What's going on with this engine???...

BIG BLUE · August 8, 2002

Hey All,

I have a 91 with 4.3L (Z) engine. 193,000 miles and ready to shake hands with Elvis I'm afraid. Ok the cliff note version; for weeks I've had a rear main oil leak and have had a lot of blow by so much so that oil is forcing it's way out the pcv valve. Leaking and burning oil not the only problem, yesterday as I'm driving home the temp gauge spikes to 260 and I have no choice but to limp it home. Tons of blue smoke out the back and loud knocking noise like a rod was thrown. Didn't quite make it home and quit about a 1/2 mile from the driveway.

Fixed the hose coming from the block to the heater core cause it had split and lost all the coolant. Filled the radiator to capacity and added a qt of oil and let idle for 10-15 minutes. Now for the test run, took it about 1/2 mile and I hear this loud "pop" (kinda like a water balloon bursting) so I get it back home and find that the oil filler cap (not the screw on type) has been blown off and the pcv has been blown out of the valve cover! The pop was so strong on the oil filler cap that it blew a hole in the fire retardant material on the inside of the hood. If I remove the oil filler cap I can see/feel smoke coming out from the filler neck and increases with throttle response.

My questions; Why is there so much pressure in the block? Ran a couple more time and same result, it keeps blowing the pcv valve out. I drilled a hole in the rubber oil filler cap to relieve pressure there. The knocking is not very noticable like it's a rod so I'm thinking possible hole in the piston? It does act like it's only running on 5 cylinders cause it's rough idle and loss of power off the line. Any way to diagnose this? Not sure what to do, can't really run it like this, not sure what else will happen. I did see a 2.5L + tranny in the local paper with 50k on them for $500 would this be an even swap for the 4.3L I have?

Any help is appreciated (sorry for the book)

BIG BLUE

95 Silverado · August 8, 2002

you may have broken the rings or one of the pistons, if so that cylinder will have much lower compression than the rest, run a compression check and see what the results tell you.

Colorado Kid · August 13, 2002

My guess is a head gasket, because you seem to be overpresuring not only the crankcase, but also the cooling system, thus the popping heater hose. If you stop driving it now it probably qualifies as a rebuildable core, but if you go very far it's just going to be an engine shaped pile of junk parts.

MarkD · August 13, 2002

Both of the ideas above are good ones. I would probably do the compression check first.

Oh, and the truck is definately out of service. You might get another 50 miles out of it, but you will destroy the motor, and it aint worth it.

Did the detonation, or the high temp condition start first?

Detonation could cause abnormal cylinder pressures, overheating, blown head gasket, and break a ring or piston.

Overheating could cause detonation and you get the point.

Overheating could cause a warped head.

tfpary · August 30, 2002

I had a similiar situation on an old 82 C10 with a 305. After the hose blew I drove it 8 miles with no coolant. She was a tad bit warm, didn't want to shut off -dieseled real bad, and the thing was rattling like #### for the last mile. Shut it off, tried to restart it, and it was siezed, wouldn't turn over. Let it sit for three days and it started right up and is running yet. I must be lucky.

tad

Zembonez · October 31, 2002

I agree with Mark. The thing is toasted. If you stop now, it is probably very rebuildable and parts are cheap for the rebuild. Most everything in it is stock 350 parts. For no more than it would cost to build, it is probably worth puttin' that rig back on the road for a few more years.

After some thought... some head scratchin' and a re-read of your post. I might have jumped the gun when I said it was probably rebuildable... You may have cracked a head or worse.

Cop_Dodger · November 2, 2002

The excessive crank case pressure by could be caued by a few things. I worked on a truck with the exact same crank case pressure problems as yours does. He kept blowing out his dip stick tube and a few intake gaskets alot. Turns out he had a cloged vacume port on his throttle body. I cleaned out the carbon with a drillbit. I didn't use a drill, I turnded the bit by hand. It seams to clean out alot easier that way. Use alot of carborator cleaner too. The best way to check this is to pull the PCV holse and see if you have vacume. If you don't, you've got a cloged vacume line.

No telling what damage you've done with overheating it. If you lost all your coolent you don't know how hot it reallly got. Your truck messures the temperature of the coolent, not the motor. Overheating could crack the block or crack the intake along with break down the viscosity of the oil and lose lubrication. This could be where you get your knicking from. Check the oil level. Make sure you don't have any coolent in the oil. If it looks like a milkshake you've cracked something. When you crack the block or intake it alows coolent to flow into the oil. This will also cause lubrication problems. Let me know what damage you find.

Chances are you're going to be better off buying a new motor. The price to rebuild, machine work, and your time working on it normally influence you on going out and getting a new motor for it especially when you get a warrenty with a new or remanfactured motor. GOOD LUCK!!!