15# Increase on Oil Pressure!

[Old Ironsides]

A few weeks ago my oil pressure rose 15# and has been consistently higher ever since. Must have had debris on the pickup screen in the pan??

Now I'm idling at 20, freeway is now 40! It was 5 and 25 before. I plan on doing an oil change soon and cutting the filter to see what it might have been.

Has this happened to anyone else?

[Mikel]

Something affected the already unreliable factory pressure gauge?

[tgreese]

Yeah, I would look to the gauge and its wiring first. See what you get from a mechanical gauge. The Summit gauge works well as a test instrument - https://www.summitracing.com/parts/sum-g2934/overview/ - cheap too. Tee in where the pressure sensor is and install under the hood, or run the tubing in to the cabin where you can see the gauge. Keep the tubing away from the exhaust manifold!

[threepiece]

Tee in where the pressure sensor is and install under the hood, or run the tubing in to the cabin where you can see the gauge. Keep the tubing away from the exhaust manifold!

I did similar on my J20. It has been great for six years and 50,000 miles.

I don't see a need for the pressure switch, especially if it is made with any plastic components. I had one that cracked. Lucky for me it happened just before I pulled into my driveway and I noticed a large puddle of oil. This story would have had a sad ending for me had I been traveling on the freeway.

I used a section of flexible hydraulic hose to connect to the engine. The movement/vibration between the body and frame could cause a rigid line to crack.

[rang-a-stang]

Did your lifter ticking go away? (I remember when you stopped by my house there was a super minor lifter tick...)

[blazer3664]

Double check with a mechanical gauge.


Stock gauges are often poked at around here as "for entertainment purposes only". They are not usually very reliable, and have been known to do very odd things.

[Old Ironsides]

No the ticking did not go away unfortunately.

[FSJunkie]

The gauge was probably reading inaccurately before because if your engine would have toasted it's main and rod bearings by now if it were truly running at 5 PSI at idle and 25 PSI at speed.

My 1977 Pontiac has the same type of oil pressure gauge as an FSJ....meaning jumps everywhere and is unreliable. I learned to basically ignore it. Normally it read about 40 PSI on the highway. One day it gradually dropped to 0 PSI in the span of a few miles, or about ten minutes. The whole time I was thinking, "either my engine is failing and actually loosing oil pressure or the gauge is failing...I bet it's the gauge"......so I kept driving with a little twinge of fear for the possibility that it may actually be real. It wasn't until the engine temperature shot up and I heard AND FELT the knocking that I realized the gauge was actually right.

I spent the next several months rebuilding that engine. It destroyed every main bearing. Wiped them out clear into the steel backing and trashed the crank too. Each bearing dropped the oil pressure as it failed. They failed one by one, dropping the pressure in incremental steps, until the last bearing failed and the pressure went to 0. The shame is it only had 7000 miles on it since the last rebuild when it happened and it wasn't the engine's fault. Misalignment to the transmission over those 7000 miles overloaded and slowly fatigued the bearings. They just chose that day to finally die.

I was 1000 miles from home on vacation when it happened. I towed the car all the way home behind a rented Uhaul truck. It sucked. The car won 1st place in it's class at a concours two weeks before. Now it had the ultimate shame: getting dragged home behind a Uhaul.


Having an oil pressure indicator THAT YOU TRUST is important. I don't care if it's a gauge or a warning light. The point is that you believe it and trust it.

[rang-a-stang]

The 79 Service manual has a procedure for checking your oil pressure gauge. Is the Oil Pressure the only gauge that changed? It uses the same reference voltage as your Temp and Fuel gauges. That 5V reference voltage is created in your Temp Gauge. If that voltage changed, it could change the readings on all 3 of those gauges.

I will tell you my oil pressure was 4-6 at hot idle (verified with a mechanical gauge) and ~24-26 cruising with 20/50 and motor honey. Allll my bearings were worn (mains, rods, and cam). My oil pump was well worn, too. Verify your oil pressure with a mechanical gauge and if it's low, step 1 is rebuild your oil pump.
(Oil pump rebuild link)
Hopefully that will help your lifter tick, too. That can be done for less than $100 (adding a timing chain since you're in there) and over a weekend. If you do decide to rebuild, let me know and you can have my left over valve grinding compound.

[FSJunkie]

A brand new rebuilt AMC V8 with blueprint bearing clearances will run 10-20 PSI @ 650 RPM and 50-60 PSI @ 3000 RPM fully warmed up with 10W30.