire switch/sending unit from a newer 5.7L.

 

[PlayingWithTBI]

Does the '90 model year 5.7L still use the same fist-sized, green-stripe oil pressure sending unit down by the oil filter as the '88--'89?

They've got a known-high failure rate. They can read too low, they can read too high, and they can just read whatever they damn well please at any given moment.

If so, many parts-store computers list the WRONG sending unit for that application. What they list is too big, doesn't fit, and the heat shield has to be forced over the thing.

I've seen you post this before, then I remembered I have a picture of my '88. It doesn't look anything like the ones in your picture. It's a 2 wire sender.

Edit: I think it came with my Dakota Digital dash? The ones I look at online parts stores shows one for a light, not gauge. I'll bet you can order one from DD.

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here's both senders, the oil pressure on the left-center, and the switch (that goes in the china rail by the distributor) on the right-center. Not the elbows are different angles too.

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[PlayingWithTBI]

Edit: I think it came with my Dakota Digital dash? The ones I look at online parts stores shows one for a light, not gauge. I'll bet you can order one from DD.

Yep it does...

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