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CANNOT Seal Thermostat Housing on 5.0

My original housing eventually leaked where the metal connector for the bypass hose entered the housing. The difference in metal caused corrosion that destroyed the tube. I had a piece of copper tube plumbing at home. I was able to pull out the old connector and with a dab of sealant as lube pounded in the copper tube. It even got a lip on it to insure the hose will not easily pull off. BTW, I did the same thing about 15 years ago on the water pump without removing it. That water pump now has 330,000 miles on it as it is the original. I have a small water leak now that I have not found. I am thinking maybe it is time to dig in and replace that pump. Other things keep getting attention first.

WP yes but sadly its VERY likely the Timing cover at Pass Side Front of Head - I have recent thread on that.
 



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DITTO to ALL the above - & Yes I cracked my Thermostat Housing when the Vertically Installed Thermostat slipped & I tightened the fasteners, so yes something to glue Thermostat in place is the WTG - There are SEVERAL different angles of Thermostat Housings so get the same one or ur Upper Rad Hose won;t fit - Gurus >>>> WHY do we need the Vented Thermostat when the PITA Bypass Hose is RIGHT THERE to vent it______?



I think that does help to get the air out after the system is opened up. These never had any air purge outlet like almost all new cars have. It is minor but some people have a hard time getting the air out. A good recovery system takes care of it when it's in good shape(a bad radiator cap will leave air inside forever).
 






I think that does help to get the air out after the system is opened up. These never had any air purge outlet like almost all new cars have. It is minor but some people have a hard time getting the air out. A good recovery system takes care of it when it's in good shape(a bad radiator cap will leave air inside forever).
You mean the allen head bleed screw on the thermostat housing? I cracked that loose while filling the system to try to bleed out any air. Unless that's just a thing on aftermarket housings.

I'll post a pic of the leak later if it's still leaking. I'm going to drive it around and see what happens. Might even be time to try that K-seal stuff if it's still seeping... ironically that was the first thread I contributed to when I signed up on here last week.
 






The factory housings don't have that, just a dead hole where a temp sensor or vacuum switch used to go on much older SBF's.
 






Just sayin - 3 pages of text on a leaking thermostat housing & not 1 pic...

In the 20th century you had to own a digital camera, in the 21st century it's a standard feature on cell phones. :)
 






Drove it around and got it up to temp, no issues at first. It looks like it may still be weeping on the left side of the housing near the bypass hose, but it's hard to tell. It's definitely wet, but I can't see it dripping. I'll look into that more tomorrow.
Anyway, after getting home from my test drive, I noticed a stream of rusty coolant under the truck... then saw it pouring out and steaming on the exhaust. Looks like it's coming out of the heater pipe towards the front of the passenger side valve cover, and trailing down around the cover and onto the exhaust manifold. It's hard to see, but it looks like it was coming from the pipe itself and not any of the hoses. Then again, it may be from the hose on the front and it was just trailing back a little I've put that hose on and taken it off several times over the past few days, so now the more I think about it, the more sense it makes. I'll add pics tomorrow of everything!

The factory housings don't have that, just a dead hole where a temp sensor or vacuum switch used to go on much older SBF's.
Interesting... so my old housing was also aftermarket.
Just sayin - 3 pages of text on a leaking thermostat housing & not 1 pic...

In the 20th century you had to own a digital camera, in the 21st century it's a standard feature on cell phones. :)
I know, I know... I haven't gotten a chance to post pics since it's hard to take a pic with the lack of lighting. I'll try tomorrow.
 






The coolant pipe has two small outlet nipples and small hoses leading to the TB. Those pipes are very good and reliable, as long as the coolant isn't bad/rusty, which will eat the pipe.

You say the leak looks rusty, how old is the coolant? With a new thermostat, we're all assuming it's fairly new coolant.
 






the 96-01 5.0 ALL had the throttle body heater hoses...........
 






Did they, sorry I bought three new ones and those had the little pipes looped into each other. I never liked those hoses, for the little good they do, they are sources of leaks when the get old.
 






Oh, the cooling system is disgusting. It's the rustiest mess I've ever seen... pure brown water in there. The radiator is caked up with rust. The whole purpose of me changing all this was to flush the system. It might have been a good idea to flush it before changing the thermostat, but whatever.

Funny thing is the previous owner mentioned that the heat didn't work too great, it's no wonder why now looking at the coolant. I ran it yesterday and it seemed to work pretty well... I guess I got enough crap out of it, but it still has some flushing to go.
 






Okay, you've got some more to do. Use a good flush additive and follow the instructions. Then replace all six coolant hoses, and replace the tiny hoses with a new short piece that loops to each nipple. Put in a gallon of real anti-freeze, a bottle of Water Weter, and distilled water to fill the rest. If you are not far up north, you don't need a 50/50 mixture, that just reduces cooling capability. Water cools better than anti-freeze, you want as little anti-freeze as possible, whatever is required for your Winters.

You might have damage to your radiator and neater core if the coolant was that bad, flow through them may be restricted.
 






Did they, sorry I bought three new ones and those had the little pipes looped into each other. I never liked those hoses, for the little good they do, they are sources of leaks when the get old.
I like to eliminate the entire metal pipe manifold dealio and run just regular heater hoses........
 






I noticed that in one of your pictures. I really like the pipes overall, but they do make you deal with extra hoses that are all molded and pricey, and tough to find.
 






Here are a couple of pics. Can’t see anything leaking, but in these it’s really hard to see anything at all. This cooling system is a real mess to look at!
 

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And the leak is right around here.
 

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Found it! The barb for one of the smaller coolant hoses is split right on the heater pipe. Guess I'll make a stop at the junkyard for a nicer one.
CAF8AD40-0EFD-41A1-A7CB-8CB92C4D8CBE.jpeg
 






Very good, now you can fix it.

I'd clean the engine bay before tearing into it for the pipe, just a mild engine degrease and water hose spray down. Use some anti-seize on bolts and thread sealant on the water pipe threads etc.
 






Very good, now you can fix it.

I'd clean the engine bay before tearing into it for the pipe, just a mild engine degrease and water hose spray down. Use some anti-seize on bolts and thread sealant on the water pipe threads etc.
Definitely, there's so much rust staining on this engine. It's nasty. I'll definitely clean that first.
 






I just picked up a 2001 Mountaineer 5.0 last week, and I made the mistake of replacing the thermostat for preventive maintenance. I figured this was a basic thing to change before flushing the cooling system and changing the leaking upper radiator hose. Nope!
First time I put the gasket on with a little bit of ultra black RTV to hold it in place. Didn't work too well, because when I went to fill the cooling system, it poured right out from the thermostat housing. Took it back apart, and it turned out that the thermostat had slipped... common problem on here from what I can tell. No biggie... new gasket, re-positioned it, and tried again. Water poured right out again. So next time, I got some Permatex water pump and thermostat gasket maker, went with others' recommendations and used just RTV. Waited overnight, filled this morning... poured right out AGAIN. Tried Permatex Right Stuff... dumped out again. ANOTHER gasket, I was extremely careful this time to prep both surfaces, used a couple drops of super glue to hold the thermostat in place, and let the RTV tack up on the housing before putting it on. Little bit of RTV on the other side of the gasket, then put it on. I was confident this time that it was good... I was wrong. It just drips right out from the bottom of the thermostat housing when I fill the system enough to reach that high.

What am I doing wrong? There's no reason I should have to do this 5 times. I've been working on BMWs and Volvos for a few years now, and I've never run into such an irritating issue that makes me doubt my mechanical abilities. I've always liked these Explorers/Mountaineers, but my first American car is proving why I've always had European cars. They are SO much easier to work on!
 



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I just picked up a 2001 Mountaineer 5.0 last week, and I made the mistake of replacing the thermostat for preventive maintenance. I figured this was a basic thing to change before flushing the cooling system and changing the leaking upper radiator hose. Nope!
First time I put the gasket on with a little bit of ultra black RTV to hold it in place. Didn't work too well, because when I went to fill the cooling system, it poured right out from the thermostat housing. Took it back apart, and it turned out that the thermostat had slipped... common problem on here from what I can tell. No biggie... new gasket, re-positioned it, and tried again. Water poured right out again. So next time, I got some Permatex water pump and thermostat gasket maker, went with others' recommendations and used just RTV. Waited overnight, filled this morning... poured right out AGAIN. Tried Permatex Right Stuff... dumped out again. ANOTHER gasket, I was extremely careful this time to prep both surfaces, used a couple drops of super glue to hold the thermostat in place, and let the RTV tack up on the housing before putting it on. Little bit of RTV on the other side of the gasket, then put it on. I was confident this time that it was good... I was wrong. It just drips right out from the bottom of the thermostat housing when I fill the system enough to reach that high.

What am I doing wrong? There's no reason I should have to do this 5 times. I've been working on BMWs and Volvos for a few years now, and I've never run into such an irritating issue that makes me doubt my mechanical abilities. I've always liked these Explorers/Mountaineers, but my first American car is proving why I've always had European cars. They are SO much easier to work on!

4.6 ford v-8 are notorious for leaking coolant under the thermostat. Many youtube on the subject. The leak will appear under the thermostat housing where the aluminum crossover is mounted to the plastic intake manifold (the o-ring seal fails). Unfortunately the aluminum crossover can only be removed when the intake manifold is removed from the engine. I had a small leak for years before I searched youtube and found out how common this oring failure is. I don't know if the 5.0 has similar issues? I had to constantly keep an eye on the coolant level and would occasionally find fluid under the thermostat housing and in the sparkplug well.

I ended up buying an intake on Amazon for about $150.
 






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