Paul Mason Posted November 6, 2017 Share Posted November 6, 2017 Recently bought a 7 and one little foible is that the temp gauge (a Racetech unit) once its up to temperature wanders around between 75 and 85 degree. Will go up to 85, then quite quickly drop to 75 and after 20 seconds or so, go back up to 85 in another 10 seconds or so. Whole cycle takes 30-35 seconds and happens pretty much continually.Car doesn't seem to run hot - fan kicks in at about 90 if stationary or driving slowly (10mph down the street to the house & parking up occasionally), so potentially a non-issue. Not sure if the car has a thermostat to be honest. I have nothing other than my own curiosity/lack of knowledge making me ask the questionJust after thoughts/experience/knowledge as to whether its not worth worrying about, a potential gauge issue, a sender unit issue (though no idea where it is) or something potentially that needs further digging?Thanks in advancePaul Link to comment Share on other sites More sharing options...
revilla Posted November 6, 2017 Share Posted November 6, 2017 What engine is it?You can sometimes get this temperature cycling, especially in cold weather with a K Series. My K VVC used to do it quite a lot. It's caused at least in part by the unusual design of the K Series cooling system with the thermostat on the return from the radiator. You can get into a situation where the water in the bypass hose is hot enough to cause the thermostat to open, then you get an inrush of a large volume of chilled water from the radiator which results in a large drop in temperature, the thermostat closes hard and water continues to circulate round the bypass hose steadily getting hotter until it repeats.If that's what you're getting, it's probably not doing the head gasket any favours. K Series head gaskets don't respond so well to repeated temperature cycles. This kind of issues was one of the reasons for so many head gasket failures in the MGF where the long cooling pipes from the mid engined installation made it worse. Eventually the repeated expansion and contraction can lead to failure of the elastomer sealing bead.There's a common modification which involves drilling a 2mm hole in the top part of the thermostat flange, which is normally done to prevent airlocks getting trapped in the thermostat housing during filling, but I also noticed in my case it was enough to completely cure the temperature cycling. I guess with the thermostat closed it allows just enough residual flow to keep the radiator contents gently circulating and preventing them from overcooling, reducing the thermal shock when the thermostat opens.If you search on here for drilling the thermostat you will find plenty of info and pictures. Link to comment Share on other sites More sharing options...
SM25T Posted November 6, 2017 Share Posted November 6, 2017 Combined with the simple modification of the hose routing as per the article in Low Flying in September 2012. Mine sits rock steady after rapid warm up. Link to comment Share on other sites More sharing options...
Paul Mason Posted November 6, 2017 Author Share Posted November 6, 2017 Many thanks RevillaIt’s a K series, 1.8 with a VHPD headI’ll have a look at the article and have to look to see where the thermostat is and modify as you suggest in case that’s the issueAppreciate your help Link to comment Share on other sites More sharing options...
SM25T Posted November 6, 2017 Share Posted November 6, 2017 It can be a swine to get at ... Under the inlet on the offside of the block. Link to comment Share on other sites More sharing options...
Paul Mason Posted November 6, 2017 Author Share Posted November 6, 2017 Thanks SM25TWill look to find the Low Flying article too - am guessing back issues on the club site?Best regards and many thanks Link to comment Share on other sites More sharing options...
Paul Mason Posted November 6, 2017 Author Share Posted November 6, 2017 Now I’ve realised where it is, guessing the airbox on the car is going to make access doubly difficult! May be a longer job for the weekend or when I have a few days off! Link to comment Share on other sites More sharing options...
SM25T Posted November 6, 2017 Share Posted November 6, 2017 I have a PDF scan of the article. Happy to email it over if you drop me a message with your email address. Link to comment Share on other sites More sharing options...
SM25T Posted November 6, 2017 Share Posted November 6, 2017 If the gauge uses the poor quality Caerbont electrical sender .... single wire sender on the water rail nearside of engine just behind and above the exhaust primaries ... they are notoriously unreliable and can be short lived. Worth replacing that first. Link to comment Share on other sites More sharing options...
Paul Mason Posted November 6, 2017 Author Share Posted November 6, 2017 Thanks SM25T email en route and I’ll check the sender too (which sounds eminently simpler) Link to comment Share on other sites More sharing options...
John Vine Posted November 7, 2017 Share Posted November 7, 2017 If the gauge uses the poor quality Caerbont electrical sender ....IME that certainly applies to the OP sender (it doesn't withstand too much engine vibration), but is the temp sender equally dodgy?JV Link to comment Share on other sites More sharing options...
SM25T Posted November 7, 2017 Share Posted November 7, 2017 Unfortunately .... yes ! Link to comment Share on other sites More sharing options...
Paul Mason Posted November 7, 2017 Author Share Posted November 7, 2017 Well, that’s one positive at least......I think it’s got a mechanical oil pressure gauge so at least that isn’t going to be a problem (he says in blissful ignorance potentially from a standpoint of believing the oil pressure gauge is actuated by a oil pipe from the bottom of the filter housing, though the large oil pressure light on the dash I think is actuated by the electric sender switch on the top of the oil filter housing so guess that could be prone to fail). I’m going to look for the sender and replace then move onto the thermostat mod and am optimistic that it’ll sort it.Pretty sure it’s not a huge issue on account of lowish miles at the mo, just one of a myriad of little things I’d like to sort ready for next year Link to comment Share on other sites More sharing options...
Paul Mason Posted November 7, 2017 Author Share Posted November 7, 2017 Just to make my confusion a little more complete, just gone to have a look and seem to have 2 senders on the water rail at the rear of the primaries?Will try now to work out how to upload a photo Link to comment Share on other sites More sharing options...
Paul Mason Posted November 7, 2017 Author Share Posted November 7, 2017 Link to comment Share on other sites More sharing options...
SM25T Posted November 7, 2017 Share Posted November 7, 2017 The single wire is for the gauge. The 2 wire feeds the ECU Link to comment Share on other sites More sharing options...
SM25T Posted November 7, 2017 Share Posted November 7, 2017 See post #9 Link to comment Share on other sites More sharing options...
Paul Mason Posted November 10, 2017 Author Share Posted November 10, 2017 So, had nose off to discover what I am pretty sure is a QED remote thermostat. Thermostat in place just in front of top left (from the rear of the radiator) connection (hot in?) into a Radtec aluminium radiator. Behind it is a sensor (not sure if this is for the temp gauge or the fan switch - left hand side on pic below)Given this set up, would the advice to drill a 2mm hole in the top flange of the thermostat remain or would this point more to the sender as the issue? Link to comment Share on other sites More sharing options...
SM25T Posted November 10, 2017 Share Posted November 10, 2017 Try the gauge sender .... it's a cheap and easy option ! Redline stock them and offer sensible P&P if you don't want to buy from CC. Link to comment Share on other sites More sharing options...
Paul Mason Posted November 10, 2017 Author Share Posted November 10, 2017 Thanks SM25TI’ll get one ordered and start there. Seems like the easy start point. Car is driving perfectly well and certainly not overheating, done getting on for 200 miles in the last week and other than the wander between 75 and 85c I have got nothing other than lots of smiles! Just want to make sure everything tip top and doing no harm to anything Link to comment Share on other sites More sharing options...
Smiffy69 Posted November 13, 2017 Share Posted November 13, 2017 I had a similar problem on mine and it turned out to be a bad earth connection. Given the sender is just a resistor that varies with temp then it may be a bit of corrosion on the threads creating a high resistance connection. Give it a good clean and see if that helps - could be a simple as that .... mine was. Link to comment Share on other sites More sharing options...
Paul Mason Posted November 13, 2017 Author Share Posted November 13, 2017 Thanks Smiffy, will be starting there ta Am also wondering if the coolant system is just very effective as a potential “cause”......radtec radiator, remote thermostat, seemingly re-routed pipework and no heater etc. so when temperature comes up and triggers thermostat, system cools fairly quicklyThe car warms up pretty quickly (water anyways, oil takes longer) never seems to get too hot (only time over 85 is when going very slowly or parking up, in which case fan kicks in at about 92 and temp drops down..That said, still don’t like seeing it so will got fettle Link to comment Share on other sites More sharing options...
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