1st TA

iTrader: (5)

Like the title says I have a 4.8 in an 08 GMC Savana that has a strange problem.
At a cold start the oil pressure goes to 20 psi + or - and will not go any higher for the first 10 minutes or more of driving. After that it will go up to 40 psi + or - and is fine. If I get right on to the interstate and try to run 70 it will start in with a lifter knock that goes away after the pressure comes up. This is a high mile motor and you would expect it to be just opposite with higher pressure at start up and then drop after warm up.
Any help?

Ls1N20

iTrader: (6)

Kinda sounds like it's either the sending unit or the gauge itself

murphinator

iTrader: (2)

the knock going away as soon as the pressure returns to normal sounds ominous...

Ls1N20

iTrader: (6)

Guess i missed that, what oil filter and oil are you running?

1st TA

iTrader: (5)

I run the ac delco filter from wally world and Penzoil. Its just very odd that this is all backwards from what you would expect. This is a high mile motor as fare as I know as this was a delivery service vehicle, but runs fantastic other than the low pressure at start up. One would expect it to be higher at start up and lower once at operating temp. It is like something is stuck and then opens or closes. I have replace the sending unit and also installed a mech. gauge temporarily . As stated in the first post pressure is low for the first 10 min. of driving and than goes up. I have read threads about the pressure relief at the pump sticking but to start low and go higher doesn't sound like the relief valve. As for the knock it only seems to happen if I get on the interstate right away and do 70. If I stay at 55 or less until the pressure comes up it doesn't tend to happen.
Any thoughts?
Thanks for the replies, keep them coming.

Ls1N20

iTrader: (6)

Maybe switch to a heavier cold oil like a 10-30

1st TA

iTrader: (5)

What would the chanced be of the o ring at the oil pickup tube not sealing cold but swells enough to seal once the oil temp comes up? Just looking for some ideas.

RockinWs6

BINGO! You could go to Walmart and grab some TransX like i did and swell the o ring back to size.

Tim94gt

iTrader: (2)

My Sierra has done the same thing for the past 3 winters. Started around 110k miles or so.

I've always ran M1 w/ a delco or k&N oil filter, doing oil changes every 3 months since brand new.

This year, I decided to try a different weight oil and went with the European M1 0w-40 and it's been a lot better. Only has issues on extreme cold days that are under 20* F, but it's around 30psi instead of 20psi.

I figured it was the o-ring as well, which I'll replace when I eventually get around to putting the heads and cam in, lol

1st TA

iTrader: (5)

So how long did you run with the TransX in it?

98Zheadsncam

iTrader: (26)

For what it's worth, I just had an issue with my motor not showing any oil pressure on a cold start. Took 5 - 8 seconds for it to show pressure. Even then, it wouldn't make the usual psi - normally 60+ and it was showing like 45.


I pulled the filter and changed the oil yesterday..problem solved. It was a delco filter. Not sure what happened...it was definitely the filter though. I'll be using K&N or Wix from now on.

1st TA

iTrader: (5)

This has been going on for quit a while. In my case I don't believe it is filter related. I have always used the AC Delco filters from wally world on this and other vehicles. This is a high mile motor and I don't expect the pressure to be fantastic but shouldn't be doing what it is doing. It is do for an oil change so I may change to different filter but I don't expect it to make any change.
Keep the idea's coming.
Thanks

1st TA

iTrader: (5)

Changed the o ring on the oil pickup tube this weekend. Did the trick. Started it up and it went to 40 psi. We'll see how it does in the morning when I head to work.