BoxsterC

Hi, I am seeking suggestions and idea for an issue that bothers me ever since I got my 2005 Boxster S in 2013.

After I top off the coolant, the coolant level drops below the min mark via coolant reservoir 'window' when the system is pressurized, regardless whether the car sat overnight (cold) or being driven (hot).

About nine months ago, the car was losing coolant, and I sent my car to a local Porsche indy to identify the leak and replace parts. Making a long story short, the shop replaced reservoir, cap, water pump, thermostat, a new 3rd central radiator and a hose with pin-hole leak. I believe the leak was fixed because I don't smell the coolant leak anymore, as I did before the repair. The shop indy uses a vacuum system to refill the coolant; hence, I hope most of the air pockets were eliminated. However, the coolant level would drop below the min mark after the system is pressurized. When I depressurized the system by opening the cap with a cold system, the coolant level would return almost to the max line. I only need to add just a little bit of coolant to reach the top line before it overflows. The impact is that I would get 'low coolant fluid' warning light after I drive it for one to two thousand miles. This boxster always lose some coolant as vapor visible on the rear trunk that is above the reservoir compartment. After the recent repair, the mist/vapor significantly improved by the repair that replaced the hose that had pinhole leak connecting the reservoir to engine. Nevertheless, I expect to lose some coolant over time.

I have read an old thread 'coolant level drop no evidence of leak" https://rennlist.com/forums/996-foru...e-of-leak.html, but I could not find the answer that helps me. Other threads suggested the following possible cause for coolant to drop below min mark:
1. Air pockets got compressed under pressure
2. Some type of leaks that resulted in coolant lose (e.g. reservoir crack, water pump leak, etc.)

Because of my recent repairs by a local shop, I hope these two causes don't apply to me. BTW, I did hear some goggling sound like air bubbles when I open the cap to depressurize the system.

Here are my questions:
1. Have you experienced the same issue? If so, what did you do to 'fix' the issue?
2. What can I do to diagnose the issue?
3. Any other possible cause to exhibit this behavior?

Your insight is greatly appreciated.

gtbrandon

Currently with the same issue after replacing the cap and topping off fluid. My thought was that there was air trapped in the system under pressure but I was told these caps are supposed to self-bleed under air pressure so I'm not sure what to do other than a full coolant flush and refill. Though it sounds like your shop did that and still the issue persists so maybe that will accomplish nothing..

BoxsterC

My shop spent 3 months diagnosing the issue. At the end, it fixed the leak, but not the problem I reported here. The shop definitely flushed the system. I wonder if I need to replace all the hoses, just in case the hoses expanded under pressure and caused the coolant to drop below the min mark. The annoying thing, of course, is that I cannot really 'top it off' and the low coolant warning returns. I should have just asked the shop to replace all the hoses.

SafetyP1

Wrong thread

Ric In RVA

I'd throw some coolant UV dye in and driver it. Then get out the UV flashlight and look for the glowing spots.

It will show up BRIGHT.

Helped me chase leaks in my old LR4....so many leaks....

Schwinn

UV dye is a good idea. Another trick is to flex the hoses - I had an old car which showed similar issues but didn't show the UV until you flexed the hoses, then you could see the dye was basically filtered by the cracks in the hose, so it wasn't apparent on the outside of the hoses as easily....

Ubermensch

It can be difficult to remove all the air from the system, even with a vacuum filling. I had the same symptoms for nearly 10 years in my Cayman and it turned out to be air in the system. A couple of points to consider/try:

1) The self-bleeding mechanism is not on the reservoir cap you can access from the trunk. You need to remove the engine cover to access the bleeding cap. You rotate the metal lever into the up position to allow venting. It's part #4 in this diagram:

Ma1.20 Water Cooling 4 Ma1.21 (autoatlanta.com)

2) The venting requires multiple heat/cooling cycles to complete. On average, I've found that three, 20 minutes drives are required to remove all the air. This was my mistake all those years. I thought one drive and then a refill was enough. Drive it, let it cool down, fill it. Keep doing this until the level doesn't drop...Maybe it's twice, maybe it's four times, but I've never had it be once.

Shark Attack

Have you driven the car with the bleed valve open? No you shouldn't expect to lose coolant. That like expecting your wife to have an affair. It just shouldn't happen. But you can tolerate it if you want too.

if it's leaking. It's not holding proper pressure. That also means it's not cooling as it should. Your coolant is maybe even boiling

iflyjetzzz

I've just accepted the system air bubbles/quirky radiator system as part of owning this car. It just seems like a poor design. Every time I check the coolant level, it is below the min line. I put in enough fluid to get it to Max. Let it sit for a while, and it's below Min again. Add more fluid. I hadn't checked my coolant level for ~6 months until last night. So far today, I've added ~1/2 gallon of distilled water, about 12 ounces at a time.
This cooling system is like no other car's cooling system that I've owned. I'm used to the cap being on the top of the radiator where I can see straight into the radiator and the radiator fluid, not an S shaped tube where only 2-3 inches of fluid is possible to be visible.
Once warmed up, my car temp always seems to be ~175 degrees with no movement. It stays there rock solid.
The coolant was changed last year when I had my water pump changed out.

I've owned the car for 11+ years and have never had the low coolant light come on, nor has it thrown a code for the cooling system.
Embrace the crappy design. And... thanks Ubermensch for posting the diagram of the cooling system - that helps. I see it's the same for the M97.