I just wanted to come here and gloat a little bit that I had a Webasto installed in my car in December. Besides being a pretty sweet addition, the car wouldn't have made it through winter without it, as half the glow plugs stopped working and my mechanic abdicated the job after the second one seized and the head snapped off (the glow plug, not the mechanic). I had been contemplating the Webasto for a while, but at this point it was a quicker and cheaper alternative to sending the head to a machine shop.
I've since resolved the glow plug issue, but still pleased to have the Webasto I have a few recommendations for anybody looking at doing the same.
First off, if you're short-tripping like I do, your battery and alternator won't keep up. The manufacturer recommends you run the engine as long as you run the heater. My commute is 7-8 minutes twice daily, but with outside temperatures of -20C the unit needs to run a minimum of 10 minutes just to move the coolant temperature needle. I found 20-30 minutes was the sweet spot for a pre-heat at those temperatures, so that creates two problems.
The first problem is battery capacity. At -20C or colder, a decent battery is capable of starting the om606, but draw 3-4 amps from it for 30 minutes before turning the key and you may find you have problems. I opted to add a couple of 9 Ah UPS-type batteries at $35 each from a local battery shop. They fit nicely under the back seat of the W210 between the factory battery and the air pump. I wired these in with a dual battery isolator that I paid $70 for at Princess Auto. This unit disconnects the secondary batteries from the main battery when voltage is below 12.5, then reconnects them when it goes above 13.5 or so. With the Webasto wired to the secondary circuit, it can draw from the auxiliary batteries without draining the main battery and leaving you stranded. As soon as the engine is running or a charger is connected, the isolator ensures that all batteries receive charging voltage.
This brings me to the next element of the plan, which is an on-board charger. Because the secondary isolated battery circuit notwithstanding, and regardless of the size of all batteries installed, you can't run a deficit forever. By running the Webasto longer than the engine day after day, your secondary batteries will inevitably deplete, and even though the main battery is protected, the Webasto won't get the juice to do its thing. By connecting an on-board charger when at work or home, you keep the secondary batteries topped up and ready to do their thing.
I bought a Noco Genius II from Canadian Tire. It has a nice feature of two separate charging circuits, which I connected to my two battery circuits. Yes, I probably could have got away with a single charger connected to the primary battery circuit, but I didn't want to risk the potential case where the secondary batteries deplete during heater operation and the charger never kicks in because the primary battery is tip top. Besides, the Genius line all happened to be on sale the week I went looking, and the Genius I was sold out. As it turns out, the dual-charger copes just fine when the battery isolator connects the two circuits; it's smart enough not to burn itself out or anything like that and it did the trick for me all winter. I think I paid $130 or so for the charger.
So in summary, here's my parts list with prices (CAD) to the extent I can remember them.
Webasto Thermo Top C - $1250
Copper pipe, elbows, heater hose and clamps - ??
2x SLA batteries - $70
Dual battery isolator - $70
As far as installation tips, the Webasto fit nicely under the rear bench on the left side. We used a metal bracket screwed to the under side of the car. The screw for the front of the bracket came through the vertical wall by the passenger's heels, but didn't breach the carpet. The exhaust hose emerges from the left side of the car just in front of the left rear wheel near the jack point. We ended up shortening the exhaust pipe a little.
We ran heater hose out of the heater unit and then copper pipe just to the left of the drive shaft. Then back to heater hose around the engine and I forget exactly where on the block. I think there was a ready-made threaded hole near the front of the block on the exhaust side of the block where the heated coolant went in, and then out somewhere near the back of the block. I put a length of foam pipe wrap on one of the pipes just to try to preserve heat, but I didn't get far with it due to the snug fit of the pipes against each other and the underside of the vehicle.
As I mentioned, the batteries and isolator fit nicely beside the main battery under the seat. The Webasto wiring harness followed some other wires through an existing hole under the back seat on the left side near the heater unit, then across to the battery circuit. The control wiring ran nicely along the base of the doors on the left side with the factory wiring, up under the dash to the controller, which I mounted on the panel to the left of the steering column.
I installed the battery charger in the trunk near the right side and ran the wires over the partition into the back seat area. I had to remove the back seat to do this, but it's not difficult. The charger body itself is bolted to the felt partition at the front of the trunk. Take the partition out to do this. Don't just use a drill bit to drill into the metal that is conveniently behind the felt partition. That is the fuel tank. Ask me how I know. The charger comes with four screws for mounting but I picked up a small pack of 1/8" stove bolts at the hardware for mounting purposes.
The AC power cord for the charger is the part of the project I am least satisfied with. For now I just run it up between the hinges of the trunk and it rests on the back window. It rattles agains the window when I drive, so I usually drop it back into the trunk when not in use. I would like to find a way to run it out of the trunk permanently such that it won't stick out like a sore thumb, or create a hole for dirt or rodents to enter the trunk.
Here are a few photos from the project. I hope somebody finds this interesting or helpful. Feel free to comment or ask questions.