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Mystery Coolant Leak

AF Ohio Patriot

New Member
July 16, 2022
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City, State
Sandusky, Ohio
Year, Model & Trim Level
2008 Ford Explorer Sport
2008 Ford Explorer Sport Trac Limited 4.6 3V
200,000 miles
I couldn't find this exact issue posted so here we go.
Coolant level drops rapidly. (1.5 gallons in 2 days)
No Coolant in the oil
Is not burning Coolant out of the tailpipe
There are no exterior leaks on the Coolant system.
I was told the heater core can leak and store Coolant in it. Figured I'd post here if anyone has any experience with a similar leak.

I've replaced the radiator multiple time (last summer was most recent)
Hoses and radiator are clean and free of any leaks.
This isn't a daily driver (only drives 3k miles per year in June and July.

Thank you

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If you don't have a head gasket issue then it is leaking it somewhere. I suggest putting some phosphorescent dye in the coolant and use a black light to spot the leak. Also, I recommend using a 16 psi radiator cap instead of the stock 20 psi part. Many of us here do this to keep pressure lower to reduce stress on cooling system parts. So far no one has reported a single issue after doing this. I have never seen my temperature gauge move any higher than it did with a 20 psi cap. The link below is the one I use. It fits like the stock cap.

16 psi Radiator Cap

There is no such a mystery thing in mechanics.

If no visual leak evidence detected,try UV coolant detector additive and exhaust in coolant check.

Inner cores leak could be easily detected by looking at the A/C drenage hose

I wasn't losing as much as you, but radiator had a constant weep. Heat of the car and air movement would dry it up and I never saw drips on the ground. Could smell it though.


An old thread, but assuming you have the rear heater, check the hoses that go up into that. The clamps rot out and they leak. Also check the crimp between the rear heater hose and the metal lines above the fuel tank.