Oil pressure question… or two questions

[7900_Blazer]

As mentioned previously. I bought an 85’ K20 for my daughter to be her daily driver.

Engine looks like to be a GM crate motor. The guy I bought it from said he just changed the oil… used 10W 40. However the intake, sides of the motor, bottom…everything was so covered in grime, oil and Oklahoma red dirt (original owner was a rancher), I’m worried that he did no maintenance at all.

When I picked up the truck it was already at operating temperature and the oil pressure gauge showed it had 35 or so psi at idle. Running up the RPM, the gauge changed a little, maybe to 40 or 45 or so… but not much.

The engine runs really strong, no smoke whatsoever.

Here are my two questions:
1. It seems odd to me that it has very little oil pressure fluctuation showing on the gauge..does that seem odd to any of you?
2. I took off the oil pressure switch (that’s what this looks to be - see pic)… since I was cleaning the engine… figured I change it out.

Might a bad switch cause very little fluctuation And does an 85’ have a switch that would kill the motor upon a low oil pressure condition?

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[AuroraGirl]

As mentioned previously. I bought an 85’ K20 for my daughter to be her daily driver.

Engine looks like to be a GM crate motor. The guy I bought it from said he just changed the oil… used 10W 40. However the intake, sides of the motor, bottom…everything was so covered in grime, oil and Oklahoma red dirt (original owner was a rancher), I’m worried that he did no maintenance at all.

When I picked up the truck it was already at operating temperature and the oil pressure gauge showed it had 35 or so psi at idle. Running up the RPM, the gauge changed a little, maybe to 40 or 45 or so… but not much.

The engine runs really strong, no smoke whatsoever.

Here are my two questions:
1. It seems odd to me that it has very little oil pressure fluctuation showing on the gauge..does that seem odd to any of you?
2. I took off the oil pressure switch (that’s what this looks to be - see pic)… since I was cleaning the engine… figured I change it out.

Might a bad switch cause very little fluctuation And does an 85’ have a switch that would kill the motor upon a low oil pressure condition?

You must be registered for see images attach

sounds similar to my readings

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first one is mine at idle or possibly slightly holding pedal(bad alt, loose temp sensor)
2nd one is someone from the forums, awesome right? but yeah they look to be idling

 

[yevgenievich]

Those are really more of a suggestion on pressure estimate than an accurate representation. Sounds ok

 

[Turbo4whl]

^^^ What Viktor said. Pressure is good.

 

[Dmack]

You are assuming the factory gauge and sender areaccurate. After changing the sender in mine twice, I put a mechanical gauge in it. Gm crate engine with unknown miles and maintenance. 40 on cold startup and 30 warm.

 

[Ellie Niner]

And does an 85’ have a switch that would kill the motor upon a low oil pressure condition?

No. But if you've still got the factory configuration, the amber "CHOKE" light in the lower part of the speedometer is actually an oil pressure warning light, and can grab your attention if oil pressure becomes critically low. It's connected to a second sending unit near the one for the oil pressure gauge, and its main purpose is to only send power to the electric choke heater once the engine is running... on the few trucks that didn't get the gauge package, the same idiot light sender was used to power the electric choke, but the warning light in the instrument cluster was red, and was labeled "OIL/CHOKE" (and was moved to the spot occupied by your oil pressure gauge).

Your oil pressure sounds pretty normal to me. I usually see 35-45psi on a cold start, and it stays somewhere in there until the oil temperature comes up... and this is usually a number of miles after water temperature stabilizes. Once oil is up to operating temperature, it's about 30-35 at speed, and around 20 at idle. After a long run on the freeway, it can hover around 15 at idle and 30 at speed.

My oil pressure gauge sender is getting ready to sh¡t the bed, and occasionally reads zero on cold starts... but since the "CHOKE" light goes out, I know I've got oil pressure.

 

[7900_Blazer]

@AuroraGirl Am I understanding that your oil pressure gauge fluctuates very little between idle and normal driving RPM?

I’ve never had a truck like this where there seems to be little oil pressure difference between idle and normal operating RPM… seems odd which makes me think something is wrong.

 

[Matt69olds]

Those are really more of a suggestion on pressure estimate than an accurate representation. Sounds ok

^this!!

Factory gauges aren’t the most accurate instruments, but are usually pretty close. The important thing is to look at them often enough to get an idea of what’s normal. That way if something doesn’t fall within expected readings, you know something is mint quite right.

 

[AuroraGirl]

@AuroraGirl Am I understanding that your oil pressure gauge fluctuates very little between idle and normal driving RPM?

I’ve never had a truck like this where there seems to be little oil pressure difference between idle and normal operating RPM… seems odd which makes me think something is wrong.

No, that left pic is my truck and I am pretty sure it was a pic at high idle or idle and the temp gauge was going up and down because the wire got loose and I was determining if I had it fixed, (I have a spade female closed over the button end on it)

also, you can see my voltage is poop, my alternator was changed, but Im saying that a truck running and pointing up there, thats good.

You only need 7-10 psi of oil pressure, really, however if your vehicle was like most and it made more than that when new, seeing that low is not a good sign. if you would like a more precise idea, you could hook up a hand held oil pressure gauge or there are aftermarket gauges that use liquid circuit or sending units which are more precise too. My gauge, hwoever, will go up towards 60 if I am on the acclerator, never goes much lower than "20" ish which is hard to guestimate based on it visually since its also not that specific overall anyway, but you get my meaning. since its not on the 0, its got some and thats probably enough

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Heres a good explanation

 

[80BrownK10]

As mentioned previously. I bought an 85’ K20 for my daughter to be her daily driver.

Engine looks like to be a GM crate motor. The guy I bought it from said he just changed the oil… used 10W 40. However the intake, sides of the motor, bottom…everything was so covered in grime, oil and Oklahoma red dirt (original owner was a rancher), I’m worried that he did no maintenance at all.

When I picked up the truck it was already at operating temperature and the oil pressure gauge showed it had 35 or so psi at idle. Running up the RPM, the gauge changed a little, maybe to 40 or 45 or so… but not much.

The engine runs really strong, no smoke whatsoever.

Here are my two questions:
1. It seems odd to me that it has very little oil pressure fluctuation showing on the gauge..does that seem odd to any of you?
2. I took off the oil pressure switch (that’s what this looks to be - see pic)… since I was cleaning the engine… figured I change it out.

Might a bad switch cause very little fluctuation And does an 85’ have a switch that would kill the motor upon a low oil pressure condition?

You must be registered for see images attach

Man I wish I had 35psi at idle out of my small block!!! Your good to go, don't worry.

 

[80BrownK10]

I had a bad sender it wouldn't let the gauge read accurate, it made it read higher than normal. Mine was going into scary territory where it would almost register zero on the gauge at idle when warmed up (this is after the new sending unit). I rolled in new main bearings and replaced the rod bearings and got an acceptable increase. Still low at idle but running pressure is much better looking now.

 

[Jacob Miller]

My old motor (350) sat at the red lights around 7-8psi and around 30psi when moving. The factory gauges aren’t always the most accurate, you might be well off to go with the advise above of testing with a stand alone gauge if your concerned.

 

[Memaloose]

My oil pressure with a factory mechanical gauge reads 38-40 PSI cold at idle and 32-35 PSI warm. I run 10W30. I wouldn't let your pressures worry you, be thankful you have that much. I worry in the summer when the temp is over 100 about low oil pressure but it never goes below 30 PSI so I'm happy. I've got about 85,000 miles on the original engine in a '75 Scottsdale.

 

[Snoots]

You're good. That's an Oil Pressure sensor; the switch is much smaller.
Only if you have an electric fuel pump (factory) will low oil pressure shut downn the engine.

 

[7900_Blazer]

Thanks everyone for the feedback...!