Ugh.... I Need Some Help Identifying a Coolant Leak - 986 Forum - The Community for Porsche Boxster & Cayman Owners

I have read post for the last 24 hours. I have used our search feature, the Rennlist search feature and Google. I believe I know what I need to do but would appreciate some opinions. Car is an '01 Boxster S with 25,000 miles. Owned since new with original water pump. After a 20 minute drive the other day I backed the Boxster into the garage and noticed a trail of coolant coming from the Boxster. It only started as I backed the car and was a pretty good flow. I read the posting regarding the caps going bad and noted that mine was the original cap ending in .01. I order a new OEM one ended in .04 and installed it. I also added about 16 ounces of distilled water bringing the tank to the correct mark. Yesterday, after the new cap and water, I took the Boxster out for another 20 minute drive. As I backed into the garage the same thing. The water flowed out. I immediately jacked the Boxster up and found the water was coming from the coolant overflow tube. It was coming out fast and a lot. I took the below photos. I took the trim piece off of the top of the fill area and noted some coolant there as shown in the photos. In all of my searches, it appears the cap should be culperate in this senario. I read where some new caps are installed on older tanks you have to trim some of the tank off to get the new cap to seat correctly. I did not do this. Another used plumbers tape to insure a good seal. I did not. I did remove the cap add some more distilled water made sure I had the cap seated properly and tightened it down well. Very well. I then went for another drive.... no leak this time. One concern I have is that this is not a cap issue but a water pump issue. I read a post that said the water pump uses this drain hose and will drain there when the pump is failing. Is this correct? As usual, timing is everything. My brother, who also has an '01 Boxster S and lives in Switzerland, is coming June 7 for a visit. We were planning on changing the water pump and related items during his stay. I bought an Airlift 550000 for the job. It would be nice to wait for him to do the water pump work but I don't want to risk a catastrophic failure. Thoughts?

Chuck did you notice how hot the temp gauge got? There is no connection from the waterpump to that overflow hose, but excellent chance the waterpump is failing due to age. I would remove your serpentine belt & spin the WP pulley to check for freeplay of the shaft. If you detect any problem with the WP change it before you drive it.

Pressure test... A pressure test will provide your answer quickly as to how/why/where your system is leaking causing coolant boil over; as opposed to throwing good $ at various parts in hopes of fixing problem. W/P, cracked coolant tank or bad o-ring on relief valve are likely suspects based on age but pressure test will reveal issue in short order. Until then, lift up carpet in rear trunk and look for coolant there... Good luck

... that there is air trapped in the coolant system. After a drive when everything is hot and pressures at the highest the air bubble exits via the pressure relief valve, through the drain hose, but takes with it whatever coolant is in front of it. This is most prevalent when driving hard in the mountains because of the changes in atmospheric pressures. Most likely when you refill your system with coolant using the AirLift System there won't be any more air inside and the problem won't happen again. Happy Boxstering, Pedro

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Damn... I meant to post that... I took the carpet out of the trunk and it was as dry as a bone. Can I use the Airlift 550000 for the pressure test? I have never used one and haven't even opened the box.

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You cannot use the AirLift to pressure test. It's the opposite. The Airlift creates a vacuum. You can test for leaks after you empty the coolant by drawing a vacuum and waiting 5 minutes. If the vacuum holds then there are no leaks. But if you're hunting for a leak, you need to put pressure in the system with coolant to physically see where the leak is happening. Happy Boxstering, Pedro

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That was what I was looking for,,, thanks. The temp gauge was a tad above the 180 mark, it's usual place. Thanks. Cool, thanks Pedro.

Chuck = assuming you have got air in the system, a quick check is to lift the chrome D ring on the pressure relief valve (pic #3) and drive the car for a couple of (complete) heat cycles with a drive of +/- 20 minutes. The open valve will allow air to be expelled without the coolant. Be prepared to top up the coolant bottle when the system cools down. If you have purged the air and it still vents out then you will have to investigate further, but my experience tells me that once the air is out, you should be OK. How the air got into the system is questionable, but possibly from your leaky old cap....

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Thanks Steve.

This is great, timely information because I was just about to post the question below to the forum. I have an 01S with 125K on the odometer. Two years ago or about 10K, the water pump was replaced and a low temperature thermostat was added. Normally in the SF Bay area afternoons, the gauge sits rock steady at the 1 in the 180 mark. Two days ago with the outside temperature about 20 degrees above normal and the air conditioning on, the gauge rose to the 0 mark in commute traffic. When back up to highway speed, the gauge dropped back to the 1 mark. Because I hadn’t seen this type of rise before except when broken ballast resistors kept the fans from running at low speed. The Durametric test showed the low speed fans work properly. So I checked for coolant level and noticed it was about 12 ounces below Max when cold. I’m wondering now where the coolant may have gone. I’ve checked externally and see no evidence of leaks. I’ve pulled the trunk carpet and there isn’t any coolant there. I’ve pulled the cover above the tank and there isn’t any coolant there either. The two guess left are: 1) cracked head or 2) a leaking heater core. If it were a cracked head, I’d expect to see intermix in the water tank or the oil sump. There is no evidence of either. I’ve got the car scheduled for a pressure test the week after next. Meanwhile, I'll check to see if the coolant drops more since I topped it off and for evidence of intermix. In the meantime, can you suggest other places to look or other possible causes for the coolant level dropping? Thanks

When was the coolant tank last replaced? On inspection, my old tank was bone dry and there was no evidence of leakage - until I unbolted it and felt (you couldn't see) encrusted coolant on the rear portion of the tank. When I physically removed the tank, there was 2 cracks which only leaked when it heated up - when cold it held the fluid and did not leak. It was enough to lose half a litre every 1000 km. The other leakage(es) could be around the pump / thermostat / radiators (bumper removed), but that would mean getting the car on jackstands and exploring for visual evidence with a strong light source.... Your pressure test would (should) simplify the search.

Thanks Steve -- the tank is original, hopefully that's the cause. There may also be a leak in the passenger side radiator. I hit a curb a month or so ago and it damaged the underside of the fender liner.