REO

I bough 2005 Express 4.8 with 141000 miles, when i turned the eng. the oil pressure went to 39psi and gradually dropped to less than 10 psi. I turned the engine off for 10 to 15 second and i turned the engine back on, the oil pressure went up to close to 40 psi the start dropping again to less than 10 psi.
I replace the oil pressure sending unit no success, is doing the same thing.
before i install the new sending unit i replace the oil and the filter, I put 5w10. any advice?

canucklehead

What oil are you using?
These new engine require dexos rated 5 w 30 oil. Not full synthetic, and not conventional. Its a semi synthetic blend.
It sounds like the oil pressure is just low at idle....That could mean the oil pump is worn, or the engine has wear or both.
Just keep the oil volume up to the right level, and use the proper oil.
I had the same issue woth my 02 express, so I switched to high mileage oil which has higher zinc phosphate, etc. It seemed to improrve things a bit. However I don't know which high mileage oil you an use, since it has to be dexos approved.
Maybe one of the full synthetics out there has a high mileage version that will help.

jr32560

having the almost same issue with a 96--305--changed oil pump-- went to thicker oil 10-30--would run 40 psi cold --warm almost nothing at idle--went back to 5w-30-still about the same--guy I got it from had engine replaced years back said it never had oil pressure at idle--upper engine clicks sometimes at idle--heard from someone that valves out of adjustment would cause a low oil pressure--I'm stumped--any help would be great

canucklehead

have you checked with a mechanical gauge? Unscrew the sending unit and put a gauge on....just to be sure.

jr32560

yes I actually installed a mechanical oil gauge for a while it showed lower readings than the one in the dash-- it has 40 lbs of pressure cold as soon as the temp nears the 100 degree mark it drops off to almost nothing at idle -as I said I installed a high volume oil pump--someone said that if the lifters were out of adjustment it would cause low oil pressure--anyone ever heard of this issue on the 305 vortec???

canucklehead

jr, you should start your own thread, as the OP has the 4.8 litre engine which is very different to a 305.
Hopefully someone with an answer will respond to this and your thread.
I did read somewhere that high volume pumps can cause extra stress on the dizzy shaft and cause it to shear off or break in some other fashion.

REO

I install a manual gauge and is doing the same, but i notice that now is getting longer to drop the pressure down, but still going to 0 psi.
fyi.
I called to guy i purchased the the van from and I asking if there was any issue with the oil pressure before, he replied no except that the van was setting on his drive way for 4 to 6 years and he never turn it on.?????????????? I was thinking oil accumulation in the and slush and oil dry out all over inside the engine.??????? Or possible plunger in the oil pump stuck half way or no working properly.
I will take the oil pan off and see the condition of the pan inside as well remove the plunger and clean it. i it does not work i will replace the pump. Any advice before i jump in.
If i replace the pump, can i put and high performance pump from Melling? I Have a Express van with 4.8 engine.
Any advice.
thank you.

canucklehead

I would call a dealer shop and speak to a tech. They may have some insight on these new engines.

canucklehead

I have also read about a cheap oil filter that causes an issue. When you changed your oil, did you put on a quality filter. Are you using dexos rated oil?
How long was it since your last oil change? Sludge buildup can cause these issues, and since they came out with the oil monitoring system, folks tent to wait longer between oil changes.....My wife's HHR would have us at over 7000 kms between changes instead of the old 5000 kms......so I change it early. Better to always have clean oil than dirty.
As for the filters, I have read that Fram ones are junk, and better ones are only a couple more bucks.

REO

It look like that the problem could be worn out bearing,because I replaced the oil pump with a Merli high volume pump, and still doingthe same, when I start the vehicle the pressure goes all the way to 40 to45psi, and then coming back down gradually to 0 psi.
Will it be worth to replace the main bearing and rodbearing?
Any advice,