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Cold TD5

All,

My TD5 tends to run cold.

While it was not too cold outside, I was accepting the argument that the engine is a big lump so needs time to warm up. Now it's a bit cold, I find that on my daily trip (about 7 miles with some traffic jams), the needle barely goes into the white. This makes me think the viscous fan is not working properly. However, yesterday evening, while the engine was almost normally hot (after a long climb), it became cold again (needle towards the very bottom part of the white) while going down a steep slope on some lane, so moving slowly. This clearly makes me think the thermostat is not working properly (and fixing this should at least make the engine run warmer even with a less than optimal fan).

So my questions are:

- Is my diagnostic correct?

- Do I really have to remove the viscous fan to get to the thermostat?

- If the answer to the above is yes, do I really need the special tool mentioned in the workshop manual to take it out?

TIA.

Cheers,

Fred

Reply to
Fred Labrosse
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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

Reply to
fanie

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

Reply to
Fred Labrosse

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.

Reply to
PDannyD

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

Reply to
Fred Labrosse

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