Explore thermostat just won’t seal!

[joshua]

I have a nos weiand intake. So I decided to put a new O’Reilly thermostat housing on. Pressure test, fails. So I dig up an og explorer unit, adding water pump specific RTV to the therm housing side but not on the intake face. Still leaks. Should I try double up gaskets? Every thing torqued correctly, and aligned. Waited 24 hours. Pressure testing at 12 psi

 

[Broncobowsher]

Are the bolts short enough? Make sure you are not bottoming out the bolts.
Opposite of that, are the bolt holes through drilled? You could be chasing water weeping up the threads.

 

[joshua]

Are the bolts short enough? Make sure you are not bottoming out the bolts.
Opposite of that, are the bolt holes through drilled? You could be chasing water weeping up the threads.

It’s seems to be coming out all around the seal. Not just by the bolts. I tried using the explorer bolts, but they were too long. So I did buy shorter ones at the hardware store. And the shorter ones are in there

 

[DirtDonk]

What about the intake manifold itself? Seems like that’s the common denominator at this point.
Although the Cover/water necks are not known for being perfectly flat, getting two of the factory ones that leak, leads me to think that maybe the manifold itself is not perfectly machined.

 

[joshua]

What about the intake manifold itself? Seems like that’s the common denominator at this point.
Although the Cover/water necks are not known for being perfectly flat, getting two of the factory ones that leak, leads me to think that maybe the manifold itself is not perfectly machined.

I should have said that this is my suspicion, wondering if using 2 gaskets with RVT in between them could fill that void. I haven’t put rvt on the manifold side yet. I don’t really want to take it to a machine shop. Idk maybe I could use glass with sand paper on it, with some guide coat.

 

[904Bronco]

You might have a crack in the intake somewhere... No, two gaskets is never a solution, just another failure point.

 

[ksagis]

Are you only supposed to apply RTV to thermostat side of gasket? I have always applied to both sides of gasket.

 

[Broncobowsher]

You might have a crack in the intake somewhere... No, two gaskets is never a solution, just another failure point.

I was thinking that as well.

 

[ksagis]

@toddz69, I can interpret your thumbsup reaction as RTV is only supposed to be applied on one side of gasket, or it should be applied on both sides.

I’ll be kicking myself for all the years of cursing when cleaning up intake side if I didn’t have to and should have only been applying it on the thermostat side. Can you elaborate which interpretation is correct?

 

[toddz69]

@toddz69, I can interpret your thumbsup reaction as RTV is only supposed to be applied on one side of gasket, or it should be applied on both sides.

I’ll be kicking myself for all the years of cursing when cleaning up intake side if I didn’t have to and should have only been applying it on the thermostat side. Can you elaborate which interpretation is correct?

I'm a both sides guy myself.

Todd Z.

 

[Oldtimer]

One of the molded silicone gaskets (dry), and a little rtv on bolt threads.

 

[Grey owl]

In this case RTV on both sides for sure .

 

[ksagis]

One of the molded silicone gaskets (dry), and a little rtv on bolt threads.

View attachment 963669

This seems like a very nice part, have you used them before and happy with it? Happen to have a link to PN?

Existence proofs that old dogs can learn new tricks! This would be way better than gasket scraping and nicking soft aluminum. Tho now my surfaces may requires RTV…

 

[Oldtimer]

That one is a Mr Gasket 737G. Summit Racing sells them. Supposed to be reusable, but I always replace. They are great for trail side repairs, if thermostat is stuck.

EDIT
@joshua note that some of the replacement thermostat housings don't have a deep enough counter bore for the thermostat to sit in.

 

[toddz69]

That one is a Mr Gasket 737G. Summit Racing sells them. Supposed to be reusable, but I always replace. They are great for trail side repairs, if thermostat is stuck.

EDIT
@joshua note that some of the replacement thermostat housings don't have a deep enough counter bore for the thermostat to sit in.

First time I've ever seen one of those - pricey bugger but if it works, it could be a good thing. I've certainly dealt with my share of leaky thermostat housings over the years.

As an aside - it's disheartening to see the inflationary costs with these parts over the past few years. I was looking at a thread from 2024 where someone mentioned that part and they stated it cost $23-24. It's now $38.99! And in my other thread on the solid state IVR - my hard copy 2024 Tom's catalog lists them for $39.99. WH and Tom's now sell them for ~$57. Roughly a ~50% increase in the cost of those parts in 2 years!

Todd Z.

 

[ksagis]

Very nice part, even if pricey. Only down side I can see to switching to it now is I may need to surface prep my sealing surfaces as I expect they aren’t in good enough shape for no RTV approach.

 

[904Bronco]

First time I've ever seen one of those - pricey bugger but if it works, it could be a good thing. I've certainly dealt with my share of leaky thermostat housings over the years.

As an aside - it's disheartening to see the inflationary costs with these parts over the past few years. I was looking at a thread from 2024 where someone mentioned that part and they stated it cost $23-24. It's now $38.99! And in my other thread on the solid state IVR - my hard copy 2024 Tom's catalog lists them for $39.99. WH and Tom's now sell them for ~$57. Roughly a ~50% increase in the cost of those parts in 2 years!

Todd Z.

Not to get off track, but yes, I keep a spreadsheet on my builds to track where I bought what, and the cost. I purchased a number of parts early for Clifford, before tariffs. Now that I am buying some of those same parts for the current project, I am appalled at the increases from just 2 years ago. Add to that the increase in shipping, or the amount you have to spend to get free shipping... I used to get things from Summit in one day, now it is a minimum of three days... And you have to spend $125 to get it. (Not hating Summit at all)

 

[ntsqd]

With aftermarket intakes I've almost decided to do two things on every last one of them before they ever get installed. Install some type of threaded insert for the t-stat housing bolts. Counter-sink those holes to a minimum diameter of 1.1X the thread's OD. File the gasket surface flat. I'd go to studs there, but you can't assemble the t-stat housing to the intake with a stud in one of the holes.

If you strip one of those threads on a 289 or 302 you can't easily fix them w/o removing the intake manifold because the timing cover is in the way. Keen-sert or Time-sert preferred, Helicoil if no other choice.
Too frequently threading the intake there leaves metal pulled up from the gasket surface. It is not usually much, but it can interfere with the gasket working as it should. The C-sinking and the filing will remove that problem.

I've been known to use Hylomar on both sides of the gasket surface. After I drill a tiny hole in the very top of the t-stat.

 

[BUCKWILD]

also check that the thermostat housing is flat and not bowed, i have seen that a lot, can be fixed by filing them down

 

[LUBr LuvR]

First time I've ever seen one of those - pricey bugger but if it works, it could be a good thing. I've certainly dealt with my share of leaky thermostat housings over the years.

As an aside - it's disheartening to see the inflationary costs with these parts over the past few years. I was looking at a thread from 2024 where someone mentioned that part and they stated it cost $23-24. It's now $38.99! And in my other thread on the solid state IVR - my hard copy 2024 Tom's catalog lists them for $39.99. WH and Tom's now sell them for ~$57. Roughly a ~50% increase in the cost of those parts in 2 years!

Todd Z.

I’ve used these twice on thermostat housings that just wouldn’t seal. Last time was a couple years ago when they were still in the $25 range. Also have run into the counterbore in an aftermarket housing being too shallow for the thermostat to seat properly.