Yes, most car manufactures against using oil and fuel additives and it is in owner manual. I first used this Synpower Oil Treatment in 2004 Honda S2000 with 7800 miles. I did not expect to see improvement in gas mileage in that car at all. What had been done was: I had second oil change at Honda dealer at 7500 miles with conventional oil 10W30 in early December 2004, the gas mileage was not changed for the first two fills at the same gas station, about 20.5 MPG as many times before, 20 MPG to 21 MPG. I added 5 oz of Synpower Oil Treatment in January 2005, after 150 miles or so the gas gauge went down much slower than before, I thought that something was wrong, I monitored the gas gauge every mile to make sure that I will not ran out of gas in middle of the road. The first fill up at the same gas station I got 23.5 MPG. I then reset trip-odometer B as I alway did, to see what will be the gas mileage for next fill up. I got 22.1 MPG on second fill up and 24.2 MPG on third fill up. Nothing else had change for this S2000, same oil, same tire pressure, same air filter, same roads and similar driving conditions.

Because of the improvement in fuel consumption in Honda S2000, I decided to try it on '00 E430 to verify what I observed. The improvement of 2 MPG for the first 150 miles may be a coincidence, that why I said I will monitor the next several fills to see how things go.

Yes, '00 E430 has trip computer. I alway reset it every week to monitor the fuel consumption since about a year ago. Before then, I only reset twice a year to monitor fuel consumption in winter and summer. Either way, the average speed and the gas mileage were very consistence, 18.3 MPG to 19.2 MPG most tanks, with majority of fills at around 18.5 MPG . I never had a tank with more than 19.5 MPG, except on long trips to Las Vegas or San Diego. The E430 is my wife daily driver with 80% city and 20% highway.

The gasoline price keeps going up, it is more than $2.30 for premium in Southern California now. I would not hesistence using high quality oil additive if it do no harm to the engine and improve gas mileage at the same time.

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'00 E430 Brilliant Silver/Ash