Chevy & GMC Vans

I picked up a new thermostat from Napa today after a busy morning of medical tests and an afternoon of waiting for a new cat to be welded onto the van. I felt pretty tired after several hours of driving as part of all that. Ordered the part and the trans seal I needed. It was not until I got home that I remembered that I need a thermostat housing gasket to finish the job. I guess I will be out again later.

Clean the housing and manifold really well and use RTV.

I think I have a tube of High Heat RTV (the red stuff) sitting around. I don't know if I have anything else. My experience with RTV is for some reason it does not work for me. Everything I have RTVed, which albeit was only the diff cover, leaked. Maybe I put it on too heavy or too light, but whatever it ends up leaking. With a trip next Monday to the Harrisburg PA area, I don't really want coolant leaking.

clean the surfaces to receive the sealant well with brake cleaner or electrical component cleaner. You need a solvent that will not leave an oily residue, i.e. the degreaser shouldn't be ..greasy.

There are two real tricks to RTV, clean and dry. The part most don't realize is to stay dry until it sets, as in don't refill until the RTV has a chance to set, overnight (12+ hours) to be safe.

Another thought, your new T-stat should have came with a special O-ring that fits around it and makes the seal, IIRC.

Yep, your thermostat should come with a rubber seal. What year van was you fitting this to?

This is what I received. So the black rubber piece running around the edge is the housing gasket?

That is correct.........no sealant needed. Clean the recess and housing anyway.

Thanks. I started opening things up to get at the thermostat, and the upper rad hose does not have one of those worm gear clamps, but some other sort of clamp holding it on. I am trying to think how to describe it, but it is something like it goes around the hose and then the one end goes in the other and they somehow clip together. How do I get that off? Do I need a new clamp to finish this job and put the hose back on?

That is a factory spring clamp. No special tools needed. Just a pair of pliers. You can reuse it. Just check for leaks after you reinstall it. If it is not leaking now just remove the t-stat housing without removing the hose.

Got it off, the clamp and hose that is. I tried doing it leaving it on and couldn't get enough space for my ratchet. Now I can't get the stupid housing nuts off. I hit them with some penetrating oil, but I don't really want to break off the stud. I have done that enough times.

Edit:

I got them off, or at least sort of. I though the nuts were coming off, but it was the studs screwing out. Either way the housing is off.

How do I get the thermostat out? I figure since I replacing it I can try to pry it with something, but I don't want to damage anything there. It is very well stuck in there.

I got the housing off, and was cleaning up the flange surface when I noticed there was a bunch of crud around where the hose attaches. I took the razor blade to that as well, and it all came off no problem. I looked at the hose to see if it was ok. I checked it when I started and it was nice and firm with no soft spots, and I discovered the problem. When someone had changed the thermostat in the past they had not gotten the spring clamp on properly. You can see the indentations from before and the most recent ones. That meant part of the hose end was not really clamped at all. The end itself looks fine. I think I will pick up a new clamp because 1. I hated getting this one off. Most of my time was spent doing that, 2. I want it clamped right this time

Oh, do I need RTV on the gasket of the new thermostat or not?

Just clean the manifold and housing really good and place the new thermostat in there and bolt it down. I would put some never-seize on the threads though so in 10 years it'll come out again. No RTV needed. Use a screwdriver or pry bar to carefully remove the old thermostat. I would use the original clamp as worm clamps can and do strip out even though they feel tight. They also rust and break when you don't want them to!

I would have used the old clamp, but I got very frustrated taking it off, which took much longer than it should have (it kept slipping out of the channel locks). I didn't want the frustration putting it back on, nor did I have the time. A simple job like changing a thermostat shouldn't take all morning. I put a worm gear clamp on, but as I think I mentioned, whoever had done the last thermostat change did reuse the old clamp and it was only partially on the hose. That let part of it unclamped and slowly leaking around where the hose sticks on the thermostat housing. I cleaned off the residue, and the hose end looked ok, so I stuck with it.

It is all together and working well. I may have a leak though, although it could be the fluid that leaked out while I was changing it. I smelled that distinctive evaporated coolant smell while we were out this evening. I will have a look maybe tomorrow and see what I can see. Possible the hose end is not as good as I think. The rest of the hose feels good and has no soft spots.