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My 2015 GLK350 gauge started to peg out at 120, however, the car was not running hot as the fans were on and the coolant was not boiling. The independent shop I took it to claimed the PCM was the cause of the false reading, they said they see the PCMs have internal fault codes often and it'll be a 2k fix. I thought that was odd, has anyone ran into this issue? I was assuming it would be a coolant temp sensor but that has become a pain as I can't see it on the back of the engine to even change it.
They just mentioned a driver fault code and an injector fault code. The temp rises as you drive like normal then will hit 120 degrees but the car isn't overheating it's staying at its normal temp, and the car goes into limp mode cause it thinks it's overheating. I just thought it was odd that a PCM would be the cause of the issue.
I was wondering if it rose to 120 in a second or two after the engine began to warm up. That would indicate a failing temperature sensor or a wiring problem. I’m not familiar with the ECM causing this, but I’ve only had one M276 to work on (mine) and it was quite reliable. You might consider changing the sensor any way. It’s a $20-$30 part, even if it’s hard to get to.
No, it rose there after the engine warmed up, upon further analysis the heater has stopped working, and the top radiator hose is hot while the bottom radiator hose is cold. I'm going to replace the thermostat, it's just weird that the engine wasn't showing symptoms of overheating
If it’s 120 it’s overheating , did you use an IR thermometer to check the cooling system , the temp sensor can go bad. Any hardware or box store will have IR thermometers cheap
Both fans run because it says it’s overheating. 223f / 106c is boiling point of 50/50 coolant mix . Buy a thermometer and test hoses, thermostat , anywhere you have coolant, get a new temp sensor or clean the connection first
223f / 106c is boiling point of 50/50 coolant mix .
Could be a lot higher than that. Add about 2.5 degrees for every pound of pressure in the system, so somewhere around 258F if you have a 15psi pressure cap.
It's not overheating though, shot a temperature gun on the radiator hose and it was 210 F while the gauge was showing 120 C plus. The independent shop said the same thing, but they're claiming the PCM is the cause. I just thought it sounded odd and was checking to see if anybody else had that problem also. I did find it odd, though that my heater quit working.
Both fans run because it says it’s overheating. 223f / 106c is boiling point of 50/50 coolant mix . Buy a thermometer and test hoses, thermostat , anywhere you have coolant, get a new temp sensor or clean the connection first
yes, a new thermostat comes in tomorrow. If it truly is the PCM, then I'll send it in to get repaired
210 is overheating, 190 is normal. IR guns are normally 3+3- in accuracy and figure you are reading a hose not the water. My fans don’t run in winter even at 40f outside. I hope you got a good thermostat not a Chinese from ace auto
No, it rose there after the engine warmed up, upon further analysis the heater has stopped working, and the top radiator hose is hot while the bottom radiator hose is cold. I'm going to replace the thermostat, it's just weird that the engine wasn't showing symptoms of overheating
what symptoms of over heating are you looking for? Blown motor?
Has coolant been changed? We had similar issue after changing coolant and water pump. M276 was a pain with air bubbles. No heat either until it properly burped.
If your engine overheats it will be toast...there won't be any warnings besides the gauge. Shooting hoses with IR gun is very imprecise.
T-stat "usually" gets stuck open vs. closed. But can be another issue.
Did you get codes run? Most any auto store does it free while you’re in the parking lot. Order what you need from fcp euro. I wouldn’t drive it!! It is overheating, one cold hose means water is not circulating either from failed water pump or failed thermostat.
The thermostat is mechanical not computer controlled, so that crook that wanted 2000 is a crook
Note too sure on the M276, but the thermostat on the OM651 diesel engine is electronically controlled, to speed up warm up time and to better/faster control overall temps.
The thermostat for M276 is 276-200-05-15. It has an electrical connector on it, but I doubt that it’s a “smart” part. It’s less than $170 from Mercedes, and fairly easy to get to.
@Djstan09 the thermostat was to be in on 02/02. How did that work out?
Last edited by Odd Piggy; Feb 5, 2024 at 02:46 PM.
the thermostat on the OM651 diesel engine is electronically controlled, to speed up warm up time
There is vacuum control on the water pump, as I understand, so it doesn't really circulate the water until the engine is partly warmed. Not aware of anything on the thermostat.
There is vacuum control on the water pump, as I understand, so it doesn't really circulate the water until the engine is partly warmed. Not aware of anything on the thermostat.
Here's some detailed reading on the cooling system operation: OM651 manual
The thermostat is mechanical not computer controlled, so that crook that wanted 2000 is a crook
That is not the case for the M276 engine,
That connector is for preheating as far as I understand. At least is electrical, controlled?
Also, the cluster reported temperature is a FAKE value. MB controls the reported temperature in ranges. 120 C is HOT since it is above the "normal range".
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