Large Coolant Leak -- Then Not a Drip

[nickelphillips]

Stock 2007 4.0 L V-6 Explorer

Hello: Yesterday my wife drove our X about 30 miles into the city and back to where I work. It was idling for about 15 minutes maybe. When she began to drive away, a co-worker noticed water/coolant starting to pour from under the engine.

I was able to look at it with our mechanic a couple of hours later. There was coolant all over the underside of the hood and all in one direction from where it had gotten on the the fan and been sprayed to the passenger side of the engine compartment. So the leak had to be in the front of the engine compartment and probably at or above the level of the fan. Put water in and found that it had lost maybe a gallon and a half of coolant. But we could not find even a drip. Cranked the engine and ran it for about 15 minutes to get up to operating temperature and pressure, and still not a drip. Baffled our mechanic, who is pretty experienced.

I've checked all 10 pages of ExplorerForum search results for "coolant" and the usual culprits are: thermostat housing, water pump gasket, water pump housing, water pump bypass elbow hose, intake manifold gasket, radiator cap, cracked radiator tank and head gasket. Heater core, radiator core, area around radiator cap are all dry, but I'm wondering if it could somehow be the cap. Maybe something clogged the (surprisingly tiny) passage between the cap and the overflow tank and the cap sprung and sprayed all over the fan? Really appreciate any insight, as this is our daily driver.

 

[96firephoenix]

Sounds like your thermostat housing has some issues. top dead center on the front of the engine, just aft of the fan.

Does the coolant smell vaguely of gasoline? This is a stretch, but when my truck popped a head gasket, it would blow coolant randomly whenever I floored it under load. Hope it's just the seal on your thermostat housing.

 

[nickelphillips]

Thanks for the fast reply. No smell of gasoline, but if it leaks again I'll green-nose it and sniff it closely. I know exactly where you're talking bout, and that's one spot that our mechanic said it might be. We were/are confused as to why it's not doing it again once the engine is back up to operating temperature and pressure, and why there's no visible evidence of leakage on the housing, when so much coolant had just come out. But at this point I'm going with this as the most likely culprit--and hoping its just the thermostat housing seal ....

 

[07EddyB]

Did you ever solve this? As I got to the end it occurred to me that maybe it didn't do it again because it wasn't actually building pressure any more.

 

[huskertodd]

If it did end up being the thermostat housing, I recommend replacing it with the metal cast one. I went through three nylon housings before I finally bought the metal one.....no more issues leaking.

 

[nickelphillips]

Thanks for the replies. Turned out to be the water pump bypass hose. Got it fixed and no further issues. Yet.