UPDATE

I'm getting the car ready to drive. We're supposed to have thunderstorms here tomorrow which should take care of the salt on the roads. I'm taking the car in to the dealer a week from Monday for the major 4 year 40K mile check. The Boxster has 21K on it now. This will be an important check, because the warranty expires on April 28. I topped the coolant up last May after driving back from Arizona to Minneapolis. I topped the coolant off at that time with distilled water, and it took roughly a quart. I'm pretty sure that it had never been looked at, because the coolant cap was difficult to remove and there was some gunk on the seal. I just added 600 milliliters (measured) after about a year and 5000 miles. Is this normal?

be any wetness present and the size of the stain can't be very big. (The techs didn't tell me how big was too big.)

If you see any build up of anti-freeze residue -- in the case of my 996 this was green -- around the bearing seals (you have to look between the water pump casting and the pump pulley) that's a sign the water pump is leaking too much and should be replaced.

A quart low is quite a bit though and I can't see a healthy water pump accounting for that much loss of fluid. I mean I've driven 5K miles in one week and never had the coolant level drop at all so if the pump is allowing any coolant past its seals it is a very small amount. Very small amount.

Another explanation and one I like is the cap is leaking. My experience is if this is leaking it can leak enough vapor to in around one month's time (using the car almost every day) to bring the level down enough to cause the warning light to come on. In my car's case I had to add a gallon of distilled water to bring the level back up to where it should be.

Up to you but with the car cold I'd remove the cap, thoroughly rinse where it screws/seats to the tank and buy a new cap. Be sure the fluid level is ok and carefully note where the level is. After putting on the new cap as you drive the car check the level carefully and if it is going down there's a leak and my money is that it is not just the normal leaking from past the water pump seals, though an inspection of the water pump is called for. Along with a careful inspection of the car's entire cooling system.

When I unscrewed the cap today, with the engine completely cold after sitting for a couple of days, there was the slightest hiss indicating a pressure equalization. I therefore doubt the cap is leaking. I will mention the issue when I bring the car in to the dealer and request that they inspect the cooling system carefully especially the water pump seals.

atmosphere when the engine and its cooling system are cold is proof there is no leak at the cap. Just the opposite in fact. (Well that there is a leak but the cap is quite often the culprit.)

My experience is the cap only leaks when the system is hot and under considerable (but within design margins) pressure from within. Once the pressure within subsides there is no leak and there will be no equalization of pressure.

There are a couple of factors I didn't mention. When I got the car home from Arizona last May and added a bit more than a quart, I did not check the coolant level again after a week or so of driving, which I should have done. I just checked the level again this morning and was able to add another 50 cc to bring the level up to max. I had the engine at operating temp yesterday, enough to cause the engine compartment fan to come on. Air bubbles may be the culprit. Now, I have all service records for the car which was leased. The oil was changed annually at the Porsche dealer in Scottsdale and had no maintenance issues. The car was driven mostly around town by the owner's wife. She had the speed minder set to 68 mph. I would not be surprised if it had never seen 100 mph before I bought it and tried out the performance at 130 mph on a two lane highway through an indian reservation on the way home to Minneapolis. Given how tight the cap was on when I checked the level last May, I surmise it had not been removed since the car was new. During a routine oil change, the dealer couldn't check the coolant level because the engine would have been too hot. The car had 15K miles on it when I picked it up, so I'm thinking a coolant loss of a bit more than a quart over 15K miles was what I originally was seeing. That would agree with my experience of a bit more than half a quart over 5K miles.

I'm going to drive the car for a week and check the level again before I take it in. At this point I just wanted to know if that was an issue to bring up to the dealer when I have the car serviced on the 21st. The warranty expires on the 28th, and I want to make sure any issues are resolved. I will let the dealer handle it any way he wants.

of the dealer. Certainly if you are seeing a drop in the coolant level over a short period of time that qualifies.

The dealer service department checked the cooling system by pressurizing it to 16 psi and looking for residue. No problem was found. I may replace the cap, but it's no big deal to add half a quart of distilled water to the coolant every 5K miles. I'll certainly keep an eye on it. I'm about to join the ranks of the out of warranty drivers, but considering the lack of trouble reports on the 9A1 engine I'm not worried about it.

Quote
SteveJ (2010 987 base, manual trans)
The dealer service department checked the cooling system by pressurizing it to 16 psi and looking for residue. No problem was found. I may replace the cap, but it's no big deal to add half a quart of distilled water to the coolant every 5K miles. I'll certainly keep an eye on it. I'm about to join the ranks of the out of warranty drivers, but considering the lack of trouble reports on the 9A1 engine I'm not worried about it.

If you think you're going to be adding a half quart every 5K miles, I'd recommend buying some of the Porsche coolant and mixing it 50/50 with distilled water so you don't eventually have mostly water. The Antifreeze not only ensures your coolant doesn't freeze, but also helps lubricate the water pump.

... asking for trouble.
The cooling system in these cars is a closed stystem that doesn't need ANY maintenance.
If your dealer didn't find a leak at 16 psi they should have tested it at 20 psi.
I have had several cars with the same issue: disappearing coolant with no trace at the cap or otherwise.
Both were the water pump that would only leak when the pressure was around 20 psi.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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and has been for minutes. Be sure the A/C is off. When you hear the radiator fans come on you know the coolant is hot. In my Boxster's case the coolant temperature is 212F.

Bring the car someplace you can check it over carefully. Ideally it should be on a lift so you can get under the car. Before lifting the car raise RPMs to over 1K and hold until you hear the radiator fans come on. Shut off the engine. Then just let the engine's heat load do its thing and raise the temperature and pressure of the coolant. Tent the cap with some foil. If you see any condensation the cap's leaking (or the tank below it). Check the water pump. Sniff the radiator ducts for any anti-freeze odor. Be careful. When I did the above test -- on the ground in a parking place where I live -- the tank split finally let go and hot coolant gushed to the ground. Had I been under the car….

Anyhow, a cold pressure test often fails to turn up a leak that is present when the system is hot.

I just got off the phone with the service advisor at the Porsche dealer. I suggested a new cap would be the place to start. They are going to cover the cost of the new cap and agreed that the issue should be tracked down. I have printed this discussion so I can leave a copy with the dealer. The warranty is good until April 28.

Steve

time you know this time will likely have run out. When the cap was leaking on my Boxster it took around a month for the tank level to drop enough to light the warning light. This was after I had topped up the tank with distilled water.

If you get this issue on the books so to speak before the warranty expires, I believe the warranty can be used to cover any repairs. This info is 3rd hand though. Speak with the service manager and be sure you understand what is required on your part (and his) to if a leak is found after the warranty expires because it was brought to the attention of the service department before the warranty expired it is still covered.

The dealer ordered a new cap. They didn't have one in stock. I should have it in a couple of days. I told the service advisor that I will not add any coolant, that they can do that themselves if the problem is not fixed. He said that would be helpful for documentation. I don't believe I need to wait for a warning light to come on. As soon as the level is significantly below the "MIN" indicator I will take it in. He kept the printout of this discussion for further documentation. It doesn't hurt that Pedro writes a column for our Nord Stern Porsche club monthly newsletter and a copy of the newsletter was on the parts counter.