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Car Forum / BMW Cars / April 2006520i temp gauge/overheating?
Hi - hope someone can help with this. I'm new to this group so apologies if this has come up before, but I couldn't find the same problem described. I have a 520i (P reg UK) and last night as I was driving home, I noticed the temp gauge go into the red zone (where the red light came on, which is what made me notice). I thought the engine was overheating and was about to stop, but when I took my foot off the accelerator it went back down to 'normal' temp. I wouldn't have expected this if the engine was genuinely overheating (e.g. if the fan belt had broken or a hose had burst) - in that case I would expect it to stay hot until I switched off. I continued to drive home slowly (only a couple of miles in all), and this behaviour repeated itself a couple of times. Does anyone know what this could indicate? Could there be a thermostat problem? I was hoping someone would recognise the symptoms and be able to advise. Thanks Flummoxed When I blew a headgasket on my 735, exhaust got into the cooling system. what would happen, tho not as rapidly as you are experiencing; would be the engine would be hot (indeed, overheating) becuase the air was at thermostat, preventing the coolant to circulate and the temp to raise to the "danger" mark. If I QUICKLY raised teh rpm or dropped it it seemed to inject enough <something> so make the coolant circulate again and coolant from teh radiator would hit the temp sensor/thermostat & then the temp would drop (only to raise again later) How's your coolant level? >Hi - hope someone can help with this. I'm new to this group so >apologies if this has come up before, but I couldn't find the same [quoted text clipped - 17 lines] > >Flummoxed --- AntiSpam/harvest --- Remove X's to send email to me. Thanks for the reply. Of course I need to check the coolant level anyway, and I will do tonight, but I didn't have time last night (it was late and dark, and I didn't need the car today). But I would have thought that if it was a simple case of the coolant level being low, the temp gauge would have stayed 'high' until I stopped the engine altogether. The strange thing here was how it went back down to normal (fairly quickly too) when I reduced revs and then went up again a few minutes later, then back down, etc. That's why I suspected the thermostat or something similar rather than lack of coolant. Anyway I'll let you know how the coolant level was once I've checked it tonight. Thanks Flummoxed >How's your coolant level? I checked the level and it was low - I put about 0.8 litres in to bring it up to the "Cold" level. Does anyone know if that would be low enough to cause the effect I described? (Of course the question remains as to why it was low, but it could be a long time since I checked the level. I couldn't see any obvious signs of a leak, although I've yet to drive it since I topped up the cooling system). Thanks Flummoxed Did you bleed the system? or just top it off? If there's air trapped in the system, topping it off won't fix it..... >>How's your coolant level? > [quoted text clipped - 10 lines] > >Flummoxed --- AntiSpam/harvest --- Remove X's to send email to me. Ooerr, good thinking. No I didn't bleed it, I don't know how to at the moment. I'll have to look it up. Cheers Flummoxed > I checked the level and it was low - I put about 0.8 litres in to bring > it up to the "Cold" level. Does anyone know if that would be low enough > to cause the effect I described? Could well be. The temp gauge on these cars isn't a straightforward thermocouple device that gives a true read out of the temp. It appears to work like one, but in fact the ECU will keep it in the middle over a wide range of actual temperatures that are within the normal running ones. Exceed that and it goes up very quickly. Under normal conditions these engines don't need topping up between services. First thing to check is that the fan clutch is working - it progressively 'locks' up when it senses the airflow through the rad getting too high and runs up to a higher maximum speed. Only usually at town speeds and you can hear the increased noise from it. As regards a leak it's often the water pump and difficult to detect without a dye/pressure test. But get the engine up to temperature and then stop it. Squeeze the top hose after a couple of minutes. It should feel pressurized. If not - ie it squeezes easily you've got a leak. > (Of course the question remains as to why it was low, but it could be a > long time since I checked the level. I couldn't see any obvious signs > of a leak, although I've yet to drive it since I topped up the cooling > system). If it turns out to have a leak and it is the pump get the thermostat and housing changed at the same time - and also the serpentine belts unless you know when they were last done. They're not as expensive as the labour to have them done later. If you say where you are in the UK you should get some recommendations for specialists. You might also consider joining the group in my sig for E39 expert advice.  Signature*Friends help you move. Real friends help you move bodies. Dave Plowman dave@davesound.co.uk 528 Auto London SW12 (UK) Co-Moderator BMW E39 Enthusiast Group http://groups.yahoo.com/group/bmwe39 Thanks ChrisJ and Dave for the further advice/help, and the pointer to the other group. (I didn't even know my car was an E39, just to show my ignorance). I've done nothing further yet to the car as I've been too busy, but I will want to sort it out soon. I'll report back once I've had a chance (hopefully by the weekend) to look into it. Cheers Flummoxed >Could well be. The temp gauge on these cars isn't a straightforward >thermocouple device that gives a true read out of the temp. It appears to >work like one, but in fact the ECU will keep it in the middle over a wide >range of actual temperatures that are within the normal running ones. >Exceed that and it goes up very quickly. are you 100% positive about that? I had heard that before, that the guage really is more of an "idiot light" made to look like a guage. Yet; when I put a cooler thermostat on my car, the guage absolutely settles a touch lower than it used to. >without a dye/pressure test. But get the engine up to temperature and then >stop it. Squeeze the top hose after a couple of minutes. It should feel >pressurized. If not - ie it squeezes easily you've got a leak. Unless he's got a headgasket leak where exhaust gases are getting into the cooling system -- then it would indeed still feel pressurized. Of course, those are based on my experiences and not specific technical expertise --- AntiSpam/harvest --- Remove X's to send email to me. > are you 100% positive about that? I had heard that before, that the guage > really is more of an "idiot light" made to look like a guage. > > Yet; when I put a cooler thermostat on my car, the guage absolutely settles a > touch lower than it used to. Yes, BMWs are actually sensors and meters (not switches like idiot lights) but the display is non-linear such that middle part of the display represents a much wider variation of temps than the sides. The intent was to keep owners from complaining about small (normal) variations in temperature. Signature-Fred W >Yes, BMWs are actually sensors and meters (not switches like idiot >lights) but the display is non-linear such that middle part of the >display represents a much wider variation of temps than the sides. The >intent was to keep owners from complaining about small (normal) >variations in temperature. hmm Interseting.. so I think what I read about it being a "an idiot light looking like a gauge" was only partially right. so it's an averaging sort of thing -- becuase otherwise, it'd be dead in the center... As an interestin gside bit -- when I had my overheatin problem, we used a non-contact thermometer, and teh guage consistently rose & lowered to the engine temp -- same now; as the engine heats up; the guage slowly rises, until it settles just below the center mark. I put the normal thermostat in; and it returned dead center.. Another bmw mystery I guess --- AntiSpam/harvest --- Remove X's to send email to me. > But get the engine up to temperature and then > >stop it. Squeeze the top hose after a couple of minutes. It should feel > >pressurized. If not - ie it squeezes easily you've got a leak. > Unless he's got a headgasket leak where exhaust gases are getting into > the cooling system -- then it would indeed still feel pressurized. Not if there's a leak in the cooling system. With the engine stopped it will depressurize quickly. A good system will keep pressure for several minutes till it cools down. Signature*A woman drove me to drink and I didn't have the decency to thank her Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. >Not if there's a leak in the cooling system. With the engine stopped it >will depressurize quickly. A good system will keep pressure for several >minutes till it cools down. Mine didn't. --- AntiSpam/harvest --- Remove X's to send email to me. > >Could well be. The temp gauge on these cars isn't a straightforward > >thermocouple device that gives a true read out of the temp. It appears > >to work like one, but in fact the ECU will keep it in the middle over a > >wide range of actual temperatures that are within the normal running > >ones. Exceed that and it goes up very quickly. > are you 100% positive about that? I had heard that before, that the > guage really is more of an "idiot light" made to look like a guage. > Yet; when I put a cooler thermostat on my car, the guage absolutely > settles a touch lower than it used to. Not sure why you'd want to change the spec of the stat but that sounds like it's running well outside the normal range. When warming up it does act like a true reading unit. Signature*Why is the man who invests all your money called a broker? Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. >> Yet; when I put a cooler thermostat on my car, the guage absolutely >> settles a touch lower than it used to. > >Not sure why you'd want to change the spec of the stat but that sounds >like it's running well outside the normal range. When warming up it does >act like a true reading unit. Yes; it rises slowly; if I turn the car off before fully warmed up and then turn it back on -- it returns to the mid point & then once the car is back on and wamring up again; continues up until it stops right below the center line. so yes; just like a real guage. --- AntiSpam/harvest --- Remove X's to send email to me. Had a similar problem witht the bizarre temperature guage problem, mine lasted like a day and then disappeared. It was followed a week later by the engine cutting out problem which was diagnosed as a faulty cam position sensor. During the replacement of the sensor, the mechanic discovered that the thermostat housing was broken. The thermostat/housing might be what's causing your problem.. Right, here's the latest: Having topped up the coolant reservoir to the "Kalt/Cool" level (it's a kind of see-through plastic reservoir next to the radiator), I took the car out for a short drive (about 5 miles) to warm the engine up. A few minutes after it reached normal temperature, it started to creep upwards towards the hot zone. But before it reached the red zone I used the electronic push-button heating controls inside the car to increase the temp to 32 deg (the max in this car), and turned the heater fan up high too. The temp gauge almost immediately returned to normal, and it stayed like that until I got home (another couple of miles). So somehow turning the heating up inside the car had the effect of returning the engine temp to normal (or so it seemed). When I got back I left it for an hour or so to cool down. I now notice that the coolant level in the reservoir has gone *up*, i.e. the level is now higher than the 'Kalt/Cool' mark. Would the above be the symptoms of the system needing to be bled? Or maybe the symptoms of some other known problem? I can't see any signs of a leak under the car or in the engine compartment, it all looks dry as a bone. When I slackened the filler cap on the reservoir I could hear a slight hissing sound indicating a pressure difference, but this might be because the engine /cooling system was still a little warm (it's actually a warmish day here for a change!). Does the above give anyone any clues as to what the problem might be? I haven't tried bleeding the system as I don't yet know how. There's a cross-headed plastic screw near the reservoir filler cap, and a similar one near the 'engine' end of the top hose from the radiator. Are these what you use when bleeding? I'd be grateful for any advice on this. Thanks for your help so far. Flummoxed > A few minutes after it reached normal temperature, it started to creep > upwards towards the hot zone. But before it reached the red zone I used [quoted text clipped - 4 lines] > turning the heating up inside the car had the effect of returning the > engine temp to normal (or so it seemed). How fast were you going when the temp shot up? Signature*What boots up must come down * Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. Dave Plowman (News): "How fast were you going when the temp shot up?" I wasn't going all that fast, maybe 50 mph, 60 at the most. I was being careful and keeping my eye on the temp gauge. I wouldn't say it shot up, it just crept up from normal towards the high zone. I slowed down to see if it made any difference (like it did when I first discovered the problem), but this time it didn't seem to make any difference - the temp gauge kept creeping up. But as soon as I turned the heating controls and interior fan up, it went back to the normal position. Thanks again for the help, I appreciate it. Flummoxed > "How fast were you going when the temp shot up?" > I wasn't going all that fast, maybe 50 mph, 60 at the most. I was being > careful and keeping my eye on the temp gauge. Right - I'd say that rules out the fan coupling as it will be all airflow that cools the rad at that speed. Signature*i souport publik edekashun. Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. "Dave Plowman (News)" <dave@davenoise.co.uk> wrote in message <4e1bc9c27adave@davenoise.co.uk>: >> "How fast were you going when the temp shot up?" > [quoted text clipped - 3 lines] >Right - I'd say that rules out the fan coupling as it will be all airflow >that cools the rad at that speed. I'd taken my instruments out and taken them apart a little. I put them back without doing up the screw bits that put the two halves of the instrument panel together. This caused the clocks to indicate that the engine was overheating. Hi again and thanks for the continued help with this. Maybe I should have pointed out earlier: in Aug 2004 I had the Thermostat & O rings, and fan coupling replaced, then in Feb 2005 the waterpump was replaced. Therefore I think it's unlikely to be any of those components, as the car has been driven since then without any problems, until now. I suspect it might be that the cooling system needs bleeding, so if anyone can tell me how to do that I'd be grateful. As I said, I've found two cross-head plastic plugs that might be the things to use to do this - can anyone confirm this? What's the correct procedure? Thanks again for the help. Flummoxed > Hi again and thanks for the continued help with this. > [quoted text clipped - 12 lines] > > Flummoxed A cooling system that needs bleeding will not result in a higher level in the overflow tank (assuming you are checking when cold) Signature-Fred W Thanks for the replies. This morning I started the car up and waited for it to warm up, then I slackened off the two plastic plugs (one at a time) that I thought might be the bleed screws. I noticed a very small amount of liquid coming out of them, but not very much at all, then it stopped. I'd have expected liquid to keep coming out once it started (like bleeding a rad in a central heating system) but it didn't. Anyway, this time I did notice that I seem to have a leak, although I couldn't work out where exactly, somewhere underneath the coolant reservoir. It's probably only a slow leak and maybe only happens under pressure (when the engine's warmed up?). Guess I'll have to get it fixed anyway. This time the coolant level in the reservoir had gone down (once it had cooled again) and it took about a half litre to bring it back up to the Cool/Kalt level. The temp gauge never went above normal the whole time, which is good I suppose! One thing I wondered: should the two large hoses from the radiator to the engine (one top right as you look from the front, and one bottom left) be full of coolant? I can squeeze them very easily as if they're empty, whether the engine's running or not. I guess they must have liquid in though, but I'd expect them to be hard to squeeze if the system's under pressure. Anyway looks like I do have a slow leak, and that must have caused the coolant to gradually leak out and then air to get into the system which probably caused the weird effects on the temp gauge. I'm still not convinced I've removed the air from the system though, as I didn't really know what I was doing. I just hoped that slackening off those plugs would allow some air to escape and fill the space with liquid. It didn't seem to do that though :( Anyway thanks for the help. Guess I'll be calling the garage in the morning :( Flummoxed > One thing I wondered: should the two large hoses from the radiator to > the engine (one top right as you look from the front, and one bottom > left) be full of coolant? I can squeeze them very easily as if they're > empty, whether the engine's running or not. I guess they must have > liquid in though, but I'd expect them to be hard to squeeze if the > system's under pressure. Correct - they should be hard to squeeze when hot and for some time after stopping the engine. You've got a leak. I had a leak on my E39 which you couldn't see. A dye test showed it to be coming from the waterpump. Exhaust all possibilities before deciding it's the head gasket. Signature*Atheism is a non-prophet organization. Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. Dave Plowman wrote: "You've got a leak. I had a leak on my E39 which you couldn't see. A dye test showed it to be coming from the waterpump. Exhaust all possibilities before deciding it's the head gasket." No, it isn't the head gasket, the leak's somewhere below the coolant reservoir, but I couldn't see exactly where from. It was just a trickle of liquid coming from somewhere round there. There's a narrow hose with a jubilee clip coming out of the bottom of the reservoir, and I wondered if it might be that but I the jubilee clip didn't seem to need tightening (at least I was unable to tighten it any more than it was already). I couldn't see any other obvious thing to try. Anyway I've booked it into the garage now - hope it doesn't cost too much :( Thanks for everyone's help. TP I would say, but others may not agree -- it's sounding exactly like my car -- which was a blown headgasket -- do you get any sweet smell out the tailpipe or soot/oil in the coolant (or worse, milk in the oil?) I would definately try to bleed the system. >Right, here's the latest: Having topped up the coolant reservoir to the >"Kalt/Cool" level (it's a kind of see-through plastic reservoir next to [quoted text clipped - 35 lines] > >Flummoxed --- AntiSpam/harvest --- Remove X's to send email to me. Josh Assing wrote: "I would say, but others may not agree -- it's sounding exactly like my car -- which was a blown headgasket -- do you get any sweet smell out the tailpipe or soot/oil in the coolant (or worse, milk in the oil?) " Well, I hope it isn't that but you could be right for all I know. No, I didn't notice any smell. I haven't looked at the oil. Guess I'd better do that. I recently checked the oil and it seemed OK, but that was before I had this temperature problem. "I would definately try to bleed the system. " Sounds a good idea - I was hoping someone would confirm the answer to my point above, about the two plastic cross-headed screws that I think might be the bleed valves. Thanks again Flummoxed One point I'd like to reiterate (as no-one has picked up on it) is that the coolant level in the reservoir went UP rather than down after I drove the car. Can anyone say what circumstances would cause that? Could it just be that when the coolant gets warmed up it expands into the reservoir? If I had a leak or a blown head gasket I'd expect the level to go down not up. Does anyone haev any ideas? Thanks again for all the help. Flummoxed "Flummoxed" <google@gunningham.com> wrote > One point I'd like to reiterate (as no-one has picked up on it) is that > the coolant level in the reservoir went UP rather than down after I [quoted text clipped - 4 lines] > > Does anyone haev any ideas? 1) The level in the radiator/system *usually* goes up when warm. Extra is trapped in the overflow system and gets sucked back when the engine/radiator cools. 2) If *both* go up, that shows air infiltration (i.e., bad head gasket) (after entire system is cool.) 3) A bad head gasket doesn't necessarily mean loss of coolant - remember that cylinder pressure is higher than the coolant's vapor pressure. 4) Another source of air might be a leak in the water pump inlet pipe (from the bottom of the radiator). This isn't high probability, since the system pressure usually overcomes the pump negative pressure. FloydR that could be air moving around teh system.. or more air pushed into the system.. >One point I'd like to reiterate (as no-one has picked up on it) is that >the coolant level in the reservoir went UP rather than down after I [quoted text clipped - 8 lines] > >Flummoxed --- AntiSpam/harvest --- Remove X's to send email to me. > One point I'd like to reiterate (as no-one has picked up on it) is that > the coolant level in the reservoir went UP rather than down after I [quoted text clipped - 8 lines] > > Flummoxed Bad head gasket. That's the only thing I know of that will cause the level in the overflow tank to increase. The leak injects some exhaust gas from the combustion chamber into the water jacket. Once you have air (exhaust) bubbles in the coolant the pump will start to act up causing all manner of strange temperature displays. Signature-Fred W |
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