Wasserboxer Bug - Splitting header tanks
 

Here's a puzzle for you guys...

I have a 2.1 fuel injected WBX in my Bug. Pumps out around 130hp.

I have split 2 header tanks / expansion tanks (whatever you want to call them) in the last two weeks. The tank is a standard Mk2 Golf item with Golf cap. I put the first failure down to a dodgy expansion tank, but 2 in a row tells me not. I'm now thinking it is the cap, but the valve in the cap seems to work, and it was all 100% new when i built it all, including the engine.

I have new cap and expansion tank coming Monday (2 actually, just in case!), but any thoughts on whether there may be something else amiss. Cooling system is modelled on a Mk2 Golf. Coolant temp never got over 95-100°C both times it split. Coolant temp does get up to 103-105°C in traffic queues before the ECU cuts the fan in, but it has done this many times and hasn't split the tank. First time the tank split the temp was barely 95°C on my way home from work (5 miles). Second tank split was 150miles later, after i had it at 100-110mph for 5 mins (much to the suprise of the Corrado i shot past who then tried to tail me...). First tank (origin unknown) split above the seam alng the back, second split along the front seam (Italian made).

Way i see it, the cap would always limit the pressure, so it must be the cap. But... any other thoughts? I'm an professional engine designer of many years experience (Ricardo), so not a novice to these things - i'll admit that coolant system design is not my top subject, but i don't believe I got it that wrong.

Rich (Ricola) or anyone with waterpumpers - Any thoughts? Did you have any teething probs like this?

Ta for any help guys...

Moog

p.s. Here's a pic...

http://mysite.wanadoo-members.co.uk/.../Img_1262b.jpg

Hi Moog,
My first thought agrees with you, definitely sounds like the cap, that's the only time I've blown any part of a system.
Other than that, is it something to do with how the heater is piped in maybe? Sounds like you run the engine very warm too, I'd have thought the thermostat on those engines would kick in a lot sooner than that, likewise for the rad fan which I'm sure you have control over anyway..
Rich

Hi Rich - Thanks for answering. I'm thinking and hoping it is just the cap, but am slightly nervous that there might be something else wrong.

Temps - The standard thermostat on a WBX starts to open at 87°c and is fully open at 105°c. I actually have a VR6 stat which starts at 80°c and is fully open at 100°c, so with normal water operating temps at 90-95°c then i figured this is fine. My choice of rad location probably does make it run a bit hotter than if i used a front mounted rad, but i don't think that it is getting too hot for the engine or system to take. I have the ECU controlling the fan - cuts in at 105°c and cuts out at 95°c. (All temps are measured at coolant outlet from the engine, so at the hottest part of the system before the coolant has gone though the rad). If i recall, the Mk2 GTI ran quite hot like this as well, so the tank should take it if the cap is working properly. Maybe i'll trim the fan operating temps down a bit as well and see how it goes.

I have found out the Golf Cap is rated at 1.2-1.5bar, while the T25 cap is 0.9-1.15bar, so will try a T25 cap with spout and an additional non-pressurised overflow/filler tank as per T25 and see if this works.

Heater matrix is a std T25 auxilliary heater under the rear seat - takes an outlet from the left head and returns into the top of the water pump (T'd into the hose from the header tank to water pump) so similar to T25 setup.

I did think it may be to do with the overall coolant volume being too small, but the standard Golf Mk2 GTi is listed as 6.5 litres coolant volume (smaller than i thought), and i have about the same.

New bottles & caps coming Monday, so i have to just sit and wait until then - very frustrating... still, at least i might get some more plastering done in the kitchen...

Ta

Moog

My first thought is also the cap

But I do have another idea.... what about vibration?? Is you header tank mounted on rubber mounts or straight onto the firewall?? You could be rattling the thing apart.

Try this. Make a plate to mount your tank onto. This plate... mount it to the firewall using 2 flexible rubber mounts (used for mounting small motors and pumps). Mount the plate onto thie mounts and mount the tank onto the plate. Then get some (2) rubber straps and tie them around the plate and the tank. This will allow the tank to be fairly rigid to the plate, while not recieving the vibrations from the car.

Hi

The only time that I had a problem with my old car with a wasserboxer fitted was the cap.

A radiator place should be able to check the cracking pressure on the cap you have now.

Will a T25 cap fit your Golf header tank OK? I actually prefer to have a recovery system like the T25, its good for getting rid of air locks.

Steve

Thank s for the suggestion. The header tank is standard golf that is supposed to be fixed to the body - it isn't meant to be flexi mounted. Plus if it was this then it would split at the mount of where connections are. Where these split is clearly due to overpressure, so i don't think this is it.

I have now replaced the cap with the T25 one with spout and an extra catch tank, and all now seems resolved. Must have been a faulty cap, even though it was new 500miles ago.

Ta for the advice all.