On the freeway, about 40 miles after startup. Hot engine, cold radiator, so I was thinking stuck thermostat. Let it cool down, added some more water since it was pushing some out from somewhere, and then about 20 miles later, overheated again, this time pushing water out the overflow. So....stuck thermostat, bad radiator cap, or......blown headgaset??

 

headgasket. definitely so. when mine went it did the same, pushed all the coolant out of the overflow and popped my radiator. how fresh is the thermostat though?

 

First thing I'd check is the thermostat for sure. Cold rad + overheating = blocked flow from somewhere. I guess it could be the water pump too. Those would be the first 2 things I'd check.

 

x2 on the water pump. the original designs suck. the newer ones direct coolant through to the center of the pump. more efficient than the originals. about $50 at a local autoparts store.

 

Didnt you just do the head gasket and studs???

 

Yeah, and the head is o-ringed. Still, some people have reported blown head gaskets after those mods, but usually they tried to take shortcuts. I feel like everything was done right, it was retorqued, and never hammered on while the engine was cold, so I am hoping it's not a h/g.

 

i suppose it could be a stuck thermostat. Mine was stuck in the open position and wouldnt warm up at all.. Your situation could very well be the exact opposite.

 

Sounds like a blown head gasket, mine did the exact same thing when it blew. do you have any oil in your water or any bubbles at an idle?

 

The thing that I don't get is why the radiator would be cold...course I guess it could be a combination of things....

 

look at the easy things first test Tstat look in the radiator make sure its not plugged , water pump. if its a blown HG you will have bubbles in the radiator fill it to the top and start it look for lots of bubbles

 

Start With A Tstat See What It Does T Stats Cheap To Replace Plus If The Rad Is Cold Its Not Opening Or There Wasnt Enough Coolent In The System To Flow Through The Rad. How Low Was The Coolent?

 

Drove the truck around a little today just to see, after adding about 2qts of water....no issues. (??)

 

it happened to me once that my coolant was too low to cause the thermostat to open, making the truck overheat making me an hour and a half late for work one day.
That might have been all your problem was... although, why was your coolant so low?

For me, it was a leaking water pump gasket.

 

if coolant was low enough to develop an air pocket in the system the engine would heat up and tstat wouldnt open causing rad to be cold..when i did the kdp on mine it wouldnt open the tstat without taking loose the heater tube at highest point and purging air out..then worked like a champ once again

 

My buddy has a gas truck and he had a bad radiator hose sucking flat and it did the same exact thing.