Thermostat housing leak

Cougar Community Classic Cougar Maintenance Restoration and Repair
21

I just replaced the thermostat and housing (Scott Drake repro) on my 68 390 GT. I followed the shop manual instructions:

  1. thin layer of sealant on each side of the gasket
  2. place the gasket on the manifold
  3. install the thermostat in the housing and turn it to lock against the flats
  4. install and torque the housing bolts to 12-15 ft/lbs

I’m waiting for the sealant to set up and fingers crossed that it works. If not, I’ll be trying some of the other tricks in this thread.

22

Just noticed today that the leak on mine is getting worse. Looks like I’ll have to re-do it this weekend. :frowning:

23

May the force be with you on that! Sounds like th did it by the book which I am not too good at doing.
I did the sealant on the housing, gasket on, sealant on top, then stuck it in the manifold. Wonder if that order really makes a diff.
Thanks for sharing Steve, love your car.

Brian

24

Bummer, is it seeping at the bottom? Just while sitting?

Brian

25

Must be seeping through the bottom while driving to/from the office. The gasket I used was from NAPA and had adhesive on one side (like a sticker). I put the sticky side toward the manifold and smeared the housing side with a thin coat of Permatex. I’m going to try just straight Permatex- no gasket- this time.

26

I did see that some have done that. I will be interested in what Permatex you use and if it works. Seems like the cheap gaskets are just a paper product, not much of a sealer. Yea, a slow leak there probably can evaporate fairly quickly and just drain the coolant over time. Did you see a little puddle underneath on top of the manifold? Let me know how it goes.
Mine hasn’t been tested yet with the engine running.

Brian

27

FWI update: I never did get around to re-installing the thermostat housing on my J code, but I think I have eliminated the slow leak/seepage issue by switching from a 13psi radiator cap to a 9psi cap. I know that the new cap lowers the boiling point of the coolant a bit, but my cat never runs all that hot anyway.

28

FWIW. I always put the housing on a large stationary belt sander to surface it flat and it has not failed me yet.

29

+1 on cracking the housing, been there.

30

X2 on what Mark said on pg1: the chrome housings are junk.

31

Had to do mine twice last time. I resorted to black RTV and let it dry at least an hour before putting fluids back in the system.