4HP20 auto and HDI combo really slow when cold

[dieselnutjob]

My 607 HDI auto is desperately slow off the line when the engine and/or transmission is cold.
After five or ten minutes it's fine, and above maybe 10 or 15mph it's fine as well.
It's as if the transmission doesn't allow enough torque converter slip for the turbo to do anything.
Does really cold transmission oil cause the torque converter to somehow become "stickier" thus altering what I beleive is known as the transmission "stall speed"?
Once the car is moving fast enough for the turbo to work in first gear it then takes off, it's just moving off from stationary that's a problem.

The problem is that a 607 is a big heavy car and with 1st gear being quite high the diesel engine below 2000 rpm with no turbo is probably making about 35bhp. Pulling out onto a roundabout can be interesting.

[CitroJim]

That's an odd one

Although I only have any direct experience of the 4HP20 on the end of a petrol V6, I cannot say I've ever noticed any difference in torque converter performance with cold oil and a cold engine. The only minor effect on a cold 'box is very slightly rough changes for a few moments.

This afternoon at -1 I pulled away quite sharply from my work parking bay and it was lively enough although it is hard to tell as I tend to be very gentle with a cold engine.

In theory I would have thought that slightly thicker (cold) oil would have made the stall speed of the converter rise a little and make it function slightly better and hence a little less slip so thereby reducing the torque multiplication a tad. If this is so, then on the V6 it is imperceptible.

On the early V6 the transmission holds first gear until the 'box oil temperature has reached 60 degrees or you've been driving for three minutes. Does yours do this?

The only other thing I can think is that it might be invoking a semi-snow mode when very cold and thus causing you to take off in second gear with very early lock-up?

Knowing how clever they've made the C5 4HP20 software, something like this happening would not surprise me at all...

Interesting...

Otherwise, it'll be purely down to the engine being very sedate when cold and at low revs. Cold diesels are often down on power until they get a bit of warmth into them. A lot of heat that could be transformed into useful power is dissipated uselessly into the cold metal and coolant of the engine. HDis may be worse in this respect...

It would be interesting to know if owners of 1.9TD diesels with the AL4 transmission notice this same effect. It may be worth posing this same quuestion in the Citroen forum where a few members have Xantias with this combination.