Not Coming up to Temperature-thermostat ?

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2007 M-B E350-80k miles. Runs great although with the cold snap 10F ambient air temp, the car temp will not rise above 70C~150F. As I slow down the temp gauge will actually drop closer to 60C. The thermostat is a 100C- OEM replacement, and in the summer the water temp is over the 80C mark. The air in the car is very lukewarm at best. Is this a classic case of stuck open thermostat? it is supposed to be electronically controlled, but it is clearly not functioning. Last, coolant level is normal, car never overheats nor runs hot either.
 

typ901

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Originally Posted By: Olas
It might be the thermostat, or it might be the gauge. D you know how to test a thermostat?
Hot water trick to see if it opens with a digital gauge in the water to measure temp, but this one is built into a housing (neck) so not certain I could tell, but I am going to order a replacement thermostat and coolant. Another weekend project for me! Thanks for the help
 
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I just did a Thermostat on a Cruze 1.4T. It too was electronic. I have seen them go bad faster than regular thermostats. This car was an automatic, not only was the heat lukewarm, the gas mileage dropped because the car was running rich longer and the torque converter would take forever to lock up. Changed the stat and problem solved (til the water pump went out a week later). In this cold weather, the added fuel you use could outpace the cost of a thermostat. Though I priced it out for your car and its about $113 through Rock Auto.
 

typ901

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Thanks guys for the help. Seems to be straightforward replacement. I ordered MB approved coolant at $25 a gallon...ouch! along with the thermostat. I thought maybe I was getting too frail to deal with the cold, until I watched the gauge go down while in traffic several degrees. Always something with cars.
 
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Just out of curiosity, what year is your MB? The reason I'm asking is that last year I had to replace the thermostat on my 06 Mazda 3. The temp gauge always stayed in the normal position, but I got a CEL that pertained to the coolant temperature taking too long to reach a certain point. A co-worker of mine has the same model Mazda 3 and he got the same CEL, but kept on driving and eventually could also notice the coolant temp dropping. So there was obviously a logic in the PCM that could detect this fault before it showed on the dummy coolant gauge. I thought that an MB would throw some sort of code as well for this condition, especially since the thermostat is electronic, but perhaps MB gauges are not dummy gauges.
 
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P0128 but it sounds like his is working enough to keep the code away by staying above 160f. The thermostat is the most common problem when they are like this. Edit: No its not not a dummy, it uses a real gauge.
 
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typ901

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Originally Posted By: Trav
P0128 but it sounds like his is working enough to keep the code away by staying above 160f. The thermostat is the most common problem when they are like this. Edit: No its not not a dummy, it uses a real gauge.
2007- I put the info in 1st line of my 1st post. Yep. No code, and Trav is correct, it is a real gauge. I've read where a lot of people get concerned as it does move up and down in hot weather.
 
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Originally Posted By: typ901
Originally Posted By: Trav
P0128 but it sounds like his is working enough to keep the code away by staying above 160f. The thermostat is the most common problem when they are like this. Edit: No its not not a dummy, it uses a real gauge.
2007- I put the info in 1st line of my 1st post. Yep. No code, and Trav is correct, it is a real gauge. I've read where a lot of people get concerned as it does move up and down in hot weather.
Thanks guys and that explains why you could catch it before the code registered.
 

JHZR2

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Originally Posted By: typ901
Originally Posted By: Trav
P0128 but it sounds like his is working enough to keep the code away by staying above 160f. The thermostat is the most common problem when they are like this. Edit: No its not not a dummy, it uses a real gauge.
2007- I put the info in 1st line of my 1st post. Yep. No code, and Trav is correct, it is a real gauge. I've read where a lot of people get concerned as it does move up and down in hot weather.
Even if a real gauge, are we certain the sender is correct?
 

typ901

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Originally Posted By: JHZR2
Originally Posted By: typ901
Originally Posted By: Trav
P0128 but it sounds like his is working enough to keep the code away by staying above 160f. The thermostat is the most common problem when they are like this. Edit: No its not not a dummy, it uses a real gauge.
2007- I put the info in 1st line of my 1st post. Yep. No code, and Trav is correct, it is a real gauge. I've read where a lot of people get concerned as it does move up and down in hot weather.
Even if a real gauge, are we certain the sender is correct?
Rolling the dice man...hoping for some heat for my cold feet! So no not certain, but if the thermostat is not it, then I will run it to my indy.
 
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Originally Posted By: JHZR2
Even if a real gauge, are we certain the sender is correct?
Coolant level ok, temp gauge responsive but lower than normal, lukewarm cabin heat, no code set. A defective sending unit would likely set a code immediately. Just getting this car scanned will cost more than the thermostat. Yes, certainly its a possibility given it is a electrically controlled unit but without an advanced/OE scan tool diagnosing that would be difficult with no codes being set. I am not one for just tossing parts at something but in this case, given the information and symptoms its a fair gamble (nothing is 100%) IMHO.
 
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Are you people actually driving your cars around at 10 degrees Fahrenheit? I don't think I'd want to leave the house at those temps. shocked2
 
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Originally Posted By: Merkava_4
Are you people actually driving your cars around at 10 degrees Fahrenheit? I don't think I'd want to leave the house at those temps. shocked2
-20c right now outside. I gotta admit the C3 has a kick butt block heater. When I start it the coolant temp is at 75c and within a minute is climbing past the 75c mark. It's not a hemi but I'm certainly happy with it.
 
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Originally Posted By: Clevy
-20c right now outside. I gotta admit the C3 has a kick butt block heater. When I start it the coolant temp is at 75c and within a minute is climbing past the 75c mark. It's not a hemi but I'm certainly happy with it.
It's 54F outside right now. In another couple of weeks that's gonna be our daytime high. eek
 
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