Good sized coolant leak-- can't find the source

[ophidia]

This is a 1999 Mountaineer 4x4 4.0L SOHC. I'd noticed recently a strong coolant smell, and the coolant bottle was almost empty. I filled it on Thursday, and today it's almost empty again. I just noticed a good sized spot of coolant on the ground beneath it. After looking around with a flashlight, crawling underneath it, etc. it looks like it's running down the bellhousing and has soaked the whole oil pan. It all seems to be coming from the driver's side of the engine.

I felt down the back of the engine as far as I could get my arm stuffed back there, and didn't find any wetness. When I look in the driver's side wheel well, I notice the first wetness behind the exhaust manifold around the rear cylinder on that side. I can't see where it's coming from.

Recent work done on the vehicle: I replaced the upper intake manifold gasket and the thermostat a couple of months ago. Two weeks ago, I replaced the alternator and tensioner. I didn't notice any coolant smell and loss then. This has shown up w/in the past week.

I don't see any wetness around the water pump, either from above or looking up from below. If it were the water pump, could it present like this? If the thermostat housing had started leaking, could it show up like this? It looks like there could be some dampness around it, but I don't see anything pooling on top of the engine.

I'm not really sure where it could be coming from. Any ideas?

 

[swshawaii]

Rent a cooling system pressure test kit from many auto parts stores, with a fully refundable deposit.
Call around for availability. Fail safe, and by far the easiest way to pinpoint leaks without guessing. GL

 

[yavapaires]

Good idea about the pressure tester. I would say look at head/head gasket as the most likely to leak. Could be intake manifold too.

 

[ophidia]

I'll look into that tonight. Last night, I looked more closely at the thermostat housing, and it was definitely wet around it. It looked like, just maybe, the coolant was running along the top of the engine, along the lower intake manifold, to run down the back... somewhere. I'm still not convince this is what it was, but I resealed it with some RTV when I put it back together.

I'm assuming the engine has to be pulled to do a head gasket, because of the rear timing chain on the engine. Hopefully that's not it.

 

[Cat Stevens]

Funny story, except I look like a total idiot.

Car overheating. Check coolant reservoir, it's fine. Figure it's the thermostat, and set it up with my mechanic. (I know-dead simple to do, but didn't feel like it.)

Dominic called me, "Uh, Tom, did you think to check the radiator?" It never occurred to me to take off the rad cap and look. Turned out the radiator was shot, fortunately I wasn't idiotic enough to drive it hot.

 

[bobflood]

Funny story, except I look like a total idiot.

Car overheating. Check coolant reservoir, it's fine. Figure it's the thermostat, and set it up with my mechanic. (I know-dead simple to do, but didn't feel like it.)

Dominic called me, "Uh, Tom, did you think to check the radiator?" It never occurred to me to take off the rad cap and look. Turned out the radiator was shot, fortunately I wasn't idiotic enough to drive it hot.

Don't feel like the Lone Ranger! Had a similar kind of issue with daughter's Maxima - heat was erratic but overflow tank was fine. Decided it need a radiator flush; took it to shop; they got about two quarts out of it and it was empty! Turns out there was a hairline crack in the nipple the overflow hose connected to; coolant would go out there and none would suck in from overflow tank - so that level always looked fine and I never thought to take off radiator cap and look. Thankfully caught it before any damage!

 

[ophidia]

It's looking like it was the thermostat housing. After finding out that it leaked, i searched for that and came up with multiple threads on it leaking, and with it running down in the exact same place I was having issues. If I hadn't been so pi$$ed that it looked like something major (or at least hard to fix) I might have thought of searching for that before even posting.

Thanks!

 

[swshawaii]

Chances are you've seen this project, excellent "how to".
Double check your part numbers, two different housings.
Replace the short bypass hose while it's apart, under $10.

http://bengrosser.com/howto/fordthermostat/

 

[ophidia]

That is extremely helpful. Thanks!

 

[swshawaii]

Your old temp sensor(s) will fit very loose in the replacement lower t-stat housing, and almost guaranteed to leak. If you don't want to replace the very overpriced sensor(s), get new automotive type heat resistant o-rings. Size is 9mm I.D x 2.5mm or 3mm thickness. (Get both sizes)
Very cheap, and returnable. Also, check Amazon for MotorCraft parts. With free shipping they were half price of my dealer, and local parts store. Pretty easy job, albeit tight, confined, and somewhat time consuming. Let us know if we can help, once you get started. Good luck.

 

[ophidia]

Thanks for the tip on the o-rings. I found this dorman branded housing on Amazon that appears to be correct:

http://www.amazon.com/Dorman-902-20...=Mercury|56&Year=1999|1999&newCar=1&carId=001

They don't appear to have the Motorcraft one. This one is about half the price of the ones they have at the local auto parts stores. I can get the gaskets locally, though. Looks like it'll be pretty easy. If I pop the plenum off it should be quite accessible.

 

[swshawaii]

I avoid non OEM repalacement parts whenever possible. It's about fitting properly and build quality.
Moog suspension and steering parts are an exception. Add up the Motorcraft parts separately, worth it IMO.

http://www.amazon.com/Motorcraft-RH144-Thermostat-Housing/dp/B000C5BW5K
http://www.amazon.com/Motorcraft-RH148-Thermostat-Housing/dp/B000C5FRHO

Use your VIN number with this link to confirm your vehicle's Motorcraft part numbers:

www.fordparts.com

 

[ophidia]

I'll take a look. I really appreciate all your help on this. I plan on doing this job this weekend if I can get the parts here by then.

 

[swshawaii]

No problem, I enjoy helping and sharing the experience I had doing this.
It took me a little over two hours to complete this repair. Half the time
was getting the short bypass hose on the lower housing, without breaking
the guide tabs on the bottom. Also, having the correct hose clamp plier would
have helped me greatly. I found it very difficult with ordinary channel locks.
You do not need a dedicated 8mm swivel socket, although a universal is
needed for the rear housing bolt. Keep posted and updated. GL