dumb RTV question - dry time

this seems like a dumb question, but do you have to wait a while for RTV to dry on a thermostat housing? the package says "fully cures in 24 hours" and that's it, but i can't imagine you have to wait that long to refill the coolant and drive it... i'm using permatex water pump and thermostat housing gasket maker...

are you installing the thermostat housing with just RTV for sealing, or are you using it along with a gasket? if it's being used with a gasket, i wouldn't worry about filling it with coolant after maybe 30-60 minutes. The gasket does the sealing, the RTV just helps out a bit.

However, if you're using only RTV (no gasket), let it set up for as long as possible. If you don't wait long enough before filling/driving (creating heat & pressure) and the RTV hasn't cured enough, it's likely that the RTV will blow out where the parts meet.

Using RTV only on a thermostat.

It cures for 1 hour, then retighten bolts 1/4 turn. Full cure IS 24 hours. Overnight works fine. And in a pinch I've driven on it with 3 hours cure time, and it held up fine. The shorter you cut it, the more likely it will blow out and you'll be doing the job over again.

It really helps if you can coat the part and let it sit for 30 minutes before assembly.

Go spend the 85 cents for a dealer thermostat gasket. It has the RTV pre applied. I installed my thermostat gasket "dry" and never had problem. I figured the Jeep engineers figured out how much RTV to apply.

I personally think applying RTV on a gasket is a poor maintenance practice if the gasket did not come with RTV applied. A gasket should be made of the right material to seal the two surfaces, if RTV is needed on it then the gasket designer screwed up.

martin said:

Go spend the 85 cents for a dealer thermostat gasket. It has the RTV pre applied. I installed my thermostat gasket "dry" and never had problem. I figured the Jeep engineers figured out how much RTV to apply.

I personally think applying RTV on a gasket is a poor maintenance practice if the gasket did not come with RTV applied. A gasket should be made of the right material to seal the two surfaces, if RTV is needed on it then the gasket designer screwed up.

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I second that. I was a Jeep tech for @ 8 yrs. prior to my current job. Any paper gasket or for that matter any gasket of any material should be installed "dry". I can't ever recall having a leak because I didn't use RTV on a gasket. In fact I made a lot of repairs that were because someone else did exactly that. The RTV allows the gasket to extrude out between the mating surfaces in some cases. My favorite was seeing a cork gasket on a valve cover hanging out all over with big gobs of RTV all over the place. I've seen it more than a couple times. Having worked on the heeps (I say that with love) as long as I did, I can sympathize with people who find engineering faults. I had to also repair many of the things the factory didn't do right. But for the most part they get it right.
As for when RTV should be used. Gaps at gasket joints such as oil pan rail/timing cover or intake/valley gaskets are one. Diff. covers are another along w/ mating surfaces of case halves on t-case/ trannys, although some are technically supposed to use anaerobic sealer. In any case the best bond seal is attained when the RTV is allowed to set up for some period of time, check the product you are using. On valve covers, I would normally allow it to setup for @ 15 min. Generally, let it set until it just starts to lose its tack. Then be careful to set the piece in place without disturbing the bead. That brings up my last point. RTV's great attribute is the ability to fill imperfections in the mating surface (ever seen the mating surface on your t-case halves, very rough machined surface). So, when it is used it is best applied in an even bead @ 1/8" to 1/4" diameter. This allows it to extrude into imperfections as the bead is deformed when assembled.
Sorry so long but I just figured I could shed some light on the subject of repairs in general.

Brian

maybe im just lucky, but ive never waited longer than say, maybe an hour and ive never had so much as a drip, most of my experience is on changing differential fluid though, any time ove ever changed a t-stat ive just used the proper gasket

awspence said:

maybe im just lucky, but ive never waited longer than say, maybe an hour and ive never had so much as a drip, most of my experience is on changing differential fluid though, any time ove ever changed a t-stat ive just used the proper gasket

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Diff doesn't generate a lot of pressure(shouldn't be any since its vented). In any case, there can be compatability issues between RTV and gear lube. This was blamed for brg. failure on some diffs due to the oil foaming when reacting to certain lubes. I think though they claimed the reaction was w/ uncured RTV. However, the typical diff service was done in @ 10-15 min. from breaking the seal on the cover to refilling w/ lube where I was so there wasn't really any cure time prior to assembly and fill and in many cases on a major driveline service the car would be dropped and picked up by the customer in a matter of a couple hours. All in the name of production I guess.

Brian

I strongly second the factory gasket, it's all set to go after you unwrap it.
I use OEM mostly on all our jeeps, 2 TJ's and an XJ, prefer them, they fit and I don't have to worry about not fitting.