M113 E500 runs cool on a run and hot in traffic

[yinujim]

Hi I have M113 E500 that seems to get up to 93c in heavy traffic but once you get on the motorway its reads a low down to 67c. I have replaced the original thermostat with a 87c Vemo thermostat and nothing has changed. There is no coolant loss, the heaters blow hot and the electric fans are working.

Does anyone know what could cause such wide fluctuations?

 

[oigle]

You say the fans are working. Have you checked the temp they cut in at? Thermo switch may be faulty.

 

[yinujim]

They cut in after 93C. In the summer in traffic it creeps up towards a high of 95, 96 and drops down to a low of 88-90 on the motorway. In the winter its a high of 89C in traffic and a low of 67C on the motoway

 

[oigle]

The only one that is out of synch is the 67° on the motorway. The thermo should prevent that unless you are travelling in VERY cold temps. Maybe consider some blanking off of part of the radiator in winter.

 

[brandwooddixon]

With the temperature dropping on the motorway I would have said thermostat is the issue even in the winter I wouldn't expect it to run that cold.
I know that you've replaced it but it could be a defective thermostat. It might also be a defective temperature sender or connector.
I'd be tempted to test the thermostat using a Pyrex jug, a jam thermometer and some hot water.

 

[yinujim]

Yes I might have to try that along with a coolant flush as it looks due for a change. There is also some slight play in the water pump pulley with you wriggle it up and down.