Coolant temperature gauge

[Alistair Kerr]

Hello there
I have a 2014 B class SE automatic 1.6 petrol with under 20000 miles on the clock . My problem is that on the beginning of a run the coolant temp gauge will fluctuate relatively quickly between 50% and say 20% while gradually increasing to the correct temperature. Once there it remains constant up and down hill.
Because of this constant correct reading my feelings are to reject the thermostat and suspect the temperature sensor itself . The water level is at the correct level
Any suggestions would be gratefully received

Alistair Kerr

 

[mercman111]

iwould replace the thermostat first,its the cheaper option

 

[mioba]

Stats and pressure caps wear out.

 

[Alistair Kerr]

iwould replace the thermostat first,its the cheaper option

Thank you for that. Is it an expensive job on a b class to replace the thermostat ?

 

[Alistair Kerr]

Stats and pressure caps wear out.

Thanks for the info I will change the pressure cap first as it is the easiest to do

 

[mioba]

Make sure you get a genuine from the dealers

 

[Alistair Kerr]

Thanks for that but unfortunately it hasnt helped. On closer inspection over several trips the fllowing situation has become the norm. On warming up the temp will vary once or twice between 60 and 80 ie it will rise at a normal rate to 80 drop relatively slowly to 60 and then rise back to 80 relatively slowly, so that to me it looks like the actual coolant temperature change and not an electrical problem After that it will rise to 90 degrees and will remain there for the rest of the drive no matter what speed or ambient temperature.
Has anybody out there had a similar experience with a B class or is it just me
Thanks in advance
Alistair

 

[mioba]

Did you replace the stat?

 

[Alistair Kerr]

Thanks for coming back. No I have not replaced the stat yet. To be honest I was hoping that it was something else at fault as it appears to be a awkward and expensive job to do.
Alistair

 

[EmilysDad]

..... No I have not replaced the stat yet. .....

I think a new stat is the first thing you need to change. If you start your car from cold and monitor the temp of the top rad hose, it should stay cold & then get quickly hot. If the stat has failed, the top hose gradually gets hot

 

[mioba]

Awkward and expensive is no excuse if thats the fault to be fair. MB stats are made of butter. Changed them on all my cars circa 10 years due to failing.

 

[brandwooddixon]

The modern "electronic" ones aren't exactly cheap either. The old wax thermostat isn't enough these days, instead its all controlled by the engine management system.

 

[mioba]

seems the new electronic ones are worse …..
Can they be tested like the old ones.

 

[EmilysDad]

The modern "electronic" ones aren't exactly cheap either. The old wax thermostat isn't enough these days, instead its all controlled by the engine management system.

The 'ECU controlled motorised valve' that is fitted in EmilysMum's Citroen in lieu of a proper thermostat was around £170 5 years ago! Plus fitting

 

[Alistair Kerr]

Thank you all for your replies I guess I will just have to bite the bullet and get the thermostat replaced. Would you recommend that I get a Mercedes one or some other manufacturer.

 

[Blobcat]

Mercedes, guaranteed to fit and work

 

[Alistair Kerr]

thanks for that

 

[brandwooddixon]

The 'ECU controlled motorised valve' that is fitted in EmilysMum's Citroen in lieu of a proper thermostat was around £170 5 years ago! Plus fitting

I had the thermostat replaced on my CL last year between lock downs and being one of the electronic ones it cost me £350.