Engine temperature / cabin heat inconsistent
Thread Starter
Junior Member
Joined: Jan 2010
Posts: 49
Likes: 0
From: North of Boston
2007 E350 4matic
Engine temperature / cabin heat inconsistent
I was having issues with my cabin heat only working when I had it set to the hottest setting so I replaced the heater control valve a few months ago when it was still warm out and everything seemed to be fine.
In the past few cold months when the outside temperature has dipped down below 20 degrees F it seems like the engine temperature struggles to reach 80C even after driving over an hour. It hovers around 74-76C and sometimes spikes to 82C then falls back down to 74-76. This has corresponded with lower cabin heat. I still get hot air blowing through all the vents front and back and on all settings but the heat is just not as hot as before even when set to high.
The indy shop didn't get any error codes when the checked it out. The owner thought it could be the thermostat but with no codes didn't want to just replace the thermostat.
In the meantime it has gotten a little bit warmer out. We had a few days of 40-55 F degree weather but I noticed that now the engine temperature would rise to close to 100C. And of course the cabin heat is hotter then too.
This morning it's cold again 22 F degrees and the same thing happens with the engine/cabin heat not getting to normal temperature.
When it's really cold out (below 15 or 10 F) I can barely get the windshield defrosted of ice. And as the weather gets warmer I'm concerned that I'm going to start having engine overheating issues.
Are these symptoms of the thermostat starting to fail? Should I just go ahead and have it replaced? What else can it be? And what should I look out for?
Thank you.
In the past few cold months when the outside temperature has dipped down below 20 degrees F it seems like the engine temperature struggles to reach 80C even after driving over an hour. It hovers around 74-76C and sometimes spikes to 82C then falls back down to 74-76. This has corresponded with lower cabin heat. I still get hot air blowing through all the vents front and back and on all settings but the heat is just not as hot as before even when set to high.
The indy shop didn't get any error codes when the checked it out. The owner thought it could be the thermostat but with no codes didn't want to just replace the thermostat.
In the meantime it has gotten a little bit warmer out. We had a few days of 40-55 F degree weather but I noticed that now the engine temperature would rise to close to 100C. And of course the cabin heat is hotter then too.
This morning it's cold again 22 F degrees and the same thing happens with the engine/cabin heat not getting to normal temperature.
When it's really cold out (below 15 or 10 F) I can barely get the windshield defrosted of ice. And as the weather gets warmer I'm concerned that I'm going to start having engine overheating issues.
Are these symptoms of the thermostat starting to fail? Should I just go ahead and have it replaced? What else can it be? And what should I look out for?
Thank you.
Out Of Control!!
Joined: Aug 2010
Posts: 12,517
Likes: 628
From: Charlotte NC area
2019 WS222 S450 4-Matic / 2007 W211 E350 4Matic (Sold) / 2008 X164 GL320 CDI
Looks like a whole batch of '07 thermostats are aging out.
Also, you won't get an error code till it gets really bad. (or it overheats)
The seem to fail in the open position. (Running cold)
As for what else to do, Have the belt checked/replaced.
Have the idlers checked (mine were good)
Have the tensioner checked. (Mine is getting a bit loose, Probably the source of a very slight squeak when cold. Will be replaced soon)
Also, you won't get an error code till it gets really bad. (or it overheats)
The seem to fail in the open position. (Running cold)
As for what else to do, Have the belt checked/replaced.
Have the idlers checked (mine were good)
Have the tensioner checked. (Mine is getting a bit loose, Probably the source of a very slight squeak when cold. Will be replaced soon)
Last edited by N_Jay; Mar 13, 2014 at 10:13 AM.
Thread Starter
Junior Member
Joined: Jan 2010
Posts: 49
Likes: 0
From: North of Boston
2007 E350 4matic
Thanks guys.
The belt, tensioner and idlers were checked at the last service and I was told they're fine. I do get some squeaking on start when it's cold out. Doesn't seem to have gotten worse but I'll keep an eye on it.
Is the thermostat an easier DIY job than replacing the heater control valve? What's the approximate cost of the part?
The belt, tensioner and idlers were checked at the last service and I was told they're fine. I do get some squeaking on start when it's cold out. Doesn't seem to have gotten worse but I'll keep an eye on it.
Is the thermostat an easier DIY job than replacing the heater control valve? What's the approximate cost of the part?
Out Of Control!!
Joined: Aug 2010
Posts: 12,517
Likes: 628
From: Charlotte NC area
2019 WS222 S450 4-Matic / 2007 W211 E350 4Matic (Sold) / 2008 X164 GL320 CDI
Part is about $100 and often comes in a kit with a gallon of coolant for about $125.
Easy job if you have a few basic MB friendly tools (Torx sockets and bits)
https://mbworld.org/forums/e-class-w...lfunction.html
Easy job if you have a few basic MB friendly tools (Torx sockets and bits)
https://mbworld.org/forums/e-class-w...lfunction.html
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