Thermostat sticking???

[red71cheyenne]

Well, got the Blazer engine started last night and broken in, Woo hoo!!!! Its running a little hot though. I think the thermostat is sticking. The upper hose stays pressurized the whole time. Is there any way I can tell if the thermostat is working? Thanks, Jeff.

[farside847]

Does the temp guage go up, then drop down at any point? Normally it will slowly warm up, then the therm will open and the temp will drop down again.

[red71cheyenne]

No down, just up until I get scared and shut it off to cool down. Last night it got all the way over to the H on the guage. This afternoon after I freshly filled it with half anti-freeze and water, it stayed around the middle of the guage, but the upper hose never did act like it lost pressure and was passing water thru the thermostat.

[69-350]

one way I know my Dodge's (read: the dodge I drive, that my dad owns. god it's great being 17 and living with mom and dad :P ) thermostat is messed up is that on occassion, it will stick shut, the engine will warm the hell up (I'm talkin like 250 degrees warm) and the heater will blow cold (all the coolant is stuck, the engine warms that up, temp gauge goes up, and it gets stuck in the heater core, so the coolant in there blows off all it's heat and has no more heat to blow off)

the only other way to for sure know if your thermo's messed up is to take a pot of boiling water, and with a hook and not touching the sides of the pan, or the bottom, hold the thermostat in the boiling water and see if it opens. If not, it's bad. But that test often is a PITA and isn't worth the ten bucks to buy a new one.

Oh yeah, and if it's running hot but it's got pressure, maybe it's stuck open, and all it does is cycle the coolant through the system. This would givve you pressure in that hose, but at the same time not allow it to cool off fast enough, thus building up heat. Just my two cents.

[red71cheyenne]

Good info, if nothing else. Think I'll pull the thermostat and see if the spring is sticking or something. I'm not running a heater core right now, just a loop from the intake back to the water pump. Here's what it looks like...

[red71cheyenne]

Not a very good pic, how about this one...

[LUV2XCLR8]

Been there, done that (The loop thingy)

[Longhorn Man]

you sure that 30+ year old guage is any good?

[Radman]

Chances are you just have a air lock in the system. Your heater hoses are looped so it makes it more suseptible to that. Remove rad cap and run eng. leave waterlevel down about 2 inches from filler neck. look inside filler neck when eng is running. if water is coming out of tubes then thermostat is stuck open. if there is no water coming out of tubes wait till eng warms up, watch gauge, if you have a 180 thermostat then at 175-185 the thermostat should open and you will see water coming out of tubes. If it just keeps getting hotter then the themostat is stuck closed. Reinstall rad cap, shut eng off, let eng cool ,replace thermostat. Refill with a/f, run eng with RAD CAP OFF till you know thermostat is opening and cycling. top off with a/f, install rad cap, fill overflow bottle to hot level marked on it. Shut eng off and let cool completly. eng may still burp some air out of system during cool down. make sure overflow tank still has coolant when eng is COMPLETLY cooled down. If not fill to cold level and run eng to make sure it is running on thermostat temp

That should take care of your cooling problems. If it still wants to run warm then the rad should be looked at. I hope you replaced it or had it rebuilt before running your new eng.

[GMCMAX]

When I put the long block in the 93 Burb, I had both engines on the floor butt to butt to swap parts, Got in a hurry and put the intake gaskets on the wrong sides. This blocked the coolant ports on the front of the heads and it would warm up and keep going to hot after a while. I pulled the stat and looked down the port and saw the blocked hole. No fun on Sunday evening after working on it all weekend. Then to have to pull it down again.....

[red71cheyenne]

Longhorn, I'm not sure its good or not, what I'm mainly concerned about is the pressurized upper hose. I've never seen that before.

Radman, thanks, I'll run your test and see if thats it. It'll be easier than draining it twice.

Gmcmax, I hope I got them right. I was only working one engine at a time, so I hope I didn't screw it up!

Thanks all, Jeff.

[Green Machine]

I always drill a small hole about 1/16 or so in the outside edge of the thermostat, that will allow almost all of the air to get out of the block when you are filling it, you don't have to wait for the engine to get hot to let the air out, just a thought.

[masterbeavis]

Did you use RTV to seal the t-stat housing in any way? If so, take the housing off and redo it minus the RTV. I have personally had a Tstat get stuck closed because we used too much RTV on the stat housing. (we used very little to begin with). The RTV squished out, eventually broke off partially, and got stuck in the tstat... RTV used elsewhere in the cooling system can and will cause the same problem. While you have the t-stat out, toss it and buy a balanced one, they fail in the open position (except RTV related issues, and are less prone to failing like the cheapies do. Robershaw used to be the brand to buy, now Prestone sells them (you see the robertshaw name on the package.

[truckdude239]

take the t-stat out put it on a string and boil it in some water to see if it opens

[Radman]

When the rad cap is on that is normal for the hoses to get stiff. The system will pressure up to whatever the rad cap is rated at. If you have a 16 lb cap then it will pressurize up to 16lbs then release. That is why it is nice to have a overflow bottle. Then when the pressure is released and your system needs more water it causes a vacumn and it pulls A/f out of the bottle and returns it to rad. I also do what green machine suggests by drilling the small hole in it.
Also masterbeavis is correct about silicone. Just clean everything very well and check thermostat housing for flatness. take housing over to vice and run a file over the mounting surface to check for flatness. Reinstall thermostat, install gasket(dry) install housing. You wouldn't believe how many times i see that in my business. Also the robertshaw balance thermostats are the best on the market. They flow more and are not as sensitve to gauge fluctuations.

[truckdude239]

another trick is pry open the stat and put 2 over the counter pain killers to hold the stat open lone enough for the air to get though hesystemthen the pill will disolove

[GMCMAX]

What ever happened? How did it turn out?

[53burb]

ttt

[red71cheyenne]

Haven't gotten to work on it since you guys gave me all those good ideas. I'm down here off the coast of SoCal shooting and catching Airplanes on an Aircraft carrier. Kind of boring I know, but someone has to do it!!!

[red71cheyenne]

Matter of fact, here are a couple of my kids doing their thing....

[CochinoFilipino]

Originally Posted by 69-350

the only other way to for sure know if your thermo's messed up is to take a pot of boiling water, and with a hook and not touching the sides of the pan, or the bottom, hold the thermostat in the boiling water and see if it opens. If not, it's bad. But that test often is a PITA and isn't worth the ten bucks to buy a new one.

I test the new ones too. The first mechanical work I ever did was replace a bad thermostat on my first 67 Mustang when I was 16. Well the new one was bad, she overheated and caused major damage.

I test it by suspending the t-stat from a wooden spoon with a string. Then turn on the stove to let teh water come to temp. I use a thermostat in the water to make sure my 180* opens around 180*. It's not that big a PITA when you consider the damage that a stuck t-stat can cause.

[red71cheyenne]

Wanted to let you guys know what I did...Took the advice and drilled two small holes in the thermostat so it could drain air out and reinstalled it with an o-ring gasket I had laying around. The paper gasket was done. I don't use RTV on them if I can avoid it, and didn't on this one either. Left the radiator cap off and ran the engine and looked for flow, but it was hard to tell if I had very much. Guage came up to mid-range and stayed there. Checked the upper hose and it never got pressurized again, so I'm guessing this fixed it. I'll run it again with the cap on for a sanity check and make sure its good to go. Its not over heating though and I am happy about that. Thanks to all for the good tips. Jeff.