Coolant leak - 986 Forum - The Community for Porsche Boxster & Cayman Owners

I was tooling along at freeway speed when the temperature gauge began climbing and the red light flashing. I pulled over and peeked underneath the car. Sure enough, I had a coolant leak, and by the looks of it a substantial one. As in split-hose substantial. I was still 25 miles from home, so I gave AAA a call. First time I've used the service. A wrecker flat-bedded my 986 to my destination. First thing I did was check to make sure there was no coolant in the oil, to rule out a blown head gasket or cracked block, the stuff of nightmares. I was relieved to see only oil on the dipstick. Coolant was dripping out behind the drivers-side front wheel, but plastic sections cover a good part of the bottom, so I couldn't see where it was leaking specifically. I put the car up on jack stands, removed the front wheel and wheel-well liner (and therein lies a tale) to have a peek at the intermediate coolant hoses behind it. Didn't see anything obviously amiss there. Next, I removed the middle plastic section underneath (and that's another tale). After adding a gallon of distilled water to the coolant tank, I started the engine. I let it run until I was certain the thermostat had opened, revving it a bit to make sure. (Parenthically, I sure do like the exhaust note of my 986, even with the stock muffler.) The temp climbed to around 200 as the light flashed. "Now we'll see what's what," I muttered. Sure enough, there was a growing puddle underneath. Creeper time. Underneath, I did not find a split hose, or a loose fitting, like I was expecting. Instead, coolant was coming out of a small rubber fitting that looked like an overflow tube. Coming out of it to beat the band. Here, have a look-see: At this point I'm thoroughly confounded, not to mention discombobulated. I haven't had much luck turning up anything that explains what's going on. I'm hoping someone here can shed some light. I'd been hoping to correct the problem with a minimum of fuss so I could flush the coolant system and replenish it with the genuine Porsche coolant I bought from Pelican. (Sure, it was a bit more than Prestone or Zerex, but what's a few bucks?) But noooooo. Ah, the trials and tribulations of a gearhead.

Spitballing here. Is that one of the condensate drains from the heater box? Do you smell coolant inside the car? If so, maybe you are looking at a failed heater core, or something of that nature? If you can get a pressure tester on the system, so you can pressurize it without the engine running, maybe you could listen your way to the root cause.

Check the water pump

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I replaced the water pump and thermostat back in February. When the old water pump leaked it was at the engine, about six feet further back. The mysterious leak from the fitting I described is a foot or so behind the front wheels. That's why I suspected an intermediate coolant hose that snakes back to the engine from one of the front radiators. Appreciate the comeback, though.

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This sounds likely:

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It's below the passenger footwell, sort of, but more toward the middle, under the right side of the center console. I lost a lot of coolant, enough to overheat rather suddenly. Does that sound like an HVAC issue?

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Picture your heater core sitting right behind the battery with coolant flowing through it continually (there is no coolant valve to shut off the heater.) The heater core is in a plastic 'box' with a drain at the bottom. The drain connects to a tube that goes down the front of the right footwell and through the floor near the center to drain under the car. Here's a HVAC system removed from a 2001. The tubes facing forward are where the heater hoses connect. You can probably pinch the two hoses off (behind the battery) to diagnose if the heater core is the problem. If they are clamped shut and the leak stops you found the problem. I have had to replace heater cores in an '04 and '99.

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I plan to follow your suggestion and pinch off the hoses to confirm the heater core as the problem. In the meantime I've been consulting my Bentley service manual and watching YouTube videos showing how to replace the heater core. Seems fairly straightforward. (I've seen a lot worse, like having to disassemble the entire dash to get to the heater core.) One thing's giving me pause. Seems like most of the folks with heater core leaks report considerable moisture, from dampness to soaking wet, in the interior carpet. The carpet on mine is as dry as a proverbial bone. But pinching the hoses should tell the tale, right? Thanks for the helpful info.

The way I see it is two types of fluid can come out that drain from the HVAC; water from condensation with the AC running or coolant from the heater core leaking. If it is not leaking from the HVAC drain, in the front of the car, there are three types of coolant lines. Big -main coolant to and from the radiators. Medium -heater hoses. Small -radiator bleed lines attached to the top corner of each radiator. That's all else there is.

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Many of those lines are exposed now. Before I tear into it I'm going to put some more water in it and run a more extended test. If there's a leak source besides the HVAC drain, I'll find it. I hope.

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Pretty good spitballing, Tom. You were first to call it with a failed heater core. Some pretty sharp cookies on this board.

You can get a coolant system pressure test kit at Harbor freight for around $100.00. The adapter fits on the coolant fill tank neck. No need to run the engine to apply pressure to the system. It would be very helpful for your situation.

LoneWolf, you can "borrow" a coolant pressure tester at Autozone and pressurize the system without running the engine.. Out of curiosity, you mentioned that you can remove the entire HVAC system without removing the dash? If this is correct, it sounds way easier than removing the entire dash.. Also, instead of pinching the two HVAC hoses off, you may want to 'connect them with each other' to bypass the HVAC core entirely and keep the flow of coolant. Good luck with your project! .

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I can't speak to removing the entire HVAC system, but replacing the heater core is a piece of cake. Once the cowl, wipers, and a few other minor things are removed the core is easily accessible from under the hood, behind the battery. It just drops in like a fat piece of bread in a toaster. It wasn't anywhere near as easy on a Pontiac, when I had to disassemble the dash to get to the heater core. Good suggestion about borrowing a pressure tester from Autozone, although I wouldn't mind having one of my own. Can't have too many tools. I just bought a new torque wrench, and it's a thing of beauty. Thanks for the suggestions.

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Blue, you talked me into it. I just ordered a kit of my own, this one: https://www.amazon.com/dp/B0BYJTZHJ2 I liked it better than Harbor Freight's. It will be here Wednesday. Thank you for your influential contribution.

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One can never have enough "quality" tools. I have also used the coolant pressure tester to "force bleed" brakes. I just have to watch the brake fluid level in the master cylinder reservoir so it doesn't get to low before topping up.

Remember, it's not a project unless you have to buy a new tool.

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Or scrape your knuckles!

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