Running at 70°C heat temp, average 25mpg on the motorway!

[Shady Pioneer]

On the way back from Volksfest I noticed my temp gauge was down sitting at 70, it had reach 90 previously in the day when I left the engine running during pack up down in the pissing rain at Volksfest. 

Flicked through to my MPG and saw after 45 minutes of driving on the motorway doing 65mph that I'd only averaged 25mpg! This is most definitely not right as I've done better driving through town. Usually on long journeys it's around 35+ depending on how fast I'm going.

What could the cause be?

[Screech16v]

Your stat may be stuck open

[Shady Pioneer]

Your stat may be stuck open

How would one check this? 

[Screech16v]

Tell tale signs are taking alot longer than normal to warm up , never reaching normal operating temp whilst being driven,will use more fuel,they cost about £6 so very cheap to replace

[dom]

My guess would also be the thermostat. I'd change it as a first step, it's cheap & easy enough to do

[dragongreengolfgti]

after this temp sender maybe the 4 wire plug thing ?

[Wayne]

Thermostat sticking open.

[Shady Pioneer]

I'll go get myself a new thermostat tomorrow then. Cheers fellas.

[Shady Pioneer]

Do I have to drain the coolant system? I did it last weekend. 

[dragongreengolfgti]

most if not all will come out once you take the thermostat housing apart might be worth getting a new housing aswell as they like to break sometimes expect a little leak once fitted again fidly little job just make sure you get the o ring sealed properly once you re assemble