So here is the gig. 98 D1 with 118k just started spraying coolant from the side of the expansion tank (a hole?) Truck isn't overheating (gauge stays stable in normal range) until I start up long hills, or stop and go traffic. Heat blows HOT, slightly over normal. Have replacement expansion tank in mail, Question is:
Is there something to check prior to attaching new tank?

While researching coolant issues there was a post regarding extra pressure building in the tank from leaking head gaskets. I've found no trace of coolant in the crankcase and the expansion tank top isn't leaking at all, just a steady, stream from the seam.

 

Thermostat?

 

i had that same problem... just change the overflow tank and bleed... thats it

 

Thanks guys ... ordered a Thermostat with Expansion Tank and a new Radiator plug (just in case!)
Still a little fuzzy on the bleeding procedures. Looks like you remove the Radiator Plug and Expansion cap, fill the Radiator completely and the Expansion to FULL mark then let the engine run. "until a steady stream flows out of rad" then plug the Radiator. Should all the bubbles stop prior to plugging, there was never a steady flow just a little burp here and there with lots and lots of little bubbles the entire time. Sound about right?

 

With the fill plug out of the radiator fill the overflow tank to the top, coolant will come out of the radiator plug hole, once only coolant comes out and no air bubbles replace the plug.
Then leave the cap off of the overflow tank.
Start engine with heater on, it will take a good 30 min for all the air to come out of the overflow tank cap.
Replace overflow tank cap, shut off engine.

 

You will want to fill your coolant bottle every night for 32 or 3 nights, if you are over heating, building up too much pressure then get it to a shop for a pressure test and possible head gaskets.

 

Spike: just to be clear, I don't start the engine until AFTER plugging the Radiator?

Mike: there is no over-heating, just lots of fluids spraying all over the engine compartment from the pressure leak. It only happens when I don't have the Heater running on HIGH, climbing long hills or Stop & go traffic. Will replace the Thermostat, expansion tank and flush/bleed the system.

 

Correct, only start the engine AFTER you plug the radiator back up BUT leave the cap off of the overflow tank.
And then do NOT turn the engine off until you have replaced the cap on the overflow tank.

 

disco mike is a big advocator of head gasket problems....