Well I've seem to stumbled upon one that has me a little confused.

Background:
I was driving my truck on a short trip in town today when all of a sudden my temp gauge pegged to H and the engine light came on. I've never seen it do that before. Usually the temp gauge sits at N in "Normal". So I pulled over and let it sit awhile. I checked the engine and it was only slightly warm to the touch. After a short while I drove it back to my office and let it sit the rest of the afternoon. On my trip home the same thing happened. I had to limp the 20 miles home at 40 mph to keep it from overheating.

Symptoms:
I no longer have heat in the cab (except slightly warm when going down hill). I can hear coolant boiling in the radiator and upper radiator hose. The feed hose to the heater core is hot, the return line is cold. Only leaking slightly from the radiator. Resivoir fills completely when hot.

Other:
About a month ago I had made the decision to do some preventive maintanance and flush out my system and replace both upper and lower hoses along with the thermostate. I havn't done the work yet because I've been debating on whether or not to replace the leaky radiator or use leak stop. The heater core was replaced three years ago.

Is it just a bad thermostate and radiator or is this a sign of something worse. No visible water in the oil. You help would be appreciate.

Thanks.

 

First of all if there is a leak the water in your cooling system will boil at a lower temp. The cooling system has to be 100% before it can do it's job correctly. The no heat in the cab issue could be from low coolant, or bad water pump. Fix all your leaks, change your hoses, then if it still overheats the water pump is bad.

 

fill the cooling system and start it and let it come up top operating temperature

are their any bubbles in the radiator?
does it act like a bad thermostat & push coolant out of the neck?