Thread: Low Oil Pressure at Idle

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Good morning all! I'm noticing lately that at idle with my 350 my oil pressure gauge sits around 0 but as soon as I give it some gas it quickly comes up to around 50.

Whats up with that? Is my oil pump going out? I run 5w-20 Mobil 1 Full Syn.

Any help would be appreciated!

--Dan

dan what year is your 350 and is your fuel pump manual?

Originally Posted by jyardgirl

dan what year is your 350 and is your fuel pump manual?

Damn. Got me again. I don't know the answer to either of those questions. I bought my car the way it sits now and I haven't even checked the block casting numbers yet.

I just had the same thing happen to the sbf in my 27. The gauge started dipping to zero only occasionally, but would go to 40 psi when I raised the rpms. I removed the sender and screwed a mechanical pressure gauge on there and when I started it the gauge read 50 psi at idle and would go to 70 when I revved it up. I bought a new sender and the gauge on the dash started reading the same as the mechanical one...........my sender was only a year old but had gone bad.

I'm starting to lose confidence in electrical gauges. My water temp gauge is 20-30 degrees off of what the actual temperature is (I have shot the engine with an infared gun and also have a Mr Gasket radiator cap with a thermometer in it. Both the gun and the cap read 180 when my dash gauge reads 200-210.

I would suggest you do the same test I did, screw a mechanical gauge in where the sender goes and see what it reads. They are cheap enough (you don't need a top of the line one for the test) and will confirm you have or do not have a problem.

Don

Originally Posted by Itoldyouso

I just had the same thing happen to the sbf in my 27. The gauge started dipping to zero only occasionally, but would go to 40 psi when I raised the rpms. I removed the sender and screwed a mechanical pressure gauge on there and when I started it the gauge read 50 psi at idle and would go to 70 when I revved it up. I bought a new sender and the gauge on the dash started reading the same as the mechanical one...........my sender was only a year old but had gone bad.

I'm starting to lose confidence in electrical gauges. My water temp gauge is 20-30 degrees off of what the actual temperature is (I have shot the engine with an infared gun and also have a Mr Gasket radiator cap with a thermometer in it. Both the gun and the cap read 180 when my dash gauge reads 200-210.

I would suggest you do the same test I did, screw a mechanical gauge in where the sender goes and see what it reads. They are cheap enough (you don't need a top of the line one for the test) and will confirm you have or do not have a problem.

Don

Thanks Don! I will give that a try. I don't hear any tapping or anything so I was kinda of leaning towards problems with the gauge, etc.

Isn't technology getting better?

One more question while I have some people's attention...

After the motor warms up I get a little bit of white smoke out of my driver side exhaust pipe. Bad valve seals?

I agree 100% with Don's approach, and I hope you find that your problem is a simple sending unit. I had a similar issue, running 10W30 Synthetic Blend oil, and my engine guy suggested getting away from the synthetic altogether. Switched to Valvolene 10W30 and I hold about 15to20 at idle, and about 50 above idle with everything warm. If you don't find it with the mechanical gauge you might try an oil change, just for grins.

Your white smoke sounds like it could be a valve guide seal, especially if it is mostly after you idle a bit, then blip the throttle and get a puff.

Originally Posted by rspears

I agree 100% with Don's approach, and I hope you find that your problem is a simple sending unit. I had a similar issue, running 10W30 Synthetic Blend oil, and my engine guy suggested getting away from the synthetic altogether. Switched to Valvolene 10W30 and I hold about 15to20 at idle, and about 50 above idle with everything warm. If you don't find it with the mechanical gauge you might try an oil change, just for grins.

Thanks for the reply. That could be another route to take.

While we are talking about valve seals, we just changed a couple of seals out on the 455 Olds in Dan's rpu. We didn't want to pull the heads and I have that special tool that allows you to remove the keepers without pulling the head, but over the years I had lost the second part of the process, the air chuck that you use to inject air into the cylinders to keep the valves up. So I went to Home Depot and bought 30 feet of 1/4 inch nylon rope and used that.

The idea is to keep the valves from dropping down into the cylinder when you remove the keepers, and you can do that by compressing air in there or by using the rope as a "filler" to push up on the valves and keep them locked into place. First you take the cylinder you are working on to top dead center, and remove the spark plug. Then you turn the crank back the opposite way it normally turns enough to bring the piston down a couple of inches in the cylinder. Now you feed the rope into the hole until it is pretty full (it took about 20 feet) and then you GENTLY turn the crank in it's usual rotation SLOWLY until you feel the rope start to compress against the valves. We were also able to look into the spark plug hole and see that happening. You do not want to force the piston up too hard and bend anything, just enough pressure to keep the valves in place.

Once that is done you can remove the rocker arm and then use the tool to remove the tension on the springs and remove the keepers and then the springs. (one valve at a time). Autozone and Advance Auto rent or sell that tool these days and also sell new seals. After you replace the seals you reinstall the spring and keeper and turn the crank counter clockwise to release the pressure on the rope, and pull it out of the hole (obviously, you have left some rope hanging out so you can remove it )

This is an old trick and I am sure many of you know it, but just thought I would post it in case some of you hadn't heard of it.

Don

I agree with the guys , gauges lie all the time,lol. If your valve guides are bad to give off a little smoke its likely the engine is in the same condition. First I would try a little heavier oil, synthetic is best IMO,since it looses less viscosity as the temp rise. I have 2 oil pressure gauges on my truck because I did not trust either, BUT, one is on top of the block and the other is on the bottom so naturally the give different readings. It does show me though how much pressure going in and how much pressure I am losing from the tired engine. I have 2 volt meters also and the are consistently different in voltage. What are your RPMs at idle? Heavier oil in a old engine has helped with some issues for me , just dont go to heavy.

Originally Posted by jyardgirl

dan what year is your 350 and is your fuel pump manual?

Ok, It's a '69-'79. Can't see the Stamp but I found the Casting number. Anyone got a pic of where the stamp is on a 350? I know it should be forward of the right side (passenger) cylinder head but I can't seem to see it...

Still don't know about the fuel pump...

fuel pump should be at the bottom or near it on the passenger side of the block if it is a manual. the numbers are on the rear behind the heads on the drivers side. the reason that i am asking about the fuel pump is that i had the same problem happen with the oil pressure on my 71 350. come to find out i had a hairline crack in my manual fuel pump and gas had gotten into my oil making my pressure all over the scale.