Rough idle on cold start, not as bad after warmed up

[ShadowsPapa]

My sons 2018 JLU had the same issue. Seems "kinda" common for that year (under torqued head bolts passenger side). We replaced the head gasket, and now it runs better than ever. Big job though...gotta remove the timing cover and everything in front of it.
On that note, it seems very uncommon for JT's (as well as later model JLU's).

A 2018 JLU may have had the pre-upgrade 3.6 if it was an early build......... it was a split year for engines.

I've heard Wrangler folks talking about under-torqued head bolts - sad, but it's apparently a thing as your post is not even close to the first time I read about that.

OTOH, it can never hurt to check such things.............

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[NonHyphenated American]

A 2018 JLU may have had the pre-upgrade 3.6 if it was an early build......... it was a split year for engines.

I've heard Wrangler folks talking about under-torqued head bolts - sad, but it's apparently a thing as your post is not even close to the first time I read about that.

OTOH, it can never hurt to check such things.............

Did you have any puffs of smoke at start up and/or listen to the exhaust on startup? I dont have smoke and there is a consistent exhaust sound. Kind of makrs sense a coolant leak. I do have to put in very little to keep it in between the min and max mark. The coolant has stayed at the min mark for awhile. Probably should fill it between the min and max and mark it and take a pic and see how long it takes to go down. Or just trade it in for some of the mad discounted Wranglers in the area.

My dealership wont do anything without codes and would probably call any minor coolant use as acceptable. I bet if I brought it in now not under factory warranty they would find something wrong. I do have an extended warranty.

Also, if it were a coolant leak in heads shouldnt there be oil in the coolant and vice versa? I have not seen any discoloration.

This all happened alittle over a year ago after I came back from a road trip and mixed 87 and 93 octane. I thought it was the gas mixture and/or bad gas but the rough idle persisted after a few tanks of 87 and injector cleaner. I run 87 when staying local but use 89 on road trips, seems to perform better and get better mileage.

 

[Pickle_Bill]

No smoke at start up. It was using coolant. The definitive answer was borescope the cylinder.

 

[ShadowsPapa]

Also, if it were a coolant leak in heads shouldnt there be oil in the coolant and vice versa? I have not seen any discoloration.

No, not necessarily. You MAY have coolant in the oil, but since it would "evaporate" with engine heat, only an oil analysis would show that unless it was enough where you could drain the oil and see the coolant in it.

A pressure test will normally reveal such things, as well as a test for combustion gases in the cooling system.
I have yet to run across one where the ONLY way was a borescope - but like I say, that's probably due to their preference of methodology, it's not because there's no other way to find it.

 

[bgott]

No, not necessarily. You MAY have coolant in the oil, but since it would "evaporate" with engine heat, only an oil analysis would show that unless it was enough where you could drain the oil and see the coolant in it.

A pressure test will normally reveal such things, as well as a test for combustion gases in the cooling system.
I have yet to run across one where the ONLY way was a borescope - but like I say, that's probably due to their preference of methodology, it's not because there's no other way to find it.

A steam- cleaned spark plug is also a dead giveaway.

 

[ShadowsPapa]

A steam- cleaned spark plug is also a dead giveaway.

We were trained on diagnosing by spark plugs - for heat range, timing, fuel mixture, detonation and more, but the most obvious that no one needs any tips on is those steam cleaned plugs -

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