Two car related questions

We have two questions:

My wife says its hard on the fuel pump when you run the car on less than a quarter of a tank. I say she’s nuts.

We have an '04 Mini Super Cooper and a '00 Toyota Land Cruiser both of which recommend premium gas (only) be used. Premium is typically 91 Octane and Ethanol is 89. We wondered how harmful, if any, would be rotating the fill-ups with these two blends. Another, less likely hassle might be to fill up with half of each, each time.

Looking forward to your responses.

Thank you.

I do not believe running the tank level down will damage the fuel pump, it is designed to operate with a minimum tank level. However, do not run it dry.

Use the correct fuel, you can get away with lower octane if premium is only recommended (not required), but why bother.

We’ve been down this octane “premium or regular?” question line many times. Go to the red banner, click on Search, search for “regular or premium”.

The fuel pump does not care at all about the level of the fuel above it. It will run happily with a minimum amount.

I have heard a lot of hokey reasons why some people refuse to let their tanks go below the 1/4 mark. I will add this one to my list… near the top.

unless you live in an extremely moist environment for a long number of years there will never be any harm in running a tank to less than 1/4 tank. Octane is not so much the concern as where you buy the octane. I used to deliver fuel to stations in Los Angeles. The general public would be amazed at what is done to stretch a tank of fuel - sometimes fillers are ordered from the provider. Be more concerned with how your cars run after buying a tank of fuel from a certain station. And, some cars will just run better on higher octane fuels. I would do more bad then good to the engine in my old muscle car if I used low octane, also low octane mileage is worse in my more modern car.

The low fuel is not the best scenario for the pump. The cars in the late eighties used to sputter when the tank got down near an eighth of capacity. I saw it happen with a Bronco II when it started trying to pump air. It is obviously better to have higher fuel levels and there shouldn’t be enough doubt to argue about. Use the premium. I don’t know why people enjoy creating their own gray areas to operate in. Not much difference running 90 octane sort of so I don’t see any bad things happening because of it. It is funny to spend all that money on cars just to cheap out on the gasoline. Act normal. Like me.

Your wife is right. First she has a point, a normal pump will not have a problem, but a marginal pump will. Second, if there is no reason to argue, with her, it is best not to.

If the manual says premium REQUIRED, use it, low test may damage you engine, if it recommends it, then it will not damage the engine, but it may reduce power and or mileage.

If the Ethanol 89 you are referring to is E85, unless your vehicle is able to use it(most vehicles will say they are flex fuel), you’ll risk damaging your entire fuel system from the ethanol blend.

My uncle has a flex fuel truck and says that there isn’t any real difference between the e85 and the regular gas he uses since you get less mileage from the e85 and wind up using more of it compared to the normal gasoline.

One reason for the recommended premium only is bacuase in Europe the regular gas is 93 Octane. The European cars are designed with that as a baseline. I dont know why the Land cruiser is premium only evhicle, whats the compression ratio on the engine.

As long as you don’t let it run empty the pump will have fuel to cool itself and it’ll be fine. I don’t know why anyone would want to do this, and if you get stuck in a snow storm or traffic you may run dry and you MAY hurt the pump.

Use only the fuel recommended in your owner’s manual or risk engine damage. We’ve had countless threads on this subject. I’m still puzzled as to why people ask.

Some pumps are more robust than others. The fuel is used to cool the pump. In a very hot climate running on very low fuel levels will heat up the gasoline to where it cools less, thereby shortening the life of the pump. Ford minivans have a history of this.

I normally tell people to kep the tank at least half full in very hot weather, and also in very cold weather to reduce condensation.

They use a different computation method in Europe. The numbers are not equivalent.

Both cars are new enough they have computers that can compensate for lower octane gas by retarding the timing. The consequense is you loose power and therefore efficiency. Thus, you can fill with low octane and not damage you engine…just be prepared to loose acceleration and power.

I doubt that is true for the mini, check the manual.

It might be a problem in certain weather conditions that would cause excess condensation. The higher the fuel level the less chance of condensation. What is hard on a fuel pump is a dirty filter!!!

I don’t know why 1/4 tank would get any hotter in hot weather than 1/2 tank, but I’m not an advocate of running a low tank anyway so it’s a moot point.

I had lunch with my daughter this weekend (as uaual) and asked her how she liked her new Civic. She said she’d happily discovered that she could keep driving for a few days even after the “fill” light comes on for the gas. I know that for the years she drove my old pickup and after she’d gotten her first Civic I’ve always stressed not to let the tank run low and the reasons why.

My guess is that it really doesn’t matter what we say. The OP’s wife is going to continue to drive with a low tank anyway. But it’s fun discussing the subject.

As for the 1/4 tank thing, in my experience it’s bogus. I routinely run my gas tank down until the fuel light comes on, then I fill up. I have done this for many years on many different cars. The ones I’ve owned from new have all gone well over 100,000 miles and none has ever needed a replacement fuel pump. None of the used cars I’ve owned has needed one either. I suspect the fuel pump failures are more related to the make and model of car than to fuel levels.

If your car calls for premium then use it. It’s only a couple bucks per tank extra. Why waste time trying to save a couple bucks? Even over a year’s worth of driving it’s trivial.

I agree that the make and model are also factors in fuel pump reliability, however if you fill up when the light comes on you’re fine. The system is designed to notify you before the level gets to the level where it endangers the pump.

Besides, for those who drive in the snow belt and near dangerous urban areas a full tank is a definite safety device. One can be stuck on the Everett Turnpike in a snowstorm for hours due to a crash up ahead…three or four times a year! I have!

I agree wholeheartedly about the octane.

Mountainbike, some people get an emotional high out of running on vapors!

One person I know does it so the fillup will come out of his next paycheck. He has burned out a few fuel pumps, but I can’t persuade him to keep the tank relatively full.

My wife drives to the mountains a lot, where there are no gas pumps. She fills the tank when it gets to between 1/3 and 1/4, purely out of habit. But then, she teaches emergency response and first aid.

As they say, to each his own.

Well, of course I’m not going to take chances on running out of gas in dangerous conditions/situations, but driving around my home town and immediate area I am never that far from a gas station that I have to worry about it. I also live on the East Coast, in less populous areas I might change my habits.