Novak Conversions Jeep Wrangler JK radiators

2011 JK 3.8 runs rough when cold

jktrailwhip

jktrailwhip

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Feb 3, 2024
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Greensboro, NC
My 3.8 w/ 146k runs rough in the mornings for about 5-10 mins after start. It's a well maintained motor and i have no complaints except for this little anomaly. To explain how it feels - it's like if your spark plugs are shot. Once it warms up all is OK. I replaced the plugs & wires thinking that might fix it but it didn't. Plugs are gapped correctly & wires have good contact. I always run 89 gas. Anybody else experience this? Could it be the ignition pack? Injectors need cleaning? I have never put any fuel treatments in but kind of considering it. Interested to hear thoughts
 
Well - good question. And the answer leads right into a can of worms. It began fairly soon after I had my head gaskets done last fall - the gaskets didn't blow. While i was trying to replace the leaky upper manifold gasket last fall, one of the bolts broke off in the head, so I had a pro shop remove the broken bolt, machine the heads & do both head gaskets. New plugs & wires too. I didnt notice the cold roughness for a month after that. Since then it's never really gotten worse, but it's always there now.

So, probably a whole lot of new information there...
 
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I know damp weather can mess with bad, dirty grounds. Might clean them and if your using the Factory battery clamps replace them with some good HD ones.
 
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jktrailwhip said:
so I had a pro shop remove the broken bolt, machine the heads & do both head gaskets. New plugs & wires too. I didnt notice the cold roughness for a month after that.
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Thx. Some additional questions based on that info.

If that happened in the Fall, it was getting colder out (maybe Winter) when you started noticing it, correct?

I would be curious to see what it does once the weather warms again. Or stick a heater in your garage and get a higher ambient temp and see if that changes the phenomenon.

At a high level it sounds like you may have a partially blocked coolant passage between the block and head so it's taking longer to warm the engine. If this is the case you may experience the opposite when the temps rise - the cooling system will have a more difficult time keeping the engine temps down.

If you have access to an engine monitor you can track the subjective engine operation with coolant temp and see if it correlates...
 
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