mcollum30

1991 Jeep Cherokee 4.0 2WD.

So while replacing the thermostat and heater hoses, I discovered that the bottom bolt hole for the thermostat housing is broken and missing a piece of it's thread/wall meaning the hole is incomplete. It is more of a "C" shape instead of a complete "O" shape for the bolt. The bolt barely threads into the hole and doesn't drive all the way in. I coated the bolt liberally in RTV in an attempt to get it to stick/prevent leaking and it seems to hold, at least enough, but im just worried about it now. What are my options to fixing the hole? Could I use a helicoil? Does it need to be fixed if I can get it to hold and not leak? Thanks guys

'90Cherokee

A 'normal' helicoil repair would force you to drill it out losing more material. There are also solid thread repair kits where it's like a bushing instead of a spring like a helicoil, but that too would force drilling and removing more metal. You could use one of the solid type bushings and a smaller bolt so you'd have a complete solid thread to screw into without removing much metal to insert it. I think the standard screw used is a 5/16" so maybe a thread repair bushing for a 1/4" bolt would let you keep most of the existing metal. My other thought is so clean it out really well, screw in a stud of the appropriate length and epoxy around it to make it a strong solid fit. You could also use a bolt with the right release agent on it and epoxy to 'rebuild' the metal that's gone. Or maybe a thread repair bushing and epoxy that in.

Bugout4x4

The stud option is a very good suggestion. In fact because there is limited room to even get a drill in there without taking a lot out of the way, it would be the one I would go with myself and be careful not to torque it anymore than is needed.

mcollum30

I have never seen these before. Is it something like this?

https://www.gamut.com/p/self-locking...-size-MzAwMg==

Bugout4x4

Yes, that is the solid bushing type he was talking about. Keep in mind you will have to remove the radiator and fan/shroud to make enough room for a drill if you go that route. Unless you have or can rent a 90 degree drill. You may want to consider his other suggestion with the stud/epoxy first. JB weld or they also make a two part high heat marine epoxy rated to 350 degrees.

mcollum30

I see two products that seem to fit the job from JB weld. They have a steelstik and a high heat putty. Steelstik says it can get wet but it can only withstand up to 300 degrees. I know that’s way more than my jeep should get but it seems a little close. High heat goes up to 400 degrees but doesn’t say anything about getting wet.
If you want to look, here is steelstik.
https://www.jbweld.com/collections/8...xy-putty-stick
and here is high heat.
https://www.jbweld.com/collections/8...at-epoxy-putty

Also, I really appreciate the time you guys have put into helping me out.

MayerMR

If you're talking about the thermostat housing itself, then buy a new one. They are about $6.

Bugout4x4

If you have decided to glue in a stud as suggested, The original two part liquid JB weld or this stuff called "Epoxy-Marine" in a blue container made by Loctite. It is a two part plunger product rated to 350 degrees, works even when wet, Glues ANYTHING, and has a 3000 PSI rating. It will be stronger if you use a liquid rather than a putty.

mcollum30

Thanks bugout.

Mayer, no it’s actually where the bolt threads into on the engine to secure the housing.

Bugout4x4

You can stir it with the bolt, Just be sure and twist it around flat at the last to make sure you have an even mix on it. Read the back carefully first. Any excess bubbling out needs to be cleaned up right away or you will have to drill the back side of the housing to make room for this excess when you bolt it up. It's serious stuff and once on there it is pretty much permanent and in the way if there is too much. You don't want to be filing on it and mess up the mating surface.

'90Cherokee

Using the part you're trying to attach as the mixing tool is a bad idea, especially a stud where unmixed epoxy will hide in the threads. The vast majority of epoxy failures I see are from inadequate mixing, second is inadequate prep. In this case you have coolant residue and rust to clean off. Kinda like a good paint job, prep is key to good epoxy repairs. I've fixed some unbelievable stuff with JB weld. I've also seen easy repairs botched and fail.

My JB weld method: I use packing tape on a smooth surface as my mixing surface and a small screwdriver that doesn't have any ridges or overly sharp corners. Once it's mixed well, scrape the surface well in all directions and scrape off the screwdriver and mix again. You can then take the piece of tape to where you need to apply the stuff then throw the tape away leaving only the screwdriver to clean. I use tape to form dams when I need to build up an area. After the JB has hardened to a hard rubber/plastic hardness it's easy to trim off excess with a razor blade, once fully cured it'll take grinding/filing to remove. Grease can also be used to keep it from sticking to surfaces it's going to run off onto, just make sure the grease isn't going to run/spread onto the pats you want to adhere. Avoid trying to make really small batches, it's harder to judge a 50/50 mix when it's a tiny little dot of stuff. Wasting a little JB beats having a failure.

This repair will be easy since you still have a good amount of solid material to start with so it just needs to be reinforced a bit and sealed against further erosion. After cleaning well use a small tool like a toothpick to apply a layer into the threads in the head, you don't need a lot but press it into the threads. Apply to the stud the same, thin layer and pressed into the threads. Screw it in and clean off excess on the gasket surface. Put a layer where the metal has vanished from and you should be set for life. If it's cool out it'll take longer to set up, but it won't be as runny as when it's warm.

I haven't used the putty type epoxies in a long time. It's good for doing a large build-up but I find it's not as good at joining stuff and can be hard to get it to really stick well.