redknife

Summary: Well running 225K mile Jasper reman (unknown date but not recent) Jeep 89 XJ 4L sustained major overheating event. After event engine runs but there is a new loud knock, uneven sounding crank, and exhaust gasses pressurizing coolant. I think there enough evidence to call the engine as needing rebuild/replacing now. I am looking for additional opinions.

Background: Most recent service was to cooling system for low engine temps. I found no thermostat, installed new T-stat, replaced water pump, fan clutch, and thoroughly flushed system. All replaced parts were bad. Ran perfectly for a few weeks with rock steady engine temps about 200 after warmup. My daughter was driving Jeep and called after engine stalled and there was “smoke everywhere”.
I found: engine block 450F by IR gun 45 minutes after she stalled out. No coolant. Coolant reservoir ruptured.
Let the Jeep cool overnight, replaced the reservoir, filled and burped coolant, drove it few miles home. New loud engine knock, irregular crank at startup.

Current: On cold startup, there is immediate high pressurization of coolant system. With cap loose, gas and coolant are rushing out around the cap. With cap closed, pressure is building rapidly in the container. I tried a chemical test for combustion products in coolant but the pressure is so severe it pushes coolant and gas into the tester rapidly. There is also a hole in the radiator made apparent once T-stat opens. There is a loud, bad sounding engine knock. The crank sound used to be consistent but is now irregular sounding (good battery). Oil is normal appearing.

Question: Is there enough evidence at this point to call the engine needing repair/replace? Would dropping the oil pan or other diagnostics change the next step of pulling the engine? I am confident the head gasket and probably the head are bad. What’s your next step?
​​​​​​​tx!

Saudade

You should perform a leakdown and compression test before you start ripping things apart.

redknife

will do

redknife

Limited time today, but:
cylinder 3 leak down at 60% loss with air coming from radiator hole confirming bad head gasket and cause of coolant system pressurization.
Starter solenoid stopped working, presumably from being bathed in coolant. Will take a day or two to get around to fixing the starter allowing compression test…

lawsoncl

Not sure a compression test is needed. Sounds like the next step is pulling the head and surveying the damage. Hopefully just a head gasket and not damaged or cracked cylinders, but I'd have the head checked regardless.

awg

The loud banging knock sounds like more than just a head gasket

exasemech

I'm amazed the thing runs at all. If it was 450 degrees 45 min after it died who knows what it was at the time. Remember that 450 or so is hot enough to ignite paper.
in addition to the obvious I wonder about the state of seals, insulation on wiring and depending on what they were made out of and how hot it got, various springs ( oil pressure relief valve , lifters, etc.
Sadly I've been around long enough to remember air-cooled (which is what you had here) engine fires (Corvair, VW, Porsche). The magnesium fueled WW fires were very impressive.
It will be interesting to see what you discover .

Saudade

Sounds like you definitely need a head gasket (at least). I don't think you need a compression test now.

Keep us posted.

redknife

It does

redknife

That’ll be my next move then. Thanks

exasemech

FWIW if there is a way to do a compression test before you pull the head. It wouldn't hurt anything to do it and it may tell you something. It would be a drag to open it up "looks OK" put a new head and gasket on it and find out later a piston had temporarily seized and the rings are smeared into the grooves or similar during this adventure.
it never hurts to have more information and it doesn't cost anything
As others have mentioned, given the knock.........

doublechaz

More info never hurt unless the knocking is tearing away a cylinder wall and turning it more makes the damage too deep to machine away. An engine that ridiculously abused is going to need every single dimension and surface carefully examined. That kind of heat and it will need to be decked, bored, line honed. I would be concerned whether the lifter bores are still round. The whole thing should be magnafluxed. If the outside was more than 450 the pistons will have reached their plastic temperature. Are the wrist pin holes still ok? Ring grooves still correct width all the way around? Some of the domes may be pushed in giving a different compression ration.

If it were mine I would have a bite of a tasty Kahuna Burger, and take care of business.

redknife

Good points. All things and thoughts considered, I am going to pull the engine and take an initial look at the bottom end. Assuming no catastrophic block failure, then likely have a local machine shop give me an estimate for testing the head and machining the bottom end, etc. Have to move her down to our pole barn so I’ll be “going dark” on the thread for a bit. Will post any findings as they come.

exasemech

Someone had to bite the bullet and say that thing is probably toast and doublechaz was honest enough to do it. Keep in mind if it's a Jasper remanufactured engine it has probably already been bored to max cylinder diameter, the crank has been ground and it may well have been line bored. There's no metal left to do more.
I would rather put my money into a junkyard pull.