how to test a factory fit Fuel pump out of the car.

[Paul99]

How is it best to test the fuel pump out of the car?  could I use water to see if the pump is working ok rather than petrol (just a safety point of view)

[dirkbalter]

Paul,
check out the end the fuel pump article in the manual.
Water is not recommended.
https://www.sl113.org/wiki/Fuel/FuelPumpRebuildEarly
Dirk

[BaronYoungman]

Make sure you test the pump for, at the bare minimum, 15 minutes.  If the armature has internal faults it will start out by going strong (1 liter every 15 seconds+) then as the armature and pump gets to proper operating temperature it will slow down, I have seen some that look great to start then after some minutes it slows down to a trickle.  Do not use water.
Bob

[MikeSimon]

  as the armature and pump gets to proper operating temperature it will slow down, I have seen some that look great to start then after some minutes it slows down to a trickle.
Bob

Interesting!!!
Bob: will this be the reason a car will stop running after it reaches op temp? Not restart until it cools down a little. Then start but die again after a while. Repeat.

[Jack Jones]

Why not use kerosene instead of gas or water.

[mdsalemi]

Why not use kerosene instead of gas or water.

Very simple: the pump was designed for gasoline, not kerosene (which has a different viscosity, vapor pressure and other characteristics). So, if you want to test it outside of the car, best to set up an OUTSIDE test procedure that will use gasoline fuel. Yes, it's messy, can be a pain, and you'll need special precautions, but that holds true for anything like this.

Also understand that the pump's mechanism has the system totally immersed in fuel during operation which I believe aids in cooling and lubrication.

[Pawel66]

Based on my own experience:

1. Go outside!!!!
2. Screw in the connectors at the pump. You do not want any sparks.
3. If using "crocodile" connectors for battery, have the battery away from the test place.
4. I had a 20L canister with gas 3/4 full and a smaller, transparent one.
5. The pump pumps considerable amounts of gas. If you want to warm it up for 10-15min before thetest, put bothhoses in the 20L canister.
6. Then you canuse a smaller bottle for the very test, it is less than a 1L per 15 sec.

There is not a lot of gas spilled. Usually...

[BaronYoungman]

I would NOT recommend doing this but I have a full set up in my garage in a Fire safe area because as Michael said the only way to know for sure is to use gasoline.  I have never had any issue but I am EXTREMELY careful.  ON ANOTHER NOTE I STRONGLY RECOMMEND PUTTING A EXTRA IN LINE FUEL FILTER BETWEEN YOUR GAS TANK AND THE PUMP.  No matter how clean you think your tank is now, if you don't use it a lot rust can form, I use a clear filter (I think I got from NAPA , I have been told Kent at Mercedes Source also has a clear one) so once a year, when I put it away for the winter I check it for rust signs. Very low cost preventative measure.
Bob
Baronyoungman@hotmail.com

[Pawel66]

I fully support Bob in all his points, just wanted to add on the additional filter - you may find on the internet one that has 10mm fittings as this is the diameter of fuel hoses in our cars. Most filters have 8mm fittings (Kent is talking about it in his video).

[BaronYoungman]

Mike Simon.. to answer your question "yes" when the armature heats up the copper wires expand and may cause shorts or dead spots and the pump slows down, sometime REALLY slows down.  It will then only take a short while for the reserve gas in the pump to be exhausted then no gas, no go, and even worse no gas in the can of the pump causing the armature to get even hotter.  This then can melt "stuff" usually the binding materials in the armature causing it not to work at all.  Bob
P.S. this is also why you NEVER run the pump without gas in it (if you must then just a second to see if it turns)

[mdsalemi]

If I were to do this (and I would not, ever: read below why) what I would do is BEFORE fooling around with any fuel, to put firm electrical connections to the pump, on a proper wire long enough to be away from the pump and fuel. I'd fix it to a battery, and add an enclosed switch--the idea is you do not want any electrical sparks at all.

I would not do this myself because I know that Bob Youngman has, through hard work and grassroots research, become very well knowledgable on the topic and I'd just send him my pump for repair or replacement. I would not attempt to learn something he has already learned and developed a skill set for.

[dirkbalter]

I would not do this myself because I know that Bob Youngman has, through hard work and grassroots research, become very well knowledgable on the topic and I'd just send him my pump for repair or replacement. I would not attempt to learn something he has already learned and developed a skill set for.
[/quote]

Bob is without question the expert on pumps. However, if all of us follow that advice, I am afraid this forum will become quiet boring. 

[Jordan]

Could you not use diesel instead of gas?  A lot safer.

[UJJ]

As Michael stated Kerosene as well as Diesel have a different viscosity and will not give you the correct results of what you are looking for.
I have learned my lesson(s) to leave tasks like that to people with the knowledge to do stuff like that.
I do almost all the work on my car myself, but with certain things I think it is not worth it.
This forum gives you the sources where to go to, like in this case Bob Youngman.
Best, Urban

[BaronYoungman]

Thank you for the praise, I will always be here to answer questions and to guide people so they do not make all the dumb mistakes I have made with these pumps.  My biggest concern is that no one gets hurt.  I am a banker by day and get very little satisfaction from what I do, but working on the pumps gives me a feeling of instant gratification.  I do enjoy it, I am amazed at the engineering that went into them and that they spend 24/7/ 365 days a year submerged in gasoline, working at full capacity from the moments before the engine starts to when they key is turned off.  Many of the pumps are 40 plus years old, I would wager there is no part on a modern car that is subjected to that kind of workload that will be functioning properly in 40-50 years.  Mercedes went above and beyond , I guess that is why I now polish all the outside cases on the pumps, for I want them to looks as good on the outside as they perform on the inside. I do try and get on the forum at least once a day to answer any questions I can. Back to the testing fluid question viscosity is the measure of a fluid's resistance to flow, molasses is highly viscous, water is medium viscous, gas is low viscous at normal outside temperatures (the grey area in the chart below). If you use diesel gasoline I do not think the change in viscosity will be enough to dramatically alter the flow, but be aware if you look on the following chart at regular outside temperatures they are significantly different so my bigger concern would be leaking from poor or misaligned gaskets if you are using a different viscosity from gasoline.

Bob

[Jack Jones]

Thank-you Bob.

The reason I suggested kerosene was for a safer working environment. I have worked with many styles of pumps and the temperature alone causes a change in the viscosity in all fluids. If the pump is having issues once it heats up, it will fail with whatever fluid you are trying to pump.