<VV> Electric vs Mechanical fuel pumps

kenpepke at juno.com kenpepke at juno.com
Wed Dec 19 07:55:41 EST 2007

> However, then you can't oil the engine before it fires up.  I've always 
> thought that it's beneficial to see the oil pressure come up while 
> cranking before the carbs fill enough to start it.

For almost 50 years my best friend has owned a junk yard in SE Michigan.  He buys old, used up cars, not late model wrecks.  Over the years several observations have been made:

A.  Mechanical fuel pumps:
1.   Leak / fail.  They have a relief hole to allow the gas to spray outside where the owner can smell it but frequently also pump gas into the oil pan.  
2.  We never saw an engine fail due to gas in the pan.  There may be enough lubrication qualities in gas to keep an engine alive for quite some time.
3.  We never saw a car burn down due to a fuel pump leak.  
4.  Because they pull the fuel to the engine rusted out or broken fuel lines draw in air and stop an engine long before they leak enough volume to start a major fire

B.  Electric fuel pumps:
1.  Fail to pump, but we never saw one leak.
2.  In the distant past after market electric pumps were used to replaced OEM mechanical pumps usually by home mechanics.  
3.  Because electric pumps are usually mounted near the tank so they push the fuel to the engine rusted out or damaged fuel lines do not stop the fuel from flowing even long after the engine has stopped due to lack of fuel. 
4.  In years past we have seen dozens, perhaps hundreds of cars burned down because of an after market electric fuel pump.   
5.  Today many or perhaps most cars have OEM electric pumps in the gas tank.  Seldom do we see an after market electric pump.
6.  It has been years since we have seen a car burned down by an electric fuel pump.

C.  Lubrication:
Over the years we have disassembled engines that have not been run for 20 or more years.  All have had sufficient oil in the bearings to sustain lubrication for a start up period.  I have known persons that fill the oil filter before installing it on the engine.  The position of the filters on some engines do not allow this practice.  It is not harmful to fill the fileter when possible but if it was really necessary the engine designer would make sure it could be done.

A person could use up two batteries and melt the starter long before enough oil could be pumped through the engine to fill collapsed lifters.

D.  Conclusions:
If someone really wants an electric fuel pump it would be best to:
1.  Adapt an 'in tank' unit ... and don't forget the overflow return system.
2.  Mount an aftermarket unit as close to the engine as possible even though the instructions recommend placing it by the tank.
3.  Either way it should be wired with a switch designed to sense engine oil pressure after start up.
Ken Pepke

Kaiser Permanente Affordable Plans
Quality health care coverage for individuals and families. 

More information about the VirtualVairs mailing list