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Anyone experienced low mpg after changing the spark plugs. I did installed the correct NGK plugs on 2011 e550. Before I regularly hit 26 or 27 mpg on long trips. Now the best I got is 24.6 on 300miles trip.
Anyone experienced low mpg after changing the spark plugs. I did installed the correct NGK plugs on 2011 e550. Before I regularly hit 26 or 27 mpg on long trips. Now the best I got is 24.6 on 300miles trip.
I recently had all 8 of my plugs replaced and I cannot say for sure that I've noticed an change in MPG. However, I do feel like the car has a little more kick to it (power/HP). If this is truly the case and not just psychological then maybe you are pushing it a little harder therefore decreasing your MPG? IDK but just a thought.
Probably a combination of things. Winter gas is worse than summer gas for mileage. However because you use a fixed air/fuel mixture, cold air has more oxygen so you make more power.
I do not mean to be condescending, as I do not know your level of automotive technical knowledge. . . but did you check the gap of those new plugs? Unless something has changed in the last few years, new plugs are not gapped to spec for any particular engine. You may need to reset them.
I pulled out 2 plug and the gap is at .32
Drove 80 miles on a flat road with cruise control on. The best i got was 24.4mpg. I noticed the thread of the plugs were wet. The piston also have some white residue on them. Is that normal.
My guess would be your car is running rich from looking at those deposits and perhaps unburned fuel up in the plug chamber/threads. Rich is always better than lean, but maybe you should look into this.
12-21-2015, 10:06 PM
Hence the loss of MPG.
