Fuelly Forums - Idea for improving fuel economy on short daily commutes

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Hello -

Here's a silly idea. Why not pump the coolant out into something like the black solar hot water pipes on the roof? If the weather conditions permit, you could "heat up" the coolant before you set out for work. The only energy cost would be the pumping the coolant to the pipes. Gravity would bring it back down. Initial cost would be the piping setup.

CarloSW2

Coolant would still flow, by convection only - the idea would be to try to stop / slow convection somehow. One way is to use very good insulation on the pipes going to/from the liquid container - this would mean that the heat loss, by conduction/convection through the water would be reduced. Possibly solenoids could also be used - but this is more dangerous as a fault in these solenoids would prevent water flowing round the radiator when driving!.

Regarding the block heater - I've got a really good one - 2.7kw + automatic coolant circulation - it warms up my engine in 20 minutes :) But I can't use it at work.

Regarding thermal mass - I calculated that a while back, that 10 litres of water will make a fairly big difference (note - I just did a recalculation, and found that, for my 150kg engine, it would be ideal to have 15 litres of water to get the engine to half the original temp of the water (e.g. if the engine was 20, and the water was 100, the final temp would be 60 degrees). This would make a big difference and bypass most/all of the enrichment phase.

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Originally Posted by landspeed (Post 42039)

Why not use the heater circuit: always circulating, and will not affect the radiator flow even if a valve fails closed. Many circulating EBHs work this way.

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Regarding the block heater - I've got a really good one - 2.7kw + automatic coolant circulation - it warms up my engine in 20 minutes :) But I can't use it at work.

2.7kw for 20 min. is 900W so you could get that out of a secondary battery that you recharge overnight. The thing is you need a big inverter (cost, and system losses).

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Regarding thermal mass - I calculated that a while back, that 10 litres of water will make a fairly big difference (note - I just did a recalculation, and found that, for my 150kg engine, it would be ideal to have 15 litres of water to get the engine to half the original temp of the water (e.g. if the engine was 20, and the water was 100, the final temp would be 60 degrees). This would make a big difference and bypass most/all of the enrichment phase.

Just curious, does anyone know how big the Prius 'thermos' is?

As found on metrompg.com

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Those crazy Japanese

Leave it to the engineers at Toyota to implement the most unique, clever and complicated method of pre-heating an engine.

Toyota Prius' 3 liter capacity coolant 'thermos' aids cold starts. (Collision damaged car shown under repair - source.)

In the latest generation (2004+) Prius, hot coolant is pumped from the cooling system into a 3 liter insulated thermos-style reservoir at shutdown, where it apparently stays hot overnight, and warm up to 3 days later.

When switching the car back "ON", the hot (or warm) coolant is pumped from the thermos/reservoir back up to the engine's head where it contributes to quicker warming for better management of combustion to reduce emissions.

I doubt it's as effective as a plug-in block heater - but then again, it's not strictly meant to replace one. (It works year round to ensure warmer starts in all temperatures.) Would be nice to have a Prius to try it out though.

It still probably makes a big difference - I find that my engine's cold start enrichment stops (my Lambda sensor readings go to the 'normal' operating levels) when the needle begins to creep just above the 'cold' mark. On my car, the 'cold' mark is probably at least 30-40 degrees C, but, if you can get the engine past that first stage, you will save a lot of fuel.