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

On Thu, 17 Nov 2005 10:09:05 +0000, Fred Labrosse <[email protected]>
wrote:

>All,
>
>My TD5 tends to run cold.
>
>While it was not too cold outside, I was accepting the argument that the

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

fanie wrote:

> On Thu, 17 Nov 2005 10:09:05 +0000, Fred Labrosse <[email protected]>
> wrote:
>
>>All,
>>
>>My TD5 tends to run cold.
>>
>>While it was not too cold outside, I was accepting the argument that the
>
> 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?

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

>
> 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.

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

Cheers,

Fred

On Thursday 17 November 2005 10:09, Fred Labrosse [[email protected]] wrote in
message <[email protected]>

> 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.

Unlikely.

> 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).

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.

--
S3 SWB Petrol Hard-top

PDannyD wrote:

> On Thursday 17 November 2005 10:09, Fred Labrosse [[email protected]] wrote
> in message <[email protected]>
>
>> 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.
>
> Unlikely.
>
>> 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).
>
> 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