Head gasket or lower intake gasket

Oldjeepsail

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1997 TJ 4.0L 245,000miles - problem started with a difficult engine start. Once started the idle went to about 2,400RPM and would not go lower. Engine temp was steady above normal but below over temp line. After a short (5-10) minute drive through residential streets I put her back in the driveway. Popped the hood and the radiator reservoir was bubbling. There does not appear to be any oil in the antifreeze. However there is antifreeze in the oil.

From the research done so far it’s most likely the head gasket which, from research, would likely result in an engine replacement, or it could be a lower intake gasket leak, which is a rather simple fix.

Any recommendations on how to determine the if it’s the head gasket or the lower intake manifold? I assume that running the engine is not a good idea.
 
1997 TJ 4.0L 245,000miles - problem started with a difficult engine start. Once started the idle went to about 2,400RPM and would not go lower. Engine temp was steady above normal but below over temp line. After a short (5-10) minute drive through residential streets I put her back in the driveway. Popped the hood and the radiator reservoir was bubbling. There does not appear to be any oil in the antifreeze. However there is antifreeze in the oil.

From the research done so far it’s most likely the head gasket which, from research, would likely result in an engine replacement, or it could be a lower intake gasket leak, which is a rather simple fix.

Any recommendations on how to determine the if it’s the head gasket or the lower intake manifold? I assume that running the engine is not a good idea.
Welcome to the TJ Forum

Most likely nothing to do with your intake, pull your spark plugs one at a time looking for one or more that are remarkably clean and take a few pic's. That should tell you what you need to know for starters.
 
Pulled 5 out of 6 plugs. Sixth is behind the AC compressor. I could pull it but it’s be a pain. All five plugs looked nice and clean no build up.

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Pulled 5 out of 6 plugs. Sixth is behind the AC compressor. I could pull it but it’s be a pain. All five plugs looked nice and clean no build up.

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When there is an issue with coolant leaking into a cylinder the plugs tend to look almost new as do the tops of the pistons, the oil will be milky and usually white smoke out the tailpipe.

If you have a coolant system pressure tester now would be a good time to pressure test the system, they can also usually be rented.

Also a bad head gasket does not normally mean an engine replacement, it's very repairable.
 
Test the coolant for combustion gases.

As has been said...the 4.0 online 6 doesn't have coolant in the intake manifold, nor does it have a lower intake manifold. That's a v6 and v8 thing.
 
I get that the bubbling antifreeze is from the blown head gasket and assume it’s combustion gasses. But is the high idle be related to the failed head gasket? I wouldn’t think it would be but it happens at the same time the gasket failed:
I’d started the car for the first time that day to drive it to get a safety inspection. It’s about 5-10min drive. I sat in line for about an hour with the engine (A/C) running. After the inspection, the inspector turns it off but can’t get the key out (doesn’t know about the button), leaves the headlights on. Not being a daily driver anymore, the battery is weak. I pay and try to start it. After several turn overs the battery dies. The shop tried to jump it but their battery doesn’t have any juice. While the hood is open is when I first notice the radiator reservoir is bubbling (it didn’t register that I had a problem) so we push it and I pop the clutch to start it. Idle immediately jumps to 2,400. The drive home 5-10min) I’m riding the brakes or keeping it in low gear because it just wants to run at 2,400 RPM. So is the gasket failure related or is it just a coincidence and I have some other issue to track down?
 
I get that the bubbling antifreeze is from the blown head gasket and assume it’s combustion gasses. But is the high idle be related to the failed head gasket? I wouldn’t think it would be but it happens at the same time the gasket failed:
I’d started the car for the first time that day to drive it to get a safety inspection. It’s about 5-10min drive. I sat in line for about an hour with the engine (A/C) running. After the inspection, the inspector turns it off but can’t get the key out (doesn’t know about the button), leaves the headlights on. Not being a daily driver anymore, the battery is weak. I pay and try to start it. After several turn overs the battery dies. The shop tried to jump it but their battery doesn’t have any juice. While the hood is open is when I first notice the radiator reservoir is bubbling (it didn’t register that I had a problem) so we push it and I pop the clutch to start it. Idle immediately jumps to 2,400. The drive home 5-10min) I’m riding the brakes or keeping it in low gear because it just wants to run at 2,400 RPM. So is the gasket failure related or is it just a coincidence and I have some other issue to track down?

Our TJ's do not perform properly if at all with low voltage so what I would do is get my battery squared away and check the integrity of the cables and clamps making sure everything is clean and tight.

A bubbling overflow tank does not immediately indicate an engine problem, could simply be a bad radiator cap. Test strips or a test can confirm that.
 
Our TJ's do not perform properly if at all with low voltage so what I would do is get my battery squared away and check the integrity of the cables and clamps making sure everything is clean and tight.

A bubbling overflow tank does not immediately indicate an engine problem, could simply be a bad radiator cap. Test strips or a test can confirm that.

He has coolant in the oil.