Finding and Fixing the Causes of Poor MPG
Cooling System Issues
One of the most important contributors to the fuel management system on a fuel injected vehicle is the coolant temperature sensor. You could almost look at this sensor like the vehicle’s “choke” that a carbureted engine uses. Engine temperature dictates when many things happen with your engine management system. If there’s a problem with the cooling system, it can have a direct effect on fuel economy and engine performance.
Now before you get all happy and replace your coolant temp sensor, think basic. Remember I said not to make things complicated. Try two things. First, make sure your cooling system doesn’t have any air in it. Here’s a video on how to do that. More info can be found in the What to Do If Your Engine Overheats article.
If you’re sure there’s no air in your cooling system and you still suspect a problem, you might check the thermostat. If your vehicle is equipped with a temperature gauge and you notice that it doesn’t come up to temperature like it should, you might consider replacing the thermostat. Your engine is designed to get up to operating temperature quickly so that it runs as efficiently as possible. If it doesn’t get up to temperature quickly and efficiently, your MPG will suffer. Aside from that, thermostats are wear items; they are mechanical devices that will eventually fail. So if you start to notice an issue with one, replace it sooner rather that later to ensure efficient engine operation.
Overheating Engine
If your engine is overheating or running hot, it will affect fuel economy. The increased heat load of your engine will equate to a loss of efficiency. I cover how to deal with an overheating engine extensively in the What to Do If Your Engine Overheats article. Check that out if you have an overheating engine.
Misfires
I touched a little on misfires in the spark plug part of this article, but I’d like to cover them in more detail here. Misfires come in all shapes and sizes. They have an equal amount of causes. In this section, and some of the sections following it, I’ll talk about the possible causes of engine misfires. The bottom line is, misfires cause performance problems as well as poor fuel economy. A misfire occurs when a cylinder or cylinders don’t put out the power that they should. Misfires make the engine work harder, making it less efficient.
Power Balance Testing
Power balance testing is one of the best and easiest ways to find the source of a misfire. The idea is to isolate each cylinder to see if it’s producing the same amount of power. If you find a cylinder that’s down on power, it’s likely you’ve found your misfire. Once you’ve located the problem cylinder, you need to find the cause of the misfire. This can be tricky, but as I said at the beginning of this article, if you take a logical approach, you’ll be successful in your diagnosis.
More information about what to do when you find a misfire, and how to diagnose engine performance issues, can be found in the Solving Automotive Performance Issues article. For now, here’s a video on power balance testing.
