I have a Fiat Ducato based motorhome (2007 2.3 litre).

It has developed the habit of the clutch pedal suddenly becoming squeaky and feeling "notchy". When this occurs I can induce clutch slip as well. This only appeared to happen after about 20 miles of driving. Eventually I have determined that it only happens when the heater is running!

It seems that the heater driver side outlet is discharging hot air straight at the master cylinder and that is causing the clutch hydraulics to become slightly pressurised.

Have I gone mad? Has anyone else come across clutch slip being caused by the heater? Surely with no pressure on the pedal any expansion of the fluid should pass back to the fluid reservoir, not increase the pressure to the slave cylinder.

In the mean time I've got cold feet!

For future reference it did prove to be as I suspected. It shouldn't happen that the heater has an effect on the operetion of the clutch, but it did!

Yes, the master cylinder must have been defective in some way, presumably internal wear on what is after all just plastic. However, replacing the master cylinder has cured the problem, whether the hearter is on or off!!!

well done Ken on your solution, just shows what else can influence the master cylinder,

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