Driving with thermostat stuck open

thanks guys. The thing that throws me off is that I have no problem getting good heat to the cab, the truck just likes to run cool and when I coast up to a stop sign or go through town it will drop down about 20* in cooler temps unless I block part of the Rad off. I'm planning on changing the thermostats out this weekend since it's supposed to be nice. They have 300k on them so it probably wouldn't hurt to change them any way.

I think part of the problem is that the changes I made to the engine allow it to run cooler and now my cooling system is too big.

 

They are 190

 

checked today and after letting the engine idle for 15 minutes the temp gauge was showing 140* and the upper radiator pipe was hot already.

 

no, but I did use a infrared thermometer to check the engine temp at the thermostat housing and it was right on with the gauge and the upper rad pipe was within 20* of the engine.

 

just an update. I changed the thermostats out today and found the problem. Somebody that worked on it previously left a rag in the housing and it was wrapped up around the thermostats causing one of them to be partially stuck open. I know it wasn't me because I use the throw away shop towels so it was either the shop that replaced the water pump or the shop that did the single turbo conversion. I'm thinking it was the latter since I really noticed the engine running cooler after the conversion but had just chalked it up to removing certain components that generated heat. Anyway, that rag had been in there for at least 160k maybe longer if it was left when the water pump was replaced. I'm surprised it didn't go through the system and take out the water pump, plug the radiator up or worse.

I took it out for a drive after wards and let the engine warm up to 140* and the upper rad hose was still cold so I knew they were closed. While driving it the engine got to 190*(which it would have never done before while empty and not having the rad partially blocked)then the thermostats opened up and the engine cooled down to 188. The whole time it stayed right around the 188-190 range.

Hopefully everything stays sealed up when the block cools down. I smeared some gasket maker on the paper gaskets to help them seal so I don't expect any problems.