I have a small leak at the upper thermostat housing. I've "fixed" it now 3 times but now I'm thinking the housing is too pitted/corroded to not leak. This last time there was no leaks for 2 days and now its developed a small leak again. It's not a lot leaking out (a couple tablespoons worth seems to collect on the part underneath it over night) but I can't tell how much is leaking while driving. My reservoir seems to be about 1 cup low the next morning after a day of a couple hundred miles driving. Anyway, I have to leave for a 1200 mile trip on Sunday and that isn't enough time to order a new housing and try to fix it again. Could I just keep the reservoir tank topped up at every stop and will my truck pull any coolant lost while driving back in to the radiator from the reservoir tank as it's loosing it or does it only suction the coolant back in after the truck cools?
Also the truck temp always stays stable on these smaller 200 mile drives. Doesn't really go above the N in N O R M A L on the gauge.

 

While I don't recommend it, you can probably get away with it if you're careful. A couple friends and I drove from eastern WA state to SD and back a few years ago in a clapped-out Chevy van with a split coolant line (which my friend who owns the thing didn't find and fix until afterwards). It survived the trip, but it did start to overheat a few times when the coolant level dropped. We filled it at the rad each morning and as necessary during the day, letting it cool first so it wouldn't make a geyser. (I wouldn't trust suction to pull coolant in when it could just as easily pull air through the leak instead.) We went through a lot of coolant on that trip! 70-80 mph in the middle of summer with the air conditioner on blast probably wasn't helping matters.

What are you using to seal the housing?

 

I had a small thermostat housing leak on my 460 that was no worse then yours for months before I actually got it to stop leaking completely and it never caused any harm, I just topped it off when it needed it.

Have you tried using a double gasket? (just put one on top of the other). It was the only way I could get mine to stop leaking

 

Just check the overflow tank when you stop for gas, add coolant as needed. Keep an eye on gauge while your driving, should be ok. Mine develops a small leak around the radiator cap every couple years, replace cap & it's good

 

Thanks guys

The first 2 times i tried fixing it i used a gasket and some RTV gasket maker as a seal, the third time someone told me to try just the RTV gasket maker and no gasket. I haven't tried a double gasket yet but went and found a replacement thermostat housing today and this guy at the place i bought it from suggested gasket with light coat of black sealant by permatex. Idk yet though if I want to try that or get a thermostat housing made to use an O ring.

this is what my thermostat housing looks like. i think it might be too beat up and that might be why none of the other ways of sealing it has worked

 

Looking at the pitting on the mating surface, yeah, I can see why that would leak! You might be able to true it up with some sandpaper on a block but if you've got a new one, use the new one.