T-Stat Housing mystery leak.

I have a 2004 Mounty. A bit of background.

November 2014, noticed massive amounts of fluid leaking from the housing. Replaced the entire assembly with a Dorman part. Came with T-stat inside. Ran beautifully for about 2 months.

For the last 2 months till now, I continue to have a slow leak.. When I am driving, it's dry as a bone. I will even come back an hour after having the car sit and still nothing. But 2-3 hours later I check it, and there is a small amount of radiator fluid on top of the housing.

Here's what I have done to correct it.

1. Replaced T-stat O-ring.
2. Replaced the upper inlet neck as recently as two weeks ago.
3. Made sure that the upper portion is snug.

Today I looked again, and still leaking ever so slowly. I cannot understand what is causing this? Is this common? Even after replacement? Did I just get a crappy part?

is there a crack in the upper part of the housing? it's possible to crack the plastic by over tightening the 3 bolts.

Have you tried replacing the coolant sensor (orings are crappy)? Otherwise May be the aftermarket housing. I tried one Dorman housing and it just didn't fit right to me so I took it back and went motorcraft again. Last 5 have been motorcraft for me. I have an explorer and mountaineer, and maintain another explorer and a ranger, on top of 1 previous explorer. (Does this make me an addict? Lol)

+3. Torque spec is only 7-8 foot pounds. Over tightening can also warp the housing. Another option is $$$ aluminum.

http://www.explorerforum.com/forums/showthread.php?t=362922

^ +1 i'm leaning towards the housing itself. I've heard Dorman ones just don't fit correctly and cause leaks.

Well, there are no cracks I have confirmed that. It does look like it's leaking right where the upper portion meets the lower.

One thing I meant to ask is, when I asked for a replacement Upper part, should it have come with an o-ring for that side of it, or is there just one for the part that fits with the T-stat only?

motc777 said:

Well, there are no cracks I have confirmed that. It does look like it's leaking right where the upper portion meets the lower.

One thing I meant to ask is, when I asked for a replacement Upper part, should it have come with an o-ring for that side of it, or is there just one for the part that fits with the T-stat only?

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Not sure. But when I replaced my Tstat last week, I noticed the gasket that seats around the the Tstat was squared off, not sure if thats due to age. the replacement gasket I ordered was completely different so I reused the old one. It would not fit properly upon reinstallation so I used some silicone lubricant to get it to seat correctly.

without that gasket, the system will leak out of the bottom and top half (duh). make sure the gasket isn't knicked, and also make sure the top half of the Tstat housing "plunger" that gets recessed into the bottom half of the housing isn't warped, knicked or cracked. this is the portion that makes the seal.

wbrudi28 said:

Not sure. But when I replaced my Tstat last week, I noticed the gasket that seats around the the Tstat was squared off, not sure if thats due to age. the replacement gasket I ordered was completely different so I reused the old one. It would not fit properly upon reinstallation so I used some silicone lubricant to get it to seat correctly.

without that gasket, the system will leak out of the bottom and top half (duh). make sure the gasket isn't knicked, and also make sure the top half of the Tstat housing "plunger" that gets recessed into the bottom half of the housing isn't warped, knicked or cracked. this is the portion that makes the seal.

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Thanks for responding guys. I've been looking at this tonight while we've been chatting.

The gasket for the t-stat is not kinked. It's sitting in there where it's supposed to be.

The new upper only seals with the o ring that sits on top of the thermostat itself. No other gaskets should be needed. I have a spare upper piece if you end up deciding to take that Dorman back. I'd send it to you for whatever it costs to ship. The new lower motorcraft housing is about the same price as the Dorman assembly, and will have a 2 year warranty if you get it from Ford. You'll need the manifold to housing gasket and a new thermostat o ring (both are o rings) don't try to reuse the o rings even if they've only been run once. Be about $6 for both. Then a thermostat. I recommend a motorcraft thermostat just because it seems to be more precise according to my scanner data, I am however running a duralast thermostat in the Merc with no concerns. Ones about $16 motorcraft is about $30-40. Temp sender I think was about $12. You'll probably come out about $50 higher than the Dorman setup after it's said and done but it'll fit right and last longer.

Also, if you already bought the orings ( I don't remember if the Dorman kit comes with them) but they too will have a year warranty if from AutoZone or oriellys.

Not to insult intelligence but have you checked the tightness of the hose clamp? I recently had a mystery coolant leak that was dumping coolant into my plug wells. Thought I was looking at installing a 2nd replacement intake but started at the t-stat housing. When I removed the hose to open up the housing and replace the t-stat and o-ring I found the clamp to be unusually loose. So much that I didn't even bother proceeding with the repair. Instead, I tightened the clamp to appropriate tightness and the leak disappeared.

Worth a try. Won't cost you a penny.

If you do plan to replace with Motorcraft parts, compare prices through eBay and rock auto. That's who I used when I just completed a full time up with all Motorcraft parts and both websites offer free shipping and significantly lower prices

Update on the saga. Wish I had seen this thread before going to the autoparts store this morning. Anyway, apparently the upper piece had a crack by one of the bolts, presumably due to my over tightening. So I got a new one, put it on, and it started leaking worse than the one that was on there!

It was also leaking in the same spot. I looked and saw that on the left side of the upper piece, as you are looking at it from the front of the vehicle, near the back bolt, it just doesn't seem to lay flush. I made sure that I tightened each bolt on the new piece all equally and not overtightened, and still it was seeping out, and this time while running. It wasn't doing that before.

Now, I know I might catch flak for this, but I took some black RTV, and I put it all around the outer portion of where it is supposed to marry up with the lower piece. I then bolted it down snug, but not over snug. I'll see what happens in the morning.

Frankly, if this doesn't work, I am thinking that A. What someone said earlier about Dorman being crap is probably true.

B. I'll have to overnight something from Rock Auto, or go into town because it's a holiday weekend and I have to get home.


As for the hose being too loose? It's not. I have a new clamp on that with new hose and it's not leaking from that area.

Duranged84 said:

The new upper only seals with the o ring that sits on top of the thermostat itself. No other gaskets should be needed. I have a spare upper piece if you end up deciding to take that Dorman back. I'd send it to you for whatever it costs to ship. The new lower motorcraft housing is about the same price as the Dorman assembly, and will have a 2 year warranty if you get it from Ford. You'll need the manifold to housing gasket and a new thermostat o ring (both are o rings) don't try to reuse the o rings even if they've only been run once. Be about $6 for both. Then a thermostat. I recommend a motorcraft thermostat just because it seems to be more precise according to my scanner data, I am however running a duralast thermostat in the Merc with no concerns. Ones about $16 motorcraft is about $30-40. Temp sender I think was about $12. You'll probably come out about $50 higher than the Dorman setup after it's said and done but it'll fit right and last longer.

Also, if you already bought the orings ( I don't remember if the Dorman kit comes with them) but they too will have a year warranty if from AutoZone or oriellys.

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I'll let you guys know for sure in the morning. However, if this doesn't work, it's Motorcraft for me. I think someone has these parts locally for the same price as Rock Auto.

Yes Dorman products used to be good, but unfortunately they have switch to a Chinese supplier so now they are just complete crap. Your best bet is to get a motorcraft one and be done with it, you may have to pay a little more but it is worth the money. It also should come as a complete assembly with the t stat inside and sensors already on it, so it just a matter of installing it on your truck and you do not have to mess with the two halves. You also can, if you really want to test it, get a cooling system pressurizer and then you can pressurize the cooling system to the psi and watch for the leak and watch the psi drop.

Accarguy said:

Yes Dorman products used to be good, but unfortunately they have switch to a Chinese supplier so now they are just complete crap. Your best bet is to get a motorcraft one and be done with it, you may have to pay a little more but it is worth the money. It also should come as a complete assembly with the t stat inside and sensors already on it, so it just a matter of installing it on your truck and you do not have to mess with the two halves. You also can, if you really want to test it, get a cooling system pressurizer and then you can pressurize the cooling system to the psi and watch for the leak and watch the psi drop.

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This is the long term plan. When I bought this part, I bought the entire assembly. I only had to separate it when I was maneuvering it into position. What's weird is like I said earlier that it didn't leak for nearly two months.

Right now I am happy to report that the RTV solution seems to be working. I drover over 60 miles this morning at 70mph on cruise and didn't see a drop when I got out. I will report back later this afternoon after it's sat for several hours. That is when it would leak.

Thanks to everyone for suggestions, comments. And to the guy who mentioned not insulting my intelligence. I want to say that 1. I am not a mechanic, so when it comes to my car, I'm completely unintelligent outside of basic preventative maintenance. LOL

2. I welcome any and all suggestions. I work in IT so I am familiar with troubleshooting. Sometimes the most easiest solution is the easiest thing to check out first. So no worries there!

Awesome, Hope it holds up for you, keep us updated and enjoy not having to stress and constantly add antifreeze lol.