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Discussion Starter #1
just curious if anyone else has had this problem, when i drive about 20 miles the temp gauge in the dash peggs at max temp. it seems be be the same time every time i go to work when i come off the freeway. i imedetely shut the car off then turn it right back on and the temp gauge shows normal again. i can watch the gauge and it goes from normal to max temp in a second so its not a gradual temp increse. i am going to replace the temp sensor tomorrow but does any one know for sure whats going on before i replce it? it does it every day to work and throws a engine overheat code, but its been doing it for a month now so i know the engine is ok.

thanks
 

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Yes the thermostat is a somewhat common issue in these cars and symptoms present exactly like yours. Replace the thermostat and those symptoms should be resolved.
 

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I am a bit confused, the thermostat fail in the open position in these cars. So it does not seem like you have had an overheating problem at this point.

I would change the temp sender first, it is on top of the Tstat housing and has a single 4 conductor connector as I recall. I believe they are under $30??

See what happens after that is changed.

I would still consider replacing the Tstat at some point as they do fail in these cars after about 7-8 years as PM anyway.
 

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Discussion Starter #5
sorry for the confustion. i think the temp of the engine is fine. the problem is with the gauge or the sensor. the car runs great its just every now and then the gauge peggs at the hottest reading.
 

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I agree, change the temp sensor first.

BUT, I am also recommending considering the Tstat as a PM, but I do not believe the Tstat is causing the temp to peg.

You could also have a loose terminal in the temp sender connector and/or a bad ground somewhere, but I would put a temp sender in it first.
 

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A quick note on changing the temp sender. With the car cold, you should be able to change the sender without draining any antifreeze.

Get the new sensor and washer ready, open the expansion tank cap, then close it back up to make sure there is no pressure in the system. Then loosen the sensor and if you quickly remove the old sensor and thread in the new sensor, you should loose very little coolant.

Hope it works out for you.
 

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i had the same problem and it was not the sensor,i replaced it.

it is your thermostat for sure.

i replaced the thermostat and the ring and problem solved.
 

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Son's M5 (build date 2/2000 IIRC) had the *exact* same problem.

We replaced the thermostat and the coolant sensor and it runs like a champ now with no problems. I believe the gauge pegging is the sensor going bad but his also ran cool so we did a 'two fer' replacement. It now runs exactly like it's supposed to and gets better gas mileage as a bonus.

This is an easy DIY job except for the two-fisted surgery it takes to remove the thermostat housing.
 

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Dude. Its already been said its the stat, but as others with a very recent join date and/or post count have chimed in here i WILL say this.

I'm not normally one for banging the "search" drum, so i'll say without doubt its the thermostat or thermostat sensor, but more likely the stat itself. I speak from experience and using the search function.
 

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Nightcrawler has a point about the production date, read the thread in the attached link in more detail, but also keep in mind that there may also be a wiring issue as well. If there is wiring issue near the portion that connects to the temp sender, changing the stat may cause the wiring to be relocated/moved slightly. I believe the temp will drop fully low if the connector is disconnected?? I have not verified this, if this is true, then a short on the same wire will probably cause the gauge to peg. The problem with the DME issue, is it will require dealer involvement and may involve a lot of expense for dealer labor and you may come out with no change?? Depends if the dealer is good and can tell you if there is a record of this reflash being done before. Hell the car is 10 years old, would be unusual that the problem has never been addressed??

http://www.m5board.com/vbulletin/e3...133090-cooler-temperature-gauge-goes-max.html

Seems there may be a DME reflash that may fix some of the temp problems, I see fan failures as well, but this will probably only show up in warmer temps during stop and go driving, and then there was the mother of all wiring problems in the above thread.

Again, you car probably needs a stat anyway, most M5 do, these stats fail all the time, but they do not typically fail closed, they fare designed ail in the open position.

If it were my car, as I have had to do a stat anyway, I would consider changing the temp sensor as it is very easy and relatively cheap (around $30 as I recall if you shop it around) then check the fan for proper function and watch the temps with the OBC, menu #7, as I now have this memorized after watching my temps due to a bad stat.

Good luck and hopefully you will get your issue resolved quickly and easily.
 

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Replace the thermostat man,solved my problem!
 
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