CARL67

Oil pressure gauge goes to zero at idle. If I press gas pedal or place transmission in neutral, oil pressure goes back up. Any suggestions on what might be the problem?

Thanks

Bustedback

Most likely the sending unit. What brand of oil filter are you using?

blakexcore

Sending unit.

lindaw1953

my 01 6 cyl is doing the same thing it drops to 10 when its idling and as soon as I give it gas it goes back up Ive changed the sensor, oil and filter cant figure it out some one said to change the oil pump and then heard something about a crank sensor I hope some one can give me an idea here getting a little flustered

blakexcore

Mine was doing this the other day. Idling around 10 psi, and around 35-40 psi with throttle. I just changed the oil and filter and it fixed it. Then again, the PO had a fram oil filter on it lol. Your situation may be different.

bigbadon

What year?? Some model years did not even have a real gauge...less than 7psi will send gauge to zero. If your worried about it look through the oil fill cap after the engine has been idling for a few minutes. If you see oil flowing across top of head your good.

Bustedback

Oil pumps do not make pressure. It's the tight clearences between the bearings and the crank, rods, and cam, also the lifter bore clearence that make the pressure. Put a gauge on your garden hose and turn the water on without a nozzle or any restriction, the gauge will read little to no pressure. Now put your thumb over the end of the hose and watch the pressure go up. It was the restriction that made pressure.

lindaw1953

Bustedback so what r u saying I should do about it rebuild my engine

Bustedback

No, I'm the just giving a tutorial of how oil pressure works. Remove the sending unit and screw a mechanical gauge into the block and see what the actual oil pressure is before doing anything else.

bigbadon

^1 Rebuilding is your call but low oil pressure does not mean your engine is going to blow up tomorrow. You have time. When the engine gets close to the catastrophic happening it will begin to talk to you. My gauge has read zero at idle for years. Verified 4 psi with mechanical gauge and 20 psi at highway speeds. If you have the time and budget to rebuild go ahead but I think you may be jumping the gun.

dave1123

Again, I'm not too familiar with Dodge V8s or the 4.0 six, but GMs small block V8s are what's known as "lifter priority" oiling systems; that is, oil is supplied from the pump directly to the oil galleries supplying the lifters first, then to the bearings. Lifter body clearances and lifter leakdown is critical to oil pressure, most notably at low engine speeds. That's why most guys rebuilding the small block install a high volume pump.

Like Busted said, check your oil pressure with a good mechanical guage, preferably with a 100 psi guage. This way you won't be near the top of the range, which isn't good with any guage.

bigbadon

Excellent point and the 4.0 is "lifter priority" also. It is strange that people overlook the lifter bores and that is the one thing that affects oil pressure more than anything else. Now the good news...if a worn lifter bores are indeed causing the low pressure the engine reliability is not impacted that much. If the engine is driven sensibly it will go a long time.

dave1123

With the Chevy small block, bad lifter bores is the main reason for blocks being trashed. Of course, any good machinist will tell you this can be fixed, but because of the close tolerances involved, nobody wants to spend the time and money to accomplish this.

I drove a company delivery truck (Chevy) for over 2 years that showed 0 pressure at idle. I kept waiting for it to blow up, but it was still going when I left the company.