Aggressively Rough Idle / Driving

[Moglocker]

Put in a new piston and send it and find out.

-Mac

If you on a budget,if not just throw a new engine in it.

 

[GoldenGorilla]

No. Mid-headbolt. Not the one that's in the front position. No idea why there's rust.



Yeah haven't found a hole. Looked up from the inside with the pan off and didn't see anything. Doesn't explain the massive amount of oil that spewed out all over the undercarriage though.

The rods all seemed to have the same play on the crank; minimal. The piston could have just failed for whatever reason. Again, I was cruising on the highway when it happened.

Regardless, a ton of oil underneath when it happened. Not sure what could have happened. Oil pan gasket seemed intact. Unless THAT MUCH OIL was able to gush through cylinder #3 and blow back into the whole system and shoot out somewhere? Just doesn't make sense.

Thoughts?

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Oooh. forbidden glitter

 

[Ol' Bessie's Keeper]

Put in a new piston and send it and find out.

-Mac

I kind of felt like trying out this scenario too, ha. Once I get time to pull the piston and thoroughly inspect the cylinder wall, I'll report back.

 

[AaronD]

I had a hole like that in one of the middle pistons of my 4.0L in 2018. It had been running rough and slowly losing power for a couple days, ending with needing 3rd gear and wrapped up tight to keep up on the highway (5-speed manual), then a sudden cloud of blue smoke on the highway and lost all the remaining power. Yes, I should have stopped driving it when I first noticed, but I wasn't exactly thinking straight.

I ended up with a short block from RockAuto. And replaced the synchros while I had it out anyway. Best I can figure is either a bad radiator cap or a cracked radiator (replaced both of those too), so that I couldn't keep water in it, and the temp gauge on the dash didn't show over-temp with air/steam. Thus, overheating without knowing, and eventually melted a hole in the piston. It looked a lot like the pictures here. I'm fuel injected, and the check engine light never came on, so I doubt I had a bad mixture. It did come on when an exhaust coupling came apart, so the light does work.

Don't know if that was the actual cause or not - I wasn't particularly scientific, just wanted to get it back on the road - so I'm interested to see what you come up with.

 

[Ol' Bessie's Keeper]

I had a hole like that in one of the middle pistons of my 4.0L in 2018. It had been running rough and slowly losing power for a couple days, ending with needing 3rd gear and wrapped up tight to keep up on the highway (5-speed manual), then a sudden cloud of blue smoke on the highway and lost all the remaining power. Yes, I should have stopped driving it when I first noticed, but I wasn't exactly thinking straight.

I ended up with a short block from RockAuto. And replaced the synchros while I had it out anyway. Best I can figure is either a bad radiator cap or a cracked radiator (replaced both of those too), so that I couldn't keep water in it, and the temp gauge on the dash didn't show over-temp with air/steam. Thus, overheating without knowing, and eventually melted a hole in the piston. It looked a lot like the pictures here. I'm fuel injected, and the check engine light never came on, so I doubt I had a bad mixture. It did come on when an exhaust coupling came apart, so the light does work.

Don't know if that was the actual cause or not - I wasn't particularly scientific, just wanted to get it back on the road - so I'm interested to see what you come up with.

Oh man....I think you may have just hit the nail on the head! Very glad you chimed in!

When I removed the head, I noticed the heater hose pipe that sticks out of the water pump was loose. I had a very small coolant leak (white cooked coolant on the downpipe) and couldn't find where it was coming from, but this is definitely the source. My check engine light very much works also, haha, but never got one for overheating. Temp always showed 210* also. The piston must have also gotten cooked like yours, which means I'm no longer gonna just pop another piston in and send it; might as well just redo all four pistons at this point.

I've been enjoying my ol' Comanche in the meantime, even had to steal a couple parts from the TJ to fix her up recently...never ends!

I'll update whenever I actually get around to getting those pistons in.