Coolant reserve tank filling up

[Valk737]

Help.   Just got back from a 700 mile ride. In hot weather and radiator was down 22 oz. I refilled it then checked the reserve tank and it was full to the top   so it’s filling up and leaking out the overflow while riding   Any ideas.  1999 IS

[3W-lonerider]

your radiator cap isn't making a good seal and when your coolant gets hot its pushing up past the cap into the overflow bottle.
take your cap off and bend the tabs up slightly to give more downward pressure on the cap to create a better seal.

[MarkT]

your radiator cap isn't making a good seal and when your coolant gets hot its pushing up past the cap into the overflow bottle.
take your cap off and bend the tabs up slightly to give more downward pressure on the cap to create a better seal.

And replace it.

[Valk737]

I’ll do both.   That’s a lot better than a head gasket.

[ridingron]

Did you check the hose from the radiator to the reserve tank for leaks? If it has a leak, the coolant won't be pulled back into the radiator. It'll suck air.

[gordonv]

coolant goes back to the rad, when the water contracts creating a vacuum. That vacuum sucks back along the over flow line to the overflow tank. Any air leak in that route from the cap to the tank, and the vacuum will suck air instead of liquid.

I think you've been given the solution by the others. Good luck and let us know what fixes it.

(I ride with a spare cap when I take my trailer)

[Valk737]

Great I’ll check

[Valk737]

I’ve had the bike for two years and it is awesome. Everyone likes it. You don’t see a lot of em