Intermittent Oil Pressure Fluctuation

[justgurn]

2001 2500HD 4x4 6.0L 181,000 miles

 

Sorry for the lengthy dissertation to get to a simple question, but I’m all about knowing how the problem came to be. By the way all to the parts replaced were OEM.

 

First a little history, I’ve put the last 150k miles on my truck. I always drop the oil hot and every 3000 miles. If some breaks I fix it. I pull a horse trailer and a flat bed trailer.

 

The problem started after pulling a heavy load where she got a little hot not overheated, but hot enough where I slowed down and let her cool down. Everything came back to normal. The next morning when I started the engine it had zero oil pressure. Gauge flat lined and the Message Center warned low oil pressure. I shut it off and check the oil it was full, so I started it again same thing. There was no knocking or engine noise. After a couple of cycles of starting the engine the oil pressure came up to 20 psi. I then drove the truck down the road and the oil pressure came up to 50 psi and remained. After that I changed the oil-sending unit, which seemed to resolve the problem.

 

Roughly, 2000 miles later I’m experiencing the same problem except the oil pressure is dropping from 60 to 40 psi after driving 3 miles and a cold start. There is a little upper engine noise. I’ll pull over and idle the engine down and the problem goes away.

 

I’ve determined if the oil pressure comes up normal (idle around 45 psi 2500 rpm 65–70 psi) I won’t have the oil pressure problem. However if the oil pressure is slow to develop then I’ll experience the oil pressure fluctuation. Here where it gets interesting. This is intermittent it can go to days and no problems then acts up.

 

Last summer I replaced the oil pan due to leaks and this weekend I replaced the oil cooler lines because of a leak, I know this is not related, but it might help.

 

Could the pressure valve in the oil pump be causing this problem?

 

I’m thinking the oil pump on this engine is a squeeze pump, so its working or not, but it has a pressure valve.

 

I’ve heard of lifters causing oil pressure problems, but think it would be more constant.

 

I’m out of logical reasons of why this is happening.

 

Thanks for any help you can offer.

[chevroletmb]

i have seen the pressure relief valve on the oil pump cause oil pressure issues also the oil pickup has an o-ring that can let air into the pump. it may have been disturbed when you changed the oil pan.

[justgurn]

Thanks for the help.

 

I think I'm going to plum in a manual gauge and watch it for a while. Hopefully, it will point the relief valve. If I'm thinking correct, I will have to drop the pan to replace the pump.

[chevroletmb]

the oil pump on that engine is crankshaft driven, so the oil pan, waterpump, crank balancer and front cover gottta come off to get at it.

[royg]

sounds like the o-ring on the oil pick up tube. had a couple of trucks do this. putting a mechanical gauge on it is good. I did that also. Pull the oil pan, remove the bolt that holds the pick up tube and see if the o-ring has a tight seal. If not this is your problem. The only thing that concerns me is the 0 psi. the ones that i hae done the oil pressure was a little low at idle about 30 psi and would not go up with increased rpm. You're going to have to remove the oil pan anyway to check the oil pump. Hope it's the o-ring not the oil pump it's a lot cheaper and and a lot less work.

[justgurn]

Thanks for your advice Royg. I've not thought about the o-ring. Here's what’s got me scratching my head. For the last five days the oil pressure has been strong (65psi) from cold to operating temp. Whatever the problem it’s not giving up easy. It’s game over for this mystery! I’ve ordered an oil pump and going to slap it on next week. I’ll make sure to replace the o-ring while I’m at it.

 

Thanks everyone for the help.

[teddeshong]

Thanks for your advice Royg. I've not thought about the o-ring. Here's what's got me scratching my head. For the last five days the oil pressure has been strong (65psi) from cold to operating temp. Whatever the problem it's not giving up easy. It's game over for this mystery! I've ordered an oil pump and going to slap it on next week. I'll make sure to replace the o-ring while I'm at it.

 

Thanks everyone for the help.

[teddeshong]

Did the new oil pump fix tyhis problem? I realize this goes back to 2007. Hope you are still around. I have the same issues on 2002 Yukon XL 5.3L Flex Fuel version (LM7/L59). My oil drops to zero at idle, light and bell come on, engine starts clicking. Has been intermittent. Will not do it at all for a week or two. I am chasing the same remedies you chased. How did it turn out? Thanks