Vortec 350 help needed

[bud77]

Hey guys, after I finished rebuilding my trans and got it in, I broke it in for a couple weeks and then last weekend I decided to put it to the test. I pulled a 16' trailer with 5 quads on it on a 100 mile round trip ride to an ORV park, and while I was there I did some offroading/mud bogging with the truck. After we were done and got all the quads loaded back up, I started the truck up and it showed 0-1 psi of oil pressure at idle, and when I hit the throttle it only got up to about 20 psi max. Before, it would normally hit 60 psi when it was idling cold, 20 when idling hot and 40 while driving. Now it was at 40 idling cold, 0 idling hot and only 20 while driving. I thought the pump was going so I replaced it again (just did it 20,000 miles before this happened) with a Melling high volume oil pump. Got it all back together yesterday, started it up and it was back to 60 psi idling cold and as soon as I hit the gas it shot up to 70-80, when it warmed up it dropped to 20, but when I hit the gas it shot back up to 60-70. Put it back together and drove it around for a while, then when it got hot the same thing happened; 0-1 psi hot idle and only about 30 while driving. Also, when it's hot it seems like the starter has a hard time turning the engine over, like there's a lot of resistance or something. Does anyone have an idea of what's going on? Is it finally time to rebuild my 265,000 mile engine? Sorry about the length of the post, and thanks in advance for any help!

[GMstrong]

i would replace the oil pressure sensor.i would have just gotten a std volume oil pump.Its possbly your bearings are worn but it shouldnt just drop the oil pressure down like that,if the bearings where worn with excessive clearance it would have low oil pressure all the time.

[bud77]

I replaced the oil pressure sensor twice and I still get the same readings. I talked to the guy at advance auto and he said the only way I'd lose oil pressure is blow by from bad rings, but wouldn't that also cause low pressure all the time? Or only when the cylinders heat up? Started it to leave work today and one of the rods started making noise so something is going on in there. Put in some STP to try to help get it home, it's staying parked in the driveway until I get money to rebuild it. 383 here i come!

[88blackchevy]

The high volume pump is pumping your pan dry and/or aerating your oil. Put in a stock pump or a high pressure pump not high volume.

[GMstrong]

Its about that time fore a rebuild then what i would do is find another way to work before you throw a rod,then the motor is basically scrap.

[bud77]

88blackchevy, I replaced the original pump with a standard volume/pressure pump about 20,000 miles before this started happening. I went with a high volume/pressure pump this time just to see if it would make a difference, and it did when the engine was first started, but once it warmed up it lost pressure.

GMstrong, I got my uncle's 01 suburban to drive until i get the time/money to do the rebuild. I definitely don't want to take the chance at seriously messing anything up and needing to buy a new block on top of everything else.

[88blackchevy]

The guy at advanced auto is wrong blow by has nothing to do with oil pressure. It is also possible that the crank thrust bearing is worn and you are loosing oil pressure at the front main cap. Also check for a cracked oil pickup tube, it's worth pulling the pan and pulling a rod and main cap and checking crankshaft end play you may be able to repair the problem( for a while anyways)

[bud77]

The oil pickup tube is brand new, and the one I took out with the old pump didn't have any problems. I'm just going to rebuild the engine and I'll look for the cause of the problem while I'm doing it. I have another vehicle to drive for the time being, so I'm not really worried about fixing that problem right now. Thanks for the help guys!