The radiator overflow tank where you "add fluid" will not typically allow the heater not to work as you originally discribed. However, if the radiator is low it will do what you discribed. Since adding fluid to the radiator overflow tank "fixed" the immediate problem, you were happy. However if the fluid in the overflow tank was not below the level that would allow air into the radiator, then the radiator is getting air from somewhere, which would then prevent it from sucking fluid in from the overflow tank which it does on a syphone type of system. As long as the radiator and coolant system is sealed, it works great but if a leak or hole in the system ever allows air in, it prevents the radiator from pulling in fluid when it cools down, and instead pulls air in from the hole/leak. If the hole is really small, as the radiator heats up, it will expand the fluid and push the excess into the overflow tank, but as it cools, it won't bring it back, thereby causing the radiator itself to become low on fluid, even though the tank still has fluid in it. If the hole is more of an ooze, than a leak then it might bring part of the fluid back for a while till the amount of air in the system builds up.
My thoughts would be to run a pressure check on the system using a coolant system pressure testor. Do it cold and hot for best results. I can loan you mine if you want to drop by and borrow it. Heck, I will even preform the test for you, no charge. Transportation costs might offset the savings, so do so at your own risk.
7710 is still sitting, work changed, cars needed to be purchased, so I am concentrating on doing a bill paydown so that I am not at the mercy of people when they want to change my work schedule. Since I now have a truck to move it with provided I can remove the duals, it is getting closer. I continue to use the JD2555 regularly.
David from jax
