According to the EPA website the '98 is rated at 26 city 34 highway and 30 combined while the '99 is rated at 26 city and 36 highway with 30 combined. The E320 in '98 is rated at 20/26 and in '99 20/28. I don't know if the '99 transmission is different or if the EPA tests were just changed for '99 to explain the difference on the highway ratings but it would seem possible that if, for example, the final gear ratio were different on the '99 it would explain why you get 31 in your '99 and we only get high 20's in our '98s.

Now, I wish I could understand why none of us sees anywhere near the mid 30's the EPA estimates for highway mileage. I don't go 85, more like 70-75 on the highway and that's the tank I got nearly 29 on with 75% highway driving. So, maybe on that tank I broke 30 on the highway but no way was it 34.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz