SQ5 BiTDI Coolant Temperature Fluctuates

wilco184

Registered User
Hi,

I have an issue with my 2013 SQ5 where sometimes the coolant temperature only gets to around 75 Deg C on the dash and fluctuates a little either side of this. Sometimes it'll be rock steady at 90 which obviously is fine.

I've investigated a little with VCDS and it seems that the ECU is asking for the coolant temperature to be 75 Deg C sometimes. The 'coolant temperature at radiator outlet: specified' value is 75 or sometimes 90. When it's set at 75 and the coolant temperature creeps up to 76 or 77, you can see the map controlled thermostat F265 duty being increased to lower the coolant temperature, causing the small fluctuation. I can't find what affects this specified value.

Has anyone noticed this with their own BiTDI or could anyone suggest why the car would want to lower the coolant temperature like this?

Many thanks,

Matt.
 

Lartza

New Member
Hi Matt,

Did you manage to find the reason for the weird behaviour? My 2015 SQ5 TDI (CGQB as well as yours) has started doing the same excact thing. The specified value drops to 75.

It has started dropping the value since summer and warmish weathers arrived.

Thanks,
Lauri
 

wilco184

Registered User
Hi Lauri,

I’ve since worked out it’s because the engine can’t keep water in the ‘block circuit’ as it should. The water in the part of the system should be held static by the control valve in the V up to 105 Deg C. For cars with this issue, water escapes back into the main coolant circuit.

It happens when the outside temp is 15 or above because EGR cooling is activated at 15 Deg C, and the main coolant circuit temp is lowered to 75 from 90.

I’ve had the thermostat and control valve replaced, but these haven’t been the issue.

If you’ve got VCDS I can give you some pointers of things to check.

Thanks,

Matt.
 
Top