Getting the best MPG from your SL

[UT_Tech]

The result of your test is very typical for a 129 chassis. What the test means is that your chassis is capable of getting mid to high 20's at 65MPH. Mid-20's is normal for a 129 chassis 320SL but not a 500SL. Mid to high teens is typical for your car. The 500SL engine is tuned for performance and you may not get enough hwy miles to make any modifications worthwhile.

Unfortuntely the real gains in MPG are most likely to be found in CIS-K injected cars like the 107 chassis 380/450SL models (and to a lesser degree CIS-KE). That's because the mechanical fuel controls in CIS-K cars are very likely to be out of calibration and it's easy to make very large changes in the air/fuel ratio in the CIS-K system with simple tools. For these early cars the coast-down test is a good starting point to rule out any of the common problems which affect MPG but have nothing to do with the engine. When tuning for best MPG it's an absolute requirement to know the chassis power numbers before starting on engine tuning.

In your case, unfortunately, the numbers are about right. It's good to rule out any possible tire/suspension/bearing/brake problems which you have just done.