jerrytr5 Posted October 4, 2015 Report Share Posted October 4, 2015 The other week, whilst heading down to Goodwood for the Battle of Britain flying the 5 started overheating in a rather inconsistant manner. Most of the time it ran fine, but sometimes in traffic started getting far too hot, but then then would behave normally. Had to stop on the way home after miles of stop start traffic after the pressure cap did it's job and ejected the coolant. Anyway, later at home, checked the thermostat and found it was opening a little late. The replacement seemed to be ok so fitted it and ran it up in the garage. Idled fine with the electric fan cutting in and out as required. Drove it to work through usual commuter jams and all behaved well. Job done. Drove over to Prescott today to watch the TR hillclimbers and the first half of the journey was fine, but then she started getting a bit warm, then down to below normal, then boiled over in the Prescott car park. So, after a bacon bap and a cuppa she'd cooled down and I took the thermostat out. For the journey home, I wasn't really expecting her to get to 'normal' with no thermostat, however after a long time she warmed up to normal, increasing temperature a little under load and then reducing on the higher air flow bits. However, hitting traffic she then got up towards the hot end of the dial which I wasn't really expecting with no thermostat. A high speed run down the M40 at one point kept her precisely at normal. So, pretty sure the rad cap and the temp guage are working correctly. Intending to remove the water pump and check the vanes, and I'll check the temp across the rad with one of those point and shoot thermometer things. I can try a different rad cap and back flush the system. What I'm finding difficult to explain is the inconsistantcy of it. If the rad was blocked or water pump failing, it would get hot and stay hot wouldn't it? How is it behaving normally some of the time but at others getting very hot, then below normal, then back to normal. All very curious. Logical explanations please. Jerry Quote Link to post Share on other sites
RobH Posted October 4, 2015 Report Share Posted October 4, 2015 Possibly an air-lock Jerry. There have been a couple of recent threads on this kind of symptom ( I think under TR6 ?) and you will find all the advice there already if you do a search. Rob Quote Link to post Share on other sites
Andy Moltu Posted October 4, 2015 Report Share Posted October 4, 2015 Not convinced of the air lock theory, especially if it still occurs with the stat removed. Would suspect that if it is overheating when running your rad may be clogged. If it is just when stationary then perhaps your electric fan isn't working or not switching on when it should. (However that assumes that the car no longer has a mechanical fan which is more than adequate for the job if present). To be honest providing you keep moving at more than 20 mph the fan isn't needed in the UK! If the rad checks out perhaps you have a blown head gasket or rarer causes such as loose fan belt or water pump failure which also may impede circulation. Quote Link to post Share on other sites
Peter Cobbold Posted October 4, 2015 Report Share Posted October 4, 2015 It might be gas accumulating from a small head gasket leak. Leaks when under load but doesnt show up until low rpm and leaked gas is then allowed to accumulate in the headand then it airlocks as Rob says. Compression check? Peter Quote Link to post Share on other sites
john.r.davies Posted October 4, 2015 Report Share Posted October 4, 2015 Check that the distributor clamp is tight. Could be wandering into retarded timing, with consequent overheating. John Quote Link to post Share on other sites
John L Posted October 5, 2015 Report Share Posted October 5, 2015 I think you can get a test on the water to see if it has some combustion gas in it, but I'm not sure who would be able to do it. Is the nut and olive tight on the heater pipe behind the water pump? it might be drawing in air at that point. John Quote Link to post Share on other sites
MikeF Posted October 5, 2015 Report Share Posted October 5, 2015 (edited) How are your hoses? Mike Edited October 5, 2015 by MikeF Quote Link to post Share on other sites
dpb Posted October 6, 2015 Report Share Posted October 6, 2015 i had a long running problem with similar but not the same symptoms as yours. Eventually after going via the rad/pump/hose/flush/thermostat replacement route - I checked the compression - seemed normal, and then checked for combustion gases in the cooling system. Sure enough it gave a clear indication of a blown head gasket (or a crack in the block!). Finally changed the head gasket - sure enough it had a small crack in it. I suggest checking the gases first, might save a lot of wasted time and money. I bought a kit off t'internet, and it worked well. Dave ==== Quote Link to post Share on other sites
jerrytr5 Posted October 6, 2015 Author Report Share Posted October 6, 2015 Thanks for suggestions. Engine driven fan got removed long ago and the electric one is working as it should. A feature of this car is that it has always had a remarkably stable temperature under all conditions - until now that is. No leaks and hoses in good condition. Fan belt fine. Haven't had a chance to check the dizzy clamp, bypass tube, compression or whip off the water pump yet. Just trying to figure out how the combustion gas detector works. http://www.ebay.co.uk/itm/FX-53-HEAD-GASKET-BLOCK-COMBUSTION-LEAK-TESTER-KIT-PETROL-DIESEL-0-5L-FLUID-/281767379988?hash=item419aa50414 Seems to be a fluid that I was expecting to mix with the coolant but the instructions say "Just squeeze the rubber bulb pump to suck the air from the radiator". But the rad is full of water not air, so do they mean air or is that a typo? Jerry Quote Link to post Share on other sites
dpb Posted October 6, 2015 Report Share Posted October 6, 2015 (edited) That's how it works. Just goes in the top of the rad where there is a bit of air. Run the engine, suck a bit of air (rad cap is off). The liquid in the device changes colour depending on gas content. It was easy to use, and gave a very clear indication to me. Cheers Dave ==== Edited October 6, 2015 by dpb Quote Link to post Share on other sites
JJohn Posted October 6, 2015 Report Share Posted October 6, 2015 I had identical symptoms on my 6 about 4 years ago. I went through all the usual checks and then removed the head. The gasket was OK but a crack test on the head revealed cracks in Nos 1 and 6 exhaust ports. replacement head fixed it. Jim Quote Link to post Share on other sites
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