How To Test For Yourself

There are a lot of variables in mileage testing, some quite difficult to manage over time. Things a subtle as tire pressure, time of day (traffic) or a change in the weather can have a significant effect. However, if you'd like to test for yourself, here's how to get the most accurate test results possible.

Stick To Your Test Route: It is crucial in testing to do everything possible to replicate the exact same driving route round trip.  Testing in only one direction can skew your results due to elevation and land changes. Going round trip will ensure that each test receives the same changes as the last, and will duplicate driving conditions and environment. This will ensure your tests are as accurate as possible.

Maintain your speed: Erratic driving patterns can wreak havoc on your fuel economy, so be sure to drive a constant speed while testing. Pick a constant speed that you can maintain. For us it was 67 mph, due to the speed limit changes that occurred in our driving pattern. To maximize our results, we found it easiest to drive at a low traffic time and set the cruise control and just let the truck roll along. Remember to accelerate consistently when merging onto on-ramps (we kept it below 2200 rpm for our test), and brake or gas it as little as possible to provide the most accurate results.

Top Off At The Same Station: Get as much fuel as possible into your truck at each fill up both before and after your testing. Make sure to fill up at the same station(s) each time, ideally, with the same pump.  Variances in the cetane levels of different stations can change your results.

Do Not Idle: Letting your vehicle idle is a quick way to throw off your mpg testing results. Since you are still consuming fuel while the vehicle is idling and you're not going anywhere obviously your fuel economy is going to suffer. Prolonged warm-ups will also consume fuel without adding miles.
Air Conditioning Use: A/C is the single biggest drag on fuel economy, accounting for a significant percentage of fuel consumption. Testing in cooler weather should yield better results than testing in hot weather, when A/C use is necessary.

MORE MPG? YOU CAN DO IT YOURSELF

Royal Purple Fluid Swap

Changing fluids in your truck is a necessity, no matter what kind of oil you use. However, in a diesel hauler, longer-lasting, slippery synthetic fluids will allow the truck to roll easier and save money in oil changes. This is one of those jobs most truck owners can readily tackle themselves.

The Royal Purple Motor Oil used in this example is a tough, long life, high performance oil that delivers superior protection and enhanced performance to gasoline and diesel engines. It extends drain intervals to 12,000 miles, and is compatible with other mineral and synthetic oils. It gains performance advantages from a blend of synthetic oils plus Royal Purple's proprietary, synthetic Synerlec additive technology.

Loosen drain plug

After oil is drained, tighten drain plug and refill

Refilling diff with Max Gear oil

To change motor oil:
1. Cool off your engine so it's easy to touch and work with. While you are letting it cool down, place the drain pan underneath.
2. Loosen the oil drain plug and remove. Next, remove the oil fill cap at the top of the engine to speed up the draining process. Then, remove your oil filter-housing cap.
3. Remove your oil filter element and the O-ring from the oil filter cap. Insert new oil filter element and install a new o-ring. Be sure to lightly lubricate the O-ring with you finger dipped in oil before you install. Finish this step by screwing on the oil filter-housing cap.
4. By now all the oil should be drained out, so reinstall the drain plug and tighten. Fill with 16 quarts of 15w40 and reinstall the oil fill cap.
5. Start up your truck and let it idle for 15 to 20 seconds to verify that you have oil pressure. Turn it back off and remove the dipstick and clean. Reinsert the dipstick and make sure it goes all the way down to the bottom of the dipstick tube. Pull the dipstick back out and verify oil is at the correct level. Assuming it is, all that is left to do is to dispose of the old motor oil properly.

Changing Transfer Case Fluid

You may not have to change your transfer case fluids as often as your oil, but you will reduce friction (heat) and vibration with synthetic ATF.

The Royal Purple Max ATF supplied for our test is a synthetic, high performance, long life, multipurpose, automatic transmission fluid. According to the manufacturer, it's more oxidation stable than other transmission fluids for a longer fluid life. Max ATF's low co-efficient of friction and high film strength help to dramatically reduce heat and wear, and is fully compatible (can be mixed) with other automatic transmission fluids.

1. Put the drain pan underneath the transfer case. Remove drain plug and allow to drain. Remove the fill plug. Wait until all the fluid has drained.
2. Reinstall the drain plug and tighten. Fill the transfer case until it is about 1/8 an inch below the fill plughole. Install the fill plug and tighten.

Changing Differential Oil

Synthetic gear oil brings the same benefits as synthetic engine oil and ATF-lower friction for better cooling, and longer life. We used Royal Purple's Max Gear 75W90 for purposes of this test. Max-Gear is an ultra-tough, high performance, GL-5 automotive gear oil designed to provide maximum protection to heavily loaded gears while maximizing power output throughout the drive train. According to the manufacturer, it outperforms other GL-5 gear oils because it combines the highest quality synthetic oils with Royal Purple's proprietary Synslide additive technology. Max-Gear makes gears run smoother, quieter, cooler and longer without overhauls.

1. Place the drain pan underneath the differential.
2. Remove the fill plug, insert small tubing into diff. and with an oil pump suck the oil out of the differential.
3. Pour in Max Gear until 1/8" of the fill hole is full. Reinstall fill plug and tighten.
4. Repeat for the other axle.