How to increase mileage in a 1998 olds 88 royle with a 3800 engine

The owners manual probably says no. Most say 89 octane is the lowest. Look in manual if you have one or they are typically on-line. With that said, test your vehicle with that fuel. Next time it is very close to empty put 2-3 gallons in the tank and drive. If the octane is too low the engine will "spark knock" or "diesel" (a rattling sound from the engine upon acceleration caused by fuel pre-ignition/detonation). If that happens put an equal amount of premium fuel in the tank and the spark knock will go away. Short-term a spark knock won't damage an engine, but longer term can by causing over heating, vibrations, abnormal stresses ... hesitation on acceleration - poor mileage and poor engine performance. If you are able to use 88 octane-15%, without getting a spark knock, make sure you check your mileage and see if, or how much, it drops. Lower octane and higher ethanol both reduce mileage. What I always told my gas customers was to check your mileage with different octanes and see what octane gives the highest mileage (and then do the math and see if its cost effective). Say you use regular normally and you get 30 MPG. Then you try the mid-grade and get 33 MPG, so you try premium fuel but you still get 33 MPG. In that case the mid-grade is your best option, assuming that your 10% increase in mileage cost you less than a 10% increase in cost! But you do always stay away from fuel that causes a spark knock.
The rule of thumb is: The higher the octane the cooler the combustion, therefore the lower the octane the hotter the combustion. Higher ethanol means that the engine is running a little leaner and a little hotter.

The factory tends to use lightweight oil,to increase fuel mileage,
not good for the life of the engine,if heavier oil was put in place,mileage could drop,but not much,maybe 1 mpg,are you sure it's not because of
extended warm up times or more idling than usual?

Yes it can be. Ive had this problem acouple of times. I had to keep my foot on the gas pedal when at stop signs to. Ran rich until I replaced o2 sensor.

HEAD GASKET GONE

Do you have a question? Let me guess, you want to know the MPG rating for the car? Easy, the US EPA rates it at 15 mpg city, 24 mpg on the highway. Your mileage may vary.

its on the fire wall yes it will help some i wouldnt expect a drastic change in fuel economy because acura dosent have a replacement schedule for fuel filters like most car companies. id check your air filter and if your check engine light is on it will seriously kill your mpg. hope this helps

I don't know how much better gas mileage you will get with a gear change. I don't think it will be worth the cost verses saving a couple mpg. The 5.4L engine is kinda small for this size truck. The better way to go would be a cold air intake and an aftermarket exhaust this will easily give 5-10 mpg increase over stock and won't sacrafice any power when towing

Winter time driving does reduce the MPG due to temp not allowing the fluids to warm to thinner viscosity allowing parts to operate with less friction. Hope this eases you a bit. Have a good day.

You should be getting close to 360-390...depending on the type of driving you are doing. Increasing your gas mileage could be as simple as getting a fresh oil and filter job, change your air filter, change your fuel filter...and a biggie believe it or not, make sure you have the proper tire pressure. This will kill your mileage faster than anything else.

City MPG: 16-18 mpg
Combination MPG: 18-21
Highway MPG: Approximately 26 mpg

change your spark plugs if they haven't been changed in awhile. check your tires for the propper psi there should be a sticker on the inside of your drivers door that will tell you recomended air pressures go by this not the recomendations on the tires. also where are you getting you gas does it contain ethanol sometimes this can burn faster.