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Several months ago, I started conducting my own experiments on fuel economy. Every three weeks I travel from Lincoln, NE to Houston,TX (and back) for medical treatment. That has given me the opportunity to track real world results in fuel economy tests. I found some interesting results, despite the mechanical issues I had over the course of some of the experimenting.

First off, my test vehicle is a 1998 Buick Regal LS. It sports the naturally aspirated GM 3.8 Liter engine. I purchased this vehicle after my previous car couldn’t reliably make the trip back and forth to Houston any longer. It was a 1-owner car that was driven daily since new. I purchased it with over 113,000 miles on the odometer, so it was more than well broken in. Each trip taken I used the cruise control set at 65 mph unless the speed limit was less. I’ve found that driving over 65 greatly reduces fuel economy (on previous trips). The tires were also inflated to 35-37 psi (slight fluctuation to see if it changed fuel economy, which it didn’t significantly).

The first trip I took with it, I didn’t perform any maintenance other than a can of BG 44K. Not because I didn’t want to, but because I purchased it literally the night before I left on one of my frequent trips. That trip I drove an even 2000 miles and averaged a respectable 28.2 mpg. Once I got back, I began some basic maintenance on it. The first was the air filter, spark plugs and wires. I replaced the stock air filter with a K&N air filter. The spark plugs were upgraded to the e2 plugs which advertise a documented power increase as well as mpg increase. I figured if it worked out on this car, I’d do the same on the rest of my “fleet” of vehicles. But those plugs are rather expensive, so I needed to know for sure that they worked before just dropping that money on all my vehicles.

My next trip showed some improvement, but a failing transmission created a faulty total accounting. While the transmission was fine, I drove 936 miles and averaged a much improved 31.0 mpg, an increase of 1.8 mpg over the previous trip. However, the CE light illuminated almost immediately upon my return trip. It ended up being the transmission. I was able to limp it home the 93x miles, but my mileage fell to a still relatively respectable 27.5 mpg.

After a new transmission was installed I didn’t see much difference between my first trip and the remaining trips. However, this was also over the winter and as many experts will tell you, don’t pay attention to fuel economy during the cold winter months as it is not accurate anyway. Well, including the first two trips with the car (yes, even the trip with a failing transmission), the first 6 trips averaged a still respectable 27.8 mpg with a total mileage of 10,829. So even with the failing transmission, it did not greatly affect the end outcome of fuel economy. It was not even the worst mileage of all of those trips. I believe this was in small part of breaking in the new transmission. I suspect the tolerances of the gears was much closer, therefore more friction was present, resulting in slightly decreased fuel economy.

My next trip, I decided to further alter some basic maintenance of my vehicle. For my oil change this time, I elected to treat the oil with BG’s engine oil additive. This additive is supposed to remove engine deposits and generally clean the internal components of the engine. It was also time for my BG 44K treatment. That is the fuel system cleaner that is recommended to be added every 10k miles. I’m not sure if it was due to the warming weather or not, but my fuel economy increased to 30.0 mpg for 1872 miles driven. It was over a 2 mpg increase from the previous six trips.

My next trip I took it a step further. I had a good response from BG’s engine oil additive, so I elected to also purchase BG’s transmission additive during my next oil change. Again, I saw measurable increases. For the first 1159 miles (all the way down to Houston, in town there, then back to Corsicana, TX) I averaged a much improved 31.2 mpg. However, around the Dallas area, I drove through a strong frontal system and from that point on was driving into 25 mph head winds which naturally decreased my fuel economy. However, even after driving for a day and a half into very strong headwinds, I still averaged an improved 30.4 mpg after a total of 1850 miles driven. I would like to say that it was settled as far as the mpg goes for the car, but on this trip, I noticed a miss at idle as well as under certain condition while under a load. It was confirmed that three ignition coil terminals were corroded and not allowing full voltage to reach half of my spark plugs. Although I’m not sure how that affected my fuel economy, I can only guess that it didn’t help it.

I now have all three coils replaced with new ones and am looking forward to seeing what my fuel economy will be for this next trip. I’m hoping I have good travel weather with minimal winds (10 mph or less) so as to get an accurate accounting of mileage on this trip. Stay tuned for further results…