You rarely use that 90 bhp. Especially not at low speeds.
Aluminium also condicts heat rather better than cast iron which means it also removes heat from the coolant more efficiently. So as regards the cabin heater you want hot coolant as quickly as possible - the temperature of the actual block being irrelevant. Ally engines often have a lower capacity coolant system due to it being easier to cast than iron. Which can help counteract the time taken for the heater to work.
but that is why one has a thermostat.
even at say 6bhp out you ought to have 8-10bhp of heat which is 5-7KW.
Possible explanation is thermostat not closing fully. Might be tested by seeing if car takes a long time to warm up from cold.
well diesels at low throttle are something like 37% efficient - that's better than a petrol engine. But you always have at least as much waste heat as you do wheel power.
Of course a lot foes into the exhaust.
Pootling along at 30 mph takes X bhp. A diesel may be more efficient at part throttle but it's still producing X bhp to do that. It may well be burning less fuel to produce that X bhp but its extra efficiency is producing more power (and consequently heat).
Well that's the job of the turbo to reclaim some of that lost heat energy, but then that's the same for petrol turbos too.
My point is that you can't put down poor heater performance to *just* increased efficiency. They may be many factors, but bhp for bhp, a diesel and petrol engine will be producing more or less (if not exactly) the same amount of heat.
Tim
I.M.E. diesels take longer to warm up. Some diesel cars I have had never reached full heating capacity until after a few miles whereas petrol engined variants had no trouble achieving this at idle, something a diesel has never done
never done
I grant you I don't know the relative fuel consumptions at idle for diesels and petrol cars. It may well be that diesels produce less heat at idle.
Tim
A 90 bhp engine produces 90 hp at the wheels. If it burns fuel at 20% efficiency, it will produce 450 hp of waste heat when working flat out. If it is 50% efficient, it will only produce 180 hp of waste heat under the same conditions. Modern engines are also much more efficient than older ones under low load conditions, and a higher proportion of the waste heat goes out through the exhaust pipe than with the older, less efficient engines. This can reduce the waste heat being dissipated through the cooling system by as much as 80%, from a few dozen kilowatts to a few kilowatts, which is why some makers need to install a secondary cabin heater.
The difference I notice is between older, less efficient diesel engines, which warm up and start heating the cabin within a couple of miles, and the newer equivalents which take many miles to warm up to a temperature where the cabin heater starts working.
They do and always have done. That's one reason why they are more economical than petrol engines - especially at part load. Less 'losses'.
In message , "Dave Plowman (News)" writes
Takes about 5 miles on a Fiesta 1600dci.
Fortunately they come with an electric heated windscreen.
>
Not enough kW on this economymobile driven gently when the outside temp is 2 degrees, and I try to run the heater full blase. This will be why some people are talking about their aux heaters.
Andy
_mostly_ at part load.
The petrol engine is a little less efficient because of the lower compression ratio, but the big thing is it spends so much time dragging air past a butterfly, and then running at a low internal pressure because it was fed thin air.
Petrol engine really want wide open throttle, or something close to it.
Anyway...
The old rule-of-thumb was 1/3 out of the exhaust, 1/3 out of the radiator, and 1/3 to the wheels. If I'm bumbling along at 40-50 in a lightweight car I may only be using 5-10kW. So I can get that much out of the cooling system. The thermostat won't open with a bang once it gets to heat - so I can't get all that 5-10kW out of the heater. And I'm heating with air pulled up from 2 degrees, then blowing it into an uninsulated (nearly) metal box with air rushing past the outside at
40-50, so I really needed that 5-10kW to get the cabin to heat quickly.It might have settled with the temp gauge at a lower setting, but I don't know what that would have done to the efficiency - so I stayed a little chilly. Until I got onto the main road and wound it up to the speed limit, when there was plenty of waste heat.
Andy
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