At work we have a 800C JD backhoe, last fall it quit throwing heat in the cab, it will not circulate coolant through the core, in fact the hoses are cold and the engine is up to temp. If I remove the hoses from the core and Hook them together, they heat right up, so the core has been replaced, hoses have been replaced, thermostats, and the water pump. There is no valve in the heater as it's controlled on the air side, RDO our dealer, said they have had this problem on other models and said the core was the problem. After replacing all the parts, it will heat if working hard, but it's servicing a tunnel pit and not working hard at all, and it's cold here, LOL,,, any thoughts ? Lee
Could try insulating the lines from engine to cab... May help a little...
So did it heat fine last winter and stopped in the fall? Pull the core again and rinse it and blow it out just to be sure. Then replace the radiator cap, and pressurize the system and burp the core with one hose loosened (might have a second guy squeeze a big hose with the hose loose at the core, or fill the line and core with the hose off at the core). Do you have a fan belt on something like that? Slipping a little? Not leaking air into the coolant are you?
Delmer, thanks for the input, I did replace the cap yesterday and it was bad, the core was replaced last week with a brand new one, I may add a piece of clear toobing to see if there is air bubbles getting in there, may be a head gasket issue. Yes it did work last fall and quit, we typically do not use the machine in the winter, but I do not recall it ever having an issue, the rig has 15,000 hrs + on it, and the pump is gear driven, Isuzu engine. Interesting you mention a belt, we mave many EX750's with N14 Cummins in them, if the heater act's up it is always the waterpump belt!, who would guess, LOL. Lee
Try reversing the hoses on the core if all else fails.
I like that answer better than any of my guesses. This problem just doesn't make sense to me. I wonder if the original "plugged" heater core is still around to prove/disprove the dealers claim? Just can't imagine how this could work out the way it has. Also don't forget to rev it up when trying to flush the air out.