6.2L Leaking Coolant at the Thermostat Housing

You got it, good luck

After consulting with several mechanically oriented friends (I thought I was among them!) and a knowledgeable guy at the Ford dealership parts desk, my suspicion is that I've been over-torqueing the bolts. Doing so may have simply put more pressure on the o-ring than it could handle, may have caused the thermostat housing (AKA water outlet, AKA gooseneck) to deform due to excessive pressure, and/or may have caused the gooseneck to deform due to too much heat being directly conducted to it via metal-to-metal contact with the engine block.

So I have in my hands a new Ford thermostat gasket (P/N F1VY-8255-A, cost $8.82), and I have a new Ford gooseneck on order.
We'll see...

Plausible.
Good luck.

The new thermostat housing hasn't arrived yet and I got impatient, so I did a little experimenting today.

I took the truck for a couple spins around the block, and then had a look to see if I could tell where it was leaking. I observed a tiny trickle of fluid from under the upper radiator hose right where the casting flash is on the thermostat housing. I'd replaced the factory spring hose clamp with a worm gear clamp, it seemed tight, but obviously not tight enough. So I tightened it as much as I thought prudent, dried everything off again, and took it for another spin around the block. No leaks visible this time.

So what I'm going to do is drain the coolant, take the upper radiator hose off the thermostat housing and dress the casting mark with a jeweler's file and some fine abrasive cloth without disturbing the o-ring, and make more and more demanding test runs to make sure that's the only place it's leaking from.

NOTE TO ALL: The next time you drain the coolant, take that opportunity to remove the upper radiator hose from the thermostat housing and inspect the casting mark. If it's not smooth and uniform with the rest of the diameter of the thermostat housing, give it some TLC.

Special thanks to @smurfslayer for making me look more closely.

Use a torque wrench on all bolts on the engine- Ford has a rating for every bolt.

I always stick with the spring clamps. They are always tight. The only trick is to get it back on the hose in the same spot where it's formed an indent. I've switched to t-bolt clamps on some stuff, but spring clamps are used by OEMs for a good reason.

You can't always get a torque wrench into an area, @EricM. A good example is the transmission pan bolts. The aft half of the tranny pan is just above a frame cross member, and you simply don't have the room there for a torque wrench or even a conventional ratchet.

Spring clamps. I have a theory. After thousands of heat cycles a spring clamp may become less springy. It's just metal. Metals fatigue, lose their temper, etc. I don't trust 'em.

Big trucks on silicone hoses use a tbolt with a spring. A dime in the coils is correct tension

Ruger said:

You can't always get a torque wrench into an area, @EricM. A good example is the transmission pan bolts. The aft half of the tranny pan is just above a frame cross member, and you simply don't have the room there for a torque wrench or even a conventional ratchet.

Spring clamps. I have a theory. After thousands of heat cycles a spring clamp may become less springy. It's just metal. Metals fatigue, lose their temper, etc. I don't trust 'em.

Click to expand...

Read the following with the understanding that I hate/loathe/detest spring clamps and my objectivity on this topic is... questionable.

Typically, springs fatigue not from a constant position (compressed) or the relatively low heat we’re discussing, but rather from cycling; that is, compression and decompression. If it’s ferrous, it’s not going to lose it’s form or hold unless you’re up over 4 digits Fahrenheit. I think Titanium begins to expand at around 800 F, but again it’s not losing form, just expanding. Iron or steel will go much higher before losing its form. That said, I’ve had bad luck with these ‘spring’ clamps and hate them. Twice I’ve had leaks, after a reassembly and fixed the leak by replacing those damn spring clamps with a traditional, ratcheting (?) screw tightened hose clamp.

I’d have a hard time believing that heat fatigue would be affecting these clamps; the hoses themselves would have a much lower melting temp than the clamps. I could be convinced with solid evidence, but I admit I’d be skeptical.

Either way, let’s take yes for an answer here.

BTW, @Ruger, you can get adapters for various conditions with a torque wrench. I’ve got at leas 3 T/W adapters in my ’smithing tool box for the various makers free float tubes. Between universals and “wrench head” adapters and such, there should be a way, albeit not always an easy one. ( he says before popping the hood to actually look at the coolant neck )... That said, I won’t publicly admit my age and the fact that I’ve yet to acquire an inch/lb torque wrench.

;-)

Well, I compromised.

I drained the cooling system, removed the upper hose from the gooseneck/thermostat housing/water outlet, and cleaned up the area of the neck where it seals against the hose. When I put it back together I used both the factory spring clip and a worm drive hose clamp. I DARE it to leak.*

So now, of course, I have a different question. Does anybody know the technique for purging the air out of the cooling system? I've poured as much back into the radiator as it would accept without overflowing, driven it until it was all heated up, let it cool, and poured more into it, and I still have coolant that I drained left over. (Houdini, where are you? I need to disappear some coolant into my engine.)

*I'm probably going to regret that statement.

NOTE: I'll publicly admit my age but only to people with old memories: I can sing a certain Beatles song with utter authority.

There is the possibility of deposit buildup in a hose. Aluminum cavitation or deposits at transition.