This is for a Chevy 1500. Not thirdgen...sorry. But it is techy.

Anyway, as I have mentioned before, I have a '96, Vortec 350 powered 1500, ECSB 4x4. The exhaust is dual back to the muffler, I assume like all '96 - '98 Vortec's. The pipes are pretty puny -about 1-3/4" I.D. I thought that was pretty weak, but figured it was designed that way to enhance low end torque.

So here is the wacky thing. The trucks we have here at work (the '96 - '98 trucks) are all 2500, SCLB, 4x4's. They have the exact same, 255 horse Vortec 350. BUT, they have 2-1/2" pipes!

What's up with that? Why would the 2500 have bigger pipes (and Cat's too), and how coudl it have the same hp rating? They have a noticable deeper exahust note to them. What gives with this odd difference?

Second question; One of the 350 vortec powered 2500 trucks we have at work siezed up last week. It has 30,000 almost all-off road miles. It had just been in the shop for a cooland leak on the intake. We replaced the intake gaskets, re-assembled, and changed the oil and filter. It ran great for about 4 days, and then one of my mechanics drove it down to Salt Lake City (about 30 miles each way, over 8000' elevation Parleys Summit). Coming back up Parleys Canyon, it seriously lost power. The operator, my mechanic, scanned the gauges and noted 210* temps and 40 PSI oil presure, accompanied by a light rod knock. He pulled over(he to because the truck was dropping speed so rapidly), checked the oil (clean and full) and then proceeded. It ran good and accelerated up to 60 mph went about a mile and did the same thing. The operator called me for advise. Having no resources to go tow him back, and knowing that the thing had oil in it, I told him to proceed slowly and causiously. At this point it had variable and generally low oil presure, and a good rod knock. He drove it another mileduring which time the engine never built more than 20 PSI oil pressure, and then it siezed up.

We pulled the motor and dropped the pan. Three spun bearings; #'s 8 (first to get oil), 3 and 4. 3 & 4 were the ones that had siezed and the rod ends are now blue. I found a piece of debris in the oil passagein the crank AFTER #3 (between 3 & 2). It looks like slag, and is ferrous (magnetic), so I don't belive that it's bearing material. There is another piece still stuck further in. Both pieces are roughly 1/8". I could find no debris before or after the #8 bearing. The oil pump looks like something went through it, but certainly not a couple of 1/8" pieces of slag!

How could debris of that size make it through the filter (CarQuest premium/Wix)? How could debris get through the pump and still exist? Then how could it pass through 4 journals, causing no damage and still be 1/8"?? What caused this failure?? Where did that debris come from? Why did the engine lose oil presure? The pump looks fine, the pick-up tube was in place and the screen looked very clean. Everything in the engine looked clean. I sure would like to know what caused the failure. Please input.

 

The Pan DID have alot of metal in it. I think it was "post damage" metal. We just cut the filter open, and it was definitely trying to do it's job; the pump side it riddled with metal filings, but the engine side (the inside) was still fairly clean.

 

where on the intake was it leaking?
If it was the intake manifold gaskets its possiple that the coolant got into the oil what did that look like after fixing the leak. having water in the oil will ruin the bearings and they wil eventally spin

 

Yeah, good point, but I already thought about that, and we checked for that when we did the gasket change.

We first checked the oil level, and it was at the full mark, where all operators maintain it, (so it wasn't too high from coolant). When we drained the oil we were very careful to look for coolant coming out of the drain and we saw NONE. PLUS, we drained it into a clear container and let it settle, then looked at the bottom of the clear pan for "drops" of the orange liquid, and again, we didn't find any.

The cooland leak was from the front cross over passage (there's none in the rear), and it was coming out the top, running allong the top of the manifold flange and down the front of the engine. I definitely realized the possibility of coolant getting into the oil and looked hard for that, but I feel confident that the leak was external only.

Some contamination made its way into the valley areaas the intake came off, despite a rigorous "blow job" with an air gun prior to lifting off the manifold. The debris that did make it down in there was cleaned out thoroughly, but some may have made it all the way down into the oil pan. I would think that the filter woudl have caught any of that though.

 

A siezed up 350 full of good fresh oil. That doesn't happen too often. I would REALLY like to know why this failed. Could that slag like material have been in the crank since it was new and just recently moved around? I mainly would like to know why the failure occured so it doesn't happen again, and to know where to place the accountability.

 

i work at a gm dealership (don't tell anybody) and i see a lot of the Low torque intake gaskets fail. the coolant leaks internally and/or externally. well if it leaks internally, the customer just adds coolant (well some don't even know where to add coolant, so filling the coolant jug would be out of the question). if it leaks externally, they USUALLY take it to get fixed. the intake gaskets are made of a hard black plastic, with soft blue rubber around the coolant and intake ports. what causes the problem is after a while the blue rubber separates from the hard black plastic causing a internal and/or external leak. the coolant leaks into the engine oil and eats the bearings causing engine failure. i have replaced several vortec 350's for this problem...including my uncle's 98 k1500 with 73k, and several 3.1,3.4, 4.3 liter motors. it is no fun replacing a 3.4 liter motor in a venture van (have to drop cradle/motor/trans as a unit) as to whom to blame....has the operater added coolant (or ran it out of coolant) without getting the problem fixed? who knows? best of luck, tom....keep us updated.