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Discussion Starter · #1 ·
I’ve been fighting a bit of a cooling system issue for the past year or so. It is keeping me from going on any extended wheeling trips for fear of some sort of catastrophic failure.



My Jeep: 75,000 miles. 3.5” lift, 37” tires, 4.88 gears, Metal Cloak Fenders, Smittybilt SRC Classic front Bumper with Warn winch. I’m including this because it may be pertinent to front end air flow and cooling system efficiency.



My problem:

  • 2 Fold - I noticed about a year ago heading up to Big Bear to do some light trails that when climbing mountain highway roads (and pushing a bit hard) that the coolant temperature reading on my TrailDash 2 was getting up to 240, and maybe 245, at times. Air temp outside was in the 80’s. On the Jeep coolant gauge in the dash it was getting maybe half way from normal (right in the middle) to about half way to full scale. This was definitely concerning. On the trails the coolant temp behaved pretty well. Then on the way home outside air temps were up in the 90’s and it was still running pretty hot (maybe getting into the 230’s on the TD2). I also noticed, when I got home, that coolant had overflowed the overflow tank.
  • Since then I have noticed that coolant seems to slowly (over weeks) pushes out into the overflow tank and does not return to the radiator. Every few weeks when the engine is cool I’ll put coolant from the overflow tank back into the radiator. I haven’t specifically measured but this has easily been 10 to 15 oz of coolant (in the overflow tank it is more than the difference from the “Min” line to the “Max” line. You can tell it needs it when I start it in the morning and there is a definite sound of water running/ flowing coming from the engine compartment.
  • Typical freeway driving, depending on the outside air temp, can get the coolant temperature up to maybe 230, but usually runs cooler.
  • In just the last 2 weeks or so I have gotten two P0128 error codes which not surprisingly has to do with the cooling system. Both times it was on a short trip at lunch time. I believe that it in a perceived error that the coolant isn’t heating up as fast as expected. I really didn’t notice any difference in how the temperature was behaving soon after starting it cold. It is supposed to be an indicator of a thermostat problem.



What have I changed / checked:

  • New radiator cap (Jeep actually recommends a 17 versus the original 18 PSI cap).
  • Replaced overflow tank and hose.
  • I purchased a coolant filling funnel that is supposed to allow proper air purging of the cooling system and done that several times. The issue of coolant migrating out into the overflow did not improve.
  • I bought a Combustion Leak tester that checks for combustion gas in the cooling system (like with a head gasket or cracked block or head leak). Per the instructions I sanity checked the tester by blowing into my cupped hand while using the tester to draw in my exhale and it correctly registered combustion gas (I think it is looking for CO2). Another test drawing fresh air into it did not show any combustion gas. I used this tester on the freshly opened radiator without any sign of combustion gas. This seems to rule out a blown head gasket or cracked head (little bit of a sigh of relief).
  • No sign of coolant in the oil, or vice versa. I even checked the little bit of ‘sediment’ in the bottom of the old overflow tank. It didn’t seem like oil, it was very water soluble.



Questions:

  • Has anyone had this issue? What needed to be done to fix it?
  • I know that this engine is supposed to operate at a higher temperature. I could probably accept the temperatures that I see if the coolant flow back and forth from the overflow was as expected and didn’t continue to fill up the overflow.



Any suggestions on how to proceed? I am leaning pretty heavily toward doing a bit of a cooling system overhaul. I was thinking about an aluminum radiator (like the Mishimoto), replace the thermostat and housing, water pump, and ?



Any suggestions on a good radiator brand?
 

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JK's run hot. When I pull the transfer case lever the cooling fan cuts in and stays on. It doesn't take much load on the engine for this to happen. Is your fan coming on?

JK's Radiators leak. If you look down the sides of the tanks you will see a crusty orange sediment. The new type coolant evaporates quickly so usually this is the only evidence. This could cause your problem but only if it is stopping your cooling system from creating a cool down vacuum . Aluminum radiators don't seem to last. the thought is that the radiator saddle flexes too much and they start leaking worse than a factory design.

Your chemical leak tester should be used on a running engine that is at operating temps. They do work but with head gaskets they can leak and not leak depending on temperature so you will have to keep testing.

Pull the spark plugs you can get at and see if one is white or yellow. You can't get them all without pulling the plenum but check the ones you can.

Flush your cooling system. unhook coolant lines and go both ways with a garden hose until clean water comes out. Thermostat is cheap replace it.

I think you have a head gasket going. It is not common but if every thing checks out what is left?
 

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Discussion Starter · #3 ·
Thanks for the reply, rl.

Yes, the fan is coming on. Notice that when the AC is switched on and seems to be working fine during warm up tests in the driveway.

Definitely have looked for leaks and not seen anything. I know some time back, at different times, had both a radiator leak and a cracked thermostat housing that was leaking. Both times coolant never made it to the ground.

Another anomaly that I noticed when replacing the Oil Cooler (back in Feb 2020) on top of the engine is when I tried to drain the coolant with the petcock on the bottom of the radiator. When I rotated it, absolutely nothing came out: I ended up just having to drain by removing another coolant line. Otherwise I didn't notice any evidence of sediment in the cooling system but it could be a sediment issue.

I haven't checked the spark plugs. Have been considering a leak down test to see if pressure in the cylinders is showing up as any bubbling in the coolant.

Thanks again for the suggestions!
 

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I have an 04 TJ so things are different, but I’ll join in. Do you have an auto? I heard you say oil cooler. I ask because my first ever feverish engine I had was transmission related. A leak in T fluid caused the transmission to get hot, which caused the engine to get hot. Is it possible that when you changed the cooler, that air in the lines is restricting the flow of coolant and heat is flowing from the tranny to the engine? Is the T fluid low?

Do you smell coolant? I guess that’s a stupid question as I reread your overflow issues. It could be your water pump is going bad causing heat and loss of pressure and flow. I’ve always been able to smell my water pumps going bad.

Aluminum radiators are over rated. But spend for the oem type. The cheap internet type didn’t last for me.

Side note…
Let me know when you go to Big Bear and I’ll go with you.
 

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More concisely, air in one or both of your systems. My transmission was picky to cooler placement with regards to plumbing. I just thought of this too, if you overfill a transmission the fluid will foam and stop flowing. I actually experienced this myself at one point. As soon as I lowered the level everything was fine.
 

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Discussion Starter · #6 ·
Auto transmission.

Actually, the oil cooler was a new one for me. I'm not sure if you are familiar but the 3.6L Mopar motor has an engine oil cooler between the heads below the intake runners. I had noticed oil leaking around my bell housing and it turned out to be the oil cooler leaking, filling up the valley and overflowing down the back side of the engine.

It could be related to the oil cooler but I don't see how I could have a restriction there. Perhaps something to check.

I don't really smell coolant right now. In the past when the thermostat housing developed a crack and then when the radiator started leaking, both fixed under warranty by the dealer. I was definitely considering changing out a few things to see if it would help (radiator, water pump, thermostat and housing).

Yeah, I've not heard great things about aluminum radiators. I just really hate the crimped plastic side tanks that seem to always leak. Although the aluminum ones don't seem to do well either. I was reading the Mishimoto V2 is supposed to be better.

Sure... a Big Bear trip sounds great. I'm really hoping to feel better about this cooling problem.
 

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I’m learning here. So you have an engine oil cooler, a radiator, and a transmission cooler. I was thinking you had worked on the transmission cooler. At any rate, check your transmission fluid level.
 

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I've been through about four or five radiators including a Mishimoto and finally went back to a new Mopar radiator and all OEM cooling system parts. It is by far the best cooling system for the I4. I have a thread on ROF about radiators where I go into a few details about my cooling journey.

One quick radiator test is to measure the temperature of the in and out hoses when the engine is at operating temperature. There should be a 20F or 30F difference
 

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Sludgy and water soluable goop in the bottom of the overflow container and the radiator drain valve suggests somebody before you got the Jeep put liquid stop leak in it. Which would restrict coolant flow....Just a thought.
 

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Casting sand in the cooling system is usually the root cause of the cooling system problem.
Repeatedly flushing and a filter in there somewhere will help.
 
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