Strange cooling issue... - 986 Forum - The Community for Porsche Boxster & Cayman Owners

This is on the daily driver. We had several inches of rain a few days ago, and the following day I had to drive out to a Llama ranch to photograph it for work. To my dismay, the last 4 miles of the trip were on a dirt road, which had turned to red-clay-mud. I proceeded cautiously and made it just fine. Back in the city I stopped at the first car wash and washed the mud off of the lower half of the car, concentrating especially on the undercarriage, the wheel wells, and the radiator cavities. All clean and moving on, about an hour later I noticed the car running at around 195-200 degrees instead of the usual 180. Odd. I checked to make sure the fans were coming on and the coolant full. Yes, both fans coming on and going off, coolant staying at MAX mark. It was not overheating, just maintaining a higher temperature than normal. Took the car home, made an appointment with the shop, and checked everything again. Fans still working, and coolant full. This morning when I started it to take it to the shop, the coolant was well below the MIN mark, and the red light flashing. No visible leaks or smell. Really strange. It's being looked over now, but... Any thoughts? Thanks!

How many miles on the engine? My first thought here could be a bad gasket or heater core, but I am just shooting from the hip on this one. Perhaps a failing thermostat that is not opening all the way. I am curious to find out what the shop says on this one. I agree that it is a bit weird that you would lose that much fluid though without a visible leak somewhere. Erik

Did you do a thorough job of checking for external seepage that might have been boiling off without leaving any drips? Usually there is a odor that results from this situation but maybe it wasn't easily noticed. I hate to say this, but if you're losing that much coolant without any drips or smell, then its most likely going out the tailpipe...

Coolant full, spray, then coolant leak, there are plastic coolant lines that run under the car that can be damaged and thus the source of your ills.

So far he's checked all the obvious stuff, radiators, fans, relays, lines, tank, and so far nothing. It's a real head-scratcher. Has currently 132,000 miles on it. Water pump and thermostat were replaced last year, cooling system fully serviced about a month ago with the proper coolant.

May be a stupid question since I am a newer 986 owner but could it have been a bubble in the line since you just had coolant system serviced last month and it finally worked its way through?

I do wonder about that. It crossed my mind.

So, I wonder if this had anything to do with the irratic cooling? Still doesn't explain the drop in coolant level, but all the lines and hoses were checked, system pressure-tested, fans and thermostat tested, and a leak-down test performed on the engine. It was then test driven for a week. Everything checks out fine. It's so weird! Could have been an air pocket, wet sensors, or some other odd thing I guess.

the increase in temp may have been enough to push the coolant out of the expansion tank and upon cooling the coolant contracted, thus leaving the level lower. my advice would be to refill the reservoir and monitor it for a few weeks. if the level stays in the normal range, chalk it up to the gremlin which lives in all of our cars.

Filthy radiators definietely affect the colling system. The left one seems to be a little bit dirty. Maybe too much farm roads on you daily routes. If the car was slightly overheated while driving the overpressure valve will open at around 1.3 bar. So you loose coolant fluid and the colling system stays save. Just another idea. Very old coolant fluid can get instable (hope that is the right term) and rusty. This coolant fluid will be less efficient. Had that problem myself with a 12 year old car, where the fluid never had benn changed. Drained the system - a lot of rust. Flushed the system with light pressure and fresh water - still a lot of rust. Flushed the system until the water was clean. Than filled it up with new destillated water and cooling fluid. No more cooling problems. But it wasn't a Boxster. So it was a lot easier to get the whole system flushed. Maybe this isn't a Porsche problem, because of the aluminium engine block - the car i had had an "iron" engine, but maybe it is worth a try.

Thanks for the input guys! I did have the cooling system serviced not long ago so no problem there. The coolant expanding and 'belching' out of the overflow seems like the most likely scenario.

Did this ever fix itself? Mine has started to do the same symptons.