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Discussion Starter #1
Hello!

Longtime lurker here. I was hoping you may be able to help. I'm concerned my head gasket may be leaking on my 2013 3.8l. I had my check engine light come on yesterday and had it checked. They saw multiple misfires for cylinders 4 and 6, which I assume are next to each other.

When I start it, it does occasionally run rough for 5-10 seconds then smooth out. It's 30 degrees here though, so I figured she was just cold.

I noticed yesterday that my oil looked good. Not milky, but maybe a tad high. (Not sure, haven't checked it since it was recently changed) but my coolant was low. There was some in the bottle, but not much. I topped it off.

If I'm leaking coolant into cylinders 4 and 6, that would explain the rough running / misfires after sitting a day and the low coolant.

OTOH, maybe I just need new plugs and have a coolant leak somewhere. I just hit 30K miles. I heard they're good for about 40K.

I thought maybe I'd pull those plugs and let it sit for a day and see if I see some coolant in the cylinders with my cheap USB borescope. Any other ideas? Are the plugs easy enough to access on a 2013 3.8?

I appreciate any advice you may have!

Thanks!
 

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If you are not seeing white exhaust, it probably is not the head gasket.

Misfires that are consistent to specific cylinders is often an indication of a faulty ignition coil pack.
 

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Discussion Starter #3 (Edited)
Thanks for the reply!
It seemed odd to me that the cylinders with the issue were next to each other, the misfires only occur on cold starts after it's been sitting a couple days and that I was low on coolant. That suggested to me that those two cylinders had coolant slowly leaking into them and they were wet, causing the misfires when I initially start it up.

If not for that, I was just going to buy new plugs, and I may anyway since I'm at 30K miles now. I could have a pair of bad coils and a slow coolant leak though. Just wanted to see what you guys thought.

Edit: Hard to tell about white smoke. It's about 5-20 degrees in the morning so there's always white steamy exhaust. If there is a leak, it has to be small. I only have the rough start after it's sat a day or two.
 

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Coolant Problems

Internal coolant leaks can foul a spark plug and cause a misfire. The problem could be a leaking intake manifold or a head gasket, and the fouled plug might be localized to one or two adjacent cylinders. The burned coolant leaves ashy, white deposits on the electrodes and insulator, creating hot spots that could cause pre-ignition and a misfire code to be set.

When the plug is pulled, it might have a chalky appearance on the ground strap and center electrode. Modern coolants do not cause this type of buildup quickly, due to the reduction of phosphate, zinc and other additives that can contaminate the catalytic converters. Unfortunately, it also means that drivers will run a vehicle with a coolant leak for several thousand miles, while the plug becomes slowly fouled. In the past, the converter would become clogged and stop the engine before significant damage occurred.
https://www.autosuccessonline.com/spark-plug-fouling-diagnostics-getting-to-the-root-cause-of-misfires/
 
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