Overheating

[RW986]

A while back driving my 2002 Boxster S, the water temp rose to about 210 or so. Aways ran just above 180. I got of the freeway and it went back to normal and has been that way until this week when I pulled into a lot and antifreeze was poring out the by the passenger rear wheel. I got some antifreeze, fill ed up and started home. Almost immediately the temp pegged far right. I stopped let it sit awhile, more antifreeze and continued home. Again in about 1 mile the temp pegged to the right again. Did this probably 3 more times in the next 2 miles. Figured since it was still losing antifreeze, must be either the pump or thermostat. Car has 73,000 on it and read that water pumps go bad often, so I ordered one. Took the old off expecting to find pieces of plastic and it was in perfect condition. So must be the thermostat. Pulled it and in 200 degrees open about 3/16-1/4 inch. That must be ok. The fans were working when all this overheating was happening. Now I had driven the car daily for 2 weeks after the origional problem. Question is: Could a air bubble in the system have caused the the origional problem and after 2 weeks got into a place that would not allow water to flow through the engine and cause the major overheating? I'm stumped. Been working on cars for 40 years, so I'm not new to this, but first problem with the Boxster. Anyone have any other ideas. Sorry so long but needed to explain the whole problem, didn't want someone to waste their time telling me it was the water pump. Please help, I'm dying here.

[JFP in PA]

Yes, it was most likely caused by an air pocket; this happens frequently with these cars when they run low on coolant due to the design of the cooling system. Refill the system using a vacuum fill, or use the alternative "burping" procedures and you will be fine.

[RW986]

Thanks so much for the quick response. Couple other questions. Since I have the new pump, would it be wise to just replace it since its all apart, and I took the thermostat housing off, but don't have a gasket and sure I would have to wait the usuall 3-5 days to get a new one. Could I just put a small bead of gasket liquid on the one side and have it hold ok.

Thanks in advance

[JFP in PA]

I would replace the water pump, but I would not use sealant on the thermostat housing. You need to clean the metal mating surfaces (non-scratch scotch brite pad does an excellent job) and then use a new gasket. I would also only use the OEM coolant (you can do a search for info about known compatibility issues) premixed with an equal amount of distilled water (supermarket item, but very important). Once you get the system filled and "burped", you will be set for many years of service.....

[RW986]

Thanks again JFP. But what if I have already added non OE antifreeze, do I need to drain the entire system and start all over. Scary part about that is I know Porsche, they probably get 100.00 a gal for the OE stuff. I will get a new gasket.

[JFP in PA]

You may as well drain everything at this point and start fresh. The OEM coolant should cost about $22-24/gal, you will need at least two, plus distilled water.