Hi I have a MK2 2011 estate with a 1.6 BSE engine.

 

I have just changed my timing belt and water pump, but now when I'm driving the temperature gauge will get to 90 but then dips down to 60/70 and then back up to 90, this is during standard urban area driving and on the motorway.

 

It was fine before I changed the coolant.

 

Could this be due to air in the coolant system? I'm happy to change the thermostat and temp sensor if it needs be, but it's just strange how it was fine before then. 

 

I've done a scan on VCDS and nothing is showing :s 

 

if anyone has any advice that I could check I'll be greatful, thanks  

Is this by chance a DSG automatic, if so the DSG thermostat causes what you experienced?  Loads of write ups about it including mine somewhere. Easy to change. I had it on a Superb 2. So check that forum. 

2 hours ago, gav_is_con said:

Is this by chance a DSG automatic, if so the DSG thermostat causes what you experienced?  Loads of write ups about it including mine somewhere. Easy to change. I had it on a Superb 2. So check that forum. 

Hi, no it's it's just a standard transmission, I ended up changing the thermostat yesterday after checking it, because I started the engine and kept feeling the hose from the thermostat housing, and it started getting warm before the engine had reached 90° and I used the laser thermometer and and both pipe in and put the engine was the same temperature, so it must have been stuck open.

 

Now it's changed the outlet pipe is staying cold untill the thermostat is at 90°

 

But the temp gauge is still going up and sitting around 60-70° for a while before the thermostat open and the coolant hits the temp sensor at the bottom of the radiator.

 

I noticed there was a second temp sensor at the coolant inlet housing to the engine.

 

I'm guessing, the sensor at the bottom of the radiator attached to the thermostat hose is the sender to the ECU. 

And the sensor at the inlet housing to the engine is the sender to the dash reading, and maybe the is why the coolant drop while driving because the coolant is changing the cycle :s 

 

but I can get 2 febi sensors for £18 so I'm thinking of just changing them anyway to be on the safe side.

I'd prefer just one coolant sensor so the dash and ECU is on the same page lol