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Another mystery coolant leak...


New Member
February 21, 2019
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City, State
Columbia, SC
Year, Model & Trim Level
2008 Explorer XLT
I’ve got a 2008 V6 4.0. I’ve searched this forum in the past, figuring someone else had probably had the same problem, but now I’m stuck. The other day it was overheating, no coolant at all and I couldn’t find the leak. I replaced the thermostat, thinking that would do the trick. The housing started leaking, but it wasn’t losing coolant as fast as before.I replaced the housing with a Dorman. Now the temp gauge spikes just below the overheating mark and then bounces back. Coolant level has dropped to about half of the reservoir, and I can’t find a leak anywhere.

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Check the oil level. Maybe coolant is mixing. Check the transmission fluid too.

Any wet hoses or hardware in the engine? Against the firewall even?

Checked the oil, looks good. I don’t see any wet hoses. I haven’t had a chance to look at it thoroughly though. Will check again this weekend.

Antifreeze can only go to three places, in the oil, out the tailpipe or on the ground (leak). Mine was leaking from both the thermostat housing and the radiator. After replacing the thermo housing, I would sometimes gets leaks from the rad and sometimes not. I started watching it all the time always looking to see if it was leaking as soon as I parked. Some days it only seems to leak while driving. Very close attention will lead you to see if it is leaking.
If your oil level isn't rising and you are not seeing while smoke out the tailpipe, a leak is a good guess.

I had a mystery coolant leak. No overheating, but luckily I happened to notice before I got to that point my reservoir was almost empty. One of the heater hoses against the firewall had a slight drip so I ended up replacing all the hoses under the hood just to be on the safe side as they all looked older. I was still losing coolant. I then came to realize the coolant leak was coming from the rear. The nipples coming off the auxiliary heater core had rotted out and cracked right where they meet the hoses. If you have the auxiliary heater in the rear I would check that. Also check the passenger side carpet make sure its not wet. That would be a sign of your heater core

Found it! Thanks everyone. Now how much of a problem is this....


How hard was it to change?

How hard was it to change?

Removed the air intake and the top two hoses were pretty easy to get to. The bottom one was a pain. Had to remove the wheel well to get to it.