Engine slow to reach temperature then losing temperature

[minniemousey]

So after solving my power steering hose failure and replacement, i'm now on to the next problem...

In the colder weather i have noticed two things...1. the engine has been very slow to reach optimal temperature (if it does at all) and doesn't often move off about 60 degrees and 2. subsequent fuel consumption is very poor.

Today I did an experiment...I had the van idling until it reached 90 (took a while), drove it around town where it held temperature until I took it on the open road where it dropped and sat between 60-70 and stayed there until i was back in town. Whilst replacing my power steering hose, I noticed that one join on the intake manifold hose was not clipped in properly. After righting it, I have noticed that the engine temperature does move a little more than it did but still nothing like it should.

Anyone else come up against this problem? Is it as simple as replacing a faulty temperature sending unit or thermostat or am I looking at a failed water pump or head gasket issue? Or something completely different?

[Sunny43.5]

Not wanting to sound flippant but wouldn't the cold weather down south have a bearing on the temp ? obviously idling there would be minimal air moving around the engine bay so the temp would reach norm . But when you drive the incoming cold air would affect the engine temp , just a thought .

[minniemousey]

I think the lower outside temp would only make it reach operating temp a bit slower, then the thermostat would keep it at the optimal temp. These fluctuations haven't happened any other winter....

[Greg Roles]

I reckon thermostat. If it's stuck open it will be very slow to heat up, will struggle to maintain temps down in chilly Vic, and will be on choke cycle a lot longer. Be worth replacing just in case, you can always pull it out and put it in cold / hot water to see if it is working.

[Notso Swift]

No question in my mind you have a sticky thermostat
May have been like that for a while but hasn't shown up until it got cold
Bonus is it is a very easy fix

[minniemousey]

Hey Notso Swift, you wouldn't happen tomhave pic's or a link for this would you? From what I understand the stat is behind the turbo and you need to take the air box out, is this correct. I haven't bothered to have a look yet.
Cheers

[Notso Swift]

Not on a TDI van. sorry, I doubt you would have to take the turbo itself off, not really sure but I think these have a the thermostat is sort of under and behind the alternator
Mr Google should be your friend as someone will have scanned a Haynes manual

[Sunny43.5]

I would ask Umai he is a VW mech and quite often has answers .

[minniemousey]

So after asking the mechanic to check the thermostat and explaining the symtoms he was sure it was a temp sensor. Very sure. After driving, he confirmed it's the thermostat.