Coolant spewing out of overflow tube
 

Just took my 2000 Boxster S on a 300-mile road trip, no problems at all, until right when I arrived at my destination...coolant poured out from just in front of the rear passenger wheel. Didn't notice any overheating, nor was the coolant steaming when it came out. I pulled out all the trunk carpeting and didn't see any puddles. I filled the expansion tank back up with water and started it up; nothing happened until the car got up to temperature, then all of the sudden the level in the expansion tank started rising rapidly, into the overflow and out of the overflow tube in the wheel well. The expansion tank seems to be holding pressure; before it overflowed you could hear air rushing when taking the cap off.

I don't see a trace of mayo in the oil cap. Smells just like oil in both the cap and the dipstick. No discoloration at all. The front radiators are still getting hot so it doesn't sound like a water pump (the coolant started spewing before the front fans came on, but they still come on with the A/C).

Any ideas here? If I need a part I need to order it ASAP as I'll only be here about a week and really don't want to get a tow all the way back home.

Reads like the coolant tank failed. They develop a split along the mold seam that is at the bottom of the tank. The tank leaks only when conditions are nearly optimum: The coolant temperature is 212F+, hot enough the radiator fans are running, and the engine is shut off. The heat load raises the coolant temperature and pressure and the tank split opens and coolant gushes out just ahead of the right rear wheel/tire.

If you let the car cool down -- like overnight -- you can add distilled water (I added just distilled water as I didn't want to mess with mixing up Porsche anti-freeze since I knew I was going to have the car in for a new coolant tank and at the same time fresh coolant) -- might take nearly a gallon -- then if you are lucky the tank won't leak as long as it remains "cool". At least this was my experience. The next day I added the distilled water and with no signs of leaks before or after I started the engine I drove a couple of miles to the dealer and had the tank replaced along with the coolant.

I refilled the tank only after the system had cooled overnight. When you filled the cooling system there might have been a air pocket which as the coolant circulated and got hot again/heated up some more pushed some coolant out the overflow.

It's not coming out of the tank itself though; it's all coming out of this overflow hose in the wheel well:

https://cimg4.ibsrv.net/gimg/rennlis...e0060dd3ae.jpg

The inside of the trunk around the tank is mostly dry. Oh, and worth mentioning the expansion tank was replaced under the previous owner several years ago, and I replaced the cap a few months ago

You desribed the exact same thing that happened to me after I bought my car. Returned from Vegas... hit the driveway... coolant and the sound...

If your tank was leaking, you'd know it (under the carpet).

Me? Based upon the advice from this forum, at the time, I replaced the coolant cap with OEM... refilled with steam distilled water... opened the bleeder valve for a few days drive around... closed the valve. Zero problems after that.

Go for the least expensive repair first.

Guess I'll give that a try. I think I need to flush the coolant and refill, since it dumped about a gallon of coolant (I also topped it back up with tap water, it's all I had at the time). Unfortunately no Porsche dealerships nearby, I'll have to purge all the old stuff and use generic stuff (should be fine from what I've heard as long as it's OAT; I picked up some Prestone Dex-Cool which is supposed to be)

Had a coolant cap leak on both my Boxster and Turbo. The Boxster lost about a gallon of coolant in under a month's worth of driving. But the cooling system never dumped any coolant out the overflow.

I cleaned the cap and where the cap threads to the tank, topped up the coolant level with distilled water then made sure the cap was securely. You want to be sure you don't cross thread the cap nor over tighten it but it does take some force to tighten the cap down to where it makes a pressure tight seal with the top of the tank spigot.

I warmed up the engine got the coolant hot enough to trigger the radiator fans then placed a foil tent over the cap and shut off the engine.

After a few minutes I looked at the foil and there was condensation under the foil. I bought a new cap and the loss of coolant went away.

When the tank failed in my car I don't recall any coolant in the trunk. Maybe luck was involved because the coolant was hot and under so much pressure the stuff just gushed straight down. I do recall the hot coolant really just poured down ahead of the rear tire.

You can do the hot pressure test to confirm cap and tank and the rest of the system is pressure tight when up to temperature.

So I drained all the coolant and got about 4 gallons out. Reconnected all the coolant hoses and put the drain plug back in. I topped up the tank with distilled water only and followed the Bentley manual procedure for bleeding the system; cap off while idling, adding until no more could be added. At this point I think of put about 3.5 gallons of water in. I then put the cap back on and held the 2500 RPM until the front cooling fans kicked in. The expansion tank level had dropped to pretty close to the bottom.

Unexpectedly, whenever I tried to open the cap, lots of steam came out and the water level would quicky rise back up, preventing me from adding any more water. Low coolant light blinking the entire time. I went on for an addition 3 minutes of 2500 RPM with the occasional 5000 RPM blip but the tank was still doing the same thing. I cut it short when I saw that the temp gauge had risen to the line directly between 180F and 250F.

I've let it cool off for a while and the tank level had dropped to about the bottom again. I filled it back up with water; guess all I can do is repeat the process, but this is sounding pretty weird to me.

Just got done repeating the procedure; this time the temp gauge stayed lower, and there was much less drop in the coolant tank. I would probably do it a third time but since this is just the flushing water I don't think it needs to be perfect. I'll be more thorough when bleeding the final coolant.

I strongly recommend that you invest in a vacuum filling system. It eliminates air bubbles immediately and also makes filling completely at one much more easy.

Wish I had one but I'm in a pretty rural location and Walmart is about all there is here. They don't appear to have any in stock

I had the same thing happen when my system was flushed. I would sweat it too much. Just keep a close eye on the temps and water level in the expansion tank.

Order it from Amazon. They have a ton of them. I'd take one with a lot of positive reviews.

I'll definitely have one on hand for the future but I'm leaving here on Saturday and can't afford to wait on a delivery. If I'd known as soon as I got here it might have been a different story

I topped it off a few times and ran it on short trips (5 miles) without any issue. I had it idle in my garage for 30+ minutes multiple times without over heat or leaking.

I just took it out again today on a longer trip and after about 35 minutes at highway speed I got a low coolant warning. I pulled over and there was a little bubbling in the tank and some coolant being released by the pressure release valve. I let it cool down some and topped off the coolant. Ran it again at idle and there was no pressure I'm the radiator hoses (hoses not that hot and I could squeeze them like they were empty), shortly overheated and overflowed from the tank again.

Possible intermittent water pump or thermostat problem?

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Check your coolant cap. Make sure you have the latest version with the part number ending in 04. Older caps tend to have a weakening relief valve spring that releases pressure at low levels. This is a very common and the fix is the cheap price of a new cap.