**I posted this a few days ago in the truck section**
I changed my oil yesterday and did an engine flush (Amsoil product), just before the change. When I started the truck back up, my truck did the normal thing, start out low, then come back up on pressure. This time it took too long to come up in pressure and the low oil pressure light came on for an instant, then shut off after pressure starting coming up. After I ran it for a little while at idle, I took it for a test spin and noticed my oil pressure didn't come up as high as it used to. I have a Thunder Racing LS-6 modified oil pump and usually can nearly peg the gauge at WOT. I tried punching it a few times, but the pressure would not come up much past 20.

I started wondering if it may have been the thicker oil that I had put in. I switched over to syn 20W-50 and thought that may have been it. That was the only thing that had changed from my normal, so I thought that must be it. So, I drained about half of it and put in 10W-30, and it did get a little better. This morning I drove it to work, babying it. Pressure stayed a little above 20. During lunch I changed the filter and 6 fresh qts of 10W-30. Not much change in pressure, so I tried to take it a little easy. So, after work I'm coming home and at idle I got the oil pressure low alert and pulled over - gauge had almost bottomed out. I checked for leaks everywhere - nothing. I cranked back up and alert was gone and pressure was up about 20.

I have it home now and am wondering what to do. The only thing I can think of is the engine flush has broken so much stuff free, that maybe my screen is clogged (wherever that is located), or my pump has crapped out on me.

Any suggestions? Has anyone seen this screen? Does anyone have any pics? And lastly, how the hell do you get the pan off with the engine still in? Does it need to come off?
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Since then, I have lowered the front diff carrier and took off my oil pan and oil pump. I checked the pickup tube screen and pump. I took off the LS6 TR ported oil pump and put my stock pump back on. Everything was fine until I changed the oil. I put this pump on in Jan and have zero problems with oil pressure until now. I have a new sending unit that I have purchased and plan to install today - maybe.

The truck, in the morning, starts up and will idle at nearly 20psi. While driving at 2k RPMs it will sit at about 20 psi. Under about 3k RPMs, it will go up to about 30psi. As it gets warmer, it starts to degrade slightly under power, and at idle and even will bottom out at idle at the red light.

I know that the fault usually lies with the o-ring seal. But, if that were an issue, would it just come out of nowhere?

 

How many miles does your truck have? When you do the engine flush and then change to Amsoil you could experience these problems IF you have 100,000+ miles.

We need to keep a sense of logic here.
--First, you changed no other parts nor did no other work on the car EXCEPT for doing the engine flush and changing the oil, right?
--This means that it MUST be something associated with this process provided you are using a similar weight oil. A 20w50 Amsoil should be thicker than a 10w30 std oil. If anything your pressure should go up.

What vehicle is this engine in and is it an LS1 engine?

 

Nope, only an oil change. The last thing I did was replace a cam about 2 weeks ago.

This is 2003 6.0L, with only 12,000 miles.

 

Really depending on you guys for help. Any suggestions? I replaced the oil pressure sending unit, no change.

Has anyone ever heard of the collar breaking that the oil pump rides on - the part that attaches to the crank pulley? I have a rollmaster double roller timing chain. What would it do if the screw on post (threaded area) for the oil filter was cracked? Or, maybe the bypass valve located just above that screw on post is malfunctioning?

What about shot bearings? Would that cause this to happen?

 

could be your oil pump about to take a dump on you.

 

I think the problem is the oil pump...like anything, it just decided to go.

 

double check the oring ? If nothing else is your motor still under warranty? You could have gm figure it out for you. I doubt its your clearances given the low milage of your truck and you said you switched the pump out already right? What does this engine flush do? Does it have any weird chemicals in it?

 

I swapped the oil pump back to stock and it didn't make any difference. Is there a chance that the o-ring went bad, just from an oil change?

The engine flush doesn't have any chemicals that would be harmful to the motor. It's made by Amsoil.

The one thing that I did was not fill the oil filter with oil before installing. For like the first time in 10 years. Is it possible that that brief moment without oil, caused engine damage - lasted about 30seconds?

 

I had something similar happen to me after I changed my cam. My pressure was great for a while and then out of nowhere it dropped off and started to get the same symptoms as yours. I changed out the pump and O ring and everything went back to normal. I'm sure it was the O ring in my case but changed the pump as well because if it turned out to be more than just O ring I didn't want to tear it back down for a third time.

 

I know this is old but Did you ever figure out what the problem was? My truck is doing the same thing 03 GMC 5.3!