Search the Community

Hi all, I've got a new issue with my 1.6 in that it seems to be overheating due to the radiator fan not coming on but it doesn’t ‘feel’ that warm. About 12 months ago I put a new radiator fan switch in and it worked fine but due to finances has been sitting in the radiator without being started since. Now I've started to finish the car I had to replace the expansion tank as I managed to break the original where the thinner hose goes onto the top of it to the left of the temp sensor (don't ask). Also, whilst replacing the tank and seeing as I had the system drained I fitted a brand new ECU coolant sensor (from GSF) as I was experiencing some erratic idling the last time the car was on the road and I want to do a belt and braces job in preparation for MOT on April 23rd. So in real terms, since this time last year when the cooling system was working fine I've replaced the expansion tank and ECU coolant sensor. However, when I started the car a couple of weekends ago it seemed to get warm (the dashboard gauge went to about 1/3 of the way around) but the radiator fan didn't cut in. Next thing I know there's what seemed to be hot coolant spraying out from around the expansion tank cap and the joints where the bottom radiator hose meets the metal pipe next to the o/s front wheel and the main/large hose on the bottom of the expansion tank had burst and were leaking. When this happened, the dash gauge did not go much further up and no warning lights came on. Now I have experienced an overheat in the distant past on the way to Leeds in 2005 so I know that, looking at the temperature gauge, it was barely over normal operating temperature and the fan should really have only been on half speed, if on at all but no sign of it coming on even though the expansion cap and bursts joints told a different story. I initially concluded that I may have an airlock that was both over-pressurising the part of the system where the joints had burst and was also stopping the hot coolant getting up to the fan switch so I drained the system, re-tightened the jubilee clips and re-filled very carefully whilst making sure the prescribed (by Haynes) 6.5 litres went in. This didn't solve the problem so I then concluded that the radiator fan switch that I fitted last year didn't like sitting doing nothing for twelve months so I ordered another new one from GSF. I then checked all the wiring (the actual wiring, not just the test plugs) and that's all fine (fan comes on at both speeds using my bit of testing wire), I drained the coolant, replaced the fan switch and re-filled (again following the correct bleeding procedure and putting back in what I took out after catching it in a clean bowl and making sure there was no crap in it!). However, the car is still doing the same thing. I started it again tonight and it gets warm after about what seems to be 6 or 7 minutes (according to the dashboard gauge) but then starts hissing from the expansion cap. However I got a bit brave tonight and started looking/feeling around as it warmed up and started to hiss and although the radiator and pipes get warm I can comfortably touch them whilst the engine's running, even at the point where I can start to hear the hissing from the expansion tank cap. IIRC, the first fan speed comes on at about 82 degrees and even at this temperature the engine wouldn’t be in an overheat situation. In my mind, I shouldn’t be able to touch the pipes and radiator with coolant at 82 degrees but I can. This tells me that the coolant in the system isn’t actually that warm (as I can touch stuff, the dashboard gauge that has always been reliable in the past isn’t overly high and the radiator fan hasn’t come on even with the new switch installed) but there’s still what appears to be steam coming out from around the expansion tank cap. However I don’t understand how this can be steam if it’s still not too hot to touch (below 50 degrees if I remember my GCSE science correctly). Sorry, I haven’t articulated that too well but basically it looks as though it’s over heating but I don’t see how it can be as I can still touch everything so it can’t be that warm. I’m really at a loss now as I think I’ve eliminated everything (fan switch, air lock, wiring etc.) and I don’t know what to try next. I have just spent an hour or so reading up on the forum about cooling systems and the only thing I can think is that the expansion tank cap isn’t sealing properly but this is the original cap that has always worked and worked last March too. The replacement expansion tank did come with a cap but it looked a bit manky and my original cap has always been fine – also I’m not convinced that a poorly sealed cap could create the issues I’m experiencing. All I’ve really done since the cooling system last worked is changed the expansion tank and the ECU coolant sensor so I’m really baffled by this. Sorry this is a really long post but I thought it important to get all the info’ in here as I can’t find any posts here about similar issues (using forum and Google searches) and (I think) I’ve been really meticulous and methodical when trying to sort this out. Whilst I’ve been writing I am thinking that if the cap isn’t sealing and pressurising the system correctly then what I am perceiving to be steam may just be pressurised coolant escaping and as the pressure is escaping this may be stopping the coolant from circulating properly and therefore I’ll be getting an uneven temperature at various points in the system – does this sound like a feasible explanation to my issue? Any suggestions or opinions on whether the expansion cap could be the cause or whether I’ve over-looked something else would be really appreciated please. I am sorry this is so long and if anyone has got to the end I really do appreciate you taking the time to read this. Ian.