Stripped down the 748 today to try to locate a persistent low level coolant leak. Expecting to find the usual split on the seam of the header tank bottle I found a 75mm crack within the top part of it. The leak was from a 10mm long part of the crack where coolant was weeping out under pressure, but it was invisible unless you knew where exactly to look. This is my third of these things to go in ten years and it appears that there was a dodgy batch of replacements about 4 years ago (of which this is an example stamped Oct 13). Have to say the HDPE is frankly too hard for this application after it has gone through a few heat cycles. It is not surprising it cracked where it did on a 90degree bend under the stress from the ignition barrel and bung that holds the bottle n place. Has anyone found a permanent fix for this or is there somewhere that can manufacture replacements that are not 'consumables'? On a brighter note the OEM replacement from MR (the incomparable Craig Richardson) is only £31.07 this time around so the price is coming down. Also what a dream it is to be able to strip the fairings, seat, air tubes, tank, air box and coolant tank in 20 minutes (then 2 hours cleaning everything that is normally inaccessible). The brown bit is the leak and if you follow its line you can see the extent of the crack. For scale the threaded insert for one of the three absolute pressure sensor mounting screws is around 6mm dia. The leak ended up around 1 litre in two weeks
I had a similar leak in my header tank a few weeks after I bought in new back in 1997. Seems it is a common problem with their design rather than a bad batch.
Had mine go twice on my 996, last one was about ten years ago. Ally ones I've seen look dire but do the job. I just replace with another 2nd hand one when they go.
Get an ally tank, it's well worth it. My original tank lasted years, then when it broke I got through 4 or 5 in a couple of years, one only lasted a few minutes - I fitted it rode 10 miles to a petrol station and as I was paying I watched it spew coolant all over the forecourt, the dealer actually replaced that one FOC but on another occasion a different but very well-known & respected dealer told me "sorry no warranty" when a tank failed after a couple of months. I bought an ally tank, not as expensive as the one Motowheels sell (but no longer made) and it's been faultless, looks good IMO, plus you can barely even see it when the tank's fitted, the only downsides are that you can't check the level without looking down the spout but I haven't needed to top up since I got it and I had to relocate the air pressure sensor.
