Hey folks. Just got my mechanical oil pressure gauge done up, engine was stone cold and the reading was about 49-55psi upon first starting the car up, it then slowly climbed down to about 20-28 psi once the engine was hot (t-stat open and all)

Curious if this is a relatively normal reading, from what I've read online it appears it is but figured I'd ask you folks since you seem to know best. It's a 1980 Olds Delta 88 holiday coupe, 307cui olds small block.

Pic

Picture is about 2 mins after firing it up. Doesn't move as much as I expected it to but there's air bubbles in the line so i expect it to be not as accurate. Just wanted to make sure we had good pressure and such but it does look like were golden!

 

Yes that's normal and just fine.

 

Excellent good to know. Thank you sir.

 

Any idea how much it should move when I'm revving the engine parked? Didn't move a ton went up to about 30psi

 

The rule of thumb is at least 10 psi per 1000 RPM.

 

There's some air bubbles in our gauge line, but when i revved it up it slowly climbed then of course dropped back down. I assume it's fine and nothing to worry about really. Nerves.

 

The air bubble don't matter. The pressure is the same in the bubble as in the oil.

 

Gotcha. Was just a cheapo gauge so I don't think it'll be dead on accurate or move fast. I'm stumped, I figure since it registered 55-60psi on a cold start it's probably fine. Would it being in park make a difference vs actually being out on the road?

 

Done some thinking on what you said, would this air bubble rule still apply if nearly the entire oil line is filled with air bubbles at idle and only fills completely when I'm on the throttle. As soon as I back off and it drops down into regular idle the bubbles form and the oil moves back down the tube. Just thought I'd clarify, it's nearly 6 feet worth of bubbles in the tubing.

 

Don't worry about the air bubbles, it's normal.

 

Sounds healthy. I am guessing 10W30 oil? When the oil light started flickering after long drives in warm weather on my 81 Delta 88 with a 307, I put a mechanical gauge on it. It had 20ish hot cruising, locked up TH250C and 2.41 gears, low rpm. It was maybe 5 psi at idle in gear. It probably had close to 400,000 km at that time. I used GM engine flush. I gained a good 5 psi, enough that it kept the engine light off at idle. It ran great another 50,000 km till the timing chain skipped. My parents bought it for $500 from the original owner. It had a stack of regular maintenance bills in the glove box, including the purchasing of it new in 1982. Great cars and usually well taken care of.

 

The pressure in the line is the same at both ends. If it weren't, oil would have to be flowing somewhere. The bubbles compress under pressure until the air pressure in the bubbles is the same as the oil pressure. Once the oil pressure drops, the bubbles expand, again until the pressure equalizes. This is physics 101. It's also how a gas-charged accumulator works.

 

OK fair enough. When you explain it like that i can understand. What's confusing me though too is in park, I gave it gas got it up to I'd say about 3000rpm, the gauge moved VERY slowly and not by much; however both at cold start and once warm it registered the pressure to be healthy, 45-50 psi cold then 20-25 psi when warm, just a very slow moving gauge. I haven't driven it under load,.since it doesn't have insurance on it currently. So my guess is that it doesn't generate much pressure when free revving VS. under load.

 

Remember the good old days, which were, what, two or three days ago? BEFORE you installed the gauge? You didn't have a care in the world. All you had then was a light on the dash. It never went on. You drove the car all day long and never worried once about the oil pressure, what it was when the engine was hot or cold, etc.

But now you have a gauge. So now you have something new to worry about, along with world peace and the price of food.

I always get a laugh when someone comes on talking about the new gauges they just installed and now suddenly they gave themselves new things to worry about.

It's called too much information.

 

I agree with you jaunty, I used to install gauges in my cars but I’d obsess over watching them. Now I use idiot lights and drive care free.

 

I was thinking that myself basically all day long yesterday after installing it. Facepalm. Maybe theyre called idiot lights because they're for idiots like me who obsess! haha

 

You can bleed the air out of the line which will help out with the laziness of the reading as it won’t have to compress all the air pockets in the line first on up pressure and reverse on going down.a shorter line is also better for response

you can’t compress a liquid so with a line that’s all oil the gage with react instantly. You can bleed it by loosening the pinch nut on the back of the gauge while it’s over a container with it running.

Only loosen it enough to slowly bleed out the air until you see no more air pockets coming through. It may still develop a pocket of air near the engine if that portion drains back, but you will get most of it out by bleeding.

your gauge is also small sweep …which doesn’t have much needle movement to start with

you won’t really know your actual min oil pressure until it’s been running under load on the road and oil is up to temp.