1996 Cadillac De Ville with 12 gallons of old fuel in tank

I have a 1996 Cadillac De Ville. It sat for 1 1/2 years due to a dead battery. I replaced the battery and the car started. I am concerned about the 12 gallons of old fuel in the car. Do I have to drain the old fuel? Can I just top it off with new fuel? In the past, this car would sit for months without being driven and I never replaced the fuel. I do plan to get the oil changed once I drive it.

Just add fresh fuel to the tank.



I have read about adding seafoam. What is your opinion on that? Should I add new fuel right away or run the car for awhile and get rid of some fuel that way and then add new fuel to the old?

You should of added Seafoam before parking the vehicle.

Seafoam is also a fuel stabilizer.

Just get it on the road and see how it runs first.



Okay, thank you Tester

I’d top it off with a “top tier” gas to get as much detergents as possible, and I’d add a bottle of Techron.


I have always put premium gas in it. I think it is usually 93% octane. By " top tier" do you mean premium? What is Techron?

Top tier is a specification for high detergent gas, regular and premium. Many name brand gas follows that specification. Google it.

Techron is Chevrons additive, it’s the one I’ve used.


I was not aware of Top Tier. I think I have used the Techron before. Thank you for your help.

Started and ran the car. I added 7 gallons of top tier gas. I drove the car two times a few miles without any problems except the last time the headlights seemed dim. The next day drove it 20 miles to an appointment without any problems. Returned to car to drive home and it was dead. Got a jump start and it died. Got another jump and while it was running it made a humming(?) noise. This noise sounded like it was coming from the back seat. The car died. Tried to restart a few times and it would not stay running. Got it towed home. The guy that jumped it said it was my alternator. Before I try to replace the alternator I want to make sure that is the issue. A few months ago I did an alternator check with my Stanley FATMAX and it showed the alternator to be okay. I also do not understand why the battery posts are so short. It makes it difficult to apply jumper cables to them. I have read that dim headlights and a humming noise could be the alternator.

Jump start it, measure the voltage at the battery terminals. Is it 14 + volts? Or is it close to 12 volts? less than 13 volts, bad alternator.

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Before replacing the alternator, inspect the positive battery terminal for corrosion.

Corrosion like this can cause a voltage drop which can cause dim headlights, and prevent the alternator from charging the battery.


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I bet the humming noise was the fuel pump in the tank. It might sound like it is coming from the backseat.

Yes, check for corrosion on a car that has been sitting this long. The symptoms you describe are either a bad connection or a bad alternator. You mention just changing the battery. Make sure the connections are good.

As for the fuel, drive the car as a daily driver for a few weeks to get a few tanks of fresh gas through it once you get the charging issue resolved. Cars do better when driven instead of sitting. Yes, changing the oil is a good idea as well.

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I am sorry I forgot to mention earlier that when the gentleman tried to jump start it his machine was showing 7 volts. He said the battery is only 12 volts and could not hold enough? I am not saying that correctly. He said that showed the alternator was bad because it was only 7 volts. Thank you.

I will check that. I wondered about the connection. Thank you. It is so hard to jump too because the posts are short, especially the negative one.

I hope that does not mean my fuel pump is bad. I had planned to drive it more often. It sat all that time because of a bad battery. I waited for someone that said they would help me. It never happened, Finally I removed the cover plate over the battery myself and got the battery out and replaced it. The oil does not look too bad actually. I have been told that if you let the car sit a long time without starting it, the battery would go dead within a week due to computer stuff in it. I will check the battery connections. Thank you.

It’s safer to attach the negative jumper cable to a hefty ground on the engine or body. But a good connection between the battery and engine/body ground is essential.

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What you want to do is remove the small bolts for the cables and replace them with these.

Now there’s something to clamp onto when the battery needs to be recharged or jump started.


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When I have jumped it I had to attach the negative to the car because I could never get a good enough connection to that negative post. The guy that jumped me that day used the negative post somehow.

Thank you. I wondered if I could replace those posts. Plus the place you have in that area for the cables is limited which adds to the problem. I mentioned that when I got the new battery that day. What do I know I am a girl!