Novak Conversions Jeep Wrangler JK radiators

Engine code and oil leak

Erbowman

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Jan 28, 2025
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Tennessee
Started getting an engine code. My cheap code reader read one of those nonspecific codes: $07E8, $07E9. I tried erasing it several times but it would always return. In my nonstop reading I did co e across the oil cooler problem these JKs have. Well sure enough mine is leaking oil too that I didn't realize although idk that by itself would trigger a code. I know I have to fix the oil cooler but any thoughts on the code? I am getting a friend to use his reader tommorrow and maybe his will show more
 
Started getting an engine code. My cheap code reader read one of those nonspecific codes: $07E8, $07E9. I tried erasing it several times but it would always return. In my nonstop reading I did co e across the oil cooler problem these JKs have. Well sure enough mine is leaking oil too that I didn't realize although idk that by itself would trigger a code. I know I have to fix the oil cooler but any thoughts on the code? I am getting a friend to use his reader tommorrow and maybe his will show more

Update: Friends code reader immediately read code P0128. I had noticed when I did reset the code it would always come back quicker when it was cold outside. I assume it's the thermostat since it does seem to take longer to warm up than it once did but I have not noticed any erratic fluctuations so I am not thinking sensor. Enlighten me if I should think differently
The oil cooler leak was just an accidental find. Now I have to see if I want to tackle the job or pay someone. Anybody have a clue what labor typically cost for the oil cooler repair???
 
The P0128 code is an easy diagnosis and I have personal experience with this code.
Cold start your Jeep and wrap your hand around the upper radiator hose. If the t-stat is operating properly, you should not feel any fluid flow thru that hose until the engine temp is around 180 or a little higher. If you immediately feel fluid flowing thru the upper hose upon start , your t-stat is stuck open. It isn't going to hurt your engine, but your CEL will remain.

Your oil cooler replacement cost is dependent on the year/engine. The older 3.8L will run you around $500, while the newer 3.6L could run you as much as $1200. This according to the shop who works on my Jeep when I need help.
 
The P0128 code is an easy diagnosis and I have personal experience with this code.
Cold start your Jeep and wrap your hand around the upper radiator hose. If the t-stat is operating properly, you should not feel any fluid flow thru that hose until the engine temp is around 180 or a little higher. If you immediately feel fluid flowing thru the upper hose upon start , your t-stat is stuck open. It isn't going to hurt your engine, but your CEL will remain.

Your oil cooler replacement cost is dependent on the year/engine. The older 3.8L will run you around $500, while the newer 3.6L could run you as much as $1200. This according to the shop who works on my Jeep when I need help.

Dang. I have 3.6L. Looks like I will borrow friends torque wrench and save some money. Do some plugs while I'm there.
 
Dang. I have 3.6L. Looks like I will borrow friends torque wrench and save some money. Do some plugs while I'm there.

You might want to take a look at a few videos of the process before you commit to doing it yourself.
I'm all about saving money when it doesn't need to be spent, but I think this particular repair may be best suited to someone that has done it before with all of the horror stories I have read/heard about the difficulty of flushing out the oil (if they mixed) & purging out the air so that it doesn't overheat afterwards...

Not to mention the "which oil cooler and which gaskets/seals do I use?" issue.
 
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Novak Conversions Jeep Wrangler JK radiators