SnoDrtRider

Hi!

This is a bit long but I wanted to cover all the bases

I recently purchased a 2006 Express 2500 series with the 4.8 engine. It has 220,000 miles but a one owner and LOOKS well taken care of.

I took it for a test ride before buying it and it ran and drove well. I did notice the oil pressure at idle was a bit low after warm up but not enough to concern me. I am a (former) ASE Certified Master Tech so things like high miles really don't concern me.
I took the truck for tires today and after warming it up in the yard the oil gauge was low and the "check guages" light came on. I held the idle up a bit and the gauge came up and light went out. I figured a bad sending unit.
I got to the tire shop (just a few miles) and noticed a slight tapping like lifters.
Once again I held the idle up and the gauge came up and noise went away. I checked the oil level and it is good.
I picked the van up and drove it to the gas station, filled the tank and drove home (4-5 miles total) the van ran great and there were no problems. I pull in the yard and I hear the tapping again and the gauge is low. Once again I raise the idle and the gauge come up and tapping ceases.
I was installing the shelving and racks from my old van and occasionally I would start the van to move it and let it run. The low gauge/tapping has not returned and in fact the gauge is now reading a higher pressure at idle than previously (what I would consider normal)

Comments, Suggestions, Possible Problems?

Also...

I was doing a search and came across a thread mentioning a filter below the oil sender on a (5.7? I think) does the 4.8 also have this filter and is it between the pump and the lifter oil supply galleys?

I plan on changing the oil and filter in the next day or two is there anything I can access externally like a bypass valve that could be getting stuck?

I also did a search for an oil flow schematic for this truck/engine so I could see the flow chart but came up blank.

Thanks in advance for any help!

SnoDrtRider

Today's update:

Went to my buddies shop and the opinion of the collective motorheads including the guy that owns the machine shop we use was first change the oil, put a good filter on it and a mechanical gauge to verify the pressure.
I did so using an AC/Delco filter and 5-20 Valvoline High Mileage. He didn't have the proper adapter for the gauge so I just replaced the sender.

No Change and probably worse because someone had put heavier weight oil or an additive in before.

Dropped the pan... Pickup is and the entire inside of the engine is as clean as a whistle.

Pulled the front cover and oil pump... nothing really visually worn in the pump and the housings still have manufacturing machine marks. The only thing noteworthy is the bypass spring is very weak. Never having one of these pumps apart we are not sure if that is normal or not. When I took the cap/plug out of the bypass bore I expected to need to keep pressure on the cap to prevent the cap from flying across the shop as we are used to on "regular" oil pumps.
Can't get a pump for a few days at the places I checked (Auto Zone) and NAPA says it is a dealer item? As are the pan and front cover gaskets (Auto Zone has the pan and lists the Timing cover) BTW AZ can get a High Volume/Pressure Melling pump which I would prefer.

I will check a few other local parts houses tomorrow as it was late today (just now) when I got done.

On an up note the 4.8 (and I assume all vortec) engine is a dream to work on! I had the pan out in less than an hour.

SWHouston

First thing I thought of was the popoff/regulator, but...
I was thinking it may have had a piece of trash stuck in it, in stead of a weak spring. That is what I think your problem is, at least in part. Last time I took one apart, I remember that spring being pretty darn stiff.

Are you sure you really need a HiCap Pump ?
A Rebuilt or new OEM with some 10/30 or 10/40 probably will get the pressure up ok.
Having that pan off, would have been a good opportunity to roll some new mains, and rod bearings in there.

Glad you got a good deal, good luck with it.

SnoDrtRider

Cleaned all the parts up today to prep for re-assembly. Pump and Timing gastets won't be here until tomorrow.
As far as the hi/flow pump it was $25 more so I figure why not... could make up for any worn bearings as long as I don't blow the valve covers off!
Looked at the cam from below and it looks like new as far as I can tell.

Never knocked even with zero pressure so I'm closing my eyes to the bearings... been there done that with a buddy. He spun a bearing and had a little rattle on a Toyota PU so we dropped the pan and replaced the rod bearings... polished the journals, Plastigauge, etc. he was suppose to get rid of of it but a month later another bearing spun. I like to leave well enough alone.

Couple issues in looking at all the old gaskets... the oil pan gasket at the oil filter passages... the built in "O" ring seems to be thinner around the passages than the metal of the gasket body... a possible bypass of the gasket was possible although there were no external leaks.

SWHouston

HA HA, I herd that !

On the Pump,,, $25 more than how much ?

The way you're going about this, I wouldn't be surprised if you didn't get another 200K out of it.

SnoDrtRider

On the pump... called the local NAPA store that we deal with all the time. I had just gotten an oil sender the day before from them. I ask for an oil pump, pan gasket and timing cover gasket. Guy says they don't list the 4.8 for that van. only the 5.7 or 6.0. So he checks for the gaskets and comes up with "Dealer Only" I tell him Auto Zone lists everything.
Anyway AZ has the pan gasket in stock and I order the pump and timing cover gasket from them.

Here is a link to the pump I ordered.
The stock no name pump was $115 or $125

Melling/Oil Pump - Performance (10296) | AutoZone.com

SWHouston

Thanks for the link !

But what's going on there ?
Does that mean that somebody dropped the 4.8 in there at some point ?
And if so, that 220K may not be as realistic as thought.

Also, except for the word ""performance", I didn't see where it said that the Melling Pump was hi output/pressure. How do you know that for sure ?

SnoDrtRider

The engine is original... apparently NAPA just does not carry the parts.

The pump number is 10296...

Melling site... Cast Iron & Aluminum Oil Pumps

When researching parts and problems Google is your friend!

BTW...

Several friends have convinced me to drop a rod and main cap to take a peek while the pan is off.

SWHouston

Again, thanks for the link, but, I thought you'd already looked n gaged the journals.

SnoDrtRider

No... that was a Toyota that I was explaining about that we did quite a few years ago... maybe I wasn't clear.