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Old 05-13-2015, 01:23 PM
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Fuel Tank Level & Fuel Pump Life ?

Years ago I had a good mechanic I trust, tell me to never let your fuel get below a third of a tank if possible. Especially in very hot weather. His reasoning was that most fuel pumps are located in the tank. If you keep your fuel level high, the pump will always be cooled by being submersed in the surrounding liquid fuel.

This will keep it cooler than it would normally be if it was surrounded by the air of a near empty tank. This has always make good sense to me. Not to mention you have far less chance of water condensation if you keep your tank full as possible.

I've always followed this and have never had to replace a fuel pump. Another tip he gave me was never start or turn off your engine with a lot of accessories running. (Lights, radio, AC, fan, wipers, etc.) If you do, when you start it jolts your voltage regulator. It won't hurt anything if you do it a few times. But over time your voltage regulator won't last as long. In most cars today the voltage regulator is incorporated into the alternator. They're not cheap.

I've always followed this tip as well, turning everything off before the engine, then starting up, then start turning on accessories one by one after waiting a few seconds. I've never had to replace an alternator either. This is what I don't like on my new Grand Cherokee. I wish the damn headlights would stay OFF until I want the things on. Not keep turning on every time I get in the thing.

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Old 05-13-2015, 01:27 PM
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Re: Fuel Tank Level & Fuel Pump Life ?

I've never done any of those things and never had to replace a fuel pump or an alternator.

Turn your headlights off and they'll stay off until you turn them on. I'm not understanding that one. Don't use auto mode if you don't like it. What am I missing?
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Old 05-13-2015, 01:29 PM
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Re: Fuel Tank Level & Fuel Pump Life ?

I had to put fuel pump in my '02 Blazer recently. In fact, it was within the first 500 miles of ownership, cost $1,200, and is a whole other story

The service writer told me the same thing - to not let the tank get below 1/4 of a tank due to heat issues. I posed this question to the Blazer forum and the response was "there's no hard facts, just opinions which vary." I don't know the right answer, but I've always been a person that keeps the level above 3/8 as a rule.
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Old 05-13-2015, 02:28 PM
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Re: Fuel Tank Level & Fuel Pump Life ?

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Originally Posted by Zhe Wiz View Post
Turn your headlights off and they'll stay off until you turn them on. I'm not understanding that one. Don't use auto mode if you don't like it. What am I missing?
I'm not using "Auto Mode". They still go on when I open the door, or pull in the garage during the day.
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Old 05-13-2015, 02:33 PM
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Re: Fuel Tank Level & Fuel Pump Life ?

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Originally Posted by BirchyBoy View Post
The service writer told me the same thing - to not let the tank get below 1/4 of a tank due to heat issues. I posed this question to the Blazer forum and the response was "there's no hard facts, just opinions which vary." I don't know the right answer, but I've always been a person that keeps the level above 3/8 as a rule.
Common sense dictates the fuel pump will run cooler in liquid than it will in air. While there may be no way to "prove" this, I think there is enough evidence to support it. Anyway, I know a guy who just had the fuel pump go in his Ford Excursion to the tune of almost $800.00.

The service rep told him the same thing. He was one of those guys who was always running around with a 1/4 tank or less, putting in $10 worth of gas at a time. Now he has changed his tune.
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Old 05-13-2015, 02:40 PM
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Re: Fuel Tank Level & Fuel Pump Life ?

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Originally Posted by billt View Post
I'm not using "Auto Mode". They still go on when I open the door, or pull in the garage during the day.
I'm still missing something. If you turn your light switch to the OFF position, they will NOT come on when you drive into your garage. I know because I do this all the time. I run around with my lights OFF, if I need them on, I typically switch them to Auto mode. If I forget they will turn on when I drive into my garage. If I have them in the OFF position, they stay off.

Through settings, you can have it the way you want it - your headlights will never come on unless you switch them on. Hell, even the DRL's can be turned off if you don't like them.
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Old 05-13-2015, 03:32 PM
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Re: Fuel Tank Level & Fuel Pump Life ?

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Originally Posted by Zhe Wiz View Post
I'm still missing something. If you turn your light switch to the OFF position, they will NOT come on when you drive into your garage. I know because I do this all the time. I run around with my lights OFF, if I need them on, I typically switch them to Auto mode. If I forget they will turn on when I drive into my garage. If I have them in the OFF position, they stay off.

Through settings, you can have it the way you want it - your headlights will never come on unless you switch them on. Hell, even the DRL's can be turned off if you don't like them.
What position is "OFF"? I have my headlight switch, (round dial left of the steering column), to the position that has a "O" or circle on it. Just to the right of "A", which is for automatic operation. The lights still come on as soon as I open the door. What position do you have to have everything in for "OFF"? What am I doing wrong? The manual isn't very explanatory with this. (I believe it's on either page 36 or 37 of the owners manual.)
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Old 05-13-2015, 03:39 PM
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Re: Fuel Tank Level & Fuel Pump Life ?

Quote:
Originally Posted by billt View Post
Years ago I had a good mechanic I trust, tell me to never let your fuel get below a third of a tank if possible. Especially in very hot weather. His reasoning was that most fuel pumps are located in the tank. If you keep your fuel level high, the pump will always be cooled by being submersed in the surrounding liquid fuel.

This will keep it cooler than it would normally be if it was surrounded by the air of a near empty tank. This has always make good sense to me. Not to mention you have far less chance of water condensation if you keep your tank full as possible.

I've always followed this and have never had to replace a fuel pump. Another tip he gave me was never start or turn off your engine with a lot of accessories running. (Lights, radio, AC, fan, wipers, etc.) If you do, when you start it jolts your voltage regulator. It won't hurt anything if you do it a few times. But over time your voltage regulator won't last as long. In most cars today the voltage regulator is incorporated into the alternator. They're not cheap.

I've always followed this tip as well, turning everything off before the engine, then starting up, then start turning on accessories one by one after waiting a few seconds. I've never had to replace an alternator either. This is what I don't like on my new Grand Cherokee. I wish the damn headlights would stay OFF until I want the things on. Not keep turning on every time I get in the thing.
Complete hogwash.

The fuel pump:

What can kill a fuel pump is letting the tank run dry and it's pumping air. If the pump actually got hot enough to need the fuel to cool it, it would be at risk of igniting the fuel vapor. It's in the tank because that's the best place to protect it and keep it close to the tank.

The alternator:

1) Every vehicle has an interlock to momentarily shut off unnecessary electronics during the cranking process. It all shuts off until the ignition switch goes back to "run".

2) The alternator doesn't even come into play until the engine actually turns over. It needs the engine to operate. Until then, your battery is carrying the weight.

3) When you're on the highway, the alternator is burning off far more power than the vehicle is using. At idle, the alternator is barely doing more than keeping up. If anything is being hurt by leaving stuff on at shutdown, it's your battery, not your alternator. Even that will charge back up when your RPMs get high enough for a long enough time to use the excess to charge.

4) If running all those accessories at shutdown were doing anything the alternator couldn't handle, they would have already tripped a fuse or breaker.

I've never replaced a fuel pump and I had plenty of times in the past where I was running on empty. My last truck lasted for over 16 years with no fuel issues. I kept my previous car for over 5.

Now, each one had an alternator replaced, but only because the brushes eventually turned to dust on them. The car was at 5.5 years, a couple months before I traded it in. The truck alternator lasted for 15 years and I ran with the headlights on day and night both.

What kills alternators? Spinning parts going thousands of RPMS. Drawing power from them doesn't. Unlike the battery, they won't ever give more than they can give. That's why they have the regulators on them: so they don't fry your batter when you're running a capuchino maker while towing a 30 foot boat.

As noted, if it bothers you, you can run all the lights on manual and turn off the settings for them to come on or stay on when getting in and out.
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Old 05-13-2015, 04:10 PM
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Re: Fuel Tank Level & Fuel Pump Life ?

You need to have the passive settings set to off in the Unconnect menu to keep the horn, headlights, etc. off when using the fob or entering the vehicle. Could that be it? I don't want mine on either and with those settings set to off in Uconnect they don't come on.
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Old 05-13-2015, 04:41 PM
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Re: Fuel Tank Level & Fuel Pump Life ?

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Originally Posted by billt View Post
I'm not using "Auto Mode". They still go on when I open the door, or pull in the garage during the day.
You are using auto mode. Do they still come on if you crank the headlight knob all the way to the right to turn them off?

BTW, I had a trusted mechanic that insisted that if you always keep a cat in the car your car will last 9 times longer. Anecdotal tales of doing this and that based on mechanic folklore has about that much to do with cause and effect--zip for most such folklore.
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Old 05-13-2015, 04:44 PM
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Re: Fuel Tank Level & Fuel Pump Life ?

Quote:
Originally Posted by BirchyBoy View Post
I had to put fuel pump in my '02 Blazer recently. In fact, it was within the first 500 miles of ownership, cost $1,200, and is a whole other story

The service writer told me the same thing - to not let the tank get below 1/4 of a tank due to heat issues. I posed this question to the Blazer forum and the response was "there's no hard facts, just opinions which vary." I don't know the right answer, but I've always been a person that keeps the level above 3/8 as a rule.
There may be some truth to the rumor as far as cooling, but that would be crappy fuel pump design of an immersed pump.

There is similar folklore [where folklore may or may not be true] of not letting your tank get too low as then you would get crud, dirt, and such from the bottom of the tank in the pump and clog it up. Although this sounds good, it would seem to ignore the realities of the terrain some folks take their Jeeps on, where anything in the bottom of the tank could not possibly stay there for long.

Oh, and always buy your gas right after the fuel truck fills the station. Or never buy your gas right after the fuel truck fills the station. Or never buy gas on a rainy or humid day.
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Old 05-13-2015, 05:55 PM
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Re: Fuel Tank Level & Fuel Pump Life ?

well billt by the look of those legs in your aviator your doing ok for an old guy i think your advise from your old mate mechanic is a little outdated it may have been the case years ago but i wouldnt go stressing on that advise given todays technologies. i guess if you dont use reverse it will last longer also, and you will never have to replace it either. come to think of it i use it all the time and it still works for me. i run my fuel weekly beyond the dte reading refilling with 100ltrs/26gallons, i run accessories 24hrs a day and start with lights/radio/heating/cooling whatever is on in the car and have not had to replace anything. less stress is good for the heart
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