AndyADD

What are the torque specs for the bolts on the thermostat housing?

SuperGlue

13 ft lbs according to Haynes Repair manual

Caish

Andy,
I've broken two thermostat water necks.
So be very careful tightening the thing down.
Tighten one finger tight plus 1/2 turn, now go to the second bolt.
Same thing finger tight plus 1/2.
Now tighten each one 1/2 turn at a time till snug.
those things are some of the must fragile necks I've seen.

SuperGlue

Yeah i completely agree, I actually went to Home Depote and bought stainless steel bolts that wont rust and break. I wouldn't suggest using the same bolts twice ever, I always replace them. Way to much of a pain to get them out when you snap them to not bother getting new ones.

AndyADD

Do you have the specs of the bolts you used? ex. length? thread?

SuperGlue

I brought in the factory bolts that came out of the thermostat housing and then had them match them up for me. Thread count, length and what not. The Home Depot I went to didn't have the best selection and the ones they matched for me were about a quarter inch longer then the OEM ones so I just used a cut off wheel to shorten them, worked like a charm and now I don't have to worry about my bolts rusting the next time I change my T stat. Sorry I dont have more info... But like I said, bring them in with you and they will match them up!

5-90

Threads are 5/16"-18, match the length underhead (I think the short one is about an inch, and the long one about two and a quarter. Check the Bolt Chart on my site to see if I have them listed yet...)

If all you can get is SAE-graded carbon steel, use SAE5 and replace them every time they come off. CRES is better, brass or bronze will be best! The preload is low enough that the material strength becomes irrelevant (you could use aluminum or even most ceramics, but I wouldn't trust Nylon...) and yellow metals are even better at resisting rust than CRES! Check a marine supply house for brass or bronze.

Whatever you use, cheap added insurance is to coat the threads and shank with RTV or PTFE paste - it also helps the threads seal, since the holes communicate with the coolant jacket.

Caish

I was not referring to boilts breaking.
I was referring to cracking the thermostat housing.
Its thin aluminum and if not tightened equally and slowly you will break the housing!.

I could care less about the bolts. Just clean the old ones up if they're not pitted from rust and electrolysis with a wire brush on the bench grinder and reuse them.

5-90

Just makin' sure...

Further swap note - you can use a 1991-up thermostat housing on a RENIX engine, just plug the sensor port with a 3/8" NPT (preferably brass) plug. However, you can't use a RENIX housing on an HO 242...