Coolant discharge from top of expansion tank

[Jactwist]

1999 Boxster S Tiptronic 57K miles.

Spent good part of the afternoon trying to get to the bottom of coolant loss from the expansion tank. Wife went to use the car yesterday and the red light started flashing, checked the expansion tank - empty. Took about 3 litres to refill.

Today I went through a 'bleed' procedure. Pulled up a spring loaded clip on top of tank, slowly filled tank, remove a fuse B1 to effect some sort of valve - apparently only needed for tiptronic system bleeds, run engine up to 90 - used cooking thermometer into expansion tank, reving engine every few minuets. There was a visible flow. The tank spilled over when it hit about 90(when the stat opened?) then settled down fine.This process took about 40mins.

Reset spring clip, refitted fuse(which stopped the instruments working whilst removed), closed tank lid and took car for a spin.

After about 6 miles steady driving pulled over and checked tank level - all good. Did another 6 miles with a blast up to about 6K revs in 3rd. Got back home and pulled over. all good. Ticked over for a few mins fine. Did one more lap of the block and pulled over; a large gush of water came out of the top of the tank -about 2.5Ltrs on to the road.

Back to square one.

Is there something I'm doing wrong?

[JFP in PA]

You did not get all the air out of the system, which is what caused the "dump". The preferred method of refilling these systems is under vacuum, which only takes a couple of min. and totally eliminates any issues. If you do not have access to a vacuum fill system, do a search for the "burping" proceedure (it ihas been posted several times on multiple sites) and re-purge the system. It takes a while, but eventually gets the job done................

[logray]

+1 to above comment.

Also, it is safe to leave the bleeder valve locked up for a few days while driving around.

You probably lost coolant when you had it up to temp with the cap removed, or somehow introduced air into the system.