I've just completed the installation of a Webasto Thermo Top C into a 300tdi Defender. It is a pre-heater that heats the block and the heater circuitl. The best place for the Thermo Top C is in the pipe run from the back of the cylinder head where it joins up with the heater matrix. This way, the Webasto heats up the engine block and the cabin heater water loop. Itís difficult to install the Webasto without creating an air lock, so I turned a bit of ali bar to make a short pipe insert with a bleed point. It work very well and the air lock is removed in seconds.
Most people appear to have positioned the heater in place of the washer bottle Ė which when has to be positioned elsewhere. I kept the bottle in its correct position and found a way to position the Webasto heater between the engine and the heater box. There is less than 1/2" of clearance, but that is sufficient. I had to make four steel straps to provide the necessary bracing and support but it work well and is solid as a rock.
With an external temperature of -5 degrees C, the Webasto heated up and block and 90 cab to a very comfortable position in between 15 and 20 minutes. I think it would be stretched to heat up a 110 to a similar level of comfort, so an air heater might be an alternative or additional option. We were drawn to the solution of a block pre-heater just to make starting easie ion winter. At -5 decrees C, and after a 20 minute pre-heat, we donít bother to wait for the glowplugs. the 300tdi springs into life on the first compression.
You will need to think about where to get the fuel from. The options are to break into the existing fuel lines or to install a new pick-up point in the tank. I would strongly advise the latter. For about £30, you can buy a simple kit that requires just a 6mm hole drilled into the existing tank sender unit. Troubleshooting becomes much easier when fuel supplies are independent.
The heater does take quite a bit of power from the battery in pre-heat mode, taking power for itself and also operating the cab blower motor. To avoid getting stranded with a flat battery, you need to limit the amount of preheat time to be no more than the subsequent drive time to allow the alternator time to replenish the battery. If your journeys are likely to be short Ė as is the case for us, then you will need to fit an additional battery just for the Webasto. Use a leisure battery with a split-charge system to keep it topped up. And if that battery should go flat, you can always do a manual recharge.
The final thing to think about is how to control the pre-heater. My refurbished kit (£420) with a 1-year guarantee came with an Eberspacher black rectangular control panel with a Mercedes logo on it. The text on the tiny display is minute which make it difficult to use and you can only create three programs. It does work well, but something else has to be better.
Come back if you want any more info.