Can a fuel pre-heater improve MPG?

I saw an article on internet saying that if one adds a fuel pre-heater
on the fuel line ahead of the fuel rail, it improves mileage by
increasing the combustion efficiency. Its easy to do on my 740 or
nearly any car, you could just bend a long piece of copper tubing into
a U-shape, silver- solder brass barb fittings on the ends, and re-rout
the fuel line through it. The pre-heater assy is mounted against the
radiator. It makes sense that hot fuel would burn better than cold
fuel being injectd into the cylinders, but whether it would make any
real appreciable diference on my 82 740 turbo or not...I don't know.
Could it possibly induce a vapor -lock when restarting the engine when
still hot?

 

There's all kinds of snake oil claiming to increase fuel economy. In
practice this won't do anything for you, the fuel injectors spray a fine
mist of atomized fuel and this hits the back of the hot intake valves
which further vaporizes it. Heating the fuel will do little more than
promoting vapor lock, as well as the hotter less dense fuel will alter
the flow rate of the injectors and increase vapor loss as the hot fuel
is returned to the tank through the return line. Manufactures actually
take steps to *reduce* the heating of fuel, hence the use of return-less
injection systems in some cars.

In a nutshell, don't screw with the fuel system. LH-Jetronic is already
very good, any "improvements" are just as likely to make things worse.

Keep up on maintenance, increase tire pressure, run synthetic fluids,
remove excess cargo, drive with a lighter foot, these all have very real
and measurable effects on fuel economy without doing any goofy
modifications. A Volvo turbo with an automatic transmission is just not
particularly fuel efficient.

 

:
: geronimo wrote:
: >
: > I saw an article on internet saying that if one adds a fuel pre-heater
: > on the fuel line ahead of the fuel rail, it improves mileage by
: > increasing the combustion efficiency. Its easy to do on my 740 or
: > nearly any car, you could just bend a long piece of copper tubing into
: > a U-shape, silver- solder brass barb fittings on the ends, and re-rout
: > the fuel line through it. The pre-heater assy is mounted against the
: > radiator. It makes sense that hot fuel would burn better than cold
: > fuel being injectd into the cylinders, but whether it would make any
: > real appreciable diference on my 82 740 turbo or not...I don't know.
: > Could it possibly induce a vapor -lock when restarting the engine when
: > still hot?
:
:
: There's all kinds of snake oil claiming to increase fuel economy. In
: practice this won't do anything for you, the fuel injectors spray a fine
: mist of atomized fuel and this hits the back of the hot intake valves
: which further vaporizes it. Heating the fuel will do little more than
: promoting vapor lock, as well as the hotter less dense fuel will alter
: the flow rate of the injectors and increase vapor loss as the hot fuel
: is returned to the tank through the return line. Manufactures actually
: take steps to *reduce* the heating of fuel, hence the use of return-less
: injection systems in some cars.
:
: In a nutshell, don't screw with the fuel system. LH-Jetronic is already
: very good, any "improvements" are just as likely to make things worse.
:
: Keep up on maintenance, increase tire pressure, run synthetic fluids,
: remove excess cargo, drive with a lighter foot, these all have very real
: and measurable effects on fuel economy without doing any goofy
: modifications. A Volvo turbo with an automatic transmission is just not
: particularly fuel efficient.

This idea took me back a few years to the time in the UK when I was the
proud owner of a 1949 Jowet Bradford. A precursor of the minivan I suppose.
After all it WAS a converted van, with seats and windows, all driven by a
horizontally opposed ("boxer"-type") flat-twin of an astounding 1005
cc........
The thing is the inlet manifold was in the form of an arch rising from each
of the two H.O. cylinders. Surrounding the manifold was an outer water
jacket.
On top of the arch was mounted the carburetor. The whole thing was in the
form of a beautiful aluminum casting.

The result: The atomized fuel and air mixture headed down the two arms of
the manifold arch towards the cylinders, heated by the coolant rising from
the cylinders, which then continued from the top of the arch forward to the
top of the radiator This was different from heating the liquid fuel.
Incredibly there was no water pump. The Owner's Manual offered one "for use
in the tropics........"

It seems to contradict the theory behind intercoolers for turbos, but worked
very well. It always started easily in all weathers, never experienced
vapor lock and reliably transported the family from N.E. Scotland to the
South coast of England on several occasions, as well as being a "daily
driver".

Andy I.

 

Well the difference there is that an intercooler is not to improve
efficiency or help vaporize fuel, but to cool the charge air to prevent
detonation. After being compressed by the turbocharger, the air can be
very hot, and it's just air, not a fuel/air mixture.

 

:
:
: >
: > It seems to contradict the theory behind intercoolers for turbos, but
worked
: > very well. It always started easily in all weathers, never experienced
: > vapor lock and reliably transported the family from N.E. Scotland to the
: > South coast of England on several occasions, as well as being a "daily
: > driver".
: >
: > Andy I.
: >
: >
: >
:
:
: Well the difference there is that an intercooler is not to improve
: efficiency or help vaporize fuel, but to cool the charge air to prevent
: detonation. After being compressed by the turbocharger, the air can be
: very hot, and it's just air, not a fuel/air mixture.

I understand that, James, but doesn't the intercooler also make the
compressed air even more dense, whereas "my" hotwater jacket would expand
the air making it less dense and so reduce the charge?

Just curious.
Andy I.

 

I always have to laugh when I read "tricks" like this. Wouldn't you
think that every car manufacturer would have implemented a fuel
pre-heater if this was improving fuel efficiency?

Let it be known that I also do not believe the consipracy stories
that car manufacturers deliberatly make their cars less fuel
efficient for the benefit of petrol companies.


BTW: my car does have a carburettor heater. That is: the carburettor has
a line to the cooling fluid. Keeps from freezing in the winter.

Maarten
Maarten

 

My first questions are who was the author on the internet, what are
his credentials as an automotive expert, has this result been
duplicated and what is the effect on mpg. My guess is that IF there
is a positive effect it is small.

If you want to increase MPG and reduce total fuel cost the following
are proven tricks:
1. Combine trips and make a conscious decision to drive less.
2. When driving keep the rpms down by upshifting as soon as
possible.
3. When driving hold a steady speed at ot below the speed limit and
use engine braking wherever possible.
4. Practice holding the gas pedal as steady as possible. Most
drivers are on and off the pedal a lot more than they are aware and
that eats a lot of gas.
5. Keep the car in tune and maintain tire pressure higher than the
minimum. 35 psi seems to work for a lot of cars.
6. Remove all the excess stuff that seems to accumulate in our cars.
Don't carry a tool box or roof rack unless needed for that trip.
6. If you car has an average and instant mpg displays, use them. The
instant mpg is a great tool for seeing the impact of driving behaviour
on mpg. If not see if an aftermarket gauge can be plugged into the
OBD port.

 

In <CwT5k.74863$bs3.42174@trnddc07>,

These are good suggestions. With 100% of my driving done in stop-and-go
traffic in a city with really bad roads (New Orleans), I was averaging
about 19 mpg in my S60 (2005 2.5T). Changing the air-filter to a K&N,
and keeping the tires properly inflated (35 psi), improved my fuel
efficiency to a steady 20 mpg. Driving with a much lighter foot gives
me almost 22 (average for the last three tankfuls is 21.7).

AC

 

Yes, the intercooler will make the air more dense, which allows more
air, and subsequently more fuel to be burned, producing more power.

A hot mixture will reduce horsepower, but heated runners may help to
prevent fuel vapor from condensing on the inside wall of the intake
runners on a carbureted engine. There is no benefit to heating the
intake runners on an injected engine, it will only reduce the power.

 

:
:
: >
: > I understand that, James, but doesn't the intercooler also make the
: > compressed air even more dense, whereas "my" hotwater jacket would
expand
: > the air making it less dense and so reduce the charge?
: >
: > Just curious.
: > Andy I.
: >
: >
:
:
: Yes, the intercooler will make the air more dense, which allows more
: air, and subsequently more fuel to be burned, producing more power.
:
: A hot mixture will reduce horsepower, but heated runners may help to
: prevent fuel vapor from condensing on the inside wall of the intake
: runners on a carbureted engine. There is no benefit to heating the
: intake runners on an injected engine, it will only reduce the power.

Thanks James. I feel that the old Jowet Bradford system has been
vindicated!

Andy I.