Thermostat O-ring, use RTV also?

[Drew99GT]

Well, I put a new thermostat in my Moms Olds 88 last summer, easy as pie. It has the o-ring seal instead of a gasket, which most cars now have. Every repair manual for every car I've seen with this design never says anything about using RTV around the housing, so I never have. Well, recently, my moms car has been losing coolent, so we had it pressure tested and it was leaking through the thermostat housing. ***? I made sure the o-ring was evenly placed around the edge of the stat etc.; **** , I even used my freakin torque wrench to the speced torque for the bolts on the housing. Do any of you guys use RTV on the o-ring type seals? I know your supposed to with a traditional gasket. I used a stant thermostat and seal. Maybe it was just a crappy one? The dealer installed a new thermostat and OEM seal. Stuff like this just pisses me off because I'm super anal retentive when working on everything, especially cars, and when stuff like this happens, it puts a dent in my ego I guess

 

[Drew99GT]

Wait a second. It was pressure tested before the intake gasket failed (everything a-ok) and this was well after I installed the thermostat, so the freakin dealer must have screwed it up during the install of the new intake gasket. Maybe I'm not a dumbass afterall

 

[GSV]

I would think a properly designed O-ring setup would be just fine BUT...

If you have enough surface area outside the O-rings diameter RTV couldn't hurt.

 

[Kestas]

The leak is probably from a bad (nicked) seal or from a nick on the mating surfaces. I always like to clean, inspect, and condition the mating surfaces. I usually finish the mating surfaces with Scotchbrite before assembly.

Don't use RTV with o-rings. I've seen it used before. It makes a mess and it doesn't work for the long term. O-rings need to float and make their own seat to seal. Under pressure o-rings move into a certain position for best sealing. RTV use can keep this from happening. I usually put a thin coat of silicone grease to help the o-rings settle in and seat properly.

 

[Shannow]

I've an issue with pressure testing cooling systems.

Put the pressure tester on, pump it up (a couple hundred CCs of air) to radiator cap pressure, say 15psi.

Say in that 15 to 20 minute period 1cc of coolant leaks into the oil. This will give you about 100ppm antifreeze in your oil.

The pressure will change on the dial by 0.075psi.

I personally believe pressure tests are meaningless, other than a diagnostic tool to find WHERE a significant leak is located.

 

[Christopher R. Wise]

Hey Drew,

If you want to use a sealant don't use RTV, use a anaerobic sealer, it is designed for machined surfaces and tight clearances.

GM has it in small tubes, Lock-tite also makes it.

For this stuff to work you need very little film, if you can see through it, that will be enough.

CRW

 

[Ed]

No! No! No!

You NEVER use any kind of sealant with an "O" ring!!!!
If there is leakage around the "O" ring It means that the "O" ring is damaged or deteriorated, or there are cracks /voids in the metal structure. It could also mean that it is the wrong "O" ring. (Wrong size or material)The use of a tiny amount of lubricant is sometimes helpful to prevent damaging the "O" ring during installation but plays no part in sealing. The "O" ring itself is designed to seal. If a lube is used it MUST be compatible with the "O" ring material. Petroleum products can be death on some kinds of rubber and silicone lubes can cause silicone rubber to deteriorate. You have know what you've got to do a correct installation.
The use of sealants may mask a larger problem and could be useful to do a temporary repair but "O" rings and gaskets are two different animals.
A lot of folks use RTV as a gasket dressing but this is overkill and can make disassembly difficult. For gaskets, a product like Permatex "Hylomar" is ideal. For "O" rings just enough compatable lubricant to make the "O" ring slightly shiny is all that should ever be used.
Dupont's "Krytox" grease is compatable with just about everything and is an excellent product. Lotsa Luck finding it though! (and it's awfully expensive)

 

[Mike_dup1]

My 1992 Chevy truck use the "O" seal on the stat. Mine never leaked and the only place I used any sealer was on the bolt threads. Many times that what leaks.

If is leaking, its because improper installation. Any sealer on the mating surfacing will create a gap and the stat seal will be ineffective.

 

[Drew99GT]

It pressure tested fine when I installed it, but failed after the dealer messed with it

They probably used a death grip when tightening the fasteners like they do for everything else, and somehow busted the seal.

 

[jsharp]

quote:

---

Originally posted by Ed:
No! No! No!

You NEVER use any kind of sealant with an "O" ring!!!!
If there is leakage around the "O" ring It means that the "O" ring is damaged or deteriorated, or there are cracks /voids in the metal structure. It could also mean that it is the wrong "O" ring. (Wrong size or material)The use of a tiny amount of lubricant is sometimes helpful to prevent damaging the "O" ring during installation but plays no part in sealing. The "O" ring itself is designed to seal. If a lube is used it MUST be compatible with the "O" ring material. Petroleum products can be death on some kinds of rubber and silicone lubes can cause silicone rubber to deteriorate. You have know what you've got to do a correct installation.
The use of sealants may mask a larger problem and could be useful to do a temporary repair but "O" rings and gaskets are two different animals.
A lot of folks use RTV as a gasket dressing but this is overkill and can make disassembly difficult. For gaskets, a product like Permatex "Hylomar" is ideal. For "O" rings just enough compatable lubricant to make the "O" ring slightly shiny is all that should ever be used.
Dupont's "Krytox" grease is compatable with just about everything and is an excellent product. Lotsa Luck finding it though! (and it's awfully expensive)

---

I'm with you on this. I was taught that o rings are a "dry seal" and the only lubricant that should be used was a small amount if required for assembly. Years ago I designed a lot of equipment to meter and dispense adhesives. Any lubricant could possibly contaminate the fluids so it was especially important to use as little as possible in that application...

 

[Christopher R. Wise]

Well you don't put the sealant on the oring.

Anarobic sealant is ok to on the flange portion to help seal. It will not cause a gap, it is designed for clearances under .010".

This is ok to use, doesn't affect orings.

Cures in the absents of oxygen, and can be pressure tested right after assembly, where as RTV to thick, needs oxygen to cure, takes to long to cure.


Been doing this for long time on surfaces that have a less then perfect sealing surface.

CRW

 

[Drew99GT]

Yea, when I meant using the RTV, I meant on the flange portion to the outside of the o-ring, not on it itself. On a lighter note, I put a new stat in my brothers truck that recently had a rebuilt engine installed. 96 4.3L Jimmy. The idiots at the place used RTV to seal the stat into the housing and then simply put the o-ring on top of the stat and put the housing on

When I took it apart, I was like, what in the **** did these morons miss with regard to slipping the o-ring around the thermostat! Makes me more confident that I will be a decent profesional mechanic.

 

[rkpatt]

Another o-ring and sealant question -


I am doing a coolant elbow (cracked) replacement job on a GM 3.8 an found that someone previous used the orange "copper" RTV on the belt tensioner assembly fitting that goes into the water pump . I did not notice any of this RTV on the cracked coolant elbow o-rings or the bosses it fits into .

Although I generally agree the the previous post, I wonder if I should use the sealant on the o-ring for the belt tensioner as someone did before .

 

[FusilliJerry82]

Use this:

http://www.amazon.com/Permatex-22071-6PK-Thermostat-Silicone-Gasket/dp/B001REV86S

 

[mechanicx]

I never use RTV or any other sealer on o-ring thermostats seals or the paper ones either, and as lond as the mating areas are clean and not too damaged they don't leak. RTV supposedely can get into the t-stat and cause problems.