should i use a sealant for coolant flange?

[Opa]

please help me out. (i'm new to this)

should i add a sealant before i mount this new coolant flange (vw cabrio). it uses an o ring as a seal which protrudes only about 0.030 above the flange surface. or is it better to not use any sealant and rely solely on the squeeze pressure on the o ring from the two mating surfaces?

also, would do you recommend anti-seize on the two mounting bolts? or use thread lock? or nothing? why?

thanks in advance for your help.

 

[matt_i]

My opinion

use no additional sealant on the o-ring. But carefully clean the flat-flange. The o-ring is designed with the proper crush-limiters in it already. If you got to a situation where the flat machined surface had a gouge/porosity, etc causing it to leak, then I'd go for some grey RTV. Which requires surfaces prepped with brake-cleaner to clean them up so the RTV will bond. But its going to require a new seal every time it was disassembled in the future.

Also I would use no additional things on the bolts. Just torque to spec. Blue loctite is an option but being on a big mostly solid somewhat stationary object, its probably not subject to high frequency vibrations that can loosen it.

 

[SteveH - CO]

I would perhaps put a tiny bit of silicone grease on the o-ring (just to help is seat smoothly in the recess and against the block) and I would use anti-seize on the bolts going into the block. As the owner of much older cars, you can almost always count on any bolts related to the thermostat being corroded and stuck. You're also screwing steel bolts into an aluminum head.

I would not use RTV or threadlock on the bolts, as neither has properties you particularly need here. I put anti-seize on essentially every bolt I remove from every car, and 25 years later, when I take apart my FJ40, I find bolts that come right off, every time.

 

[Opa]

thanks so much matt i and steve h. i appreciate your feedback.

 

[2oolhound]

I've been away from auto work for many years (since before there were plastic parts) so when I did a new thermostat on my cherokee I did like Matt suggested and used a little RTV on the mating surfaces and blue thread locker on the bolts. The low torque specifications on the plastic part scared me enough to do it that way.

 

[sz0k30]

There are no mating surfaces. There's an o-ring.

 

[2oolhound]

Oh I see, the o-ring is in the middle of the mating surfaces so there is little room for RTV as well. My jeep was different, there was lots of room for ATV as well. I still would be tempted to put a very skinny bead of RTV around the very outer edge about the thickness of the o-ring, lightly assemble so it's snug to the o-ring and tighten to torque the next day once the RTV has "hardened". That's how I did my jeep and it's been good for the few months it's been on the road. I had time to let it sit for the day the RTV took to set which may not be an option.

 

[dogdog]

That looks like the one for the MKIV Jetta 2.0

I used it (red rtv I think) + the o-ring, just apply rtv till it's tacky then place the oring and install, then wait.... or if want you can always buy another o-ring for it.. it's the same (size) one as the thermostat flange. 56mm or was it 55mm something to that extend.

 

[Wrench97]

RTV blows out way more often then a oring.
If the oring seals properly it will push all the RTV out of the sealing area to the outside edges, if there is a gouge the RTV will seal for a bit but eventually start to leak.

 

[sweetk30]

lots of o-rings or rubber style gaskets now react to the liquid there sealing up and swell up after contact with it . if you add any sealer even to just hold the gasket or seal or o-ring it can void the swell up factor and the seal will be no good .