Fuel Consumption during the cold snap
Printed From: Bavarian-Board.co.uk - BMW Owners Discussion Forum
Category: Technical & Model Specific Forums
Forum Name: BMW 5 Series
Forum Discription: This forum will deal with any issues on the BMW 5 Series (E12, E28, E34, E39, E60 & E61)
URL: http://www.bavarian-board.co.uk/forum_posts.asp?TID=47460
Printed Date: 06-May-2024 at 11:40
Topic: Fuel Consumption during the cold snap
Posted By: stephen520i
Subject: Fuel Consumption during the cold snap
Date Posted: 29-December-2010 at 23:09
|
From March 2010, once I got my coolant bleed, my fuel consumption was a steady 9.0 to 9.4 l/100km. However, during December (artic air and all that) my consumption shot up to 10.5 to 10.8 average. Now that the thaw has set in, all is fine with a spin today averaging 9.1l/100km. Any reason for this? Surely the ECU does not take into account the ambient temp, and the auto box was always in Economy mode. Could the auto box oil cooler be an issue, not allowing the auto box into the highest gear possible? A full tank fill of €90 has to last longer than 400 miles these days. ------------- E34 520i auto leather Previous: E36 93 316i M40 Boston Green |
Replies:
Posted By: Peter Fenwick
Date Posted: 30-December-2010 at 13:34
|
I'd say it's down to how long the car takes to warm up. When it's very cold my car takes a good few miles more to get up to temperature. Also when it's colder the air will be dneser so you will need more fuel to maintain the correct ratio. This should give more power but could also make the car less economical. ------------- Entering an age of Austerity and now driving a Focus Diesel. |
Posted By: speedy
Date Posted: 30-December-2010 at 17:39
|
My 520 has been the same. It takes alot longer to warm up during this cold weather. ------------- 1995 520i se auto 24v saloon |
Posted By: stephen520i
Date Posted: 31-December-2010 at 17:03
I would have taught that colder air (winter time) was better for an engine than warmer air (summer) and thus an engine would not need to be feed as much fuel as normal. Thus I should not have seen my MPG go thru the roof.
I wouldn't say that the car takes longer to warm up, heating system is fine and well capable of keeping the car warm. Thankfully, normal winter temperatures are now the norm and all is fine. Just something I noticed over the cold snap. ------------- E34 520i auto leather Previous: E36 93 316i M40 Boston Green |
Also when it's colder the air will be dneser so you will need more fuel
to maintain the correct ratio. This should give more power but could
also make the car less economical.Posted By: Peter Fenwick
Date Posted: 31-December-2010 at 17:20
The density of a gas is dependant on temperature. The lower the temperature the greater the density. So the mass of 1 litre of air is greater at 10 degC than it is at 30 deg C. It follows then that 1 litre of air at 10 degC contains more oxygen than air at 30 degC. Combustion requires oxygen and the more oxygen there is present the more fuel can be burned. Your car takes in a fixed volume of air, dictated by the engine dimensions but as the temperature changes so does the mass of air, hence the requirement for a MAF. The greater the mass of air the more fuel is required to give the correct air/fuel ratio. ------------- Entering an age of Austerity and now driving a Focus Diesel. |
Posted By: Andrew Rolland
Date Posted: 31-December-2010 at 17:57
|
I'm only getting 25 to 26 mpg at the moment down from 28 to 29 mpg. Car is idling in the driveway while I scrape ice off the windows in minus 13 deg temperatures. I was stuck in traffic for 2 hours on one of the bad snowy days. Combination of slow traffic and low temps always make my car sip just that bit more unleaded. Spring time and the figues improve I would say its nothing to worry about. ------------- Be exclusive and drive a Petrol 5 Series! Current '13 62 F10 535i MSport Auto Previous '04 04 E60 545i SE Auto '03 53 E60 545i SE Auto (Stolen) '98 S E39 523i SE Auto |
Posted By: johnnydev
Date Posted: 02-January-2011 at 22:40
|
There are too many variables to consider all the previous comments are correct you can only compare like for like driving conditions. the recent cold spell has caused lower average speeds due to traffic congestion, lower gears being used and more stops mean lower mpg or in your case kpl |
Posted By: UweM3
Date Posted: 05-January-2011 at 19:29
|
In the good old days we used to cover half of the rad up in the winter when temperatures went below 0 degress.
Just watch you temp gauge, it takes much longer till you have reaced normal working temperatures and the ECU just keeps richen up. I also dicovered that my thermostat is probably broken. I had this on my old 528 and after fitting a new one the engine reached temps much much faster. The metal part of the thermostat sit in little plastic prongs and they break and the thermostat sticks open a little and lets cold water pass. BTW my 530 isn't even going 400 miles per tank in the very cold conditions. ------------- E61 520d, slow and buzzy but my wallet likes the mpg..... |
Posted By: Andrew Rolland
Date Posted: 06-January-2011 at 08:39
|
Us youngster with todays new fangled modern computer powered cars have adjustable air rams. Behind my kidney grills are slats which are controlled by the ECU to either let plenty of cold air in to keep it cool or shut to keep the cold out. With the engine off I can push the slats open quite easily and then see into the rad, but on a cold morning on idling just after start up the slats are locked shut and I can't push them open speeding up the warm up. At the start of November in minus 3 weather with the heater on full, after driving for 14 miles on a mixture of B Roads, M8 and Glasgow city centre traffic, my thermostat had not opened and the rad was stone cold when I parked up. Granted the engine hadn't worked hard i.e. not above 55 mph or even 2,000 rpm it just didn't get a chance to heat up with the heaters sucking any warmth out the engine to heat the cabin. Andrew ------------- Be exclusive and drive a Petrol 5 Series! Current '13 62 F10 535i MSport Auto Previous '04 04 E60 545i SE Auto '03 53 E60 545i SE Auto (Stolen) '98 S E39 523i SE Auto |
Posted By: Dergside
Date Posted: 06-January-2011 at 10:15
|
After the end of the recent cold snap I checked my tyre pressures that had previously been set in the depth of the cold. The tyres were about 4-5psi over inflated as a result of the rise in temperatures. ------------- Now: BMW 523i SE '00, 318i SE - e91 '07, 325i Coupe '93. Prev: e46 328i SE Touring, 330Ci, 318Ci. e39 523i SE. e36 325i Coupe *2, 323i SE, 316iSE. e30 325iSE 2dr, 320i Conv, 320i 2dr, 316i. |
Posted By: Peter Fenwick
Date Posted: 06-January-2011 at 10:40
Indeed. It's worth keeping an eye on stuff like this when there is a significant change in ambient temperature. ------------- Entering an age of Austerity and now driving a Focus Diesel. |