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Discussion Starter #1
hey guys i have used the search button and still cant find someone with this same problem. just bought the car a week ago and am starting to find some little things that are wrong with it.

this has only happened at freeway speed if that really matters but every once and awhile while driving the temp gauge will just go to strait hot, doesnt slowly get there it just drops from normal to overheating and then about one second later it will climb back up(or cooling down i should say) and takes about three seconds to get back to normal range.(12) it never drops the other way though so i dont think its the thermostat and it does it very random
i have already checked for air bubbles in the system
could it be a warning of a bad water pump, last owner had receipt showing changed 40 thousand miles ago.
any help would be greatly appreciated
 

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First of all, STOP driving it. You will cause substantial damage if the car truely is overheating. The water pump won't work intermittently, it either does or doesn't so if this happens every time you start your car, it very well could be. If not, look elsewhere. I agree that it's not the thermostat so that gives you two options if you can verify that the system was properly bled. Either the fluid isn't circulating or there's a leak. If the problem is intermittent, then look for a leak or faulty temp sensor.
 

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this has only happened at freeway speed if that really matters but every once and awhile while driving the temp gauge will just go to strait hot, doesnt slowly get there it just drops from normal to overheating and then about one second later it will climb back up(or cooling down i should say) and takes about three seconds to get back to normal range.(12) it never drops the other way though so i dont think its the thermostat and it does it very random
i have already checked for air bubbles in the system
could it be a warning of a bad water pump, last owner had receipt showing changed 40 thousand miles ago.
any help would be greatly appreciated
Thermostats can stick closed, as well as open.

Scan codes first. And don't drive it either.
Sticky thermostat intermittently? Agree if it was just stuck open, but a random come and go problem?

OP, how often does this happen and how long does the gauge needle stay at each spot (cold, normal, hot)?
 

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Discussion Starter #6
i scanned for codes and the only one i got was a p1092 so guessing thats the o2 sensor. so the car warms up normal and stays at the 12 position until just random times this happens, only on the freeway. it takes like less than a second to go from normal temp to over heating and stays at overheating for one second then climbs back to normal. sometimes once it reaches normal it will go strait back to hot again and do the same thing but most of the time it stays normal for at least a couple of minutes. sometimes i can drive for 30 minutes and not even have the problem. i tried to bleed the system to make sure there werent any air bubbles and only coolant came out. i was planning on flushing the system anyway so probably will pick up a new sensor and thermostat as well.
Thanks for the quick replies.
 

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Discussion Starter #7
First of all, STOP driving it. You will cause substantial damage if the car truely is overheating. The water pump won't work intermittently, it either does or doesn't so if this happens every time you start your car, it very well could be. If not, look elsewhere. I agree that it's not the thermostat so that gives you two options if you can verify that the system was properly bled. Either the fluid isn't circulating or there's a leak. If the problem is intermittent, then look for a leak or faulty temp sensor.
alright so i just did a second scan with a peake scan tool this time and now its saying i have 19 oa e6. what does this mean? oa is a engine sensor but which one? is it the engine coolant sensor or the radiator outlet sensor. do these things fail very often. does anyone have a part number. thanks again guys.
 

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alright so i just did a second scan with a peake scan tool this time and now its saying i have 19 oa e6. what does this mean? oa is a engine sensor but which one? is it the engine coolant sensor or the radiator outlet sensor. do these things fail very often. does anyone have a part number. thanks again guys.
Peake Codes Table 19

0A: Engine Coolant Temperature
E6: Pre-Cat O2 sensor, bank 2

My guess is your coolant temp sensor kicked the bucket along with the pre-cat O2 sensor.
 

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I'm going to assume that you also checked the antifreeze level and that its full and you have found no signs of a coolant leak. Could well be the sensor, or it could be something else. I agree with what was written so far; the thermostat can either stick open (running colder than normal) or it can stick closed (running hotter than normal), usually though, the thermostat will not randomly go from either to normal and then back again. Have you checked the fan? Checked the belt? Unlike the 325xi's that have no fan attached to the motor, all electric, your fan is driven by the motor and has a fluid coupler. If this fluid coupler is bad, you can get random overheating, especially at constant highway speed. A bad water pump will not normally act this way, either. Did you also pull the oil dip stick to see if the oil is milky white in color which would indicate a blown head gasket?
 

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Discussion Starter #10
I'm going to assume that you also checked the antifreeze level and that its full and you have found no signs of a coolant leak. Could well be the sensor, or it could be something else. I agree with what was written so far; the thermostat can either stick open (running colder than normal) or it can stick closed (running hotter than normal), usually though, the thermostat will not randomly go from either to normal and then back again. Have you checked the fan? Checked the belt? Unlike the 325xi's that have no fan attached to the motor, all electric, your fan is driven by the motor and has a fluid coupler. If this fluid coupler is bad, you can get random overheating, especially at constant highway speed. A bad water pump will not normally act this way, either. Did you also pull the oil dip stick to see if the oil is milky white in color which would indicate a blown head gasket?
yeah the coolant level is normal at the max line after letting the engine cool down. the oil is normal as well( no milky color). i have not checked the fluid coupler but i will do that thanks.
 

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Discussion Starter #11
just checked with the previous owner and he said he never had this problem before. always stayed at normal temp. but i just looked at the service records that came with the car and looks like the o2 sensors,where changed back in 08 by the dealer and the thermostat sensor was changed in may, nov, and dec of 08 three times in a couple months. the thermostat was also changed in may of 08. could it really be 3 faulty sensors. im thinking there has to be something more going on.
 

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i would bet a faulty temp sensor.. replace it and see if it continues. Even if the car is truly over heating it will climb to hot slowly, not just instantly JUMP to hot... if its just jumping like that i would say its the sensor.
 

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If your coolant system is full, the belt good, there are no signs of coolant leaking, no coolant in the engine oil, and you are not truly overheating (you could slowly and carefully open the fill cap when the gauge says its overheating and stick a thermometer in to get a reading), then I would also agree with a previous poster, you probably have a faulty temperature sender (they do get a build up on them which can affect how they work besides just going bad). This is an inexpensive part to replace. IF the problem still exists after replacing the sensor, then look towards the fan clutch like I previously said. If the fluid coupler of the clutch is bad, the fan will not pull enough air thru the radiator at highway speeds to allow the coolant to "cool", thus increasing the coolant temperature.
 

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I had this same problem with my 2005 330xi awhile back. For some unknown reason the temp would would not just get hot but would instantly peg full hot. I would shut off the car and turn it back on and the temp would be normal. The problem I found was not any sensor or fan/clutch, it was the thermostat. The thermostat stat will usually fail open. Yes it can fail closed too. I don't know how long you have had this problem but, I knew mine failed open this last winter when I couldn't get heat driving down the road in sub freezing temps. Once I changed the thermostat, I haven't had a problem since. I'm not a expert on fluid thermodynamics but my guess is with the open flow in the system caused by the failed thermostat allowed heated vapor to set off the temp sensor. Just a guess but the new thermostat fixed my problem. Oh ya, I didn't have any fluid leaks or replace any sensors either. Hope this helps.
 

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I have a similar problem. One thing I noticed was that my temperature gauge when the car is fully cooled down overnight is still at the first notch above the blue. It never goes under that. And when the car fully heats up, it just hang souts right under red but never goes higher. The shop I took it to says that the car's internal temp is normal, the gauge is just reporting it wrong.. then he said that I need to replace the instrument cluster that was going to cost over 1k...not sure if he even knows what he's talking about. Looking on ebay, it looks like there are used clusters under 100 so i think ill move in that direction instead. Although the guy says my car is running normally, its still nervewracking to drive with the meter that high.

Anybody else see this?
 

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thinking this over, if the temp gauge was still active even after the car was shut off, i decided to reset the battery. This seemed to work fine and the temp is sitting steady in the middle!
 

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Discussion Starter #19
alright guys here is my update. it has been almost 2 months and still have the same problem. I have changed the thermostat, 2 different temp sensors (lower radiator hose sensor and the one under the intake manifold) i tried resetting my instrument cluster, i flushed and bled the entire system, and changed the fan clutch. im glad i changed all these things now that i dont have to worry about them for awhile but still have no idea what else could be causing this. i guess the next step would be to change the instrument cluster itself with a different one. One other thing that i thought it could have been was that i found the wires that were going to the thermostat housing were all exposed( the plastic cover had broken to pieces and fallen off.) and they were all pressed against the engine block. i put a new cover on them and put them where they were suppose to be and still have the same problem.
 

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Discussion Starter #20
so i have done some more research and im starting to think that it might be something with the DME. they say the problems that show with scan is the o2 sensor and the temp gauge will slam to red hot. (sounds familiar) anyone know what i can do? reprogram by dealer? how much does that cost?
 
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