1990 K5 thermostat housing leak

[CelBlazer702]

Looking for any advice or suggestions on how to remedy my thermostat housing leak. I recently replaced my thermostat due to the prior one not opening until about 220 degrees. Didn't leak a drop prior to the change. Since the change, I made a 5 mile trip and it had the top of the intake all puddled up. I took it apart, surfaced the housing on a flat piece of metal and sandpaper, black RTV'd the gasket and let it set for 12 hours. Went for another 5 mile trip and it almost seems like its leaking worse as now it started on the upper hose as well. It only seems to leak once its up to temp, not upon startup. Any suggestions? Would a faulty closed thermostat cause this? Bad radiator cap? I should also mention I added a 1/8" hole to the thermostat flange to aid in burping the system. Temp never got above 195 degrees driving.

 

[imiceman44]

Looking for any advice or suggestions on how to remedy my thermostat housing leak. I recently replaced my thermostat due to the prior one not opening until about 220 degrees. Didn't leak a drop prior to the change. Since the change, I made a 5 mile trip and it had the top of the intake all puddled up. I took it apart, surfaced the housing on a flat piece of metal and sandpaper, black RTV'd the gasket and let it set for 12 hours. Went for another 5 mile trip and it almost seems like its leaking worse as now it started on the upper hose as well. It only seems to leak once its up to temp, not upon startup. Any suggestions? Would a faulty closed thermostat cause this? Bad radiator cap? I should also mention I added a 1/8" hole to the thermostat flange to aid in burping the system. Temp never got above 195 degrees driving.

Do you see the leak from the flange?
It could be the hose.

 

[CelBlazer702]

It was leaking from the flange and the upper hose. I plan to cut a section of the hose off today and pick up new clamps. Also intend to get a new gasket and some Permatex "The Right Stuff" to see if that does the trick. Upon fireup and it's cold there are no leaks, it's not until it gets close to when the thermostat should be opening.

 

[Blue85]

If the leak is above the thermostat, there may be no coolant there until you get up to temp. Also, the pressure builds as engine gets warm, making any leak worse. If you know it's leaking from the hose, how can you be sure it's also leaking from the flange? The coolant will follow the thermostat housing down. It's likely that a good inspection of the neck and hose will show some pitting or damage. You might get by with wire brushing the neck clean, cleaning the hose and skimming it with silicone before reassembly.

It's also possible that coolant is coming up the thermostat bolt threads.

 

[Wes Harden]

What kind of metal is the t stat housing made of ? If you have an Aluminum radiator, and this housing is pot metal it maybe corroding do electrolysis, mixing many metals in the cooling system make this problem worse. But something easily inspected and inexpensive to replaced is the best way to manage this. You may need a new one. A gasket shouldn't need RTV if the surfaces are clean flat and pock free. You should use a sealant on the bolt threads, like Teflon, tape or liquid.

As for the hose, when you disturbed it to resurface the housing flange, the crusty stuff moved, make a good seal difficult. Or the is a break or cut in the inner hose lining allowing coolant between the inner and outer layers. The coolant will follow the nylon netting out the ends. A new hose may be needed to solve that leak.

 

[CelBlazer702]

The leak from the hose was coming from the back side towards the throttle body. The flange was leaking from the front on the right side stud, or so it at least appeared. I thought the bolt holes were blind and not thru holes? I'm not physically there to check it though.

 

[Wes Harden]

could be blind or open, might have rusted enough to be no longer blind.

 

[CelBlazer702]

Just a quick update. The holes are blind. I filed both housing and intake slowly to ensure flatness. The housing showed a little warpage yet. The old gasket looked like it had great compression around the thermostat though. I put a new gasket, skimmed it w/ Permatex-The Right Stuff and snugged it. I also added washers to the bolts. I plan to torque them tonight. Cleaned the neck, cut the old section of hose off and put a new clamp on. Praying it will all have a tight seal tonight when I fire it up.

 

[rampage]

Just a quick update. The holes are blind. I filed both housing and intake slowly to ensure flatness. The housing showed a little warpage yet. The old gasket looked like it had great compression around the thermostat though. I put a new gasket, skimmed it w/ Permatex-The Right Stuff and snugged it. I also added washers to the bolts. I plan to torque them tonight. Cleaned the neck, cut the old section of hose off and put a new clamp on. Praying it will all have a tight seal tonight when I fire it up.

Just an FYI: A regular hose clamp gathers material at the screw as you tighten it which can be a potential leakage point. There are better clamps available that apply a more consistent pressure around the circumference of the hose.

 

[dyeager535]

Just an FYI: A regular hose clamp gathers material at the screw as you tighten it which can be a potential leakage point. There are better clamps available that apply a more consistent pressure around the circumference of the hose.

Yep, I'll repeat this a few times I'm sure, project farm on YouTube did testing on various hose clamps, so there is some pretty good info if people watch that.

I've got a weird lower water pump hose leak, I'm going to try some of the breeze brand clamps first, if that fails, may have to try some of the more evenly applied pressure designs.

 

[imiceman44]

Yep, I'll repeat this a few times I'm sure, project farm on YouTube did testing on various hose clamps, so there is some pretty good info if people watch that.

I've got a weird lower water pump hose leak, I'm going to try some of the breeze brand clamps first, if that fails, may have to try some of the more evenly applied pressure designs.

My experience has been that any good quality clamp, even worm style, if the hose is already snug fit on the fitting, and that fitting has a ridge.
I lube the hose so it slips on easier and spreads evenly around the fitting then I put the clamp right against the ridge so the hose can't get off.
That position also seals better.
If the hose is loose, no design will guarantee a leak proof connection since it will bunch up and there will be some spot that is not perfectly flat on the fitting and could leak under pressure

 

[dyeager535]

Anymore with today's parts I can't rule out that the pump outlet is not round. It's an aftermarket aluminum pump, so who knows? I doubt in the OP's case the thermostat neck isnt round, it's the same part before/after, I'm in a different boat.

I can see an oblong surface making effective clamping significantly more difficult, especially with what might be an older hose, and unknown quality hose clamp.

First time I've had a problem that could possibly be attributable to a bad clamp.