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Coolant mystery

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I recently had my tatty header tank refurbished on my 1984 S3 turbo.When I disconnected the hose that fits to the bottom of the tank I used a synthetic wine bottle cork as a bung to prevent any coolant escaping from the hose and softly clamped the two thinner air bleed and overflow top hoses for the same reason. On reassembly I simply connected the three hoses and refilled the header tank to a couple of inches from the top. (no problem easy peasy.)

However, I had returned from a 60 or so mile drive keeping a close look at the temp gauge (which remained at the usual temp throughout the journey) the car was sat on my drive ticking over nicely when "whoosh" several litres of coolant was gushing from behind the O/S/F wheel. I quickly turned the engine off, and on inspection saw that the otter (fan switch) had blown off the elbow pipe. firstly thank god this happened on my drive, but the real mystery, is that the coolant in the header tank had not moved from the original level when it was refilled (2 inches from the top). Surely with such a large amount of coolant loss from the front of the car, this would have disappeared or reduced significantly? Even after leaving the car a day, gravity should have reduced the level? I disconnected the top bleed pipe and blew down it, this resulted in a gurgling coming from the elbow pipe where the otter switch was still removed, so I guess that rules out a blockage on that route, but could there be a blockage somewhere else in the system? which is preventing the header tank coolant from falling? I figure after the refitting of the header tank there must have been some kind of air lock for the otter switch to be blown out,but I never thought it necessary to bleed the system, plus I have never had any cooling problems for the past three years I have owned the car, but I'm more concerned that the water pump or the thermostat may have packed in by coincidence. Does anyone have any clues to diagnosing the header tank coolant level situation?? or things to check out before I flush,refill and bleed the cooling system?

Kind Regards


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Sounds like you had an air pocket. There should be a bleed hose that runs from the outlet pipe (thermostat) back to the coolant expansion tank. Pull that hose off and check for a restriction. If that is plugged it would help explain the trapped air.

When you go to start the car up have the coolant cap off and run the car until you see water entering into the expansion tank. Probably will see air bubbles and then a constant stream of water. Turn the car off, check water level and replace the cap.

Good luck,


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Prob too late now but losing the otterswitch this way does happen. I know when Pete at PNM put a new one in for me he wrapped a long length of retaining wire (looked a bit like fuse wire) round the switch and pipe, to stop this happening. Point to consider for your next one?




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