"Winter Diesel"? - anyone else noticed a drop in MPG?

[Trabi601]

Matthen said:

Yup, the cold weather (heater on, lights on, wipers on as well as the increased warm up time) along with the winter blend diesel can cause this. I'm curious to know if the UK changes to a winter blend petrol as well; seems they do in the states, anyone know if they do here?

Yes, there's a winter spec. petrol, too.

[dannyDC2]

Loyly said:

I've always wondered, how much does using the heater effect the engine warmup time? Naturally, the first thing you reach for when you get into a cold car is the heating control. You feel that air flow gradually warming up as the coolant heats up, and of course, the oil temperature lags some way behind. How much cooling effect does using the heater have? It's drawing heat from the cooling circuit, but does this cause any net loss to the overall coolant temperature, and does that slow the overall engine warmup down?

On my A4 it makes a massive difference. So much so that I switch the climate control off until it's at least above 50c on the temperature gauge!

[CraigyMc]

spookly said:

Loyly said:

I've always wondered, how much does using the heater effect the engine warmup time? Naturally, the first thing you reach for when you get into a cold car is the heating control. You feel that air flow gradually warming up as the coolant heats up, and of course, the oil temperature lags some way behind. How much cooling effect does using the heater have? It's drawing heat from the cooling circuit, but does this cause any net loss to the overall coolant temperature, and does that slow the overall engine warmup down?

Depends where the heater takes its feed from. If the heater matrix is connected to part of the cooling system after the thermostat then you won't get any heat until the thermostat opens anyway.

If the heater matrix is connected to the coolant circuit before the thermostat, then yes, of course the heater will be robbing some energy from the coolant which would otherwise have contributed to a warmer engine. Yes, it would slow engine warm up, and increase engine cool down.... how much would depend on a great many factors.

It also depends on implementation of the electronics.
My BMW won't shove air through a cold heater matrix if you're asking for hot air; it gradually ramps up the fans as the matrix warms up so you don't ask for hot and get a blast of cold.

I'm a bit bonkers with this stuff so I typically drive about for the first 5-10 minutes with everything off to keep the load as light as possible and heat the engine up as quickly as possible, where there's no actual need to run HVAC components. (Obviously I will run it and aircon if there's a need to demist).

[JakeT]

CraigyMc said:

spookly said:

Loyly said:

I've always wondered, how much does using the heater effect the engine warmup time? Naturally, the first thing you reach for when you get into a cold car is the heating control. You feel that air flow gradually warming up as the coolant heats up, and of course, the oil temperature lags some way behind. How much cooling effect does using the heater have? It's drawing heat from the cooling circuit, but does this cause any net loss to the overall coolant temperature, and does that slow the overall engine warmup down?

Depends where the heater takes its feed from. If the heater matrix is connected to part of the cooling system after the thermostat then you won't get any heat until the thermostat opens anyway.

If the heater matrix is connected to the coolant circuit before the thermostat, then yes, of course the heater will be robbing some energy from the coolant which would otherwise have contributed to a warmer engine. Yes, it would slow engine warm up, and increase engine cool down.... how much would depend on a great many factors.

It also depends on implementation of the electronics.
My BMW won't shove air through a cold heater matrix if you're asking for hot air; it gradually ramps up the fans as the matrix warms up so you don't ask for hot and get a blast of cold.

I'm a bit bonkers with this stuff so I typically drive about for the first 5-10 minutes with everything off to keep the load as light as possible and heat the engine up as quickly as possible, where there's no actual need to run HVAC components. (Obviously I will run it and aircon if there's a need to demist).

In my 3 series it also takes longer to warm the car with the climate above 16. I tend to leave the heater off on anything I drive until The temp gauge shows warm. On an old Fiesta turning the heater to full heat when the car had just warmed up would put the gauge back to cold!

[Loyly]

CraigyMc said:

It also depends on implementation of the electronics.
My BMW won't shove air through a cold heater matrix if you're asking for hot air; it gradually ramps up the fans as the matrix warms up so you don't ask for hot and get a blast of cold.

I'm guessing pretty much any car with an electronic HVAC will do this. In the old days of manual controls, you had the freedom to blow cold air on a hot setting if you hadn't warmed the engine up. My old 106 Rallye just had two sliders, mixing vents and temperature. It would provide extremely hot air on the hottest setting, I've never known another car that could readily supply that much heat.

[RizzoTheRat]

Having had a landrover conk out due to fuel waxing and blocking the fuel filter I'll happily accept a slight drop in fuel economy other waiting in the snow for a tow truck.