hendrixswhitestrat Posted June 6, 2012 Share Posted June 6, 2012 Posted elsewhere about a related issue but would appreciate a sensecheck from BC bods... Car is overheating, fan not cutting in and coolant is bubbling in expansion tank. Worst case I'm assuming some kind of head gasket failure (but no creamy gunk in the rocker cap or sump) so other things I intend to look at before whipping the head off are; - thermostat cooked/ jammed - temp sender unit on the blink ? - leaking hoses/ tighten jubilee clips - air lock (unlikely) Anything I've missed ? Any other reason which may explain why the fan isn't cutting in ? Cheers all... - leaking rad Link to comment Share on other sites More sharing options...
James_Russell Posted June 6, 2012 Share Posted June 6, 2012 What about the radiator fan switch itself? these do fail from time to time. Link to comment Share on other sites More sharing options...
Lee Fowler Posted June 6, 2012 Share Posted June 6, 2012 Thermostat or air lock. Lee Link to comment Share on other sites More sharing options...
johnv Posted June 6, 2012 Share Posted June 6, 2012 why don't you bypass the fan switch (ie switch the fan on manually when you would expect it to come on) and see if it goes on to overheat Link to comment Share on other sites More sharing options...
ashaughnessy Posted June 6, 2012 Share Posted June 6, 2012 By "expansion tank" I presume you have the original standard set up, with a filler cap near the thermostat. This is very prone to losing water, which gets spat into the expansion tank but doesn't get sucked back in again, leaving air instead. Eventually, the water level will drop below the level of the fan switch, which means the fan won't turn on, which then makes the problem worse. You'll also need to take care when refilling to ensure no air in the system, by various means including jacking the car up at both ends in turn to dislodge air, manually jiggling and squeezing the bottom hose, etc. All these troubles disappear if you convert to a fully sealed system with a header tank (see picture here - you can see the header tank next to the fire extinguisher). I had your problems for years before switching to this system, and have now driven without trouble for years since. Normal behaviour on my car is to heat up to high 90s when stuck in a traffic jam, at which point the fan cuts in and cools down again. With your setup, this is likely to result in much water being spat out and lost. Anthony Link to comment Share on other sites More sharing options...
hendrixswhitestrat Posted June 6, 2012 Author Share Posted June 6, 2012 Cheers all... Yes Anthony..this is my set up here Car normally runs fine so would like to 'fix' it and them may convert to a sealed system as you say...just want to make sure it's nothing more sinister Link to comment Share on other sites More sharing options...
cskip Posted June 6, 2012 Share Posted June 6, 2012 I would highly recommend converting to a sealed system. I always had to check and refill my open system. I know this doesn't help the diagnosis of your problem, but at least you know you wouldn't be losing water from the catch tank. A few years back I started losing coolant through the catch tank. There was a lot of coolant being pushed from the stat to the tank and more than the capacity of the tank. The water in the tank was very hot and bubbling. At the time I thought it was the radiator that had a leak and therefore the pressure was not holding. The Radiator was replaced along with all the hoses and the stat. Now I am not so sure that the radiator was leaking. The end result was a cracked bore with coolant getting into the Oil. I am still not sure to this day whether the result was the cause or the effect! In my case, if I had been running a sealed system, it would have been possible to monitor the level of coolant. And it would have been more obvious that I was losing water within the system. With an open system you just don't know what is being lost to the tank naturally and when there is a problem. Link to comment Share on other sites More sharing options...
hendrixswhitestrat Posted June 7, 2012 Author Share Posted June 7, 2012 Chers cskip...yup might go that way in the final analysis.... Link to comment Share on other sites More sharing options...
Baz Hemsley Posted June 7, 2012 Share Posted June 7, 2012 I would not think changing the system would correct the fault. I have used the standard system on my xflo for the last 33,000 miles with no over-heating problems, apart from a blockage between inlet manifold and head, thermostat, head gasket, hose split, rad leak, cracked piston, and a back-fire which caused the whole bloody lot to over-heat. Off to France tomorrow. Looking out the window, dont look like I will have any heating problems. Link to comment Share on other sites More sharing options...
ashaughnessy Posted June 7, 2012 Share Posted June 7, 2012 Baz, that's an interesting reply. My overheating problems only really occurred either when in traffic jams, or when I hadn't taken care to top up the water very regularly. Eventually it would lose enough water to cause a problem. Whether you see this as the result of a fault that needed to be cured, or simply as an ineffective design is up for debate. Caterham Midlands were of the former opinion, and thought that upgrading the radiator, replacing the thermostat, and replacing the filler cap should be enough but this was no help. Changing to the sealed system has resulted in zero problems since. It still gets hot in traffic jams but doesn't lose water and so the fan works reliably and keeps it under control. I never had any trouble as long as I avoided slow moving traffic but this is difficult in most parts of the UK :-( Anthony Link to comment Share on other sites More sharing options...
hendrixswhitestrat Posted June 9, 2012 Author Share Posted June 9, 2012 Looks like my fan's buggered.... I changed the thermostat itself this morning and the temp gauge sender ( which has cured temp gauge needle fluctuation) but fan resolutely refused to cut in so I switched car off..definitely no airlocks so suspected fan switch u/s but when I connected the two spade connectors on the thermostat housing to check the fan nothing happened... So I guess fan itself isn't working ? Link to comment Share on other sites More sharing options...
hendrixswhitestrat Posted June 9, 2012 Author Share Posted June 9, 2012 ...suppose it could be a blown fuse ? Link to comment Share on other sites More sharing options...
Roger King Posted June 9, 2012 Share Posted June 9, 2012 I can only add that when we insisted that our racing customers changed to sealed header tank systems, the incidence of overheating/head gasket problems, dropped by over 95%. There is simply no comparison in the efficacy of the two systems. Link to comment Share on other sites More sharing options...
ashaughnessy Posted June 10, 2012 Share Posted June 10, 2012 The fan switch is situated on the radiator, I presume this is from where you took the two spade connectors and connected them directly to a 12 volt source? You said you took some spade connectors from the thermostat, which obviously isn't electrical, so I'm wondering if you took the spade connectors off the temperature gauge instead of the fan. I'm sure you did the right thing, just a poor choice of words. Anthony Link to comment Share on other sites More sharing options...
Stationary M25 Traveller Posted June 10, 2012 Share Posted June 10, 2012 You take the connectors off the fan switch in the radiator and touch them together. This simulates the switch closing at the set temperature. Link to comment Share on other sites More sharing options...
hendrixswhitestrat Posted June 10, 2012 Author Share Posted June 10, 2012 Hi guys...the switch is located towards the bottom of the thermostat housing, traced the problem to a blown fuse and when it was replaced and the spade connectors were touched together the fan worked fine. Reconnected everything and ran the car and all fine and fan now cuts in ( and out) when it should. Thanks to everyone who posted on this and other thread. For anyone who has similar probs (though mine were coincidental rather than connected) this is what transpired; Misfiring at higher revs : traced to HT leads breaking down Overheating: traced to thermostat u/s and blown fuse for fan. I think I will convert to a sealed system shortly , convinced by the various posts, but for now looking forward to getting back on the road and thanks again to all who took the trouble to post. HWS Link to comment Share on other sites More sharing options...
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