Based on sound, Nobel prize winning physics principles, two magnets fitted to the vehicle's fuel line make cleaner leaner fuel burning
Do they work?
I used the Magnofuel pair. Yes, overall they improved my fuel consumption from 8.2 miles per litre (36.9 mpg) to 9.4 miles per litre (42.3 mpg) on a diesel Renault Espace.
How Do They Work?
Trying to keep this simple! The work of Felix Bloch (Stanford University) and Edward Purcell (Harvard University) led to the Nobel Prize for physics (1952). Their work pioneered the early day Nuclear Magnetic Resonance Imaging systems used in medicine. Applying these principles to everyday fuels (which are principally hydrocarbons petrol, diesel, liquid propane gas, methane etc) the magnetic field induced in the fuel causes changes in the molecule's behaviour such that:
the nuclear alignment allows hydrocarbons to flow more evenly and therefore burn more efficiently
the positive ionisation in the hydrocarbon (fuel) attracts the negatively charged oxygen which ensures complete combustion and a greater release of energy
increased energy release from less fuel ensures better engine performance from less fuel burnt and so you save fuel and as a consequence ~ money!
Independent tests on cars have shown reduction of the greenhouse gases (prinicpally CO2) by as much as 97% at high speed and idle speed 97%. The lowest improvements were 37% at high speed and 55% at idle speed. Hence you will improve the CO2 emissions (which will help at MOT time!).
Older engines build up carbon which can 'coke up' and become less efficient. The ionised fuel burns this carbon build up too. Sometimes with older engines you might see a decrease in performance as the ionised fuel burns the 'coke' away, this might take 1000-3000 kM. Eventually the engine performs better and so does the fuel use.
Smoother engine. This builds up gradually so you may not notice it at first, however easier starting compared with previous days will be first evidence of the engine's improved performance.
Improved torque. This is most noticeable where a turbo is fitted where instead of the feel of 'turbo cut in' which could cause consternation to the passengers, the acceleration is much smoother.
Fit once, unlike fuel additives which you have to repeatedly buy. Hence the savings keep on improving.
As this is a clamp on additive to the car is does not affect vehicle manufacturers' warranty or insurance premiums.
Incredibly low, almost zero maintenance. It pays in the first few weeks to check you've tightenend the cable ties properly, after that the very occasional check.
My Personal Experience
I own a ten year old Renault Espace RT DT 2.2. Thats a 2.2L diesel engine. Considering the size of the bus the fuel consumption wasn't bad. It had done 40,000 miles when I bought it and then fitted the magnets. At the time of writing I'd done 7000 further miles in it enough to see a significant saving. At £5 a gallon the old bus takes £75 to fill! It still does cost £75 to fill, however over Christmas when the family tour of four adults involved seeing all the rellies I drove 914 miles and achieved 61 mpg (13.5 mpl), though this was mostly motorway.
Are All Magnets the Same?
All magnets will attract metals, but some more than others. The best effect for fuel saving is:
Use magnets that wraps completely around the fuel line. Surface strapped magnets will give some effect, but not as well as the complete wrap.
Additionally a further magnet (ideally placed a minimum of 10cm away from the first magnet) will increase the magnetic field and so the ionisation of the hydrocarbons (fuel) is greater.
Ferrous magnets will not retain their magnetism to the same extent as modern day permanent magnets. Modern magnets carry a lifetime guarantee and are able to withstand the high heat of the engine compartment.
Magnets encased in a protective coating will ensure they are well protected from the elements.
In my experience it took approximately 1000 miles before I could see a real tangible benefit. The Christmas tour was the most revealing, and I had done some long haul journeys before that which didn't show much difference in the mpg. The makers do suggest that the de-coking effect of the magnets may see a slight rise in mpg before the full savings are seen. The lesson I learnt here was stick with it!
Who Else Uses Magnets in Fuel Lines?
The fuel companies do pooh pooh the magnetic theory. However, on long overland fuel lines, large magnets are clearly observable to ensure the fuel flow is optimised. Interesting eh? They don't want us to save fuel as this will damage their profits!
As early as the 1940s the US Air Force used magnets on the fuel line in their Mustang aircraft to improve fuel performance. This was also adopted by the RAF in the Spitfire and Hurricane and obvious benefits were derived. The quality of aviation fuel was particularly poor during the War.
There are other ways to save
Many reviews have been written on 'economic' driving and are strategies worth adopting. Some very simple and obvious things are:
Avoid harsh acceleration
Do not let the engine idle for long. If in traffic, switch off the engine if you feel you are going to be stationary for more than two minutes.
Keep in as high a gear as possible. I can use fifth at 30 mph in my Espace!
Take the roof rack off (unless you're using it!).
Keep the vehicle regularly serviced and consider more frequent tuning (longer service intervals can mean the engine tune can be less than optimal for longer.
If you own a diesel engine, ensure the cambelt is checked and changed at the prescribed intervals.