W124 Heater / Fuel Consumption

[Mercky]

Hi,
This is a weird one, I've noticed that when I have the heater on in my 1994 E320 Coupe during winter months that my fuel consumption increases by about 10%!! The engine temp is fine and remains constant and thermostat etc are all working ok. I've tested the theory by keeping the heater off for a period and clearly the consumption improves. Anyone got any ideas? Thanks in advance.

 

[television]

This is a weird one and nothing that I can think of or have heard of, see what others think

 

[kth286]

Do you have the fan blower on as well as the heat turned up ?

If so, the blower takes a lot of current and that in turn puts a heavy load on the alternator which means it is harder to turn by the engine, hence more fuel is consumed.

I hardly use my air blower, I leave the pointer directed at the position where the forward motion of the car forces the air to be distributed inside the car automatically.

Helped another 124 owner out the other day as his fuse box had melted at the air blower fuse point to the extent that the fuse would not make anymore contact with the bottom terminal due to the metal melted down into the base.

Hence we had to buy a new fuse base (cost nearly £60) and rewire the whole thing (about 50/60 wires).

He always has his blower motor on and last year had to have a new blower motor at approx 145,000 miles. Have you seen the price of those and the hassle of all the dismantling to fit.

 

[television]

Do you have the fan blower on as well as the heat turned up ?

If so, the blower takes a lot of current and that in turn puts a heavy load on the alternator which means it is harder to turn by the engine, hence more fuel is consumed.

I hardly use my air blower, I leave the pointer directed at the position where the forward motion of the car forces the air to be distributed inside the car automatically.

Helped another 124 owner out the other day as his fuse box had melted at the air blower fuse point to the extent that the fuse would not make anymore contact with the bottom terminal due to the metal melted down into the base.

Hence we had to buy a new fuse base (cost nearly £60) and rewire the whole thing (about 50/60 wires).

He always has his blower motor on and last year had to have a new blower motor at approx 145,000 miles. Have you seen the price of those and the hassle of all the dismantling to fit.

I agree David with you on the wear on the motor, but the current consumed is little in proportion and it could not make that much difference, even with air con its only 2 MPG

 

[GEORGEROV]

If this is the air conditioning we are talking about being on all the time then 10% would be about 2-2.5 mpg and would not be excessive given the drag on the engine due to the compressor.

 

[television]

I do think that mercy is having us on.

 

[maxicab]

Is it mercy or mercky (or murky)?
David says........'I hardly use my air blower, I leave the pointer directed at the position where the forward motion of the car forces the air to be distributed inside the car automatically'.
I'm guessing this is the "." position halfway between "0" and "I"? Is that right?
My fuse holder has also melted through at some time in the past and a "flying fuse" has been wired in - and that looks like its melting too. So I probably shouldn't be leaving my blower in the "I" position should I?
I get worse mpg in winter too - I assumed it is because the car is barely warmed up from a cold start to a decent running temperature by the time I get to work. Maybe Mercky too does fairly short trips from stone cold?

David

David

 

[television]

Is it mercy or mercky (or murky)?
David says........'I hardly use my air blower, I leave the pointer directed at the position where the forward motion of the car forces the air to be distributed inside the car automatically'.
I'm guessing this is the "." position halfway between "0" and "I"? Is that right?
My fuse holder has also melted through at some time in the past and a "flying fuse" has been wired in - and that looks like its melting too. So I probably shouldn't be leaving my blower in the "I" position should I?
I get worse mpg in winter too - I assumed it is because the car is barely warmed up from a cold start to a decent running temperature by the time I get to work. Maybe Mercky too does fairly short trips from stone cold?

David

David

Good point though he says that he has the heater turned off to check,, my car are much worse in the winter

 

[Xtractorfan]

I wonder if mercky is using actual amounts of fuel used, as opposed to using the inhouse computer readings that can vary wildly..and again fuel used on a price comparason basis at the moment wouldnt be a good indicator...

 

[Mercky]

Thanks for all your replies and yes, it's Mercky not Murky!! and no, I'm not having you on!! I have a standard commute every day to work of about 12 miles so my driving pattern is fairly consistant. I get a fairly consistant 250 miles per tank which lasts me about 10 days. Last winter I noticed my mpg dropped off significantly and I was getting about 225-230 per tank, this was sudden and was not apparent in previous winters which led me to believe it was caused by a fault, the only thing I could think of that was different from winter to summer (except for temp) was that I used the heater (and blower at normally second mark) in the winter, I then tested this by reluctantly not using heater & blower for a tank and noticed my consumption returned to it's normal 250m per tank, my commute involves some heavy traffic and takes about an hour hence the not great mpg, on a long run I'd get up to 350m per tank. I was wondering could it be related to a faulty heat sensor that was been 'over cooled' when I run the heater and it in turn feeds the control unit which now thinks the car is cold and runs it richer (as in start up mode), probably rubbish but just a thought!!

 

[television]

Now we are getting somewhere,, I thought of it as I was reading your last post,, if the engine is not getting up to its correct temp, then the use of the heater will knock it down again.. the running temp must be around 80-90c if it does not reach this after say 2-3 miles then the thermostat could be stuck, or is one of the fans (engine) on all of the time

 

[wireman]

Has a fuel burning extra heater unit been fitted to this car?
Most of us have heaters that use waste engine heat but I believe arctic/scandinavian spec cars can be fitted with an auxilliary heater which burns fuel to provide heating under light load/not runing conditions, if you have one of these expect to pay extra for heat.

A little technical blather:-

(Based on Bosch technical info and inspired guesswork)

The mechanical power consumed by an over loaded alternator could be as much as 2-3 Kw and whilst it will use a more fuel it wont make any massive difference to overall fuel consumption. Alternators have a conversion efficiency of 20 to 70% dependent on load and speed, it falls with both speed and load.
The head lights and heated rear glass will take around 100 watts each and the blower won't consume any more than 50 watts so you can ignore its load completely. It is likely that the total mechanical load with all the electricals on (say 400 watts) will be around 1.5Kw worst case (alternator speed >12,000 RPM) which is probably one tenth of the power required to shift the car along the ground at 30-40 Mph. that would satisfy an apparent worst case fuel consumption increase of 10%.
This is a most unoptimistic guess, in reality the engine (at 30 mph) will be turning slowly and the alternator speed will be quite low as well, putting it in the speed range where it is at near peak efficiency, this suggests a real mechanical loading of about 600 watts which could increase fuel consumption by as much as 5% if you have almost every electrical accessory runing. Extrapolating from the above the 50w heater motor will add 0.5% or so to your fuel bill.

The big chrysler people carrier things which use a merc diesel engine use an auxilliary heater as the only source of cabin heating and do use more fuel in very cold conditions, perhaps this is going to be a future trend since the reason is to enable a faster engine warm up to achive the requisite carbon emmisions.

 

[maxicab]

Fascinating stuff! I wonder, if Mercky is crawling along in Dublin's terrible traffic at an average over an hour of 12mph, with the car in "Drive" and his foot on the brakes at every stop, with the engine speed barely above tickover for much of the journey, whether his alternator efficiency is low and therefore the effect on consumption greater?

P.S. I presume an Irish gallon is the same as a UK gallon and not a US gallon (my wife who's Irish wasn't sure!)?

 

[Xtractorfan]

I think an irish gallon is a bit longer.........

 

[E280T]

I have a different theory.

The thing is, with both my cars (W124 280T and R129 300SL) when the blower is running - whether hot or cold air is selected - the aircon compressor is ALWAYS running. In most other car brands one has to select the aircon option with a special button (mostly blue with a snow symbol on it). The only way that the aircon compressor is not running and actual outside air is blown into the interior is when one presses the EC button. Even in the manual of both cars it says that by selecting the EC button fuel is saved cause the aircon compressor is switched off... In my W124 I find this annoying because the EC button is combined with the button that sends the air to the middle and lower vents. So if I wanna select warm air for the front windshield I always have to run the aircon compressor...

 

[citroennut]

i'm with malcolm on this one, if the blower isn't used then the heat from the engine is staying there and running more efficiently, using the blower is taking the heat from the engine to heat the car. colder winter as well, heater turned up higher.


simon

 

[E280T]

i'm with malcolm on this one, if the blower isn't used then the heat from the engine is staying there and running more efficiently, using the blower is taking the heat from the engine to heat the car. colder winter as well, heater turned up higher.


simon

I don't read anywhere that Malcolm is saying the blower is cooling down the engine cause hot air is needed for the heater. He is talking about a potentially stuck thermostat. I still wonder if the car has an EC button and if this is used or not. It is a fact that this makes a difference in fuel consumption...

 

[ndrepebx]

Hi guys,
I have a similar problem with my C220 CDI T-reg 1999. I normally get about 400 miles or more on a full tank and now i get about 280 to 300 miles and i have to refill the car with Diesel again. There is no leakage any where and i am not sure what the problem is.
I have used some fuel flush as i was told that may clear the injectors but that did not do anything.
Does any one have any idea of what the problem could be???

 

[teddycatkin]

What a strange lot of answers ????
All cars take longer to warm up in cold weather! --using a richer fuel mixture means using more fuel.
(In the 50's/60's you manually pulled out the choke to do this--nowadays its all done by magic on modern fuel injected cars most poeple cannot tell when its running rich -i.e. extra fuel being used till it reaches the correct running temperature?)

 

[ndrepebx]

What a strange lot of answers ????
All cars take longer to warm up in cold weather! --using a richer fuel mixture means using more fuel.
(In the 50's/60's you manually pulled out the choke to do this--nowadays its all done by magic on modern fuel injected cars most poeple cannot tell when its running rich -i.e. extra fuel being used till it reaches the correct running temperature?)

Ok, you can understand extra fuel been used but this is quarter of the tank extra so i don't think its normal.
I have had this car for four years now and other winter's have not been like this.

An other thing is that the blower fan sometimes goes up and down without adjusting anything so not sure if that has anything to do with this.
Also Temperature normally is quite low at about 40-60 and only goes up to about 90 when the weather is warm and stuck in trafick.
Thanks