• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

chunk broke off head, lower tstat housing bolt on 4.0

M

Motorcharge

NAXJA Forum User
Location
Richmond, VA
I bought a 92 XJ a couple weeks ago and last week it developed a coolant leak. I looked while it was running and it was coming from the tstat housing on the bottom. I figured it was an easy fix and just time to change the tstat gasket, however I was wrong unfortunately. It seems the PO had overtightened the lower bolt on the tstat housing and apparently cracked it. When I went to tighten the lower bolt it went loose again as soon as it went tight. I figured I'd rung out the threads but when I took the housing back off about a 1" chunk of the head was out of place from the front to the rear of the bolt hole.

I've searched and searched between Google, here, Cherokeeforum and Jeep forum but haven't found but one thread with the same problem on here from back in 05 or so and it didn't really have a solution.

Do I have any options aside from replacing the head? I work at a Subaru dealership and the guys there are swearing up and down I can just JB Weld it back in place, but I somehow don't see it working, at least not long term.

I can get pictures if need be but not until Thursday since the Jeep is at work and we're closed for the holiday tomorrow.

Motor is a 4.0 with 260k on it.
 
get a pic of what you're talking about, I have NEVER, EVER heard of anything like this happening. the bolt should strip and/or snap long before it ever pulls anything out of the head.
 
The best way I can describe is the front, bottom corner of the head broke off from the back of the bolt hole to the front. As far as height goes it broke off roughly halfway up the width of the bolt. If I held the chunk in my hand it's about the size of a thumb drive or one of those mini Bic lighters.

I wish I had the piece with me to take a picture of, but it will have to wait until Thursday. The Jeep is locked in one of our holding lots and I don't have any way of getting in til then.

I never expected to have broken a piece off, but it had to have been cracked there given how easily it broke off. I know the motor is fairly old, but I've replaced tstats on XJs of mine that were over 350k original miles and never so much as broken a bolt off.
 
I've done similiar stuff, best results were to put a piece of threaded stock ( or a cut off bolt) in there and tack weld it. Make it a stud instead of a bolt.

You can weld to the head or any cast iron, clean it well and use the highest heat setting on your welder, rod or MIG. Use a few tacks instead of trying for a bead.

You can even silver solder a stud in what is left of the threads, though you need it really clean and an Oxy Acetylene torch.

I broke off the end studs on my intake/exhaust manifold, drilled it out, thought about threading it and going to the next bigger sized bolt. But decided to bevel it, welded a stud in there, dressed it flat, it's lasted 10 years so far. Not nearly as much stress on a thermostat housing as the exhaust/intake manifold.
 
8Mud said:
I've done similiar stuff, best results were to put a piece of threaded stock ( or a cut off bolt) in there and tack weld it. Make it a stud instead of a bolt.

You can weld to the head or any cast iron, clean it well and use the highest heat setting on your welder, rod or MIG. Use a few tacks instead of trying for a bead.

You can even silver solder a stud in what is left of the threads, though you need it really clean and an Oxy Acetylene torch.

I broke off the end studs on my intake/exhaust manifold, drilled it out, thought about threading it and going to the next bigger sized bolt. But decided to bevel it, welded a stud in there, dressed it flat, it's lasted 10 years so far. Not nearly as much stress on a thermostat housing as the exhaust/intake manifold.
Click to expand...

I'd solder or braze - welding to cast can be a pain, if you want to maintain integrity of the casting (castings have an amourphous grain structure, and pre- and post-heating of the weldment is generally advised. For a structural weld, it's required.)

Clean everything well, then use silver solder or brazing alloy to fix the stud in place. This would also allow the use of a dissimilar metal (brass or bronze won't corrode as quickly as steel - not by a long shot!) and makes it easier to replace later (if you have to use carbon steel, and it starts to hollow out from corrosion. This is common in cut fasteners, since the cut end is not zinc-plated.)
 
It hadn't even occurred to me to switch it over to a stud. I'd toyed around the idea of welding the chunk back on, but I think that switching it over might do better.

I may just try that this weekend if I can get my hands on a 220v MIG machine. I don't think my 110 is going to cut it for that.
 
5-90 said:
I'd solder or braze - welding to cast can be a pain, if you want to maintain integrity of the casting (castings have an amourphous grain structure, and pre- and post-heating of the weldment is generally advised. For a structural weld, it's required.)

Clean everything well, then use silver solder or brazing alloy to fix the stud in place. This would also allow the use of a dissimilar metal (brass or bronze won't corrode as quickly as steel - not by a long shot!) and makes it easier to replace later (if you have to use carbon steel, and it starts to hollow out from corrosion. This is common in cut fasteners, since the cut end is not zinc-plated.)
Click to expand...
Where the hell were you on my JF thread? :twak:
 
Motorcharge said:
Where the hell were you on my JF thread? :twak:
Click to expand...

I may not have seen it. Also, if I see something that looks like it's been cross-posted, I'm only going to answer it once (if I remember, I'll post the link in the other threads - but trying to get tech answers through a bunch of boards can get you disjointed responses and a connection might not be made. This is why cross-posting can be difficult, trying to get a decent sensible answer...
 
Don't sweat it, I wasn't serious.

I'm just going to put JB weld on the piece that broke off, the inside of the threading on the head, and on some threaded rod and put it back together and solder the cracks on the outside. I'd like to think that'll hold for a good while. I'll probably end up putting a remanned motor in it at some point anyway so as long as it holds til then I'll be happy.

If anyone still wants a pic out of curiosity let me know.
 
I would not solder on top of a JB weld job, not a good idea at all.
 
I'm trying to picture how deep the threads are and exactly how much of the block broke off.

If you have threads left below the broken off piece, just put a stud in there. Really not much stress on that bolt.

You heat up that JB weld and it is likely to outgas, which will likely kill any chance of getting any sort of bond with silver solder, brass or tin.

I'd leave the broken chunk off and tack/point weld a stud in there. Four points should be sufficient. When you are point welding, hold the MIG wire on the block next to the stud for a count of three and then flick your wrist so the weld travels onto the stud. The stud is going to want to take the weld a whole lot quicker than the cast iron will, so you want to concentrate your heat on the cast..

You can silver solder over MIG weld, you just have to clean as much of the carbon off as possible. The Silver solder flux will cut through most trash.

Or use Soda and brass or better yet Tin and Boric acid as a flux. You can buy a rod of body Tin with flux in the middle. You just need a torch hot enough to get the job done and clean an area of cables and anything else that will melt. I've never tried body tin on cast, but really no reason it won't work as long as the metal is reasonably clean.

It really doesn't have to look good, it just has to hold.

I've put a thermostat housing on after cleaning the block and housing really well and put silicon on both sides of the gasket. After it cures IMO you don't need the bolts anymore. You stick the thermostat housing on there with Indian Head cement ot Permatex type one and you are going to play heck ever getting it off again.
 
How much of the broken surface is corroded? That will tell you how long it has been cracking/cracked for.

No matter what you do I would get a new head at the JY and a new HG and keep them around just in case... a casting that cracks due to a thermostat bolt can't be all that good.
 
Geez I have a similar "errosion" problem at the bottom of my head from a clueless PO too. When I got Larry his temp was all over the place and I guess bad T-stat - Yea! It came out in 4 pieces but the head looked like HELL also. My new T-stat/housing job is seeping slowly again and I'm hesitant to dig into it for fear of what the OP has had happen.

8Mud said:
I'm trying to picture how deep the threads are and exactly how much of the block broke off.

If you have threads left below the broken off piece, just put a stud in there. Really not much stress on that bolt.

You heat up that JB weld and it is likely to outgas, which will likely kill any chance of getting any sort of bond with silver solder, brass or tin.

I'd leave the broken chunk off and tack/point weld a stud in there. Four points should be sufficient. When you are point welding, hold the MIG wire on the block next to the stud for a count of three and then flick your wrist so the weld travels onto the stud. The stud is going to want to take the weld a whole lot quicker than the cast iron will, so you want to concentrate your heat on the cast..

You can silver solder over MIG weld, you just have to clean as much of the carbon off as possible. The Silver solder flux will cut through most trash.

Or use Soda and brass or better yet Tin and Boric acid as a flux. You can buy a rod of body Tin with flux in the middle. You just need a torch hot enough to get the job done and clean an area of cables and anything else that will melt. I've never tried body tin on cast, but really no reason it won't work as long as the metal is reasonably clean.

It really doesn't have to look good, it just has to hold.

I've put a thermostat housing on after cleaning the block and housing really well and put silicon on both sides of the gasket. After it cures IMO you don't need the bolts anymore. You stick the thermostat housing on there with Indian Head cement ot Permatex type one and you are going to play heck ever getting it off again.
Click to expand...

Geez! You guys talk about metal like I do instrumentation or automation - I wish I know 1/10th as much about metalworking as several of you in this thread do!
 
Here's the piece that broke off. It's smaller than I originally thought, but I was so mad at the time I just walked away and hadn't messed with it sense. I don't think there's any threading left because the bolts was turning freely after the chunk popped off.

14c3zuo.jpg


hrzbyg.jpg


The bottom/front part is where the gasket would go on.
 
Last edited:
it looks like that was cracked for a decent amount of time from the rust that has formed on the break, i can't believe you could torque on the bolt hard enough to cause that without cracking the thermostat housing. my buddy actually just cracked his 2 weekends ago when the thermostat came unseated and slipped just barely out of it's hole.

I hope you get it worked out, that would definately be a "oh shit" moment for me and then a "damnit" and a "well i guess its beer time"
 
GrimmJeeper said:
it looks like that was cracked for a decent amount of time from the rust that has formed on the break, i can't believe you could torque on the bolt hard enough to cause that without cracking the thermostat housing. my buddy actually just cracked his 2 weekends ago when the thermostat came unseated and slipped just barely out of it's hole.

I hope you get it worked out, that would definately be a "oh shit" moment for me and then a "damnit" and a "well i guess its beer time"
Click to expand...
It had to have been because I barely put any torque on it for it to break off. As soon as the bolt started to go tight it went loose again and could just spin freely.

I'll update you guys on the fix as soon as I can get to it. My hood latch is broken and it's sitting on asphalt so I haven't exactly been jumping at the chance to climb under it while it's been 100+ degrees here every day.
 
You must log in or register to reply here.

Similar threads

T
Temp gauge stuck ?
Replies
6
Views
2K
Tonyt22
T
V
High temp woes
2
Replies
21
Views
414
Vitzaa
V
B
Oil leak.
2
Replies
38
Views
6K
Bmfinney
B
Root Moose
Cooling System Reset (2000 XJ)
Replies
1
Views
1K
Rob Mayercik
R
D
1996 4.0 No Crank, Starter Works When Jumped
Replies
19
Views
274
Saudade
Saudade
Back
Top