Bit of help, I’ve got a 2004 TD6. Gearbox stops driving when hot, I’ve flushed and changed oil and filter, replaced the oil cooler with a new one, checked I have atf flow to the cooler. Flushed the radiator and checked that water is being pumped out the right port of the radiator when engine is running.

Before I buy a radiator is there anything else it could be before I throw more money at it in the wrong direction. It drives well when cold (on the new ATF FLUID).

Literally 15 miles and it’s done

I only bought it as a stand in after engine failure on my disco4

I think you’re looking at this the wrong way. The fluid is supposed to get hot. It should settle at the same temperature as the engine coolant. The transmission has a temperature sensor and you would get a TRANSMISS’N OVERHEAT message if it was overheating. Overheating fluid doesn’t cause the transmission clutches to slip. However, if the transmission has an internal leak e.g. from a piston seal or a worn valve body, at higher temperatures the reduced viscosity of the fluid will increase the volume of the leak until potentially the oil pump can no longer keep up. At this point, the pressure on the clutches reduces, allowing a clutch to slip. When the transmission cools down & the fluid viscosity increases, the transmission goes back to operating normally again.

Is the TRANS. FAILSAFE PROG message being triggered when the transmission slips?

Phil

Not at first then eventually I get the message

If you switch off the ignition and re-start, does the problem persist? Des

2005 (2006 MY) L322 4.2sc Java Black, 2010 facelift conversion
1965 Lenham Lemans GT 1310 , Gulf Racing blue, FIA spec and road legal
2018 F56 Mini JCW, Thunder Grey/Black, Mulgari St2 tuned, FMIC, short shifter and Eibach springs

The problem goes away but only for a few minutes

The controller should have stored the fault code for the failsafe message (e.g. indicating which clutch is slipping) so, usually, the next step would be to get the codes read. However, the GM 5L40-E transmission is infamous for its lack of durability in the L322, with many TD6s being on their 3rd or 4th transmission by now, and often this comes down to worn valve blocks. Did you notice if there was ‘glitter’ in the fluid when you changed it? A possible route forward would be to send off the valve body assembly to somewhere like Valve Bodies UK and they could test it on one of their Hydra-Test machines to check if it’s maintaining pressures and that all the solenoids are functioning properly. The valve body assembly can be removed and replaced without having to remove the transmission from the vehicle.





Phil

There was glitter as you described however the fact it is fine when cold would indicate that it has the ability to be ok. I’m not looking for perfection just a useable farm truck lol. I have spotted a couple of valve bodies for sale, and am considering swapping it out, then seeing if there is a difference. I don’t have a ramp so a gearbox swap would be me on the floor wrestling and it’s a big old lump to wrestle with lol