Replacing the Spark Plugs for Better Gas Mileage

In my ongoing attempt to keep my old car moving at optimum efficiency and gas mileage, I am constantly making tweaks. A couple of weeks ago I got around to replacing the spark plugs in my Mercury Mountaineer. They were probably overdue for a replacement: they were the original plugs on my 2002 SUV.

It was time. The factory specifications for the gap on Motorcraft Platinums was .052 inch (52 thousandths). The plugs in the back 2 cylinders had worn to .091 inch and .092 inch gaps.

That’s not good. Gaps are the distance between the electrodes and the spark plug  More gap means more space for the spark to have to travel, and engines run more efficiently at the manufacturer’s specified gap. Once I realized that the Mountaineer still had the original plugs, replacing the spark plugs went to the top of my car maintenance to-do list.

The Mountaineer now has new Bosch Platinum +4s and it runs a lot better.

The Bosch guarantee is that you will “experience quicker starts, smoother acceleration and improved fuel efficiency” or your money back. No need for me to get a refund. I have seen my city gas mileage go from around 16 MPG to around 17. That’s a 6.25% improvement. I haven’t done any trip driving so I can’t tell what improvements I’ll see highway, but I have no doubt there will be some.

I did the spark plug change myself so my cost for the maintenance was around $35. Since this was a 2002 SUV with 162.000 miles on it, removing the original plugs was so hard it was laughable. As an old pro using my Snap-On professional tools, I expected this would be easy. Not this time! I could barely get the plugs out.

When I installed the new Bosch plugs, I put anti-sieze compound on the plug threads, just in case I ever have to take them back out.

I’m hoping these plugs will last the life of the vehicle, but there’s no need to make replacing the spark plugs any more difficult than it has to be.

The next project on the Mountaineer is to replace the differential fluid with a light weight synthetic blend. This will decrease the amount of drag the differential puts on the drive train and should create an incremental increase in gas mileage. It may only be an increase of 2 or 3 percent.

Changing the differential fluid will pay off short term, but it will also pay off even more when the weather turns cold. That’s because the greater viscosity of the old differential fluid creates more drag and that effect is magnified by cold weather. The lighter weight synthetic helps mitigate this cold-weather effect.

When you add that 2 or 3 percent to the 6 percent from the plugs and the percentages from all of the other tweaks I’ve made and it starts adding up to real gas savings. These tweaks (and my slow and steady driving style) are the reason I’m not only meeting the EPA estimates for mileage on my car, I’m exceeding it.

What tweaks are you making to make your car work more efficiently?

8 Responses to “Replacing the Spark Plugs for Better Gas Mileage”
    • Jon Jividen 05/31/2016
  1. Allan Liwanag 05/24/2016
    • Jon Jividen 05/31/2016
    • Jon Jividen 05/31/2016
  2. Terry 08/03/2017

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