1996 K3500 5.7 vortec help troubleshoot

Logan Lanfear · November 1, 2017

Man, 100,000 on an engine and the head gasket went? Sounds a little unusual to me

green 788 · November 1, 2017

I had overheated it pretty badly a couple times in the past year... I guess that did the head gasket in. Oh well...

green 788 · November 15, 2017

Garage found 2 blown head gaskets... blown between cylinders 4 and 6 ... valves on cylinder 4 bent (I saw the head)... so I had 2 rebuilt heads put on the engine, and a new spider injector system, and new exhaust manifolds on both sides.

Cat converters were clogged. We "unclogged" them. This is probably where all of the trouble started, honestly.

Truck is running great as of now, better than in recent memory. I do hope it'll continue to do well. Bottom end seemed good, 102k on that crate motor, so now with new heads I hope the rings hold out well. Time will tell.

Lessons learned...

Check catalytic converters often. Replacing them with high flow units on older trucks is probably a good idea. Either that, or ventilate them (so to speak)... :o

Don't assume that just because there is no coolant coming from the exhaust or bubbles in the radiator that your head gaskets are good. If they blow between 2 cylinders the classic symptoms may not be present.

If someone does a cylinder leak down test for you, be sure they know what they're doing. All plugs need to be removed, not 1 plug at a time as the first mechanic did. He told me he was getting air in the crankcase which meant blown piston or rings. He advised to junk the engine and replace it. Fortunately, he was mistaken. He put air on cylinder 6 and heard air coming from the dipstick tube, and figured the piston and/or rings were bad. But what was really happening is he was blowing air through to cylinder 4 (via the blown head gasket between 4 and 6) and the air went on into the intake through bad or open valves, and with the PCV valve still hooked up (you're supposed to disconnect it) the air went into the crankcase via the intake plenum.

I'll add more later, if necessary. I just didn't want to do what 8 out of 10 motards do and leave a thread hanging with no resolution. :o

Logan Lanfear · November 15, 2017

23 hours ago, green 788 said:

Garage found 2 blown head gaskets... blown between cylinders 4 and 6 ... valves on cylinder 4 bent (I saw the head)... so I had 2 rebuilt heads put on the engine, and a new spider injector system, and new exhaust manifolds on both sides.

Cat converters were clogged. We "unclogged" them. This is probably where all of the trouble started, honestly.

Truck is running great as of now, better than in recent memory. I do hope it'll continue to do well. Bottom end seemed good, 102k on that crate motor, so now with new heads I hope the rings hold out well. Time will tell.

Lessons learned...

Check catalytic converters often. Replacing them with high flow units on older trucks is probably a good idea. Either that, or ventilate them (so to speak)... :o

Don't assume that just because there is no coolant coming from the exhaust or bubbles in the radiator that your head gaskets are good. If they blow between 2 cylinders the classic symptoms may not be present.

If someone does a cylinder leak down test for you, be sure they know what they're doing. All plugs need to be removed, not 1 plug at a time as the first mechanic did. He told me he was getting air in the crankcase which meant blown piston or rings. He advised to junk the engine and replace it. Fortunately, he was mistaken. He put air on cylinder 6 and heard air coming from the dipstick tube, and figured the piston and/or rings were bad. But what was really happening is he was blowing air through to cylinder 4 (via the blown head gasket between 4 and 6) and the air went on into the intake through bad or open valves, and with the PCV valve still hooked up (you're supposed to disconnect it) the air went into the crankcase via the intake plenum.

I'll add more later, if necessary. I just didn't want to do what 8 out of 10 motards do and leave a thread hanging with no resolution. :o

Sounds like a good bit of work, thanks for the update.

green 788 · November 16, 2017

Pic of my engine at the garage with heads off... I was able to get 2 rebuilt heads from a vendor in North Carolina (found him on ebay)... they're working great.

If I'd have cleaned out the catalytic converters last year I'd have probably been fine... an expensive lesson for sure.