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1988 Jeep Cherokee 4.0 6cyl
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Discussion Starter · #1 ·
I replaced my thermostat and gasket, coolant was leaking. I then purchased a new thermostat housing and another gasket, still leaking. I've used RTV both times and it's still leaking. What am I doing wrong? Should I use an actual sealant?
Also, when I put the new thermostat in, it fits but it's comes out VERY easily. I could blow on it and it falls out. So when I put the housing on, I have to do it very slowly. Is that common?
 

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1988 Jeep Cherokee 4.0 6cyl
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Discussion Starter · #2 ·
I've let the RTV sit both times over night. When I put the coolant in, it takes a second then starts to fall out of the bottom of the housing. So much coolant wasted :(
 

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Are you sealing the bolt threads? How clean is the block and housing. Make sure the bolt hole and bolt threads are clean and not corroded.
 

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1988 Jeep Cherokee 4.0 6cyl
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Discussion Starter · #5 ·
1988.
Ok yea the top bolt (longer one) was definitely rusted. But the bottom one is good? How would I clean those out
 

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Are you sure its the thermostat? If your waterpump is on its way out it will start seeping out a little hole just behind the pulley mount. When the seal is going bad .
 

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1988 Jeep Cherokee 4.0 6cyl
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115 Posts
Discussion Starter · #7 ·
I just had the water pump replaced as well. And the bottom radiator hose
 

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1988 Jeep Cherokee 4.0 6cyl
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Discussion Starter · #8 ·
How would I go about cleaning the bolt holes? I can go buy some new bolts today. I'm going to buy a better sealant as well. This is the 4th time though I've had to take the whole thing off, luckily it's not too complicated.
What about the thermostat moving any time I go to touch it?

This might be a dumb question, but you wouldn't seal the actual thermostat in correct?
 

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A thread tap would be the easiest way to clean the threads in the bolt holes. If you don't have one, I have cut a groove down the length of the bolt threaded it in and out a couple times to help clean out the threads. Just use pipe sealant on the threads. No don't seal the t stat into the block. You can put a little silicon on the gasket and use it to hold the t stat in until you get the cover one. Make sure your block isn't rusted or pitted making a poor sealing surface.
 

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1988 Jeep Cherokee 4.0 6cyl
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Discussion Starter · #10 ·
I scraped the block pretty good, it had some rust for sure. Should I go over it with steel wool or something?
 

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If your block is rusty it has to be clean, shiny clean, no rust . steel wool or a scotch brite pad will work. If you have the tools, a 1/4" angle grinder and some buffer pads, that will polish it up nicely. Be cautious on the t stat housing cover, it's aluminum and can scratch real easy. Deep scratches can cause leaks.
 

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1988 Jeep Cherokee 4.0 6cyl
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Discussion Starter · #12 ·
Oh boy. Ok so what I'll do is.... Buy some steel wool and clean the block, buy a new gasket, buy gasket sealer, buy thread sealer, and clean the bolt holes. I don't have a thread tap though. So maybe run the new bolts in and out, wiping the excess rust until there's no more?
That should be it right?
 

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Yes. You can message me your phone on here and I can call you. Sometimes it's easier over the phone. But you got this. Get the few things you need, take your time and you'll be better than factory in no time.
 

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Silicone will seal the gasket and the holes. And chasing the threads with a tap is the best way to clean them up
 

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1988 Jeep Cherokee 4.0 6cyl
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Discussion Starter · #15 ·
So I think I found the issue. The coolant isnt supposed to come out of that bolt hole right? Looks like the bolt being used went through the metal on the inside? I'm going to have to seal that up
228693

228691
228692
 

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Wow that is nasty. Yes the bolt is supposed to go through. That's why is important to seal the threads. Also, you have a lot of cleaning of the block to do. Whatever the gasket touches, has to be shiny. It looks like many years of neglect, and from the amount of rust. Not many coolant changes. I would recommend a flush. You can flush it with a garden hose. Install the t start. Add some radiator flush and cleaner to plain water. Run it up to operating temp, to confirm no leaks and then drain and refill with 50/50.
 

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1988 Jeep Cherokee 4.0 6cyl
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Discussion Starter · #18 ·
Yea the person who had it before me did NOT take care of it. Ok I'm at Walmart now and I'll grab some things. What do I do about the bolt? Just add sealant to it and hope for the best? I'm not sure there's much I can do about that right?
 

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I did not use thread sealant there and wondering why I don't have this problem.
Looking back over my pictures I realized why.
Apparently the head is different on a '88.
I used this for my black pipe on the water pump.


I also think that needs to be cleaned so much better.
And get the channel that the thermostat fits in really clean too.
I also recommend using a FelPro gasket there.
With as little gunk as possible.
 

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1988 Jeep Cherokee 4.0 6cyl
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Discussion Starter · #20 ·
Wow that's clean and beautiful! Is there a difference between that and this?
228695
 
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