Stuck Thermostat?

[pembssurf]

so my 2013 C250 CDI is really struggling getting up to temperature now it’s goletting cold. Today after 7 miles of the commute at 50mph it was struggling to get much past 55degrees and even after 25 minutes at the 17 miles mark I was struggling to even get 80 degrees. Noticed as soon as I coasted any amount of time it would immediately drop to 70 and as soon as I put my foot down and rwLly floored it for a few seconds I could get it to around about 80. Never got anywhere near 90. Also my fuel consumption has plummeted from 49 to 41mpg.


Question is, is this typical winter behaviour or is this a stuck thermostat. My approved used warranty is about to run out in 2 months and would like to get it sorted.

Thanks

Adam

 

[BTB 500]

Normally you can check easily enough by feeling the top radiator hose after starting the car from cold. If the hose starts to get warm the thermostat is stuck open.

 

[Yugguy]

Sounds like classic thermostat failing aye.

 

[pembssurf]

Local Merc dealership refusing to acknowledge its a problem because nothing is flagging up on Star. They are also trying to tell me a thermostat replacement would f be covered under the approved used warranty which is utter tripe.

 

[zipdip]

Well look on the bright side it could have failed closed then you would not be able to drive it very far,buy a new one and fit it but before you do boil it up on the stove to make certain it opens,it has been known for new ones not to work.

 

[Wolfie1]

This is very easy to diagnose, start the car leave it idling for ages head first against a wall/in a garage so there is no air flow and see if it heats up to 90, then go for a normal drive if the temp drops down and keeps dropping you have a stuck thermostat

 

[a111r]

OP's car should be at 90C within 10 miles, even in winter.

From his description, it's an 'open and closed' case of a failed 'stat.

 

[Joderest]

Have to agree, classic failed thermostat symptoms, failed in open position and not controling water flow effectively.
As an engine components I would have thought covered by warranty as not a consumable like brake pads.
Go back and moan at workshop manager.

 

[Martin 1]

Same symptoms on my CLK ragtop, had it changed today and the difference is dramatic. You only really notice, the first time it gets really cold and need the heater at its best.

 

[pembssurf]

Quick update. Went armed to the service desk with a big list of symptoms written down and demanded that it was given to a mechanic or service manager to look at. They eventually accepted it was prob the Thermostat. Took them 2 days to manually diagnose and also replace the thermostat despite it being pre booked with part in stock. Anyway long story short it’s all fixed now and covered under approved used warranty. Drove it back and car was at full temp 87 degrees from cold in 6-7 miles at 40mph and mpg is back in the low 50’s as opposed to high 30’s. When they took the stat out it was as we all suspected completely goosed. I honestly don’t know why they put up such a fight! Thanks for the advice everyone.

 

[exvolvoman]

For the price of a thermostat, only a few pounds, wouldn't it be easier just to replace it??

 

[pembssurf]

Well after driving to work in 4 degree weather today I can report the problem is still there. This either means they didn’t touch the car or that this is how it normall behaves. Did not even get to 80 till after 20 miles of 60mph. Sound right?

 

[clk320x]

Well after driving to work in 4 degree weather today I can report the problem is still there. This either means they didn’t touch the car or that this is how it normall behaves. Did not even get to 80 till after 20 miles of 60mph. Sound right?

Something's wrong there mate..... take it back.. mines upto 80c very quick

 

[Wolfie1]

Sorry if this comes across as stupid but you are looking at water temp as opposed to oil temp?
If it is water there is a secondary coolant line which runs the water either through the exhaust manifold or through the egr cooler (depends how new the car) to get the car up to temp quicker, possibily pipe has blocked/collapsed?

 

[Uky]

Got interested in this thread as I had a thermostat problem with my old M271 CGI. On those Engines, it is acknowledged by MB that they have a quality problem with the thermostat which is a multi-stage thing with partially electric control (heater). Inside there is a rubber gasket which loosens and make the valve go stuck in a partially opened state. The thermostat was not extremely expenceive, but it was a bit messy to change it since some servo oil hoses and the hose to the turbo had to be removed in order to get access.