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Oil Pressure flunctuating??

1989 C1500 350 auto, 143k miles. It runs good, nothing strange, except the oil pressure gauge jumps around at idle. Running down the road it sits at a steady indicated 45psi, but at idle it's erractic. You'd think there was a loose wire that's making contact most of the time, but opens up just for a split second every few seconds. The needle bounces around, but always settles back at 45.

I'm wondering if the oil pressure sensor is just an on/off switch that's set to read 45 when the sensor detects some minimum pressure. I know some vehicles are configured like that. If so, that would mean that either the sensor is going bad, or my idle pressure is getting low and dropping just under the sensor's minimum. It's not burning any, just worn valve stem seals that puffs a bit of smoke on startup. Still gets 15-16 mpg in mixed driving.

Any guesses or words of wisdom?

Reply to
JG2U
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Sounds exactly like what my 90 GMC Sierra with 130K miles does. The truck has a 350 V8 and automatic tranny. The oil pressure gauge has done this for years. Local shop says everything is fine and the motor will go another 100K without any major work. By the way mine doesn't burn oil either. Just like yours there is a puff of blue smoke at first start up each day.

Bob

Reply to
Bob M

How erratic? I've seen fluid coupled meters jump around at idle. At 143k I would suspect your pressure at idle is lower than 45.

Reply to
Meat Plow

Jumps 20+ psi. From 45 it drops to less than 30, then back to almost

  1. It doesn't stop on anything, it's always moving unless it's stabilized for a couple of seconds on 45.

Is it a true analog gauge, or just a gauge representatoin of an idiot light?

Reply to
JG2U

replace the sending unit. And no, GM doesnt copy fords fake gauge.

Whitelightning

Reply to
Whitelightning

Bad sender. What is causing the jumping gauge is the resistor element is starting to go bad.

Reply to
Steve W.

Interesting. What models did that? I am familiar with their instrument voltage regulator issues. It was always fun to watch all the gages on a truck swing to max. Didn't know they had idiot gages on some models.

Reply to
Bob La Londe

The fake oil pressure gauges are on just about everything Ford had in the lineup from 1986 on up or so. (Diesels and heavy trucks as well as some of the mustangs have real gauges) They are real easy to spot. Turn on the key look at the gauge, it will drop to zero, start the engine and the gauge will jump to a spot in the green/normal range and stay there. no variance regardless of temperature of the oil or rpms of the engine.

Ford even issued a statement about the reason behind it. They had a lot of people complaining that the oil pressure gauge moved when the engine was running and (DUH)so they installed a fixed resistor in the system so it stayed put in the green zone. The sender on some is actually just a switch (just like an idiot light) others have a real pressure sender that feeds the computer and the gauge still has the resistor so it stays put.

Some can be converted to real gauges and some cannot.

Reply to
Steve W.

Wow! Interesting stuff there.

My dad is still a strong Ford fan. I think I'll forward that to him.

Reply to
Bob La Londe

It really pays to keep it in mind because it means that you cannot trust the gauge. The oil pressure hits 5-9 pounds and that is enough to put the gauge in the "normal" area. So if someone with a ford shows up and the engine has a nice rattle but they claim it has good oil pressure "looks good on the gauge" you get to run a pressure test and show them the truth.

Reply to
Steve W.

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