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small mystery coolant leak

Austin Healey

October 8, 2016
Reaction score
Northern Virginia
Year, Model & Trim Level
1997 Ford Explorer XLT
My '97 Explorer with OHC 4.0 engine has been sitting for about a month while I do stuff (lots of stuff -- the worst kind of shipwright's disease.) There is a very small coolant leak from the front left (driver's) side of the engine and I can't find it. The engine hasn't been run for weeks, so there's no pressure in the cooling system, but enough coolant drips out to maintain a puddle approx 2-3" in diameter on the floor.

I've been underneath trying to find where the leak is coming from, and no luck. I did notice that on the biggest radiator hose, there's a thin white line below the top clamp, indicating a leak (maybe under pressure), but it's not leaking now. Also, I've recalled seeing various alarming references to the radiator thermostat -- as in "don't mess with it unless you have to." Could that be the source?

And, speaking of coolant hoses, are any of them likelier than others to go kablooie? This truck is new to me so I'm still learning its defects. And if I replace hoses, should I reuse the OEM spring-type hose clamps, or go with screw-type?

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Thermostat housing issues seem common with these trucks. This forum contains a lot of information about this, if you use the "search" function. I do not think any of these hoses are significantly more likely to fail than any other hoses. The white stain on the hose sure could indicate a history of a leak.... maybe you can get your system pressure tested

It might be a good idea to replace all of the coolant hoses given the age of the truck and unknown maintenance history. The OEM style clamps seem to work easily and nicely, but only if you have the specific tool for them. Not aware of any particular issue with thermostat itself.

Good luck with your '97.

Connect a cooling system pressure tester to locate the leak.

I had a small leak from the front of my engine a while back and couldn't locate it until a friend of mine got in and revved the engine and, lo and behold, revving the engine made a small stream of coolant squirt out. Would not do it at idle but would drip coolant down the block and when sitting in driveway it would pool up. It was from the intake manifold gasket. There are two little water ports that go into the intake manifold and the gasket split and only under pressure did the coolant leak out.

Reuse the clamps if they are in good shape. Note how fast you're losing coolant as this may be a waiting game to find it unless you want to replace *everything*.

This might have been the radiator cap. I replaced w/ a new one, got engine up to full operating temp, and no leak.

Freeze plugs are possible or lower intake gasket is common.

The factory spring clamps are best to use provided in good condition. I used to like those aftermarket screw type clamps, however you have to realize they dont provide constant pressure to keep hoses in place, you have to re-tighten them which is why manufactures dont use them. The factory clamps are springs and keep a constant squeeze on the hoses so they dont loosen and eventually leak, (but you already knew that). ANd yes they can be a pain in the azzzz without the correct tool to open them.