I thought I'd update this older thread with some newer findings.

As it turned out, after a drive the coolant level of my 160 still rose frighteningly from the max level at the seam of the expansion tank, almost to the rim, percolating as an old coffee pot. On a drive from The Hague on the A12 we got stuck in the Traffic Jam from the Apocalypse. Temperature on the coolant gauge rose to just above the halfway indicator, but then, still stuck in traffic dropped to the level I was used to in the 160 (slightly higher than my 135). Without me having heard the fans come on, rad nor engine bay.When I opened the boot lid at home, the expansion tank was wet on the outside. As it turned out after cool-down, I hadn't lost much coolant.

I decided to bleed the cooling system again for good measure. I unclipped the soft top, got the isolation out, removed the "bonnet", filled the expansion tank, slid a drip tray under the car, and started bleeding: radiator first, heater next, then coolant rail. I let the coolant gush out before redoing the bolts. Not a single air bubble in sight. I removed the hose leading from the jiggle valve to the expansion tank at the T-piece, shoved in an unused caulking gun nozzle and blew into the hose to see if the jiggle valve was stuck. Which it wasn't. I refitted the hose, started the engine and let it idle for almost half an hour. I let it cool down a little and restarted the bleeding process – this time without testing the jiggle valve. Again, no air bubbles. I screwed on a new expansion tank cap , and have made several trips since.

The coolant level rises somewhat, but not nearly as much as it used to do. No percolating. No visible loss of coolant. The needle of the temp gauge sits rock steady at the level of my 135, so somewhat lower than what I was used to in the 160, even in warm weather and dense traffic. I now tentatively permit myself to conclude the issue is resolved. But what was it that did the resolving? The second bleed? Did I unstuck the plastic ball from the jiggle valve? Is it the new cap?

Richard

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