Re: In-the-tank fuel pumps cause death and destruction

Where were the heaters mounted? H

this also means you should keep your tank level from getting too low. Otherwise you can shorten the life of your pump.

-------------- Alex

About 6" above and rear of the pedals. Personally thought it was a stupid design, but then again the Beetles were never the greatest for heat I'd heard.

Another urban legend.

Matt

Not totally. Running the pump VERY low on fuel reduces cooling and lubrication and CAN hasten the pump's demise.

I'm not sure what you saw, but that wasn't a gas heater. Gas heaters were mounted inside and parallel to the left front quarter panel, under the front deck lid. They were/are roughly the shape and size of an old Electolux cannister vacuum.

Personally thought it was a

Actually the heaters were ok but the defrosters were horrible. Add a gas heater and you could almost cook a roast in one.:-) Btw, I still have two, a '62 sunroof and a '69 vert. H

Absolutely not on lubrication. It is impossible not to have gasoline in the pump at the bearings if the vehicle is running off of fuel from the pump since the bearings (more accurately, bushings in almost all consumer vehicles)are within the internal pump volume (the shaft and bearings are surrounded by the fuel as it flows thru the pump. If there's no gasoline at the bearings, neither is there fuel getting to the engine, i.e., the engine will not run, and most likely neither will the pump for very long at all (and that's not "low" in fuel - that's "out of" fuel). The bearings running dry or even slightly low is not a credible situation at all - not even at the point that the engine cuts off due to your "running out of gas" (at which time the pump still is full of fuel).

As far as the cooling aspect, yeah - you might have that on a technicality, but you do have a steady cool volume of the fuel running thru the complete internals of the pump/motor assy. So, probably the outside surface of the pump (case and magnets, which are on the inside surface of the case) will rise a few degrees, but the insides (armature, brushes, bearings/bushings) would rise *very* little (due to the volume flow rate of ambient temperature fluid that bathes those components. I doubt that those thermal effects are at all significant in pump life.

IMO...

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

It is amazing how these myths get started whenever there is a change in technology and just refuse to die. I wonder how the old style pumps that were connected to the engine block ever managed to stay cool! :-)

People don't understand that electric motors can be designed to run at fairly high temps. If the above assertion were true their would be a lot more electric fuel pump failures as I know a lot of people who run low on gas, and even out of gas, fairly frequently. It is almost the same things as the exploding gas tank myth. Even people who won't accept a logical technical argument have to admit that is just isn't happening in the real world. There is a reason for that!

Matt

I'll have to take your word on that, despite how worked & was used as.

You are forgetting when the tank is very low the pump can "suck air" on corners, hills, stop and go...and that is very hard on a vane type pump. It seems to kill GM pumps alot more than Fords. I just helped a friend change one on his blazer-he said- I thought I was just out of gas, the tank was low and I was trying to make it to the next gas station. I guess it could have been coincidence, but I really doubt it IMO.

The vane pumps are worst for failure contributed to by low fuel - and the old in-tank pumps on carbureted engines DID have this problem. In the early eighties? there was a buletin from Toyota IIRC. Although the "low fuel warning" light came on with about 30 miles worth of fuel left in the tank, the factory recommended you treat it as short term emergency reserve only.

I replaced a few pumps in those days.

Why is it very hard on vane type pumps?

Matt

When you say "vane" type pump, is that roller vane, or some other type of vane?

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

I dont really think it would matter. Even if it was some type of turbin or what I think they call a slide? I believe there are 3 problems in the case I mentioned above. One is cooling by the fuel, another is lubrication by the fuel, and the worst one of all I think is the fatigue from a gas to a liquid instantly. Think of your boat prop. If it catches air, the force when it hits water again is sometimes enough to break the shear pin in the prop, almost like hitting a log in the water at full throttle. I would say the problem is the higher the speed the pump turns, the more the problems with all the above. Does that make since or do you all think I'm caaaraaazy? :)

It's called cavitation. Yes - that may be a problem.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

I don't think you are crazy, I just don't think the problems you mentioned are significant. If they were, you'd see cars littering the road side with failed fuel pumps, and that just isn't happening. I've owned several cars over the last 20 years that had electric fuel pumps and I've yet to have a single failure.

Matt

No, cavitation occurs when the inertial forces are so high that pockets of vapor from the liquid form. This isn't the same as liquid starvation, which is what I believe he's referring to here, at least judging by the boat prop example. A prop that "catches air" usually means it came out of the water. A prop cavitates while completely submerged in the water.

Matt

I've got access to an '88 K2500, '90 C2500, '93 C1500, '98 C2500, and a '01 K1500.... so far the '01 hasn't had the fuel pump fail on it.. yet. both the '88 and the '90 on their third pumps.

-Bret

My 94 K1500 is doing fine at 86,000 on its original pump. You must just be hard on equipment!

Matt