[QUOTE=SD1too;2775726]I didn't say the ECU knows what type of fan is fitted. It's simply down to the differences in motor brush and relay wiring and is totally independent of the ECU. So, when the 2-speed replaces a 3-speed all four brushes in the motor are permanently in circuit and it runs at what might be described as 'medium' and 'high' speeds. In effect, the old low and medium duties are both provided by 'speed 1' in the new system.

But to justify your doubt you should also ask if any KV6 3-speed owners have witnessed heat soak operation. I'd expect similar statistics since the potential for engine-off 'after boil' exists whether it has a 3-speed or a 2-speed fan. I can confirm that the MEMS/2-speed triggers heat soak cooling in the 1.8T - for up to five minutes as I recall. I note the KV6 is set for up to ten minutes, logically because of its larger thermal capacity. I don't think heat soak is covered by RAVE, the MGR diagram is from elsewhere.


TC

All evidence is potentially useful but on the face of it the "heat soak" condition would not trigger the fan on a 2 speed system. This is because the connection which the ECM earths (UY) to achieve this is not connected to the fan control box at all! This is why I am interested only in the 2 speed system.
That's incorrect I'm afraid. The chart which you have reproduced is from RAVE.

Simon

The heat soak cooling on a 2 speed fan certainly works.

:smilie_re: https://the75andztclub.co.uk/forum/s...d.php?t=297755

I've just re-read that thread and charlie_22 actually says the opposite. Here's an extract from his opening post describing that his fan doesn't run after stopping the engine:
Unfortunately he doesn't ever tell us whether or not his coolant temperature reached the threshold of 115 degrees so the thread doesn't help us.

Simon

I have re-read the thread too and you are quite correct! :}

Sounds like the cars heater system needs a good clean out on the liquid side of things for the cold and hot footwell.
The fan on the cars coolant Rad I would expect to run full time engine on or off if the sensor was above 115 degrees. Your fan has four speeds or three depending how you look at it.
1: not running
2: low speed
3: medium speed
4: high speed
Hope this helps


Sent from my iPad using Tapatalk

Poor flow through the heater won't cause high coolant temperature Alan.
Dave's fan has two speeds, as he states in the post you've quoted.

Simon

So the KV6 'after-boil' protection is likely absent where a 2-speed fan is fitted? It seems implausibe and something that should be checked out. Just needs a few volunteers and a hot summer.



TC

Plus, I would contend, a faulty cooling system.

I have the original 3 speed fan. I have never heard the radiator fan operate after stopping the engine, even in the hottest summers (after all, the coolant temperature has to climb to 115 degrees).

Simon

But that doesn't prove much does it.
Maybe try hauling a big caravan, at the limit, in hot weather, perfect cooling system and you hit a road block. That's volunteering.


TC