[paulgato]

That looks excellent Mr OIl Pan.

The more you use the less you lose, when it comes to heating an engine. In theory at least. I personally would be nervous of using a 5kw heater though, in case something went wrong, ran dry, or the pump failed.

I don't know what temperatures you have to deal with where you are. Around here in Oxford winter temps are pretty mild, but the 1800w engine preheater I installed a couple of years ago is working well and is saving a good amount of fuel. Actually I use it all year round, and have a remote key fob thing so I can switch it on an hour before I drive off. (Of course a simple switch on a socket inside the house would work just as well, but I like being able to switch on the engine heater while still lying in bed - he he.)

One thing I found though is in the winter there's no real point trying to use the engine preheater to heat the cabin and to clear ice or condensation from the windscreens via the car's normal cabin heater. The cabin heater drags way too much heat out of the engine, and anyway the cabin heater is not really very efficient until the engine is nearly at full temperature.

Instead what I've done is install a normal household mains power socket on a short lead under the dash, in the passenger foot well. I modified an ordinary household fan heater, so rather than having a 2kw setting and 1kw setting it now has a 1kw setting and a 500w setting. (2kw together with the 2kw engine preheater would overload the outdoor power circuit, which has a 3kw limit. That's 13A, and 230 volts in Europe of course.)

That mains socket in the car is live when the engine preheater is live, so both heaters are controlled with the remote key fob thing. (The on-board battery chargers are powered up all night of course (alternator delete) but although they are quite powerful (600w max?) by morning they are down to a trickle charge so any risk of overloading the circuit is very minimal.)

I've found it much better to heat the cabin separately like that, as the cabin then starts to warm up from the initial switch-on time, an hour before drive-time, and that gives plenty of time to warm the cabin and melt any ice on the screens all around, and the engine warm up time is not prolonged in the process.

In fact, if a winter morning would normally involve sitting on the driveway with the engine running just to clear the screens so you can see where you're going, then simply having a 500w or 1000w fan heater sat in the passenger footwell should enable you to drive off straight away with full visibility, even if the engine is stone cold. It's such a simple and cheap thing to do, and very effective.

I would really recommend NOT relying on the engine preheater to give enough heat to clear the screens, when that can be achieved so easily and directly with a household fan heater. In fact, as long as the screens are clear, the engine only really needs to be up at about 50 degrees Celsius to avoid the really bad fuel economy on a cold morning. That's my feeling anyway, just from watching the in-dash real-time mpg meter with a stone cold (0 degree C) engine vs a 50 degree C engine vs a fully warmed (92 degree C) engine.

The really bad mpg hit occurs below 50 degrees C engine temp, but a 50 degree C engine is pretty useless at clearing ice from screens and heating the cabin, because the temp gradient across the coolant/air heat exchanger in the car's cabin heater is insufficiently steep for significant heat transfer until the coolant is up at around 85 degrees C or more.

...

Oh, and by the way, I don't point the household fan heater at the windscreens. I've heard of people cracking windscreens that way in extreme cold, but also it's not necessary or efficient. I sit the fan heater as far forward as possible in the passenger footwell and have it blowing hot air towards the passenger's feet, as it were. With 500w or 1000w there's no danger of overheating any upholstery materials if you have a half meter or so clear space in front of the heater, and the heater has a built-in thermostat of course. That works, and over a half hour or an hour warms the whole cabin evenly. It's satisfying to look out on a winter morning and see frost/ice/snow covering all my neighbours' cars, and none at all on mine. I see them wrapped up in coats and gloves, laboriously scraping ice off windscreens while their engines chug away, belching steamy exhaust fumes into the street, and I just saunter out with my coat under my arm, get in and drive away.