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!

+1 to the water pump. Same thing happened to my BMW.

Replace the water pump, thermostat, and accessory belt (and pulleys if necessary) while the car is in the shop. Good idea to replace the AOS and coolant expansion tank at the same time.

Well......my guess is the hoses (20 year old hoses). But I'll report back after it goes in tomorrow.

Well.....for everyone that said it was the water pump that was the cause of the leak YOU WIN! (and I lose). My shop is installing a new water pump, thermostate and belt and I should have it back tomorrow. The cost quoted is $1350 out the door. I'm not sure if that's high, low or average for the Chicago area but it seems OK to me. My 20 year old 98' with 86,000 miles is my "fun summer car" and since it hasn't ever been maintenace "hog" I'll fix her up and drive on........

a water pump kit is around $350.00 I believe it includes a new belt and t-stat.
So your paying around $1000.00 for labor. If your fine with that more power.to you!
But that $1000.00 is why I always do my own work;)

3 hour job, tops, for a mechanic who knows what he's doing.

I'm not a mechanic. I replaced my water pump. Once. I could do it again in less than 3 hours.

I'd be finding another mechanic. One who doesn't take advantage of the unsuspecting.

If you were in SoCal I'd do it for you for free.

Best wishes.

If that includes a full flushing of the coolant, that sounds about right. Make sure the shop is using original Porsche or VW/Audi coolant.

Yes, that also includes a complete flushing of the system and replacement of Porsche OEM coolant. I was told the filling process is very specific and proceedural to get it right. While I'm sure that if one wants to tackle it themselves they'd "save money"...assuming you have the tools, equipment, knowlege and desire.....I don't. I also accept the fact that IF I use a professional shop, they deserve to make a profit.

I save money by doing the things I can do myself, (grass cutting, landscaping, house painting, deck work, etc etc)........so I have the $$$ to pay others to be "grease monkey's"...lol.....but thanks for the feedback.

Hey Rob175,
Nothing wrong with paying someone else to do work you can't or don't want to do.
That's what keeps the economy going. I just like to do car work myself because I can.
The money I save I just gets spent on something else;)

Boom! I'm with ya.

Helps that wrenching, for me, is a hobby and stress reliever.

I'll pay the yard guy to cut grass, trim, blow... as I find zero satisfaction is doing that job. Unless absolutely necessary, I'm not paying anyone $100-$150 an hour to work on a 20+ year old car that's worth hardly anything.

$1350 for WP, thermo, and coolant flush? LOL. **************** that.

$15 an hour to schlep around the yard? Yeah, I'll pay that. ;)

I wish I had the ability, tools and facility to do some DIY work but I just don't.....and I don't have anyone to to ask for help. If you do, you're lucky!

It's all good. Each of us has different strengths and abilities. I'm sure some of us pay lots of money for something you can easily do. Like Blue62 said, that's what keeps the economy going.

The important thing is that you still enjoy the car, and if it's worth it to you to have someone wrench it, go right ahead. No judgement here!
:cheers:

Well said, Piper.

+1

I am a DYI owner on the stuff I can do. I’ve replaced the air filter, cabin filter, oxygen sensor, ignition switch, dash speakers and window switches..... so I DO do some work myself. I have an Indy do my Mobile 1 oil and filter changes ($105)...... I seldom spend more than that each year. (I only out about 4,000 miles a year on the car and never drive it in the winter).

OK.....water pump has been replaced so the obvious leaks in front of the rear wheel on the passenger side are no longer........BUT......

I now have some very small coolant drops (at engine cool-down) appearing behind the rear passenger wheel with a few drops where the bumper cover screw is located (the one closest to the passenger rear tire). I pulled the truck lining up and the lining along with the truck floor is bone dry BUT THEN I realized that there is what looks like a "black masonite material" that creates a sub-floor which is raised up from the steel body. After removing the section of "sub-flooring closest to the coolant holding tank there is a very small amount of the newest bright yellow coolant that I soaked up with paper towels. I've NEVER had a leak under that portion of the car and there really wasn't very much....AND it was the yellow colored coolant my mechanic used to refill the system after he drained (the old coolant was more greenish)....so I know it's the new stuff used for the new water pump2 weeks ago.

I wiped the tank and the connecting hoses with paper towel and the towel was dry.....only the metal trunk floor had a little bit of coolant, which as I said, I dried up with paper towel.....

So here's my question, since I've never before had any sort of drops coming from the rear bumper cover area and know its the NEW yellow coolant added 2 weeks ago during the water pump install job (complete coolant flush and fill), and all sides of the tank and hoses are dry, could it just be a coincidence or could it somehow be related to the water pump install? (overfill, sloshing around in the tank, etc)......where does the tank overflow to?

Any thoughts?

Obviously, I plan on driving the car in the next day or two and then once again checking for any additional coolant in the trunk again.

I'm guessing it burped... maybe some air in the system, or too much coolant.

We're you running it hot and hard before you shut it off/down? I believe the recommendation is to, after running the engine hard, is to let it idle for a couple of minutes in the driveway... then shut 'er down.

Wiser minds?

I suppose....but IF it "burped" or it was overfilled I would assume it would flow out of the overflow tube (IF there is such a tube) and not deposit a little bit in the trunk.
As I wrote it just seems too coincidental to the water pump replacement 10 days earlier.

I guess I'll remove the trunk carpet and sub-floor after I drive it next and inspect it again.

Check the dimple in the middle of the underside of the coolant tank. That was where mine had a crack and the coolant was seeping out into the trunk. The coolant was then leaking around the rubber plug in the trunk floor eventually ending up in the same location you described above.

If it was me I would leave the carpet and sub floor out for a number of drives and check it each time I drove it. Then I would know for sure. Also there is a wire loop on top the coolant tank it is a bleeder valve there is a gasket under it which can go bad and cause some coolant weeping. Or the service tech could have just spilled a little around the top of the tank and it found its way to the ground.

Thanks for the suggestion.....I removed the carpet, drove it all day, stopping several times to check the trunk. It took about 3 trunk checks before the leak once again showed up. I drove it to my "indy" Porsche guys and sure enough the bottom far corner of the tank (seen with an inspection mirror) has what looks like stress cracks (btw, the plastic tank is very dark brownish/yellow). These cracks appear to be dripping coolant once the coolant gets hot and the system gets pressurized. It holds the coolant for awhile than just "spits" it out all at once, then pressure goes down a bit, the coolant stops leaking from the cracks, until the pressure builds up once again and it "spits" again.....and the process just keeps repeating. That's why it sometimes appears that the leak is gone in between clean-ups.

So.....it goes to the shop tomorrow for a "genuine" Porsche coolant tank replacement. Between the new water pump replacement 2 weeks ago and a coolant tank replacement this week i'm "tapped out". My 1998 Boxster has never cost me as much as it has in the last few weeks. Hopefully it won't need anything else for this driving season. I can't really complain because the car has barely cost me anything over the 15 years that I've owned it, except for the usual maintenance, tires, brakes, oil changes, battery, etc etc.

Before anyone suggests I perform the work myself, don't bother. I have no way to lift the car, nobody to assist and limited space and expertise to attack it so I "pay the piper"....LOL