Here good video about how LR pre-heaters with different makes/systems works in stock.
&t=1087s&ab_channel=LRWest

Reading the workshop manual it seems that the changeover valve is "open" when engine is runing. If that's correct I can't see how the valve position effect warm-up time when driving because the FBH will not be isolating the heater matrix from the rest of the system.


 2012 Range Rover TDV8 4.4

Yes, thats correct. Changeover valve "close" only when use the FBH as pre-heater. Isolate the engine to get more heat in cabin, thats it. But thats not good in my opinion.
Coolant circuit when pre-heating: FBH-matrix-FBH
Coolant circuit when additional heating: FBH-matrix-engine-FBH
Since I have fully manual FBH now, I can see how the coolant temperature change when driving in cold conditions and FBH is off (just temp. gauge I mean, not reading with diagnostic tool): on highway there is enough heat always from the engine, even with -20. On city driving and idling gauge drops down even with -5, so additional heating needed.

Just by way of an update it seems that going for the eBay special wasn’t the right choice, after weeks of chasing a very slight leak, and skinning my knuckles changing the hose clamps for jubilee clips and wasting another 5L of coolant I have realised that the valve itself leaks intermittently. Just waiting on the motor factors to confirm return or refund.

Westridge177 wrote:

Thanks again for your input and the info that you can’t repair using seals from the dual valve kit. I’ve seen the genuine valve at over £300 and copy parts at 1/10th of that. As it’s not exactly a crucial part I’m tempted to have a punt.

Any thoughts?