Oil pressure issue

[Norwester]

My 350 has around 30K miles on it. Something new has taken place.

When I start the engine, I watch the oil pressure and up till today, it always jumped up very quickly. Twice now, when I started the engine, the gauge stays at "0" for maybe 15 seconds or so and then it jumps right up. I have great pressure running down the road.

The engine runs great and uses very little oil.

What should I be looking for? Is it a sign that the pump is wearing out? Something more serious?

Thanks in advance.

 

[1987 GMC Jimmy]

What I'd do is borrow a diagnostic pressure tester from Autozone and see if you get those same results. If not, it's likely just a faulty sending unit. If so, something's up. It could be the oil pump, but I think the bypass in the oil filter could be plugged or something like that so maybe try replacing the filter and making sure the pickup is unobstructed. I wouldn't think it's sludge, failing internals, or anything that you'd normally see with a tired engine. What kind of a filter are you using? Wix, Delco, STP, and NAPA Gold are a few good ones that I've used. Most are good, but Fram is very bad. Don't use that one. If you're running a PCV valve, give it a shake and make sure it rattles since we're on the topic of oil.

 

[74 Shortbed]

Sounds like the anti-drain back in the filter is stuck open and the filter has to fill back up to have pressure.

 

[Norwester]

I do appreciate the responses, Fellas. Gives me something to think about. As for the filter, I have no idea as I don't do my oil changes. I shined a light and all I see is that it's black in color. Filters are cheap...maybe I'll replace it and see what happens.

Thanks, again.

 

[1987 GMC Jimmy]

Ahh, well if you take it to a Wal-Mart TLE, I can guarantee you it's got a Fram on it. Anywhere else, it just depends. My mom took her current vehicle there for fourteen years, but I told her she should stop, and I change it now. Most of the people working at that particular place are the lowest common denominator in the auto repair industry.

 

[chengny]

My 350 has around 30K miles on it. Something new has taken place.

When I start the engine, I watch the oil pressure and up till today, it always jumped up very quickly. Twice now, when I started the engine, the gauge stays at "0" for maybe 15 seconds or so and then it jumps right up. I have great pressure running down the road.

The engine runs great and uses very little oil.

What should I be looking for? Is it a sign that the pump is wearing out? Something more serious?

Thanks in advance.

You should have a CHOKE warning light on your dash. With the ignition switch in the RUN position, that CHOKE light should illuminate and stay lit. Only when the key is moved to START and the engine fires, should the CHOKE light be extinguished - almost immediately.

The reason I mention the CHOKE light is because it is switched on/off by engine oil pressure. As soon as the engine is fired up and sufficient oil pressure is established (approximately 10 psi), the oil pressure switch closes and supplies power to the coil of the choke heater. This causes the choke plates to open as quickly as possible.

So, in your case, during that lag period (after the engine starts and before your dash gauge indicates pressure)...watch the CHOKE light.

If it immediately goes out when the engine fires, you can assume a problem with the oil pressure gauge or its associated wiring.

On the other hand, if the CHOKE light remains lit (or flickers) during the period that the gauge doesn't move off 0 psi (and only goes out when the gauge jumps up)...it might be that there is an oil flow problem.

Oil pressure gauge operation is the opposite of the other gauges; as the oil pressure increases so does the resistance across the sender - and increased resistance in the gauge's sending leg will drive the needle higher. Conversely, lower resistance in the sending leg will tend to pull the needle towards the low end.

So, taken to the extremes:

A disconnected/broken (high resistance) lead to the sender will peg the gauge high.
A short circuit to ground in the sensing leg will keep the needle pegged low.

Since your truck only has 30K miles, I would suspect a failing sender before a wiring issue.

Observe the CHOKE light operation first.

 

[HotRodPC]

I'm going to go with the check valve in the Oil Filter is bad. It's cheap enough, I'd start there and see what you got and go from there as far as diagnosis.

 

[74 Shortbed]

Filters are cheap...maybe I'll replace it and see what happens.

Put a WIX on or a Napa Gold since they are a Wix..

 

[Norwester]

I want to thank everybody for the comments. As always, you guys have a wealth of information. I'm pretty much a non-mechanic so I appreciate the help.

 

[AustinDube]

I have a 76 k10 and I had the same issue. Mine had 30,000 miles but sat a long time. I had to do the rms anyways so I threw a high volume oil pump and now I get about 45-50 on startup-warmup and 25-35 when idling