Just got the expansion tank replaced today, as there was a slight leak in it, and it would not heat up properly and pressurize. Exp tank now gets hot ok, and car gets up to temp when reved 90c. However when driving, air flow over rad drops back to 60c. Gge reckon rad temp sensor could be faulty coz fan kicks in early , when idle.

cant see that, as when driving this has no affect.

I think thermostat jammed open thus keeping water cool when driving , and heating up when reved on idle ?????

Ironically this weather my ford focus diesel struggles to get up too temp, at least its better than over heating !!!

Just a thought on this, as its got colder is the anti freeze mixture strong enough????

My oil temp didn't get to 90Deg C until I had driven 60 odd miles at weekend and temp was ok here 8DegC! Coolant temp takes about 1/3 of the time oil does for me I think. But I was in a T-shirt and didn't even feel need to turn on the climatronic thingy ma bobby at all.

Engine speed on a Diesel is governed by the amount of fuel delivered. At tick over the quantity is miniscule, there just isn't enough waste chemical energy left to warm up the engine properly. That's why they are economical round town. Plus they are inherently more thermally efficient at greater load as a result of the higher compression ratio.

As someone mentioned, put the engine under load and it will use more fuel, be less efficient and pass more heat into the cooling system, which you can then use to warm the interior up. Result!

Idling and light use are your driving conditions and what seems to be causing the difficulty, so go the long way round, have a ball and get warm. But then I live in the country, don't do towns, traffic and all that poo anymore.

Added problem of course is the Octavia heater is NFG in COLD weather, which it may be up there.

Quick addition to this topic FYI. 2008 Octy 1.9Tdi PD 1Z5 BXE. After a 100m drive in cool conditions, the temp gauge wouldn't move past 70C. Got home fine. A couple of days' later, car went into limp mode, but no lights on dash. Temp gauge was stuck at around 65C, but would be a little erratic (rising a little, then dropping a little). Decided to go for coolant temp sensor replacement initially, as warm air was coming through the vents (indicating no thermostat issue).

Replacing the sensor was easy, only requiring the removal of the air box for access. Removal of battery, etc, was not necessary. Replaced with a Hella sensor - £11. After clearing the codes, the car is off limp mode and heats up to 90C after a drive and some stationary fast idling. Cools back down to around 75C on very cold days (like today), but increases when stationary.

Had no dash lights at all at any point.

One thing I did forget to do is to clamp off the coolant reservoir to minimise fluid loss. Fortunately, I had plenty in!

Probably a bit late to this. But one off my vectras had a similar issue once. It was the thermostat stuck open.

Decided to replace the thermostat as well. All sorted now. An account of it is on the VW TdiClub Forum under Mr Nexus.

Edited 9 January9 Jan by beezera10