So i was filling up the coolant system after replacing the thermostat, and i noticed coolant started running down behind engine. I continued filling until radiator and reservoir were full. I started truck and it stopped leaking, it doesnt overheat but it does seem to run a little hot. Is this a head gasket? No white smoke, no milkshake in oil dipstick, and it only ran down behind engine when i was filling the coolant system after draining it.

 

The block and head are both very thin at the back of the motor, not much material to clamp with. Over time the head gaskets and aluminum deteriorate due to coolant soak and allow an external leak. Doesn't leak into the combustion chamber but it does allow pressurized coolant to eventually exit. Your at the point when the block is cold it leaks but it's only a matter of time before it leaks all the time, running or not. It's not a hard or expensive job to replace the gaskets it just takes planning and time. Good time to get to know your motors condition too.

 

Thanks for that info

 

I had a small leak after doing t-stat. Turned out to be my upper hose leaking into the valley and running out the back. Might be worth a look at the hose.

 

I'll check it out. Thanks