sam726 29 Report post Posted February 8, 2014 Hi Guys, I have a 525i with the M54 engine and have recently my radiators decided to start a leak. It's done about 130kms now so that's to be expected really and I'm going to be getting a new radiator put in today. My problem/question is that I've still been driving it around (no other car to drive), and have just been monitoring the KTMP on the 'hidden' OBD menu everytime I drive it with this leak just so I can keep an eye on things. 95% of the time the operating temperature is as it should be, somewhere between 88-96 degrees. A few times however it's shocked me a little and headed up to 105 degree and on one occasion I almost stopped on the side of the road as I saw it go up to 112 degrees. This anomaly has happened maybe 3 times in the last week, when it does happen I'll be driving normally along at constant speed (not stopped in traffic or anything) and when the car finally 'figures out' its too hot the temperature will drop back to 96 in a matter of maybe 5 seconds or less. Now, I do plan to do a full cooling system overhaul in the coming months as I know the radiator is only going to be the start of my problems but for now I can't afford to do a full overhaul so my question for the BMW experts is what could be causing this sudden temperature fluctuation and is it normal? And then is there a certain part replacement I should be prioritising to the top of my list to get done? I'm wondering about the thermostat but not sure if it could be causing this issue. Thanks for any help, Quote Share this post Link to post Share on other sites
aja540i 1903 Report post Posted February 8, 2014 Are you ABSOLUTELY sure it has plenty of coolant in there?? Keep in mind that with a leak in the system it wont suck any coolant back from the overflow tank as it cools down, so you may have a bit of air in the system. Wouldnt hurt to fill it and bleed it, but if you are getting a new radiator tomorrow just dont drive it till then!! Quote Share this post Link to post Share on other sites
sam726 29 Report post Posted February 8, 2014 (edited) I've been filling it up every couple of days with the engine running just to make sure it's always topped up. Have had the check coolant dime a few times but I've never kept on driving it after it tells me its low, luckily I live close to work and don't drive any real distances unnecessarily. Actually heading over to my mechanics now to get the radiator put in but I'm wondering whether I should be leaving it there and getting a thermostat come Monday or taking it with the new radiator and then monitoring KTMP after that. There is a possibility there could be some air in the system, I suppose once the radiators done and properly filled & bled that would rule that out. Either way I definitely want to do my cooling overhaul, only my funds limit that at the moment but if it comes down to being a faulty thermostat in need of replacement then I'll make room to get it done ASAP. Can't have her overheating on the Cannonball Run now can we! Also sorry this got posted three times, my computer & internet connection had a moment there! Edited February 8, 2014 by Sam G Quote Share this post Link to post Share on other sites
Allanw 1052 Report post Posted February 8, 2014 Yeah... Make sure it's full of coolant when it's cold (like overnight cold) - leave the bonnet up for a while to coool it down faster. It could have a sticky thermostat, but the usually don't fail that way. 112C is pretty hot for an M54, though the OBC over heat warning doesn't come on until 120C or 125C on the petrols! I'm not 100% if the original thermostats had a 97C mechanical rating, or if it was initially higher and BMW changed them later. The V8's have a 105 or 110C mechanical rating. If you can, I'd do the radiator, thermostat, waterpump; in that order. The water pump is less likely an issue, but they can fail (though my original was absolutly fine when replaced at 125K, impellor 100% intact). The thrmostats are a different story - they don't usually cause overheating, but are pretty unreliable. Both the mechanical part and the electric heater for the Map Control Cooling. It's possible to convert them to a mechanical thermostat, but you probably don't want that expense as well. Had you monitored temps before the leak? Was it ever that high before? I'd be limiting driving as much as possible! M54's don't like overheats, and the headbolts can strip the threads in the block - requires a timesert fitted to each hole to replace the threads. Quote Share this post Link to post Share on other sites
jeffbebe 1559 Report post Posted February 8, 2014 If it's peaking and going back down I'd hazard a guess that you need to bleed the cooling system. Sounds like you've got air bubbles trapped in there. Does the cluster temp gauge register the spikes or just the KTMP on the hidden menu? Quote Share this post Link to post Share on other sites
BM WORLD 1264 Report post Posted February 8, 2014 dont drive it , it wont be able to regulate the correct temp with air in the system . and these m54's run pretty hot normally and wont take much to push it over the edge and damage the head or head gasket cheaper to get a taxi than a new engine Quote Share this post Link to post Share on other sites
sam726 29 Report post Posted February 9, 2014 If it's peaking and going back down I'd hazard a guess that you need to bleed the cooling system. Sounds like you've got air bubbles trapped in there. Does the cluster temp gauge register the spikes or just the KTMP on the hidden menu? It was just the hidden menu that was registering the spikes. I think you were right about the air as its not doing it now. dont drive it , it wont be able to regulate the correct temp with air in the system . and these m54's run pretty hot normally and wont take much to push it over the edge and damage the head or head gasket cheaper to get a taxi than a new engine All fixed now! So good to go for another 100kms on that radiator Yeah... Make sure it's full of coolant when it's cold (like overnight cold) - leave the bonnet up for a while to coool it down faster. It could have a sticky thermostat, but the usually don't fail that way. 112C is pretty hot for an M54, though the OBC over heat warning doesn't come on until 120C or 125C on the petrols! I'm not 100% if the original thermostats had a 97C mechanical rating, or if it was initially higher and BMW changed them later. The V8's have a 105 or 110C mechanical rating. If you can, I'd do the radiator, thermostat, waterpump; in that order. The water pump is less likely an issue, but they can fail (though my original was absolutly fine when replaced at 125K, impellor 100% intact). The thrmostats are a different story - they don't usually cause overheating, but are pretty unreliable. Both the mechanical part and the electric heater for the Map Control Cooling. It's possible to convert them to a mechanical thermostat, but you probably don't want that expense as well. Had you monitored temps before the leak? Was it ever that high before? I'd be limiting driving as much as possible! M54's don't like overheats, and the headbolts can strip the threads in the block - requires a timesert fitted to each hole to replace the threads. I'd never monitored the temperature before the leaks so couldn't comment on that. Have had the new radiator put in today and no more leaks! The temperature is also staying nice, hasn't gone over 96degrees once and in fact is keeping closer to 90 than 96. We checked the thermostat and the housing and thermostat both looked in really good condition, possibly even replaced before, so that can wait for another day. Did the Vanos seals while we were at it as well since I had them lying around and waiting to put in and wow I can feel the difference. Time will tell if my fuel economy will start to drop, 14.0L/100 is pretty shocking I think. And last but not least we removed my windscreen washer reservoir and cleaned the gunk out so now my washers work again! Productive day! Time for a beer I think... Quote Share this post Link to post Share on other sites
yng_750 247 Report post Posted February 9, 2014 The 540i often hit 110c with hard driving but the 6cyl shouldnt getvthat high. The v8 got as high as 113 but that was after 45 mins on the track non stop Quote Share this post Link to post Share on other sites
Allanw 1052 Report post Posted February 9, 2014 Does the cluster temp gauge register the spikes or just the KTMP on the hidden menu? If an E39 temp gauge ever moves above 12 o'clock, the engine is VERY hot. The gauge will sit at normal until at LEAST 115C, probably higher though. Your V8 can run up to about 110C in "normal" conditions. I've never tried to test the high end, but I suspect "normal" will be displayed until about 120C. On the weekend I just set aja540i's OBC warning to go off at 120C, because it was factory defaulted to 130C!!! cheaper to get a taxi than a new engine Very! All fixed now! So good to go for another 100kms on that radiator Tidy. Quote Share this post Link to post Share on other sites
