pnichols wrote:
jfkmk wrote:
At issue is you have two pumps working at the same time wearing out at the same rate. Your second pump might not fail at the same exact time but it would be close. You'd be better off cost wise replacing the pump at a given mileage interval.
Two wearing out "at the same time" is not going to happen. Take a quick study of the probability statistics concerned with the failure of electro-mechanical devices and it'll show you that: The probability of one electro-mechanical item failing - mulitplied times the probability of another identical electro-mechanical item failing while in service along with the other - equals the resultant probability one must live with of both "going bad at the same time". These two probabilities multiplied together make for a very, very, very small probability of paralleled in-tank fuel pumps ever failing at the same time and leaving one stranded in a busy intersection or out in the middle of nowhere. Of course along with parallel in-tank fuel pumps one should have some kind of indicator on the dash telling when the first one to fail has, indeed, failed -> hence you're now relying on only one of the two in-tank fuel pumps and bettter do something about it.
jfkmk wrote:
The newer serpentine belts will go 150k plus miles and require releasing the tension at one point. It took me less than 5 minutes to replace it on my SUV and that was from opening the hood to closing it.
This seems to NOT be the case for the V10 engine in the common Ford E350 and E450 cutaway van chassis under a lot of Class B/C motorhomes. The mechanic that last changed mine in our rig (per my request at 45K miles for preventative maintenace) needed a special tool to do it (I think it had something to do with holding back, and/or maybe completely removing, the tensioner pulley to install a new belt). Plus ... I looked quite some time under our motorhome's van nose hood on our E450 and it's packed in there. I could not get near it's serpentine belt without removing the radiator shroud and then probably having to lay on the ground underneath the engine to snake a new belt up and around all the bottom sides of the various pulleys. I wouldn't want to have to do this out in the desert somewhere. Nevertheless, I carry a new spare serpentine belt anyway, just is case I can figure out how to replace a broken one should I have no choice - since one is entirely dead in the water when a serpentine belt breaks. At least with the old multiple belt design if, say, the alternator belt broke ... I could keep on driving with no alternator ... since some motorhomes can go a long distance running off the engine battery in conjunction with the coach battery(ies) powering all the engine functions (like ours can using the emergency boost switch).
By the way, a fuel pump tank access port will not be of any help in getting to the fuel pump in a motorhome ... unless the motorhome builder installed an in-floor access port directly above the tank access port.
Right. I never said both pumps would fail at the same time. I know all about probability and how it applies to risk (in this case the risk of both pumps going at the same time) and know it's practically impossible. My point is, if there wa s a spared pump in the tank, and it was running all the time the vehicle was running just like the primary pump, it would reach its end of life expectancy at the same time as the first pump. They wouldn't fail at the same time, but would be ready to. Even in industries where a pump is critical enough to have a secondary pump, the secondary pump would not be running all the time the primary pump is, "just in case". It would be switched over if the primary pump fails.
In the case of a vehicle, I go back to it would cost the manufacturers a fortune to provide the option of a second fuel pump. The cost would have to be passed along to the buyer. Most drivers can't check the air in their tires, do you think a spare fuel pump would mean anything to them? Probably so few would opt for this that. The relatively few who would want to would say forget it, I'll just change the pump out at 100k miles and save money.
A serpentine belt is infinitely easier to change than the multi belt set up and the belt is far superior, at least in my experience. If you had to remove the radiator etc to get to ONE belt, could you imagine trying to get to 3 or 4? The beauty of the serpentine belt is it takes up far less depth than the multi belt setup did. I have one of those "special tools" for replacing the serpentine belts. It's basically a long flat wrench to get to the tensioner and costs next to nothing.
I fully understand that when a chassis is built bu one manufacturer and sold to another to have the body they can't put an access port for the fuel pump, I just thought it was pretty cool that GM had thought about it for the Grand Prix that Burbman spoke of.
