Cold TD5

I tend to agree with your diagnosis. The thermostat should control the temp regardless of what the fan is doing (assuming that the fan does enough when called upon).

Can't help with the TD5 but I can tell you that the 300 Tdi has the temp sender just after the TStat and removal of the TStat is a very simple job - I can't imagine how the fan would enter into it?

You can static test the TStat in a kettle or similar with a thermocouple measuring temp against the opening and closing specs for the TStat and see if it is doing what is required.

I would just get a new thermostat and see how the engine does with that.

Regards Stephen

I think it's just that it's in the way. I'll have a look tomorrow.

I'll probably do that if I can get to it.

Cheers,

Fred

Unlikely.

Most likely the thermostat, as you say.

My S3 with a fixed fan gave the same symptoms you've given and when I took off the thermostat housing I found the previous owner had somehow managed to smash the top of the thermostat over to one side so it was always open.

Beamends sent me a new one for a piffling amount of money, postage was very reasonable and arrived promptly too.

Right. I did some tests last weekend.

Removed the plastic cover at the top of the radiator so that I could touch it, started the engine from cold and monitored the temperature everywhere (with bare hands).

At idle, water gets warmer at the exit of the engine and most of that warm water goes to the heater matrix (temp higher before than after the separation). Good. Very little heat goes anywhere else. When accelerating, more heat is produced and the top of the radiator definitely becomes warm, warmer than the by-pass hose. And this is still with the engine being cold (heater gauge in the blue).

The conclusion is: thermostat in need of change.

Does that make sense?

Cheers,

Fred