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I reported in an earlier thread that the beast experienced overheating and that I got a "check coolant" message. Turns out that the whole thing was caused by a bad thermostat. The car probably wasn't actually overheating, as the coolant had not boiled out the escape valve in the radiator cap even though the temperature guage rapidly climbed into the red. It was merely a false reading. However, fixing this took flying in the parts (thermostat and O rings), a wait of a week to ten days, and $500. These thoroughbred cars can be temperamental and expensive machines, but I guess we knew that when we bought them.
 

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I reported in an earlier thread that the beast experienced overheating and that I got a "check coolant" message. Turns out that the whole thing was caused by a bad thermostat. The car probably wasn't actually overheating, as the coolant had not boiled out the escape valve in the radiator cap even though the temperature guage rapidly climbed into the red. It was merely a false reading. However, fixing this took flying in the parts (thermostat and O rings), a wait of a week to ten days, and $500. These thoroughbred cars can be temperamental and expensive machines, but I guess we knew that when we bought them.
If it was a false reading, then why would you change the tstat? If it was a bad tstat, then the reading was accurate. Seems it can be one or the other, but not both.
In any event, glad the beast is back on the road!
Regards,
Jerry
 

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Jerry,
I guess what I'm trying to say is that the coolant was circulating properly through the engine and was not at dangerously elevated temperature, even though the thermostat said that it was. Therefore, the mechanic determined the thermostat was bad and replaced it. Now the guage reads normal operating temp and the car runs well. The guy had a ***** of a time with pinched and leaking O rings, though, and had to take the air box off twice.
 

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doesn't the engine management system take coolant temp readings into account when calculating proper air / fuel mix? the high reading would have had an affect on performance - though minimal.

glad it's running again, i hate those long waits while they're in the shop. I have to check every day for a status report.
 

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Jerry,
I guess what I'm trying to say is that the coolant was circulating properly through the engine and was not at dangerously elevated temperature, even though the thermostat said that it was. Therefore, the mechanic determined the thermostat was bad and replaced it. Now the guage reads normal operating temp and the car runs well. The guy had a ***** of a time with pinched and leaking O rings, though, and had to take the air box off twice.
OK, but for clarification, the thermostat doesn't measure temperature, it simply regulates water flow. The temp sensor tells the thermostat when to open and close.

Not sure which one was actually bad, perhaps the mechanic simply replaced both while he had everything apart. But as long as it is fixed, it is worth the $$ for the repair!!!:thumbsup:
Regards,
Jerry
 
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How many miles on your car? I think when we post failures of common parts, we should all get in the habit of posting mileage, so that others can know when to expect similar problems, and also if they want to try and head them off by changing parts before they fail. Glad your beast is back to normal. Aloha!
 

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How many miles on your car? I think when we post failures of common parts, we should all get in the habit of posting mileage, so that others can know when to expect similar problems, and also if they want to try and head them off by changing parts before they fail. Glad your beast is back to normal. Aloha!
Need4Speed,
I have just 38,00 on this '01 M5.
 

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OK, but for clarification, the thermostat doesn't measure temperature, it simply regulates water flow. The temp sensor tells the thermostat when to open and close.

Not sure which one was actually bad, perhaps the mechanic simply replaced both while he had everything apart. But as long as it is fixed, it is worth the $$ for the repair!!!:thumbsup:
Regards,
Jerry
Is the thermostat on M cars different from others? I'm familiar with mechanical thermostats which use a form of wax or gel that reacts to water temps on the engine side, which in turn opens the valve to allow coolant flow. I guess that's the reason for such a high replacement cost. :confused:
 

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I just had a similar problem where the coolant temps increased to borderline overheating @230F+. I replaced the thermostat and my coolant temps are now at 185F in warm weather conditions.
 

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What?! There is way too much bad info running around in here. The thermostat is purely mechanical. When water gets to 79C it begins to open and continues to open until fully open at what temp I am not sure. However, if it gets stuck, due to whatever reason, and its hot outside, the car will overheat, which is what it sounds like happened in the OPs case. The temp sensor merely "reads" coolant temp and reports it to the guage on the dashboard(and the ECU, but that is neither here nor there in this case). If only the coolant temp sensor was bad, the OP got taken for a ride. However I strongly suspect the car overheated. Just because it didn't overflow does not mean you did not overheat. ALWAYS trust your indications.

Did the mechanic replace the temp sensor? Did he tell you the line about it likely not overheating? If he did, I'd find a new mechanic because he is either a liar or is clueless.
 
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