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Old 05-29-2017, 06:39 PM   #1
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Coolant tank leaking only when driven hard

Hey everyone,

I know this cracked coolant tank issue has been beaten to death but I'm having a difficult time finding any information on leaks that are present only when driving the car fairly aggressively

I've been trying to figure out where this tank is leaking and I just cannot pin it down so I started running tests.

If you drive the car basically like grandma would drive it I don't see evidence of any leak at all however if you drive the car aggressively there is evidence of spray in the trunk like it's just spewing out somewhere

Is this typical of a crack? I know that most of these cracks form behind the unit where you can't see but the spray pattern is in the main trunk compartment


Any thoughts?


Last edited by michael_J_brown; 05-30-2017 at 06:03 PM.
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Old 05-29-2017, 06:52 PM   #2
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If you are just getting steam around the cap, and on the trunk lid above the cap, replace the cap, it is a common point of failure. I would also ensure that the coolant tank is not overfilled. If it is not just steam, look for white residue around the coolant tank, the OEM fluid leaves it behind to help identify leaks. Also try reaching under the carpet near the tank to see if it is wet.
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Old 05-29-2017, 07:09 PM   #3
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There is also a seal under the vent valve(the one with the s/s wire bail on it) .That could leak?
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Originally Posted by rick3000 View Post
If you are just getting steam around the cap, and on the trunk lid above the cap, replace the cap, it is a common point of failure. I would also ensure that the coolant tank is not overfilled. If it is not just steam, look for white residue around the coolant tank, the OEM fluid leaves it behind to help identify leaks. Also try reaching under the carpet near the tank to see if it is wet.
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Old 05-29-2017, 07:24 PM   #4
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Around post #63 of this thread might help, but you should really read the whole story from the start:
http://986forum.com/forums/general-discussions/59015-1st-boxster-7th-porsche-we-now-have-4-family.html
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Old 05-30-2017, 06:14 PM   #5
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So weird

I drove the car to work today (about 10 miles each way) with the A/C running. I've removed the carpet and foam trunk liner and placed a towel under the coolant tank. I was very gentle and as far as I can tell not a drop of coolant leaked in the trunk or on the towel.

If I drive the car aggressively and rev the engine is when I experience coolant loss. It's obviously a pressure issue and I'm really wondering if a seal has failed. I checked the coolant cap and removed the plastic shroud that's at the top of the coolant tank and there are no signs of a leak.

When the leak happens I can't locate coolant on the back of the tank either so I'm not sure the tank has cracked on the back.

Is there a seal at the bottom of the tank?

I just hate to go through the expense and time of replacing the entire coolant tank if it's not necessary.
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Old 05-31-2017, 06:00 AM   #6
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Quote:
Originally Posted by michael_J_brown View Post
I drove the car to work today (about 10 miles each way) with the A/C running. I've removed the carpet and foam trunk liner and placed a towel under the coolant tank. I was very gentle and as far as I can tell not a drop of coolant leaked in the trunk or on the towel.

If I drive the car aggressively and rev the engine is when I experience coolant loss. It's obviously a pressure issue and I'm really wondering if a seal has failed. I checked the coolant cap and removed the plastic shroud that's at the top of the coolant tank and there are no signs of a leak.

When the leak happens I can't locate coolant on the back of the tank either so I'm not sure the tank has cracked on the back.

Is there a seal at the bottom of the tank?

I just hate to go through the expense and time of replacing the entire coolant tank if it's not necessary.
Then pressure test it, that will tell you if it is tight or not in about 15min.
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Old 05-31-2017, 06:44 AM   #7
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The coolant bleeder valve can sometimes cause problems, either by cracking or just due to worn o-rings underneath.
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Old 05-31-2017, 09:46 AM   #8
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The worst case would be a blocked coolant passage in the engine, causing a hot-spot and steam. Hope it's not that. I'm pretty sure that's the case with one of my engines that had a water pump impeller come apart. Easy driving, no problem. Hard driving on it loses coolant. Tank was replaced air purged, and leak checked. At least in my case, I never liked that engine anyway.
Do the pressure test as JFP suggested. That way, you will know if it is a true leak or an over-pressure problem.
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Old 05-31-2017, 10:07 AM   #9
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Tank Will Fail

If your Boxster has more than 75,000 miles on it, I'd recommend changing the tank, it is not the easiest replacement to undertake but it is well worth the effort. The tank will fail eventually. Besides the coolant in your trunk and carpet, look at the color of the tank, if it's yellow it is on its way out. You'll see your new tank will be bright white. I had the same indications, many times the level would be fine, then I'd have periods when I'd have to top off weekly then it got worse and I had a coolant in my trunk. Get a ring clamp extension tool, order a new tank and some coolant from Pelican, get a six pack of beer (German of course you'll need it when your done) and a buddy, do some stretching and replace the tank. Then every time you open your trunk and see a nice new tank and pink coolant at the perfect level you'll get the satisfaction of a job well done.
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Old 06-21-2017, 03:22 AM   #10
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Poor quality coolant tanks

My 2000 Boxster S has 104k miles on it and it's in the shop today for a pressure test. If it's the tank, it will be the third time it will be replaced. Is there a good replacement part? I've been using Porsche parts, and this is getting quite expensive. This is crazy, I've never had to replace a overflow tank on a vehicle before, caps yes, but not tanks.
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Old 06-21-2017, 05:52 AM   #11
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Originally Posted by 78F350 View Post
Around post #63 of this thread might help, but you should really read the whole story from the start:
I read your post #63 and it is very interesting!

On my car the water pump got replaced a couple of months ago and recently I noticed that the water level was over the max level (Cayman), and yesterday moved the clip on the bleeder valve to the upper position as I may have an air pocket on the system, so I will drive it like this for a couple of days.

My car has a bit over 99k and was thinking that perhaps may be a good time to replace the entire valve assembly and not just the seal.

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Last edited by Gilles; 06-21-2017 at 05:56 AM. Reason: keep trying to write proper English...
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Old 06-23-2017, 04:33 AM   #12
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The valve opens and closes while driving under pressure. Keeping it UP for a few days allows the air trapped to move up into that tank. Parking the car rear end high is helpful. It's a big loooong system that needs time to burp.

You need to know if there is a thermostat in there. It slows the flow of coolant down so it can shed the heat to the air. No therm can equal overheating when revs are high.

Have you cleaned in front of the rads between the AC condenser and the rads??
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Old 06-25-2017, 06:37 PM   #13
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The valve opens and closes while driving under pressure. Keeping it UP for a few days allows the air trapped to move up into that tank. Parking the car rear end high is helpful. It's a big loooong system that needs time to burp.

You need to know if there is a thermostat in there. It slows the flow of coolant down so it can shed the heat to the air. No therm can equal overheating when revs are high.

Have you cleaned in front of the rads between the AC condenser and the rads??
"On my car the water pump got replaced a couple of months ago and recently I noticed that the water level was over the max level (Cayman), and yesterday moved the clip on the bleeder valve to the upper position as I may have an air pocket on the system, so I will drive it like this for a couple of days."

Update:

Well, I left the valve open for three days and the water still reminded at the same level (over the max level..) in other words didn't help to burp the air pocket.

Yesterday, I decided to run the engine a little harder for a while (since I live in the densely SoCal area, I ran in the freeway in 4th gear at about 4500-5500rpm for about 1/2 hour) but this time I moved the heater lever to the 'Max' position with the windows open as the outside temp was almost 90 degrees.. since I left the engine cover off (Cayman) you can imagine the noise and the heat inside the cabin and when I made it back home I noticed that even if you moved the lever to the closed position the valve was left open (no difference with the clip up or down) and this morning, after letting the car cool overnight I checked the coolant level and it was back between the Min and Max tabs (the way it's supposed to be)… Running the engine at higher rpm's with the heater fully open did the trick.. :-) I am happy that it's back to where it's supposed to be :-)

PS: Another thing that got my attention while running without the engine cover was the fact that the engine gets much louder as soon as you close the throttle and Not during hard acceleration (I have the IPB intake plenum with the GT3 throttle body), the sudden noise reminded me of the turbocharged engines that suddenly close the over boost valve..

.


Last edited by Gilles; 06-25-2017 at 06:43 PM.
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