Disappearing coolant leak?
 

Very strange....... I have been experiencing several small drops of coolant under the right rear end of my 98 Boxster (next to the rear wheel) after I shut down and the car begins to cool down. The reservoir is not leaking and the trunk is dry with zero signs of any kind of moisture. So, I suspected the hoses or the water pump but was procrastinating because I didn't want to spend the money until later in the season............well suddenly, the last 4-5 times I've driven it there have been ZERO coolant drips upon cool down! The reservoir is still filled to its proper level and the trunk is still dry as a bone. So, did it suddenly "fix itself"?

Any ideas or thoughts would be helpful.

What's the coolant cap version?
 

I am not very experienced mechanic, so please take it with grain of salt. My guess will be following

The drips you see could also be from overflow means when there was access pressure in the tank some of the coolant was overflowing.

Another thing is probably the coolant temp is not going as high as before may be better traffic, lower environment temp?

Check coolant cap version if it is not latest, replace the cap

Yes, that is where the overflow/relief valve is. What you’re seeing is not unusual, especially on warmer days. Just look out for bigger leaks. ;)

You might also replace the reservoir cap, when you stop the car, the temperature and pressure will spike, because the coolant is no longer circulating. If the cap is marginal it might let a bit of coolant out. My cap (only three years old!) started doing that recently, so I replaced it an it appears to have solved the problem. My cap was an actual Porsche part that was the latest part number, but it still was starting to fail.

I'll double check the cap, but I did replace it 3 yrs ago, so I would think it's still good. Thanks.

I just noticed that the coolant leak by the rear wheel has stopped....... a new issue was discovered...... today I notice more coolant on the ground further forward under the car in towards the middle of the car forward of the engine.
Last night while driving it was getting a bit cool outside but rather than raising the top I just turned up the heat and blower motor, drove home and parked in the garage. The inside of the car is dry and there is no smell of coolant. The reservoir was at a normal level, the heater worked fine (but I can’t recall the last time I used heat since it only a summer car)
So, any more ideas?...... I’ll be taking the car out later today for a drive and I plan on checking underneath in the morning to see IF anymore coolant is under it.

Are you sure it isn't water dripping from the A/C evaporator?

Yep.... slippery, colored and I haven’t used the AC in months. But thanks.

If it’s further forward than before and more in the center, check your water pump.

So freaking strange.......so today I took it out for a 100 miles drive, parked it in the garage, let it cool down for 6 hours.....and now ZERO LEAKS....ZERO!
I'm out of ideas....except "it fixed itself".

Take the front engine access panel off and look for residual spots indicating a water leak. If your water pump is on it's last legs and it stops working, you may overheat and cause the head to warp

Well... I spoke to soon. I guess 6 hours of cool down wasn’t enough. I woke up this morning, looked under the car and found a small amount of coolant under the car again. It’s far forward of the engine area. It’s almost directly under the very center of the car.... sort of under the gear shifter, if you were to measure.

So I guess the only alternative is to bring it in.

That area is where the evaporator drain exits the body of the car. By any chance do you have the temperature set to auto with the snowflake showing.

If not, I'd suspect a coolant line is leaking. Unfortunately, I don't recall the exact routing of the lines that link the radiators to the engine so it's unclear if you'd see coolant on the ground where you suspect its coming from.

Actually I did turn on the AC while driving yesterday but only for about 3-4 minutes mainly out of curiosity to see that it could still blow cold air. (I seldom if ever use the AC) but once I could tell it was working I turned off the AC and continued to drive for about another 30 min. and maybe another 15 miles.
I think it’s strange that nothing leaked for more than 6 hours after parking the car. It wasn’t until this morning, a full 10-12 hours later, that a small amount of coolant was under the car. Also, I don’t get it why coolant would relate to running the AC anyway, since the AC uses refrigerants not anti-freeze. On the other hand the heater, I believe, does pass air through the heater core to blow hot air..... but not cold.

Mystery still prevails I guess.......a question I have is why it doesn’t leak until the car is totally cooled down. I would think I’d be leaving spots of coolant all the time.

In part, the issue is where is the leak occurring. If it's in the middle of the car, between the front and back wheels, there are three possibilities. One is water from the evaporator draining after A/C use. The others are a leak in the heater core or hoses that finds its way out of the car possibility where the evaporator drain tube passes through the body or a leak in the coolant tubes that circulates coolant between the engine and radiators.

If the stuff on the floor is coolant, which you think it is, then the last two items are possibilities.

Thanks Thom...since it IS coolant (I can verify that) are the last two possibilities you mention costly to fix?.... just curious. (Lol.... most things on this car are costly to fix.... lol)

If its the external hoses - probably not costly of you can do the work yourself. Replace parts and refill the system with coolant, which can be a pain.

If its the heater core, then it could be really expensive if you have to take out the dash to get to the core or its hoses. There may be a back door way to avoid disassembling the dash. Look for some threads where people to reseal re-foam the control flaps without removing the dash unit. These threads usually mention black pieces coming out the vents

Thanks again. I just took the car out for a drive again, got about two blocks away and the “low coolant” light on the dash began blinking so I drove right back and added 2/3’s of a cup of 50/50 to the tank in the trunk to raise the level for the sensor. Drove out again, made a few errands and returned. I placed a large cardboard sheet under the car ....... after 5 hours of sitting..... not one drip!
I would think that it would start losing coolant since it obviously did that yesterday (thus the low coolant level light today on the first ride).

My thinking is that IF it’s going to leak it would be leaking all the time especially when it’s pressurized and hot.

Enough is enough....Monday it goes to my Porsche indi guy for diagnosis and repair.....hopefully my 98' w/86,000 miles won't cost me an arm and a leg!....maybe just "an arm".......
I can confirm that the dripping is coming from the engine area as opposed to the front or middle, so it's NOT the heater core or radiators or the lines running to the rear. So, my "uneducated guess" is a hose or connection. To my knowlege, the hoses are either original (20 yrs old) or at least 16 yrs old, because that's how long I've owned it. I don't know the symptoms of a failing water pump other than possbly overheating, which I'm not experiencing, so my hope is that it's jsut a hose, clamp or other connection.

It's the water pump. The reason you don't see a leak when it's hot is because the coolant is evaporating due to the heat. When it cools off it doesn't evaporate and you see the puddle. My water pump leaked for a while before it went out but I never saw a leak, but there was evidence in the engine compartment that it had in fact leaked.
Good Luck!