Thermostat not opening.

[parlusk]

The other day I noticed that my thermostat was not opening, top hose was swollen and lots of pressure on the cooling system. I have yet to put a gauge in (its on the to do list but the dummy light was not on. Well I went to napa and picked up a 381-191 (hockey puck) thermostat. Well, I installed it today and drove the truck for probably 15 minutes, enough time for it to heat up and open. I popped the hood and yet again top hose was swollen. I thought the thermostat was bad, so I pulled it, went to the kitchen and dropped in a pot of boiling water. After a couple of seconds, the thermostat opened... Any help would be greatly appreciated!!!!

 

[parlusk]

Anyone????

 

[phil2968]

Test your cap. It controls pressure in the system. It may not be venting or you could have a soft worn out hose.

 

[Keith_J]

Could also be coolant pump, dirt in radiator or head gasket leak.

 

[Squid in a CUCV]

I have cracked heads and it pressurizes the cooling system. When you fire up the truck and then turn it off can you hear bubbling?

 

[Iceman3005]

blown head gasket or a cracked head.

 

[parlusk]

Running it without the thermostat and everything is fine, no swelling of the hoses etc. I am pretty sure my heads are fine. No water in the oil and no smoke. I checked my cap and it is working right now but that doesn't mean that it was working at the time. That is the only think i can figure. It took an act from God to get the cap off the first time it tried to remove it.

 

[Keith_J]

Caps are cheap. Yes, they can stick. I would not recommend running without a thermostat because of excessive flow that can cause turbulence and uneven cooling in the heads. Thermostats are proportional devices, they have a range of flow to keep coolant at a certain temperature. They can soft fail, meaning they don't open fully or don't open rapidly. The simple dunk it in a pot of boiling water test will not find sluggish ones. And they are cheap too.

 

[hbranchcreek]

Run motor with the radiator cap off check for bubbles or water rising and falling.

 

[MarcusOReallyus]

Caps are cheap. .... Thermostats are ... cheap too.

Yep. For the few bucks involved, replacing them is the only thing that makes sense to me.

 

[spectre6000]

If you think your thermostat isn't opening, your top hose should be all but empty. According to the GM 6.2L Diesel manual, water is pulled into the pump from the lower radiator hose and into the block.

Additionally, note the orientation of the thermostat.

 

[rustyshakelford]

I installed a manual water temp gauge in the volt meter hole. theres room to place it next to it also. cheap insurance and you will be able to see right where you are. I removed the stock sensor on the front side of the DS block. Took about 10 mins. stays right at 190 with 1k lbs of water in the bed.

brett