[W126 Coupe] Economy gauge: 1990 560 SEC

[Elm Zobens]

Lou,
The 'Economy' gauge is nothing more than a vacuum gauge connected to manifold vacuum. The theory is that the higher the overall average vacuum (or "Economy") reading on the gauge, the less fuel you are consuming (relatively speaking) since the engine is in it's most efficient/lean state when you are running at high vacuum. 
 
As the engine works harder, it requires more fuel- As you step on the accelerator, you see the gauge go down (IE when accelerating or climbing a hill) since more fuel requires more air and opening up the throttle increases the airflow and drops the vacuum inside the engine until the engine accelerates and achieves high vacuum once again. 
 
Since you can't avoid pulling or accelerating, the best you can do is to accelerate gradually to prevent the gauge from falling lower than it needs to for you to reach your cruising speed and on hills, use the best gear to maintain the highest vacuum reading for your desired speed. Bottom line, the less time the needle stays in the red, the higher your average mileage should be. What that difference equates to varies on the driver, the engine and the terrain.  

Elm
--- On Fri, 10/2/09, millerlh at earthlink.net <millerlh at earthlink.net> wrote:


From: millerlh at earthlink.net <millerlh at earthlink.net>
Subject: [W126 Coupe] Economy gauge: 1990 560 SEC
To: "mbcoupes" <mbcoupes at mbcoupes.com>
Date: Friday, October 2, 2009, 11:22 AM




While I'm posing questions to all you learned brethren (and sistern) of the Coupe Groupe, I had one more question that has been nagging me about my 1990 560 SEC.
 
I live in a modestly hilly area of NJ. 
 
I drive my Coupe daily in all conditions, including a 12 mile commute through the countryside over twisty roads which are continuously up and down over modest hills. I also drive it almost daily on divided highways and interstates.
 
In the daily commute, I have begun to do the drive primarily in 3rd gear, because I noticed that the "Economy" gauge invariably registers 3rd gear as being more "economical", up hill and down, and even during acceleration, at speeds which are below 45, which is the entire commute.
 
I was wondering if the gauge is really registering "Economy" which I would interpret as "using less fuel", or if it would have been more accurate to have labelled the thing "Efficiency", which I would have interpreted as meaning the engine is operating more efficiently. The difference isn't much, but I do think I am actually seeing a small difference in fuel consumption, for the better.
 
Does anyone have a true German car with the German word used on the gauge, which may or may not give a translation of the intent of the English word? 
 
I also noticed that the gearshift slot for the gear lever has 4th and 3rd gears in the same plane, so I assume it was intended to commonly make this shift between 4rd and 4th, as opposed to having to make an extra deviation to get into 2nd or 1st, for what that's worth.
 
Just curious to know people's thoughts.
 
Lou MIller  
 
 
millerlh at earthlink.net
EarthLink Revolves Around You.
 

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