My old has rubber around it but it needs to be replaced. I cant find one. The dealer doesn't show one. Should one have come with the new stat? Would love to get it back together this weekend. What does the rubber do anyway? To me it just looks like it helps keep the stat centered when you put it back together.

 

first things first, did you buy a motorcraft (or international) thermostat, or some other brand? if its any other brand, take it back and get the motorcraft one. it really does matter.
from there, all engines i've worked on use either a paper gasket plus silicone or something that resembles an o-ring with a slot on the inside that slips over the thermostat. never had it off my 6.9, so i'm not sure which it is. either way, gotta have what its gotta have to make sure it seals.
a quick check at oreillyauto.com shows that there is a rubber seal like you described, and it comes with their house-brand thermostat, which is the only one they list.

so in short, find that rubber, its the seal and you gotta have it

 

Yes I bought the motorcraft stat from the dealer. No rubber boot that goes on the bottom of it. My old stat that i just took out was a motorcraft stat that has a boot but needs replacing. when i talked to the dealer they dont show any kind of rubber boot. Now what?

 

I got another stat from the dealer that has a boot!! I was happy till i tried to install it. Can someone help? Is the rubber suppose to fix snug when you install the stat? There's a good size gap with mine and wouldn't seal anything.

 

Motorcraft RT1049

there is black rubber or something wrapped on it,but im not sure why your worried about it.just toss the thing in there and run 'er.
the gasket that comes with it,is what seals the goose neck.
i was just reading on oilburners where someone says they like to remove the rubber to help keep the engine run cooler - i wouldn't dream of such an action.you want her running 200-210 most of the time to help ensure max efficiency.strange how some people are so afraid of letting their idi run upwards of 220-235 when working 'em good.these are not gas jobs.

i just had to replace mine,and got a bad one right out of the box.thought for sure it must be a water pump issue so replaced that and still same issue haha.so i got another rt1049 (looked the same of course) and that one cured what ailed her.

 

I just want to know what's right. Some on here say it seals but if mine is right it seals nothing. I don't want to have to pull it all apart again. That's what I'm worried about.

 

your worrying too much brother.
if it's Motorcraft RT1049 it's correct.no other t-stat is correct.it's really that simple.don't worry about how it's made.trust the ford engineers.they know what they were doing,and these engines have been running proven for several hundred thousand miles with this t-stat without over heating when working correctly.

 

I replaced my t stat a few months ago and noticed the same thing. The old t stat that I pulled out of the truck had a rubber boot around the bottom. The new rt1049 motorcraft I put in had no rubber boot at all.

I only have the stock temp gauge to go by and I'm not sure how accurate it is but it runs MUCH cooler than before. With the old t stat the needle would sit in the middle of the gauge and now it barely gets past the bottom end of the operating temperature range. I'm thinking there is so much coolant bypassing the t stat that the engine can't get to operating temp.

Shouldn't there be some sort of seal on the t stat? Mine is just metal on metal, is that normal? I've never replaced one before so I don't know.

 

I don't know either but I installed mine anyway. I should have it all back together tomorrow so I'll let you know. Tried to upload some pictures but I can't figure that out.

 

A new one should have a little rubber sleeve around the lower half, there is also a large o-ring that seals the t-stat to the block. I got mine from Ford and it came with the sleeve glued on and the o-ring in the box.

 

Well that sucks, guess I'll be replacing that thing again if I can find the correct one. You don't know if your getting the right one even if it is the motorcraft rt1049

 

I don't know about any o ring. My old one and new one didn't have any o ring.

 

I started out with a $4 Stant from Rockauto, that's been a fine brand in my book. On perusing here I decided to go for the $14 Motorcraft as I'm really chasing a creeping temp problem, radiator shop suggested I try thermostat before getting invasive with a perfect looking radiator.

New Motorcraft looks just the same as the Stant but comes with a rubber gasket, no o-ring, no plastic wrap as seen on the pic at Rockauto. Not sure what I'll find when I dig into this....

Best,
- Jeff