Low mpg 2000 lesabre limited

[2000ltd]

I have 87k and just did a 195° thermostat and coolant flush. Car runs at 200°F and has new plugs, wires and coils. I've cleaned the MAF sensor with MAF sensor cleaner. Tires are at 38 psi. My dic computer says I get 30 mpg but I checked it at the pump and I get 20 mpg mostly highway miles. I think I may have an issue somewhere and I need help. I don't wanna parts cannon it if possible. Any ideas? All help is welcome.

 

[MelsRegal]

I have 87k and just did a 195° thermostat and coolant flush. Car runs at 200°F and has new plugs, wires and coils. I've cleaned the MAF sensor with MAF sensor cleaner. Tires are at 38 psi. My dic computer says I get 30 mpg but I checked it at the pump and I get 20 mpg mostly highway miles. I think I may have an issue somewhere and I need help. I don't wanna parts cannon it if possible. Any ideas? All help is welcome.

Explain how you checked it at the pump?

 

[2000ltd]

Explain how you checked it at the pump?

I filled up and drove 14 miles then filled up at same pump and checked pump. It said .689 gallons so I divided 14 by .689

 

[RD_Atlanta]

Try to expand expand your test. I prefer to fill the tank then drive until the tank is near empty then refill at the same pump and try to achieve the same fill level.

 

[2000ltd]

Try to expand expand your test. I prefer to fill the tank then drive until the tank is near empty then refill at the same pump and try to achieve the same fill level.

Ok I'll do that next time I fill up

 

[MelsRegal]

I filled up and drove 14 miles then filled up at same pump and checked pump. It said .689 gallons so I divided 14 by .689

I agree with prior comment, driving 14 miles is not a valid test. You have to use close to a tank full to obtain a valid number.

 

[Buckthebuick]

You can see exactly the mpg you just got in short trips if you can keep it FULL, and when you're broke I know how it goes putting in 2.37 in the tank with a mix of pennies dimes and nickels. But if possible financially I'd do this -fill your tank, reset your trip mileage, drive until about ¼ tank. I don't go any lower as I treat my Buick like a baby, but after driving a considerable amount of miles. Usually 300-350 miles from full, fill it again. Take the amount of miles driven. Devide that by the amount of gallons of gas put in the tank and, bam, there's your mileage. I drove 350 miles and put in 13.7 gallons of gas. That's 350/13.7=25.54 I got 25.5 mpg. Unless you can afford to fill your tank every single time you fill up, don't worry about your mileage as it won't matter.

 

[2000ltd]

I retired it like you just suggested and came up with 23.7 mpg after driving a full tank. I'm satisfied with that. It was a mix city and highway. Pretty decent. My 4cyl Mazda gets 28 mixed driving the same route.

 

[JGBuick]

I have 87k and just did a 195° thermostat and coolant flush. Car runs at 200°F and has new plugs, wires and coils. I've cleaned the MAF sensor with MAF sensor cleaner. Tires are at 38 psi. My dic computer says I get 30 mpg but I checked it at the pump and I get 20 mpg mostly highway miles. I think I may have an issue somewhere and I need help. I don't wanna parts cannon it if possible. Any ideas? All help is welcome.

I don't think you have an issue. The computer calculates using many factors and the best way (To calculate mpg) is to fill-up the tank and then drive normally.
The more miles you travel and the more gas you use helps the average MPG. You cannot get an accurate reading by ONLY driving a few miles.

- What RD_Atlanta mentioned above. 👍

And.... whatever you do - Don't OVERFILL your gas tank by trying to get every last drop of gas in the tank. Click, click...click. It's terrible for your EVAP system.

200degs - Great. That's good. 23-28MPG??? Normal.

 

[2000ltd]

I don't think you have an issue. The computer calculates using many factors and the best way (To calculate mpg) is to fill-up the tank and then drive normally.
The more miles you travel and the more gas you use helps the average MPG. You cannot get an accurate reading by ONLY driving a few miles.

- What RD_Atlanta mentioned above. 👍

And.... whatever you do - Don't OVERFILL your gas tank by trying to get every last drop of gas in the tank. Click, click...click. It's terrible for your EVAP system.

200degs - Great. That's good. 23-28MPG??? Normal.

Yep I'm relieved that it came out normal. At 20 I was worried that something was wrong because I've heard of people getting 30 on highway and I was only getting 20. But 23.7 mixed is very good imo

 

[RD_Atlanta]

There is a 'Fuel Mileage Scale Factor' in the PCM which will allow you to scale the accuracy of the DIC displayed MPG but it unfortunately requires adjusting and downloading the program. It sure would have been nice if GM would have permitted car owners to adjust the MPG scale factor via the DIC because it seems they are usually not accurate.

 

[JGBuick]

Yep I'm relieved that it came out normal. At 20 I was worried that something was wrong because I've heard of people getting 30 on highway and I was only getting 20. But 23.7 mixed is very good imo

Yes, sounds about right. Funny thing.... If I'm in the country and filling-up for gas, I'll reset the MPG button and cruise at 60mph on the highway. I will see 33-34MPG if I keep it under 60mph. Just goes to show you how that computer operates.