Replaced a thermostat on a 22 year old Deere Tractor. This genuine Deere gasket cost me doing the job Three times. First time, used type 3 gasket sealer, filled with Deere Cool-Gard II coolant... it leaks. Remove exhaust stack, Remove aux pipe, Remove fan guard, Drained system. Okay, maybe I didn't get the parts aligned. Clean everything, recoat, double check alignment, Put the stack, aux pipe, & guard on. Fill system with remaining Cool-Gard II ... Darn... It leaks again. Drain coolant. remove stack, aux pipe, & fan guard Go to local parts house get RTV, Clean housing and engine block till it cries. Smear RTV as directed. Install t-stat & aux pipe (Left stack & guard off... I'm slow but still alive) Wait 24 hours as directed, Fill with last of coolant and some that I saved from draining. Glory be ... No leak ! Drive tractor back to shed. Button everything up and look for what I did wrong ... Depended on Deere to provide the proper gasket. There is a definite thickness difference between the old & new gaskets. Is there someone I can call at Deere to spread the pain ... uh ...word ...to ?
I RARELY let the monkeys at the parts counter order my parts. Deere has a pretty good website with exploded diagrams and part numbers. I usually place my order online and pickup at the dealership. Before I learned my lesson I did run into an older pair that worked at the closest ag deere dealer who knew their ****. Those two were great to deal with.
I always use silicone sealant with all gaskets and never have a leak, it does 2 things, keeps the gasket in place during assembly and stops any leaks for what ever reason there may be one....might take a little longer doing it that way but much less time doing it twice....
Or three times ... I didn't use the gasket the last time. Just the RTV. The gasket was ordered using the Deere p/n from the web site. It's genuine Deere. (At least the bag said so ) It fit exactly except for thickness. The downside to the RTV was time. Directions called for 24 hours BEFORE filling with coolant. Hobbytime ...Do you wait using the RTV plus gasket ??
In 1975 at a Chevrolet dealership I learned to file the bottom of thermostat flat because many of them distort. I prefer to use a gasket and an Indian Head type sealer. RTV skim on both sides of the gasket is OK and fire it up. If done that way on cork gaskets it often allows the gasket to slide out the side. If you are using only RTV with a lot of space, Front and rear of aluminum intake on old ford V8's, I like to give it at least 12 hours. It is really hard to judge how much RTV is enough and prevent ending up with it in places you don't want it. On badly pitted housings some times I use a little weather strip adhesive.
I've used paper thin gaskets on my Deere regulator housings with zero issues. Sounds like one or both sides were distorted.