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2002 Boxster S - Coolant Dumped Under Car, Need Help Locating Issue

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2002 Boxster S (130,000 miles) - Brief history:

  • ~500 miles ago: changed the oil and filter myself about 500 miles ago (Mobil 1, 0w-40). Didn't notice any leaks.
  • ~100 miles ago: had a shop replace the rear toe arms with adjustable ones since the toe was way off on the right rear and couldn't get dialed in with the stock toe arms.
  • 2 days ago: neighbor asks if my car was running hot because the fan was running loud when I parked at home after driving for an hour.
  • Yesterday: drive 10 miles and when I park, I get out, walk about 5 steps, then coolant starts gushing out of the center between the rear wheels, and steam coming out of rear passenger side vent. Coolant tank is empty, but no leaks in the trunk (checked under the carpet liner and foam panels). Have it towed back to my house.


Now I'm trying to diagnose what went wrong. I took off the underbody liner to get a better look at the water pump, etc. It looks like there is oil and coolant sprayed in multiple places. Coolant drain plug is tight and dry. Oil level at dipstick is fine. Water pump doesn't feel loose from what little I can tell with the serpentine belt on. 


I poured about a pint of distilled water into the coolant tank in the trunk (which is yellowed and should probably be replaced whenever I find what is wrong) and noticed water dripping from the open end of a hose (see attached photo). I'm not sure what this hose goes to or if it's supposed to be open. 


Any thoughts on what to try or look at next? Any help is MUCH appreciated!

I have more photos I can upload if that's helpful.


Leaing Coolant Hose.jpg

Edited by Jon986
Added Mileage
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Hard to tell where the arrow is going but it sounds like you probably dumped from the coolant reservoir overflow hose, possibly due to an overheat or over pressure in the reservoir.  I would first refill with distilled water to see if it will hold without leaking. You might have a bit of residue from the previous dump. Make sure it is filled properly and burp as much air out as possible without overfilling. Common culprit is the cap. Make sure you have the latest revision and/or that yours is functioning properly. I would start there. If you confirm you don’t have latest revision then replace it, refill with distilled water first to confirm it solved your problem and then properly refill with coolant. 

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Ok, thank you for the insight. I do have the updated cap because a couple years ago it was leaking out of the top of the old one. This one seems solid.

I did fill the reservoir with distilled water today and a little bit dripped out of that hose (if there is a reservoir overflow hose, that's a safe bet for what that hose is I guess) but it seemed to be staying level after that. I attached a couple photos of the reservoir tank. In these photos, it is empty, even though that faded mark makes it look like there is coolant in there. I also attached a different photo showing that open hose (that may be the overflow hose)


Would possible culprits be:

  • Water pump failure? It didn't seem to be a source of any issues when I was under the car, but I've read how failed water pumps cause coolant dumps
  • Thermostat not working? If my neighbor noticed my fan working too hard the other day, it seems like the system was working hard even before it leaked all the coolant.

I had it towed to a shop today so they will pressure test the system and I should know more soon. From what I've read, it sounds like whatever the issue is, I should take this opportunity to replace the coolant reservoir, the water pump, and the thermostat. Anything else I should do that is a common maintenance issue while they are in there? I'm not sure how old the belt is...I've only had the car about 20k miles.


Thank you


Coolant Tank in Trunk.jpg

Inside of Coolant Tank.jpg

Open Coolant Hose.jpg

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If the reservoir has never been replaced then I'd recommend it.  You have clearly had some kind of leak in there given the red crud all over the trunk.  Many 986 owners suggest changing the water pump every 30k miles as preventative maintenance, which I subscribe to personally as well.  It is relatively cheap and an easy job.  While in there, I would put in a low-temp thermostat.  Same price as the standard one and your car should run cooler.  Unrelated to this area specifically, but related to the overall cooling of the car, a good cleaning of the front radiators has always been very effective for me personally.  It is amazing what gets stuck in there over a couple of years of driving.  If yours have never been cleaned at 130k mi, then you will be shocked by the content.


If you don't yet own Durametric, then I highly recommend it if you're going to keep the car for a while and you enjoy a bit of DIY work.

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