6.2L Leaking Coolant at the Thermostat Housing

[xtela]

From the Ford shop manual:

 

[Ruger]

Thank you @xtela !!!

 

[Ruger]

I had not fully drained the system and was getting hot air from the air vents, so I have opted not to remove the hose to the heater core as the instructions indicated. I have read that the difficulty with these systems is that the heater core is so high up in the vehicle that it tends to trap air. (That's probably why the maintenance manual tells you to remove the heater hose and fill the radiator till it runs out of that hose.) So what I did is jack up the front of the truck so that the radiator is hopefully above the heater core and the air trapped in the system is driven out of the heater core to the radiator. To assist that further, I jacked up the driver side of the vehicle a little higher than the passenger side because the radiator cap and overflow reservoir are both on the driver's side. Then, per the maintenance manual, I started the truck, turned the heat knob all the way up, the fan on high, opened the AC vents on the dash, and let it idle until it reached normal operating temperature and the upper radiator hose was hot to the touch. That took well over a half hour. Now I'm letting it cool, and we'll see if the system will accept any additional coolant. If not, I'll have to jack it up even further and repeat. Good thing there's beer in the house because this is going to take all day. I can't believe that the Ford mechanics tie up a bay all day to do this.

 

[xtela]

I think most mechanics use something like this: https://www.amazon.com/dp/B0002SRH5G/?tag=fordraptorforum-20
The shop manual lists a procedure for using one. It also checks for leaks before you fill. You use compressed air to pull a vacuum on the system. If it holds you should be leak free. Then you use the vacuum to pull in the new coolant. Its fast.

 

[Ruger]

Thanks @xtela. My compressor only produces 60 psi. Turns out I didn't need to spend $150 on that tool and buy a new compressor anyway, and thank goodness!

I knew there was only a little air in the system for two reasons:
- I got 160 degree air from the vents when the truck was at temperature, and
- I kept the fluid I'd drained out, used that to refill the system, and only a few ounces were left.

So I drove it. I went to town 20 miles away, got a half-ton of pellets for the pellet stove, drove back home, parked the truck on my inclined driveway with the nose high, and let it cool completely. That did it! After it was cooled down I was able to pour the remaining coolant that I'd drained into the radiator, and needed a little more to bring the level in the reservoir to the fill line. I conclude that jacking up the front of the truck would have worked if I'd jacked it up a whole lot higher than I did. The trick here is to have the radiator higher than the heater core.

Many thanks to all who helped and advised.

 

[Skiracer3]

Can you tell me where to get the "Square" O'Ring? Do you have a P/N? I have access to the round O'Ring (8255) but can't seem to locate the square one that goes on the thermostat. Additionally are you putting the round O'Ring in as well? The 8255 O'Ring does not have a groove for the O'Ring to sit in.

 

[MTF]

@Skiracer3

No, you do not use both, only the housing gasket that the thermostat fits in.

If someone tried to use both and tightened the two bolts too much,
It will deform the the thermostat housing and it will leak.

1991-2025 Ford Engine Coolant Thermostat Housing Gasket F1VY-8255-A | TascaParts.com

1991-2025 Ford part # F1VY-8255-A - Engine Coolant Thermostat Housing Gasket

www.tascaparts.com

 

[EricM]

Just gonna say "torque wrench" again...

Amazing how many guys tighten bolts by guessing at the correct torque on mission critical stuff.

Bolts need to be stretched a certain amount to both provide a clamp load and to not back off. Going beyond that stretch is a problem, and coming up short of that stretch is a problem as well. When you add in o-rings, overtightening is even more detrimental.

You can get a torque wrench on the t/stat housing bolts, so there is no reason not to use it other than being too lazy to get it out, or too cheap to buy one.

 

[Skiracer3]

@Skiracer3

No, you do not use both, only the housing gasket that the thermostat fits in.

If someone tried to use both and tightened the two bolts too much,
It will deform the the thermostat housing and it will leak.

1991-2025 Ford Engine Coolant Thermostat Housing Gasket F1VY-8255-A | TascaParts.com

1991-2025 Ford part # F1VY-8255-A - Engine Coolant Thermostat Housing Gasket

www.tascaparts.com

Thanks for the info. I'll give it a shot! This stupid leak, even though it's very small, really torques me!

 

[602Raptor]

@Skiracer3

No, you do not use both, only the housing gasket that the thermostat fits in.

If someone tried to use both and tightened the two bolts too much,
It will deform the the thermostat housing and it will leak.

1991-2025 Ford Engine Coolant Thermostat Housing Gasket F1VY-8255-A | TascaParts.com

1991-2025 Ford part # F1VY-8255-A - Engine Coolant Thermostat Housing Gasket

www.tascaparts.com

I am in the process of doing this service. I purchased the F1VY-8255-A gasket and it is indeed an o-ring. it is NOT a "square" gasket and the thermostat will NOT fit inside this gasket. From reading this and other threads, I believe the correct part is indeed an o-ring as that's whats shown in the ford manual linked here. Similarly, I purchased Motorcraft thermostat TL3Z-8575-E which has a etching showing 88.9* C (192.02*F) IS this the correct part?

If I'm incorrect regarding the tstat or gasket, please let me know.