My BX always seems to run toward the top of the temp gauge. Probably not surprising here in South Texas during the summer. However, yesterday the gauge went to the hot mark so I stopped and noticed the overflow tank was bubbling (not boiling) from the radiator cap. I let it cool for 30 minutes and checked the fluid level - seemed full, but the overflow tank was empty. Upon restarting, everything seemed OK, but I did not stress it much after that. I'd been cutting dense 2 ft grass for over an hour (Bahia?) at top speed. I do keep the radiator area clean with a strong ego blower. Hope I've done no damage.
The overflow tank seems to be working properly then.
As the machine heats up…the expanding coolant eventually over-pressures the radiator-cap relief and the coolant escapes the radiator tank.…into the overflow tank (also called a reservoir.)
Before the use of overflow-tanks…that coolant would be lost onto the ground, never to be recovered. Radiator tanks were oversized to allow for large air-pockets to exist above the coolant in that radiator tank when it was cool.
Newer designs utilized an overflow tank (reservoir) to capture that hot, excess coolant. When the machine cooled back down…the coolant contracts…creating a suction which sucks the coolant from the overflow tank back into the radiator tank…. and so on, and so on. (The advantage being that the radiator tank was always completely full during operation regardless of temperature. This also avoids atmosphere from entering the radiator tank….reducing oxidation of coolant and corrosion of radiator.)
A small amount of coolant should always remain in the overflow tank. If your radiator cools down and sucks the overflow tank completely dry…then you might add a pint or so of coolant to the overflow tank…. Then observe it for several operationa-periods… until it stabilizes with a couple inches of coolant always remaining in the overflow tank.
Hope this helps.
