Coolant overflow? | Ford Explorer Forums - Serious Explorations

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Coolant overflow?


Active Member
May 5, 2010
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Year, Model & Trim Level
99 Mercury Mountaineer
Ok I got my new radiator put on my 99 Mountaineer 5.0. I filled the radiator with coolant and filled the plastic resevoir to the correct level, but for some reason the small hose that connects to the radiator near the cap keeps leaking coolant.

The coolant inside the radiator is being forced up into the hose and starts leaking. Should I put a clamp on this hose to stop the leaking and not worry about it?

I figured it was air forcing the coolant up into that hose, but for some reason it doesn't seem to quit even though I would think all the air should be out of the system by now.

The reason I'm asking is because it never leaked coolant like that before. The truck runs fine. I let it warm up to operating temp and took it for a drive. It never got hot and I did see the temp gauge adjusting properly. It rose steadily until the thermostat opened and then it leveled out.

Is there anything I need to be concerned about or am I overly paranoid? :)

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that hose should always be filled with coolant. you can add a clamp but it could be that it's time to replace that hose.

That hose should be connected to the bottom of the coolant reserve tank. As the system heats up, expansion happens, coolant is expelled to the reserve tank. When it cools down, the liquid contracts and the radiator cap's valving allows coolant back into the system.
It's called a closed system. That hose constantly transfers fluid as the system cycles.

Make sure the hose isn't plugged or restricted to the coolant tank. Dirty coolant clogs BIG hoses and passages.

I recently had the same problem with the hose leaking when I replaced my rad. I suspect the hose had conformed to the size of the old rad's hose fittinng and there's a very slight difference in the size of the fitting on the new rad.

I just put a plastic zip tie on it and it's fine. If you use a clamp be careful you don't overtighten it and break the fitting. Just slightly snug is all it needs, hence why I used a zip tie.