coolant boiling in expansion tank

[scudderdan]

I got a 2006 955i. I was in stop and go traffic this weekend in Las Vegas. It was over 90f. At stops the temp guage climbed to just below red (never reaching red). I noticed the coolant was bubbling in the expansion tank. Is this normal?
thanks[/i]

[iansoady]

No.

If it's bubbling it's probably got air in it - could be just the pressure cap.

[blacktiger]

Did you notice the cooling fan coming on? In my experience, the gauge shouldn't get beyond half way on the dial before the fan comes on and keeps it at that level.
It's an easy thing, when the tank fuel tank and air box has been off, to forget to connect the electrics to the fan.
Otherwise I'd try a new radiator cap.

[wanderer505]

Mine did that last year (06 955i).  Replaced the radiator cap with a generic auto cap from NAPA, still boiled in tank.  Ordered one from Triumph and the problem went away.

[daveb]

Similar thing happened to me a short while ago

http://tigertriple.com/forum/index.php/topic,8892

[Chris Canning]

How do you quantify the word 'boil',mine looks like it's boiling and always has done,it's just fluid moving in the header tank.

[D-Fuzz]

With my Steamer, if the bike was idling at the proper operating temperature, the expansion tank would start to fill up and I'd get bubbling in the tank.  It would eventually build up pressure and spit out a bit of coolant through the overflow hose.  Since replacing the rad cap, the problem has stopped.  No more bubbling in the tank and no puddles on my driveway.

For the people who didn't have success with the automotive rad caps, did you get one with a 16psi rating?  When I went shopping for mine, I noticed there were a couple that fit, but one was only rated to 13psi.  I read on here it needs to be 16psi, so that is the one I bought.  Works good for me.