Best thread sealant for exhaust studs into water jacket

-
70Hardtop

70Hardtop

Well-Known Member
Joined
Oct 14, 2009
Messages
333
Reaction score
68
Location
Australia
I did a search and found a post from someone who recommended Loctite 567. However this is absolutely not the ideal sealant. I am talking about the end exh manifold studs that go into the water jackets. Loctite 567 is not a thread locker and is classed as a low temp (max 150 degrees C) and low strength pipe and thread sealant, not recommended for vibrating parts. These studs are within 10mm of the exhaust port (600+ degrees?) and in a fairly harsh vibrating environment. More ideal would be Loctite 5770 which is a medium strength, high temperature (275 degrees C) thread locker and sealant and suitable for areas in constant vibration. Also there is Permatex high temp thread seal which is rated to 400F or 204 deg C. There is also the good old Aviation gasket sealant, been around since the '40s, however that is only rated to around 175 deg and goes very runny with even normal engine heat. My problem is that due to the mild corrosion in those threads and multiple fasteners being screwed in and out, the studs are not screwing in nice and firm, there is quite a bit of movement of the stud so a good high temp sealant is needed. I will have to keep looking as I believe that the threads in this area on a hot day (and we get some damn hot days 45degrees+) would well exceed 400F. Combined with the high pressure of the coolant there as well.

BTW, one hole has been tapped out to 3/8" but is still not tight anymore, the others are 5/16" but I am not pulling the heads off to retap them. Thanks for reading.
 
JBurch said:
I have good luck with Liquid Teflon pipe thread sealent
Click to expand...
thanks for the tip, Teflon is certainly a high temp rating - do you have a brand name i can look up? As I can only see Christy's brand here and there is no temp rating on it.
 
I used this on mine and have not had any issues. Looks a lot like liquid teflon but not sure it's the same chemistry. Used it on intake bolts as well to keep oil from weeping around the bolts.

ARP THREAD SEALER
 
If the threads are shot you're asking the sealant to do more than it was designed to. I'd suggest drilling it out and tapping for the next size up fastener. I'm not a fan of thread repairs in this application but usually going up to 5/16 vs 1/4 won't negatively affect anything.
 
mullinax95 said:
I used this on mine and have not had any issues. Looks a lot like liquid teflon but not sure it's the same chemistry. Used it on intake bolts as well to keep oil from weeping around the bolts.

ARP THREAD SEALER
Click to expand...
Thank you! I will do some research on that

EDIT: Wow I just looked up the specs. it says it's good to 550deg F. That's is pretty good in my book. But I wonder how well it locks.
 
Last edited:
I agree with moper... the main problem is the loose threads. IMHO, you will need something that is a medium strength thread locker, like the Locktite 5770 that you mention, or the Permatex product that Lelo Dart cites. (Blue Locktite would be better too but its temp rating is lower.) The traditional teflon and pipe thread sealers are all low strength types, and I suspect will just 'flow' when subjected to these particular conditions; the low strength sealers are just fillers, not lockers, and depend on the the threaded parts fitting tightly to provide all of the mechanical rigidity.... which you don't have in this situation.

FYI... With the medium strength types, they take a day to cure to nominal full strength at room temp and will be stronger if left to cure for several days.
 
nm9stheham said:
I agree with moper... the main problem is the loose threads. IMHO, you will need something that is a medium strength thread locker, like the Locktite 5770 that you mention, or the Permatex product that Lelo Dart cites. (Blue Locktite would be better too but its temp rating is lower.) The traditional teflon and pipe thread sealers are all low strength types, and I suspect will just 'flow' when subjected to these particular conditions; the low strength sealers are just fillers, not lockers, and depend on the the threaded parts fitting tightly to provide all of the mechanical rigidity.... which you don't have in this situation.

FYI... With the medium strength types, they take a day to cure to nominal full strength at room temp and will be stronger if left to cure for several days.
Click to expand...
Thanks yes, you are correct in that. A friend brought over some of the Loctite 567 that I mentioned and we tried it on one thread but looking at the specs, it is not suitable for this application. So I will remove that stud and clean the threads and start again. I think I will buy the Permatex stuff, although even the claimed 400deg F (204C) I think is a bit low for this position. I wonder just how hot those studs do get on a hot day and right next to an exhaust port? We would never know unless there was some accurate sensor that could be screwed in there. Those laser temperature probes are great and could be shined onto the stud itself but the temp of the actual thread inside would be far hotter. I know it is also right next to the coolant which is running at less than 100deg C, but it is less than 10mm away from the wall of the exhaust port. I'm probaly just being too pedantic. As far as the threads go, they are not damaged, it's just that the studs are more loose than I would prefer. I had an idea with that Permatex. Tell me what you think... I was thinking of getting a small screwdriver and loading the threads inside the heads with the Permatex thread stuff, letting it cure, then when it had set, inserting the stud in with more of the Permatex on the stud. I don't see why that shouldn't give a nice tight fit. Moper mentioned retapping - of course that is the ideal solution (factory is 5/16, not 1/4 like he said) so I would be tapping up to 3/8. However in the OP I mentioned that I don't want to pull the heads off just to do that. I'm selling the car but even if I wasn't I would not pull the heads to do that.
 
moper said:
If the threads are shot you're asking the sealant to do more than it was designed to. I'd suggest drilling it out and tapping for the next size up fastener. I'm not a fan of thread repairs in this application but usually going up to 5/16 vs 1/4 won't negatively affect anything.
Click to expand...
I had that problem on SBM head many years ago, when I was a machinist. I drilled it out to a pipe tap-drill size. I don't remember the size, maybe 1/4" NTP? After tapping, I coated the threads with red loctite, and screwed in a square-headed steel pipe plug, ground off the square boss, and redrilled and tapped for the original size stud. I then installed a new stud, and never had another problem with sealing there.
 
Pendantic.... that is a big word LOL.

While you might want to do some pre-loading of the head's threads, IMHO insert the stud right away, so the sealer/locker will flow and fill nicely around every thread. Then let it cure for at least a day before loading the stud.

As for the temp? My pure 1000% guess is halfway.... 400F LOL. BTW those IR temp guns have a spot size of their 'view' so I doubt you could focus on just the end of the stud.

Permatex data sheet:
https://441py33rout1ptjxn2lupv31-wpengine.netdna-ssl.com/wp-content/uploads/tech_docs/tds/59235.pdf
 
nm9stheham said:
Pendantic.... that is a big word LOL.

While you might want to do some pre-loading of the head's threads, IMHO insert the stud right away, so the sealer/locker will flow and fill nicely around every thread. Then let it cure for at least a day before loading the stud.

As for the temp? My pure 1000% guess is halfway.... 400F LOL. BTW those IR temp guns have a spot size of their 'view' so I doubt you could focus on just the end of the stud.

Permatex data sheet:
https://441py33rout1ptjxn2lupv31-wpengine.netdna-ssl.com/wp-content/uploads/tech_docs/tds/59235.pdf
Click to expand...
 
Yes, the temp wouldn't be accurate, esp with the exh header or manifold right there. So it's all a guess really. I looked up the ARP thread sealer, that is 550F which is probably what I would prefer. However it is $30 here and that is a bit out of my budget, when I can get the Permatex for $11 delivered. Pendantic is a big word yes, and also doesn't exist, no offence intended :D . Pedantic is the word and I use it quite a lot because I think I suffer from Pedanticism hahaha, which is being overly fussy about small academic details.
 
If you just needed a "thread sealant" than yes, the Permatex high temp is the best for that.
In regards to temperature for exhaust studs, there are absolutely no issues. This is what the product is
designed for. Besides timing covers, water pumps, thermostat housing, fuel pump, etc.

Now if you have an issue with threads not tightening, or semi stripped,or whatever you want to call it.
Thats a whole other story. Permotex is a sealant, and not a loctight. So if this is what you need to do, some sort of loctight will be in order. I wouldnt give any guarantees on this, but you can try it.
Good luck !
 
70Hardtop said:
I did a search and found a post from someone who recommended Loctite 567. However this is absolutely not the ideal sealant. I am talking about the end exh manifold studs that go into the water jackets. Loctite 567 is not a thread locker and is classed as a low temp (max 150 degrees C) and low strength pipe and thread sealant, not recommended for vibrating parts. These studs are within 10mm of the exhaust port (600+ degrees?) and in a fairly harsh vibrating environment. More ideal would be Loctite 5770 which is a medium strength, high temperature (275 degrees C) thread locker and sealant and suitable for areas in constant vibration. Also there is Permatex high temp thread seal which is rated to 400F or 204 deg C. There is also the good old Aviation gasket sealant, been around since the '40s, however that is only rated to around 175 deg and goes very runny with even normal engine heat. My problem is that due to the mild corrosion in those threads and multiple fasteners being screwed in and out, the studs are not screwing in nice and firm, there is quite a bit of movement of the stud so a good high temp sealant is needed. I will have to keep looking as I believe that the threads in this area on a hot day (and we get some damn hot days 45degrees+) would well exceed 400F. Combined with the high pressure of the coolant there as well.

BTW, one hole has been tapped out to 3/8" but is still not tight anymore, the others are 5/16" but I am not pulling the heads off to retap them. Thanks for reading.
Click to expand...
I used Permatex liquid Teflon which failed, after cleaning the stud and hole I used Permatex No. 2 and it worked just fine.
 
Last edited:
Johnny Dart said:
If you just needed a "thread sealant" than yes, the Permatex high temp is the best for that.
In regards to temperature for exhaust studs, there are absolutely no issues. This is what the product is
designed for. Besides timing covers, water pumps, thermostat housing, fuel pump, etc.

Now if you have an issue with threads not tightening, or semi stripped,or whatever you want to call it.
Thats a whole other story. Permotex is a sealant, and not a loctight. So if this is what you need to do, some sort of loctight will be in order. I wouldnt give any guarantees on this, but you can try it.
Good luck !
Click to expand...
Thanks, well as I mentioned the threads are all good, just a touch loose. All those other applications you mentioned are all normal engine temp areas; these studs are a lot higher temp being where they are. If the truth be known, the rated temp of 204C is a conservative one which companies do to protect themselves in the 'safe margin' and could possible go a little higher. But in a situation like mine where there is a little more space to fill between the threads, how will it seal after 15 years and thousands of heat cycles? But I will just go ahead and use the Permatex the way NH9 suggested and will sleep well.
 
GM used liquid teflon on many things back in the late 80s and early 90s. It failed. They issued several TSBs about it. That's why I've never used it for that purpose. I always use red high temp Permatex and it has never failed for me.
 
Yeah - I use liquid Teflon for oil and coolant, but I wouldn't use it directly adjacent to the exhaust port. I doubt it will get past 600* given coolant is surrounding it on 3 sides - but everything has it's limits.
Sorry on the size I stated being wrong.
Not sure which port it is but I've done this in the chassis many times. Loosen the mounts, use an angle drill & the socket type tap driver. I just think relying on sealants and lockers to retain the stud in worn threads is temporary. But it's your car.
 
70Hardtop said:
Thanks, well as I mentioned the threads are all good, just a touch loose. All those other applications you mentioned are all normal engine temp areas; these studs are a lot higher temp being where they are. If the truth be known, the rated temp of 204C is a conservative one which companies do to protect themselves in the 'safe margin' and could possible go a little higher. But in a situation like mine where there is a little more space to fill between the threads, how will it seal after 15 years and thousands of heat cycles? But I will just go ahead and use the Permatex the way NH9 suggested and will sleep well.
Click to expand...

I mentioned the other applications, to let you know all the other uses of Permatex high heat sealant .
I use nothinig but Peramatex on the exhaust studs, that is what it is for !
Banging head.
 
Johnny Dart said:
I mentioned the other applications, to let you know all the other uses of Permatex high heat sealant .
I use nothinig but Peramatex on the exhaust studs, that is what it is for !
Banging head.
Click to expand...

Don't worry about it. Your stuff will remain leak free, while his may not.
 
You must log in or register to reply here.
-

Back
Top