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Coolant Tank Replacement
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Pelican Technical Article:

Coolant Tank Replacement


4 hrs





Applicable Models:

Porsche 986 Boxster (1997-04)
Porsche 986 Boxster S (2000-04)
Porsche 987 Boxster (2005-08)
Porsche 987 Boxster S (2005-08)

Parts Required:

Coolant tank, level sensor, coolant tank cap, coolant

Hot Tip:

Replace the tank when you have the transmission out

Performance Gain:

No more coolant in the trunk

Complementary Modification:

Replace coolant level sensor, clutch replacement
101 Performance Projects for Your Porsche Boxster

This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your Porsche Boxster. The book contains 312 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 950+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website for more details.

The replacement of the Boxster coolant tank is probably one of the top ten jobs that typically need to be done on an older Boxster. The coolant tank is one of the worst designs I have seen ever come out of an automotive company. Six separate coolant hoses feed into the tank, with three of them internal to the tank mechanism itself. The hoses from the tank feed into an integrated manifold on the engine bulkhead that is manufactured out of plastic and is prone to breaking. In addition, the plastic tank itself often cracks with age and leaks coolant in the trunk compartment. Porsche had redesigned this part several times over the past decade, and to this day, there are still problems with the tanks.

When should you replace your tank? If your tank is looking old or yellow, or if you are finding a pool of coolant in your trunk area, then it's probably time to replace your tank. Lift up the carpet in the rear of your trunk to check. I also recommend replacing the coolant tank when it's really old, particularly if you have your transmission out for a clutch job. The hoses inside the engine compartment can be difficult to reach, and having the transmission out of the car makes a very difficult job a lot easier.

If you are losing coolant from your engine, and you're not sure where it's going, then you can perform a few relatively simple tests to check. First, get an air pressure adapter that will allow you to hook up a shop compressor to your coolant tank cap. Then, pressurize the system to about 13-15 psi. Let it sit and see if you can hear or see any coolant escaping. If the coolant is getting past the head gasket into the crankcase, it will mix with the oil, and you will be able to see that easily when you empty the oil (Figure 1). If the head gasket is leaking coolant into the cylinders, then they will begin to fill up with coolant, and you can see this when you remove the spark plugs.

The first step in replacing the tank is to drain the coolant. I recommend replacing all of the coolant if you are swapping out the tank: refer to Project 29 for complete instructions on how to empty the coolant from the car.

The most difficult part of this project is the disconnection of the existing hoses from the back of the radiator tank manifold. With the car completely assembled, it can be very difficult to reach these hoses. It is possible to reach them from inside the engine compartment, but you may not be able to get tools onto the clamps that hold the hoses. It's also possible to reach them from below, but you need to remove the lower suspension support bars and the transmission cover plate (see Pelican Technical Article: Changing Automatic Transmission Fluid). Photo 2 shows the hoses that you need to disconnect from the engine compartment side of the radiator tank.

Once the hoses are disconnected, move to the rear trunk, pull back the carpet and flooring that surrounds the coolant reservoir. Remove the electrical sender plug in the bottom of the tank, and gently pull out the dipstick tube from the top of the coolant tank. Four screws hold the tank to the chassis: remove them as shown in Figure 4. Remove the oil cap and coolant tank caps. You should be able to remove the tank at this point from the car.

With the tank out of the car, transfer the coolant level sender, the large top tank seal, the bulkhead manifold / oil filler, and the three right-angle hoses to the new tank (or install new ones if you wish to replace everything with new parts). Don't reuse the spring-type clamps: use new ones or clamp-style hose clamps instead. Installation is pretty much the opposite of removal. With everything back in place, refill and bleed your cooling system as per the instructions in Pelican Technical Article: Coolant Tank Replacement.

Shown here is the lower engine sump plate removed from an engine where coolant and oil mixed heavily.
Figure 1

Shown here is the lower engine sump plate removed from an engine where coolant and oil mixed heavily. The oil will turn a light brownish color with streaks of light brown running through it. If you see this or anything similar to this when you empty your oil, then you most likely have a head gasket leak that needs to be addressed right away. When coolant mixes with engine oil in this fashion, the oil looses its ability to function as a lubricant for the engine bearings, and you can damage the crankshaft and rods.

Here's the best photo I could take of the hoses in the engine compartment.
Figure 2

Here's the best photo I could take of the hoses in the engine compartment. They are so difficult to reach that it's even very difficult to get a good accurate photo of them. This photo was taken with the transmission out of the car, which is indeed the best time to replace the coolant tank. The arrows point to the hoses that need to be disconnected: Oil filler hose (orange), Oil cooler hose (green), Radiator vent hose (blue), Coolant filler hose (yellow), Coolant overflow hose (shown removed, mates to the nipple shown by the red arrow). The lower left inset photo shows the coolant level sensor unplugged. The lower right inset photo shows the top of the tank.

If you're having difficulty reaching some of the hoses from underneath, you may be able to gain some additional access by pulling out the tank and loosening the hose clamps through the rear trunk compartment.
Figure 3

If you're having difficulty reaching some of the hoses from underneath, you may be able to gain some additional access by pulling out the tank and loosening the hose clamps through the rear trunk compartment. For this photo, I was able to first disconnect the filler hose, and then I had enough room to pull the tank out to reach some of the other hoses. You can also push the DME wire harness grommet into the engine compartment and gain some additional access that way (see Photo 5 of Pelican Technical Article: Engine Drop / Removal).

Shown here are the screws that attach the coolant tank to the chassis.
Figure 4

Shown here are the screws that attach the coolant tank to the chassis. The blue arrows point to the nuts that hold the plastic manifold to the chassis. The yellow arrow points to the coolant sensor. The green arrow shows another mounting point for the bottom of the tank. In the inset photo, the red arrow points to a bolt that holds the top of the tank to the chassis, and the purple arrow shows the oil dipstick tube pulled away from the top of the tank housing.

Shown here is the new tank, along with a brand new coolant level sender and a new expansion tank cap.
Figure 5

Shown here is the new tank, along with a brand new coolant level sender and a new expansion tank cap.

The oil filler tube / bulkhead manifold is one of the goofiest designs I've seen in a long time.
Figure 6

The oil filler tube / bulkhead manifold is one of the goofiest designs I've seen in a long time. On our project car, just as we started up the 3.4 engine transplant, coolant started spilling all over the place from a broken plastic nipple on this manifold. After staring at the puddle on the ground for several minutes I "fixed" the design of the manifold and simply cut a hole in the manifold and ran a hose directly from the engine compartment to the bottom of the tank. This was designed to be a temporary fix until I was able to replace the entire piece, but frankly, it's worked flawlessly and is still installed in this configuration today.

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Comments and Suggestions:
Red Comments: The coolant light on the dash went on yesterday. I added distilled water and started driving. While driving I noticed a rattling sound from the engine area probably the water pump, but I didn't know that at the time. When I get to work, puddle of coolant near rear right wheel.

The sound seems to indicate the water pump needs replacement, but the puddle is right near the tank in the trunk. Would the tank leak cause rattling noises from the water pump? Or would a water pump failure lead to a puddle near the tank?

Car is at work, so can't jack it up to diagnose. I'm trying to determine whether it's safe to drive home 5mi or if I need a tow.
August 23, 2016
  Followup from the Pelican Staff: The tank would not cause a rattle, well unless it broke free and is moving around. Easy to check, is it secure?

Water pump is the most likely cause. - Nick at Pelican Parts
Jed Comments: While a bit more difficult to work with, spring type clamps apply even pressure around the connection. Using screw clamps is likely to break the plastic nipples and/or leak from uneven pressure around the connection down the road. There was a time when I always tossed spring-type clamps for screw clamps, but I have learned my lesson. There is a specific tool for spring clamp removal in hard to reach locations.
July 28, 2016
  Followup from the Pelican Staff: Love that tool, have had one for years. Thanks for the tip. - Nick at Pelican Parts  
philipjadler Comments: I do have another question on this, what tools do I use to cut the hole for the oil dip-stick tube?
April 11, 2016
  Followup from the Pelican Staff: A drill bit of the correct size. - Nick at Pelican Parts  
philipjadler Comments: Any chance of siphoning out the coolant from the tank and the clipping the manifold hoses? I've got a really small/slow leak, the hoses look great and the coolant looks clean. Would I then save the step of having to bleed the system, and then bringing the pressure back up?
March 30, 2016
  Followup from the Pelican Staff: Yes, you can save some time. You will still want to perform the top up and bleed procedure. Also, be care clamping the hoses, if they are old, they may fail shortly after. - Nick at Pelican Parts  
Roman986 Comments: I have a cracked coolant tank and i noticed yellow powder on the exhaust muffler body.coolant water on tank is clear and engine oil is also clearnone intermixIt is possible that coolant water is draining on the exhaust body?Or it is a problem with engine?
March 24, 2016
  Followup from the Pelican Staff: It is possible you have a head gasket issue.

I would pressure test the cooling system. If the system will not hold pressure and there are no external leaks the head gasket may be faulty. - Nick at Pelican Parts
owl Comments: Problem: The oil filler tube separated at the beginning of the flex section while replacing my coolant tank. Is there a way to fix this with tape or something similar, or is there too much pressure that I need to replace the whole tube? I already had a very difficult time getting to any of the hoses/tubing in the engine compartment and would probably pay a mechanic to do it, which I would guess would be a several hour job. We barely had clearance to wipe the broken section with rubbing alcohol and then apply gorilla tape for a temporary fix.

Longer version: Had a broken water pump bad pulley that possibly caused a leak to the coolant tank. I had no coolant leaks or anything prior to the wobbling pulley, which also broke the accessory belt.

We replaced the water pump and thermostat in the morning. We filled the coolant and found there to be a leak in the trunk water pump and thermostat were fine with no leaks. We decided to replace the coolant tank. After some work, we finally got everything installed, but we found that the flex tubing for the oil separated we initially though it just separated and need to be reattached.

Is this piece fragile and does it break often? Is there way to repair without replacing? picture attached

Thank you.
September 5, 2015
  Followup from the Pelican Staff: No, you will have to replace the tube.

Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
dougler986 Comments: Hi - I've got a very slight leak from the top of the 3 flexible hoses connecting to the tank. Until it's removed, we won't know if it needs a new hose or whether there's actually a crack in the tank - but what we do know, is that when we apply pressure to the clip at the top of the top hose - the leaking stops.

So, i'm going to attempt to replace just the clip first, and see whether that works.

In trying to find the very specific part required, i found this, which I think would be really useful for anybody looking to understand precisely which part is required.


August 18, 2014
  Followup from the Pelican Staff: If applying pressure to the hose stops the leak, I bet the hose is the issue. Thanks for the link. - Nick at Pelican Parts  
TheRebl Comments: While checking the water level in my 1999 boxster I noticed something floating on top of the water. It appears to be an internal plastic part that somehow dislodged and it is to big to fish out of the hole where the tank cap goes. The car is not overheating and I am not losing water anywhere, any idea of what is floating around in my coolant tank??
June 7, 2014
  Followup from the Pelican Staff: Could be a piece of the water pump impeller. C - Nick at Pelican Parts  
racecardriver Comments: Hi guys, I was just as confuddled confused and befuddled about this water coolant reservoir tank as all of you. I could not understand the clamping issue inside the trunk and on the other side clamped in the engine compartment with the 'goofy' plastic connectors in between the trunck / engine. However all of the info is really helpful and even though I have a Boxster manual, there is way too much disassembly to get at way to little. I finally found a nice diagram of all of the connections / clamps to make all of this more readily understood.

This might link work to connect to the picture on whole assembly overview.
May 31, 2014
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
SCD Comments: Coolant System Leak: I need help - had an intermittent leak - the local garage in MA replaced the reservoir said it was cracked drove the '98 convertible to its new home in Sunny Florida at Thanksgiving - all is well. Wife calls me back in Massachusetts, coolant leaked out, she filled tank, was gone by the time she got to new garage we are using. Car sat for a day, mechanic filled coolant, ripped bottom of vehicle panels to look, pressured system - NO LEAKS. Help - catastrophic leak from under engine one day - no leak and no loss during pressure test two days later - Guy even checked water pump after running up to temperature, etc.. - any ideas???? Thank YOu
January 31, 2014
  Followup from the Pelican Staff: If you are unable to find an external leak it may be a head gasket. I would pressure test the cooling system, if the system does not hold pressure and there are no external leaks, suspect the ehad gasket. - Nick at Pelican Parts  
markmalin Comments: Wayne, I ordered a new tank and there is no hole for the oil dipstick...but my car's current tank has a dipstick. Do I just punch a hole in the new one for the dipstick tube?
January 24, 2014
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799. They can ake sure you received the right part. - Nick at Pelican Parts  
Rob Comments: We're converting a 986 to an auto-x and track day car. Is there any reason why we shouldn't just make up a pipe fitting manifold and use an aftermarket aluminum header tank mounted on the rear bulkhead of the engine compartment?

I've ordered your book!

July 23, 2013
  Followup from the Pelican Staff: As long as the capacity and routing are OK, it should work fine. It might take some experimenting to get it right, but shouldn't be too bad. - Nick at Pelican Parts  
force44g Comments: A tip to make this change easier is that once you have one or two of the coolant pipes disconnected from the engine bay side there will be some play in the others.

You can have one person pull the tank away from the bulkhead. It will give by ~1", which is just enough to get some pliers in the gap to undo the remaining hose clips from the boot/rear trunk.

On refitting the same applies - i.e. the first hose or two you can get connected from the boot/trunk side before the others have to be done from the engine bay side.

Also, if you raise or cap off the bleed valve then you disconnect it you'll only loose the tank coolant and not have to refill the whole system. This reduces the final bleeding of the system time by quite a lot.
July 15, 2013
  Followup from the Pelican Staff: Thanks for helping our readers - Nick at Pelican Parts  
Tommy Comments: hi Wayne..long time follower, 4 years with my boxster 986. 2 years ago I replaced the tank, following these instructions. Difficult, but not impossible : While driveing the other day, the boxster overheated..BADLY. The temp shot up to the peg and I continued to drive, not noticing it. Than I smelled oil. Than I pulled over! Just as I was pulling off the road, the engine made a clunk clunk clunk sound and died. towed car home. Turns out the oil got so hot that it melted? the oil filter, and oil started dripping from the oil filter housing. Lost about 2 Quarts. Water tank empty. Filled with water and it started pouring out of the overflow hose as well as a spot next to the rear of the tiptronic trnasmission. This spot looks like it has some sort of vaccum valve near it and the hose goes through a plastic piece one that looks like a coupler. I have determined that this was the root of the failure, as it appears cracked and leaking unpressurized water. I do not what part this is?
BONUS: the engine now seems to run fine, as I had to start it to back it into the garage. No knocks, no rattles, and it starts right up. This amazes me. Without compression testing it, I do not know the severity of the damage, and I have yet to drive it to see if it is down on power until I can get the coolant leak fixed. what is this part that failed!? in the photo, the part with the orange piece that appears to be vaccum operated is what is leaking water when I fill the tank What damage would you suspect has been done, and what preventative maintanance would you recommend AFTER the system has been repaired and pressurized. Oil change a given... Thanks!!
May 8, 2013
  Followup from the Pelican Staff: It's hard to see what you are referring to in the photo. Is it the oil hat exchanger that failed?

I would pressure test the cooling system, repair any leaks for find. If the engine was overheated, I suggest replacing the thermostat. - Nick at Pelican Parts
blake Comments: in reference to the fix that ted found, i tried a similar approach, and it has worked for me so far 2k miles
i bought some of that plastic weld stuff made by jb weld 9the same stuff used to fix bumpers and stuff
its rated at 300f i believe,
the only difference is that i sanded the area profusely before applying the compound. my leak was coming from the bottom of the tank as well. i didnt have to take out the tank, but i did drain it, and it would have made my life a lot easier.
its a temporary fix, but has not given me problems since.
November 27, 2012
  Followup from the Pelican Staff: I would not recommend mending a crack in the reservoir. There is too much risk. if it cracks again and your vehicle overheats you risk severe engine damage. - Nick at Pelican Parts  
Kissdaring Comments: I am still confused, the tank is in the trunk. The tubbing is also in the trunk. What I need to replace is in the trunk.

Between the trunk and engine there is a plastic tube mount with 2 bolts holding it together. I don't need to change that.

Why can't I just remove the coolant tank and remove the hoses from within the trunk? Why do I need to even touch the black plastic connector that attaches the hoses from the trunk to the other side?

Is it not possible for me to just remove the hoses from inside the trunk and leave that plastic mount Alone?
July 3, 2012
  Followup from the Pelican Staff: It will become obvious why this needs to be removed once you start the project. You can also look at the bonus photos for this project here: You will see that there is a connection that mates in the engine compartment directly to the back of the tank - you cannot easily see that with the tank installed in the car. In addition, the manifold piece (what you call the plastic tube mount) is attached to the tank, and needs to be removed in order to detach the tank from the car. I believe it is possible to do this without disconnecting *all* of the hoses in the back, but the task is not easy either way you go. - Wayne at Pelican Parts  
Kissdaring Comments: gowestwardho: Funny thing is i was thinking the same thing as im having the same issue and dont get why i need to get behind the fire wall when all that needs replacing is in the trunk! Can some one please clarify for both myself and gowestwardho. I am looking to start this project first thing tomorrow morning.

thanks guys.
July 2, 2012
  Followup from the Pelican Staff: It's quite simple - all of the connections to the tank / manifold piece are located in the engine compartment and are very difficult to reach. The tank is a one-piece unit with a funky plastic manifold piece that mates to the rear of the trunk. - Wayne at Pelican Parts  
gowestwardho Comments: The more I read on this the more confused I seem to get. If ALL I want to replace is the tank itself since I know the leak is underneath it, why do I need to monkey around with anything on the other side of the firewall and inside the engine compartment??? On my 2001 S there are only the three c-clamped hoses, the oil dipstick hose, and the oil fill tube. That's it. So why can't it release those, unscrew the four bolts on the tank, and remove it without doing any of the stuff inside the engine compartment?? It looks easy, but I want to be sure I'm not missing something here before getting into it. THANKS!
June 25, 2012
  Followup from the Pelican Staff: If you can get to the hoses you should be fine. I think you would want access to the engine compartment if replacing the coolant hoses or removing the oil filler. - Nick at Pelican Parts  
philip Comments: My 98 boxster has a defective coolant level sensor. Is it easy to replace? How long should it take an experienced mechanice? Thanks.
May 27, 2012
  Followup from the Pelican Staff: The sensor is located in the bottom of the tank, and I honestly can't remember if you can remove that sensor without taking out the whole tank. I'm not 100% sure, so I will copy this question to the forums, and someone there can probably chime in on this. - Wayne at Pelican Parts  
Seppe Comments: Ted, can you provide any additional information or steps on how you used the plastic Welder to repair your leaking coolant tank? Where was your crack located? How bad was your leak? Did you completely drain the entire coolant tank? Did you apply the plastic welder on the inside or outside of the tank? Also, how long have you been driving the car with this welder to test it's integrity?

Thanks for the suggestion. I would much rather spend $7.00 than $300, but I'm not sure how long this fix will last.

March 14, 2012
  Followup from the Pelican Staff: I would not recommend mending a crack in the reservoir. There is too much risk. if it cracks again and your vehicle overheats you risk severe engine damage. - Nick at Pelican Parts  
Ted Comments: Here is a ghetto fix - try this before removing coolant tank

I tried J-B Weld $6.75 Home Depot takes 15 hours to cure sucks to work with handles temp range did not work then I tried the J-B Weld Putty $6.50 Home Depot - cures in 1 hour - did not work period.

Then I did some research and found VersaChem Plastic Welder Part No. 47809, cream color $7.00 O'Reilly's Auto Parts - this product handles temps up to 300 degree and 3500 PSI - easy to work with after a 2 minute wait time, cures in 15 minutes, hardens fully in 24 hour, WORKS great saved $295 on new coolant tank. You would need to unscrew all 4 bolts on the tank to get it to move around so you can get your fingers into the leaking spot used paper napkin to trace leak and empty coolant out of tank. Hope this helps someone...

February 13, 2012
  Followup from the Pelican Staff: I would not recommend mending a crack in the reservoir. There is too much risk. if it cracks again and your vehicle overheats you risk severe engine damage. - Nick at Pelican Parts  
bobatious Comments: artandscience's comments reflect a broken link at bottom of article.

Rather than the "recursive link" should be a link to flushing the coolant system project, which is

This has the intended content.
December 28, 2011
Rog Comments: How do I remove the trunk liner so I can check for coolant tank leaks under the liner. I have a 2006 Boxster
December 27, 2011
  Followup from the Pelican Staff: The trunk liner is held on simply with a set of plastic screws & snaps. Take my word for it - you will break a bunch removing the liner, so just order some new ones (from Pelican) to have as spares. - Wayne at Pelican Parts  
artandscience Comments: What am I missing? This article appears to be Coolant Tank Replacement but I cannot find any instructions to refilling and bleeding the cooling system. Instead, just a reference at the bottom of this article to "itself" for details.

Am I missing something? Love your articles and on the recommendation of a local shop who knows I do a lot of my own work bought your book on the Boxster.

Looks like a first-rate piece of technical writing! Thanks for the great contribution to keeping our cars alive.

October 30, 2011
  Followup from the Pelican Staff: Thanks for the kudos. See the last sentence in the article, it has a link to our other article on bleeding coolant systems. Here it is again: - Wayne at Pelican Parts  

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