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Coolant reservoir leak

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My MY97 has developed a coolant reservoir leak since I started using the updated coolant cap. Upon releasing the pressure by opening the cap, the leak stops. I have switched back to the old cap now. It's much better to have a slow loss of coolant over months through steam than to have a quick loss of coolant over days with over-pressure.

The question is, for those who have replaced the coolant reservoir, where was the leak coming from? Anyone have a photo? The plastic of the reservoir is very thick. I can't see how it could leak. If it does leak through a crack in such a thick walled plastic, one would think the leak would be constant and not just at pressure.

I suspect it's a seal or something. But the leak is behind the reservoir in my case, as is the case for the majority of the leaks described. So I can't see. Is there a seal/hose there?

Edited by Jinster
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Mine was almost in the center bottom - it will vary. I found a picture online that appeared to have a leak near the same area as mine. I have circled it. I had a hard time finding the leak also and it only did on heavy pressure. If you can feel around, you should eventually find residue solidified around the area. I never pinpointed it until it was removed.

PITA to replace, but in my opinion, worth a DIY :-\


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Mine was like the first pic with a crack along the bottom. Have you pulled up your trunck carpet? My leak got quickly worse from the first time or two I topped off the coolant to when I fixed the problem (about a month later).

Not a terrible job if you heed the directions on the various forums. Took me about 4 hours, most of which were spent trying tighten up one of the hoses upon reassembly.

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Thanks for the replies and pics, guys.

Maurice, I wish my leak was there. It would have been be quite easy to patch that, I would've thought.

dghii and por986, I had a feel underneath my reservoir for the leak, and all those dimples got me confused. But I think mine might be in a very similar location. Strictly aesthetically speaking, that's one dam ugly reservoir Porsche used!

It's been leaking for a month, since the day I changed the coolant cap and flushed the coolant system with the new red coolant. And I have been driving it with the bleeder valve open since then, and kept refilling it. When it got to about 10L of top up, I realised something must be wrong, and pulled the carpet and had a look... precious red coolant dripping down the bottoms of the reservoir...

I have switched back to the old cap and so far the coolant levels are holding up and no drips over the last three drives.

I thought if I can get an idea as to where it might be coming from, I can do a simple "patch" with bits of soft plastic and superglue - perhaps even do it blind, seeing how hard it is to disconnect and reconnect the hoses, not to mention wasting even more coolant. Hehehe....

Dam the new cap that broke my reservoir! Did Porsche update the coolant reservoir to make it stronger? Maybe the new cap shouldn't be fitted to the un-updated reservoirs.

Edited by Jinster
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It is not the new cap that broke the coolant reservoir, it is the old cap which is defective and therefore loose cooling system pressure, no pressure no leak. Driving without pressure in the cooling system increases the chance of overheating significantly.

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You will have to remove the tank to repair it, and there will be no guarantee that using an epoxy weld or similar will hold up for any duration. With the time you will invest to "hopefully" seal it, you might get a leak very soon after it is pressurized. Since you can get a tank for under $300, I would just replace it with new.

Before I replaced mine, I was thinking of trying to repair mine as well. Every shop I talked with essentially talked me out of it.

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To date, we have never seen a repaired tank that worked, they always start to leak again. And, as it is nearly impossible to repair the tank in place, while you have it out, just throw it away and put in the newer one with thicker walls, it will not only solve your issues, it just might save your sanity as well.................

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  • 1 month later...

Ok. Thanks for all the suggestions.

I just want to post an update. Since going back to the old cap, I have not lost any additional coolant - whether through steam or leak of the reservoir. This compares very favourably against the situation with the new coolant cap, where I was losing about 500ml to 1L every couple of days.

So I just want people to know the potential problems a new coolant cap could cause - precipitate a leak in your reservoir.

As to whether the additional pressure in the cooling system provided by the new cap (and a new reservoir if you get a leak) actually provides much benefit to the cooling system, my thoughts are it shouldn't really do much benefit, so I will stick with the old cap for now - and marvel at the geniuses at Porsche for extracting money from the owners: update the cap.... got a leak now? get a new reservoir.... $$$

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Thanks for sharing your miss-fortune Jinster.

I was about to change my cap (blue color but ending with 01) as a precautionary measure but since temperature keeps below 85C and I don't have leak, I'll pass on this one but will keep an eye.

Edited by ChrisJP
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The coolant system is designed to operate at about 18.2 PSIG for optimal cooling performance. The early caps often did not get the system up to that pressure, or lost the ability over time, causing slow loss of coolant. That said, running a car with a leaking coolant tank is asking for a problem. These tanks have been known to fail catastrophically, stranding the car and requiring flat bedding; or even worse, overheating the engine which led to other, more severe and often permanent issues. Even slow leaks can cause “hot spots” in what is already a system that operates way too hot to begin with.

If you have a leaking tank, replace it as soon as possible; don’t try and “band-aid” the problem.

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