[cjvervaet74]

Good morning, everyone. I have the ugly cousin of the 2007 Ford Explorer, it's the 2007 Mercury Mountaineer with the 4.0L V6 engine and is AWD.

Anyway, it's the exact same motor and this is a mechanical question. I had a hose crack while on the expressway a couple months ago, the fix was easy and life was fine. While under the hood I noticed that my thermostat housing was leaking, just enough to annoy me. So I swapped that out, replaced the housing and put a failsafe 192F thermostat in.

It's all sealed up tight, no visible signs of leaking, but my coolant level keeps dropping. Coolant temp usually tops out around 192F, and that will go up or down depending on driving and weather. It's been hot here in Michigan, this morning it maxed out at 199F until it leveled off to the thermostat temp (192F).

Pressure looks right, I can't see any white smoke from either the engine compartment, or exaust system.

I'm at a loss. I have no idea why the level keeps dropping. I need to check the rear heater core for leakes, it's given me issues a few years ago with bad hose clamps, but other than that I'm open to any suggestions.

Maybe someone can point me in the right dirrection?

 

[ILFLASH]

I know this may sound obvious, but have you checked your coolant caps? If they aren’t working properly, they be letting coolant escape as steam when it gets hot. Just an idea as I have no idea how much you’re losing and over what period of time. Other than that, check your floorboard carpet for something leaking inside you may not have noticed yet. Good luck. Keep us posted…..

 

[cjvervaet74]

I know this may sound obvious, but have you checked your coolant caps? If they aren’t working properly, they be letting coolant escape as steam when it gets hot. Just an idea as I have no idea how much you’re losing and over what period of time. Other than that, check your floorboard carpet for something leaking inside you may not have noticed yet. Good luck. Keep us posted…..

Thank you and sometimes it's the obvious stuff. I went and checked the coolant caps just to be sure, and looked for any residue or colapsed hoses as well. Floor boards are dry as a bone as well. Really a mystery here. I checked my oil for milky color and nothing. Looks clean as a whistle. Maybe it's a leak that I'm not seeing underneith by the heater core, so I'll crawl under there tomorrow.

 

[J_C]

A couple tests you can do are add dye to the coolant and do a pressure test (or just run the engine to temp to make the pressure) then look for leaks. May be easier if it's a UV dye and UV flashlight, but then you need the flashlight too.

Other test involves looking for bubbles in the coolant reservoir and using a kit that detects exhaust gases, in case you have a head gasket or head crack or warp, leak.

You can also do a compression or leak down cylinder test, on all cylinders.

How long does it take, to get how low on coolant? If a minor leak, could be drying up before it makes a noticeable puddle from dripping off. That could be something as common as loss out the weep hole of the water pump.

Another possibility is that when you did the prior work, did not get all the air bled out of the system and it is happening now, and once it is all out and coolant topped off, you're good.

 

[cjvervaet74]

Thanks, everyone. The issue was the water pump. It was a little hard to see, but I was able to locate the leak. I ended up swapping the pump out and it's been running pretty good since. Fluid level seems to be stable even in the hot summer weather.