Hey now,
I am the proud new owner of a 89 Westy, Rosebud as we have named her. anyway we are having confusing cooling issues. 1st of all the person that sold her to me thought that a head gasket was bad (so we got a good deal) rebuilt engine 20,000mi-she is not leaking any fluid anywhere! so when you drive her on the freeway or up a mtn.aty a good rate of speed the refill tank(behind the license plate) starts to fill to the point of overflow!-this has only happened once as I keep a really good eye on the gauge-as it climbs I let off the gas and get where I can pull over-making sure I don't overheat., really only seems to happen under load and not all the time- so I took her to trusted mechs, thjey drove her for 2 days- no troubles - so far we have driven her 1200 miles -overflowed twice- not quite ready to take heads off yet-sometimes coolant level remains same level overnite sometimes refill tank goes into overflow tank after she cools all the way down-once again no consistency  with issues- going on family vacation in 2 weeks so trying to get bugs ironed out..please help
Michael