Thermostat housing bolt size questions (1 Viewer)

[nickolai]

Hi All,

I'm getting ready to do a big refresh of my relatively new to me 40's cooling system for summer in the southern Hemisphere. Main reason is because my heater valve is stuck open, thus heat is always on (not so great in summer).

Since i try to do things as completely as possible im doing the valve, water pump, all hoses, thermostat and housing and the radiatior, along with a grunty flush.

Anyhow, what size are the bolts that hold the 2 halves of the thermostat housing together? I've searched and found 8mm x 50 but no thread pitch?

And what size are the bolts that hold the complete housing to the head?

Thanks and apologies for my longwindedness!

Thanks!

 

[Weber Sarge]

8x1.25 .
If you use a cold weather thermostat and a different one for hot weather I'd recommend the use of studs and flange nuts .
Sarge

 

[bsevans]

I use Stainless Steel bolts with antisieze and find it makes for no issues removing the top housing years later. I also use SS bolts and antisieze to mount the lower housing to the head.

 

[nickolai]

Thanks all, im going to go with stainless and antisieze.

Cheers!

 

[Weber Sarge]

I made the point of studs due to thread wear inside the cast aluminum parts , anti-seize is our friend but over the years the threads will wear quite a lot in cast .
Sarge

 

[65swb45]

I made the point of studs due to thread wear inside the cast aluminum parts , anti-seize is our friend but over the years the threads will wear quite a lot in cast .
Sarge

I am also a follower of the stud and flange nut school...for the same reason.

Best

Mark A.

www.marksoffroad.tripod.com

 

[Weber Sarge]

My biggest drive to use studs comes from my side gig - tig repairs on hard to find parts .

Also a huge fan of using Syl-Glide on cooling hoses since they can cause advanced electrolysis and rot cast thermostat housings . Had to patch four bad holes in mine last year.

Sarge

 

[FJ40Jim]

Sarge, do you recommend for or against Sil-Glyde for hose installation?

I haven't noticed probs with using it, but if your experience is different...

 

[Weber Sarge]

I have never had a problem with hoses blowing off using Syl-Glide , even high pressure race engines running 20-25psi cooling systems . It's real benefit is keeping rubber parts from welding themselves onto radiator , heater core n thermostat necks . It also stops hoses from rotting at those connections .
One really cool use for the spray can version is gaskets - don't put thermostat housings or carb gaskets on dry . I soak 'em good with the spray Syl-Glide and they become re-useable . Always did this on my Weber builds so customers could service the jets without having to replace the air horn gaskets . It's also a great preservative for machinery surfaces like my lathe that likes to rust .

Been using their products for 30yrs or so....
Sarge

 

[FJ40Jim]

Cool, that's also my experience w/ sil-glyde.

 

[beermanharp]

Complete beginner here - I need to replace the bolts that connect the upper and lower housing, along with the housing to the head. Am i reading correctly that 8x50 is the former and 8x1.25 is the latter? I need to know exactly what to ask the parts store for. Recently purchased a 76 FJ40 so my first "simple" project of replacing the thermostat has turned into a little more.

 

[Weber Sarge]

The main housing bolts are 8x1.25x50mm long . Not sure the exact size of the housing to head bolt size offhand . I prefer studs for the thermostat housing , read above why .
Sarge

 

[FJ40Jim]

Lower housing to head is M10x1.25 thread, 25mm long.

 

[nickolai]

Thanks for all the replies guys, got this all buttoned up last week, all in all was pretty straightforward, apart from the usual dodgy stock temperature gauge thinking things were getting too warm. Have installed an Autometer gauge and all is well in 2F land.

 

[beermanharp]

Thanks for the info everyone. Thought I would let everyone know my findings after successfully replacing the thermostat, thermostat housing bolts and gaskets in my 76 FJ40. The upper to lower housing is connected by 8x1.25x45 bolts. The housing to head is connected by 10x1.25x25 bolts. Confirmed measurements of both with a caliper and thread pitch gauge....plus, they fit perfectly when I installed them. Hope this helps the next person out. For what it's worth, the local O'Reilly's parts system recommends the wrong thermostat and gasket...and the Toyota dealership system recommends the wrong sized bolts. I went with SS for both and used anti-seize as many folks recommended.

 

[Weber Sarge]

That's odd - I just bought a hotter (192*) thermostat from O'Reilly's last week and installed it yesterday - perfect fit and MotoRad brand . Might post up a pic , maybe you have a later type housing as I think there was a change in them .

One note - I have yet to find a correct diameter top thermostat gasket - the one that seals the top of the thermostat to the inside of the housing . They all seem a bit small - even the one from Toyota ?
Sarge

 

[FJ40Jim]

The 8x45 bolt is the correct size per the Toyota parts catalog.
PN is 91611‑60845. The last part of the PN indicates 08mm diameter, 45mm length.

Sarge, that has been my experience with a lot of gaskets also. Just 1mm too small in ID, so they don't like to lay flat on the top of the stat. A little sil-glyde ensures that the gasket is able to deform into place as the top housing is bolted down.

 

[nickolai]

Sarge, that has been my experience with a lot of gaskets also. Just 1mm too small in ID, so they don't like to lay flat on the top of the stat. A little sil-glyde ensures that the gasket is able to deform into place as the top housing is bolted down.

I was concerned with this too, the old gasket had been siliconed in by the naughty PO.

I heated mine very slightly with a heat gun and it fit perfect. Those smarter than me may say this was a bad plan but it seems to have worked fine.

 

[Weber Sarge]

I just used some spray high-tack to hold the gasket into the housing - I hate being anal but the dumb thing should fit the machined part of the housing . The issue here is if you went to any other material you risk changing the durometer of the rubber and not allow it to seat the base housing gasket . Seems to work fine , no hot coolant in the upper hose until the thermostat opens so I think so far all is good . Engine does seem to run better so far but it's been nearly 40* here , odd weather for our state in January . I use liberal amounts of sil-glyde on the gaskets to prevent them sticking and getting pulled out of alignment , sure makes it nice working on stuff years down the road too .

BTW- the top interior rubber gasket is nearly 3/16" too small overall - I'm going to look into some plumbing gaskets I've found for black plastic pipe connectors for sinks as some of those look promising .

On a side note - due to our temp swings here in Salt of The Earth Illinois I may run a fluid heat riser on the intake since I run a header . Maybe a dumb question , but if the heater valve is working correctly this should work fine for summer use (last year we saw 104* days) since coolant won't be flowing with the heater off ??
Sarge

 

[FJ40Jim]

Yes, that's the beauty of the fluid heat riser: it adds heat when you & the engine want it, and doesn't heat the intake when you & the engine are comfortably warm.