Getting the best fuel economy from an automatic

[JeffT]

Listen there are 2 types of torque converters, the old style, the kind that don't lock-up and the kind that do.

The old kind that don't lock-up don't suffer from any REAL loss in MPG from the lock-up kind. The kind that do lock-up and then for some reason fail to lock-up will slip a hell of a lot more than the older style converters do. A lock-up converter that fails to lock up will reduce MPG in a car.

As I stated before, and as Fritz stated: "VW says that TCL (torque converter lock) is utilized for the purpose of lowering transmission operating temperatures. A slight increase of fuel economy if (sic) of secondary significance."

This IS the case. Automatic transmissions are more reliable than they used to be due to the lock-up converter, but it doesn't increase MPG. THE LOCKUP CONVERTER WASN"T DEVELOPED TO INCREASE MILEAGE. Any claims by the automakers to the contrary are simple puffery. There is probably a very small increase that they are hanging their hats on, but a non-lockup torque converter will give you the same MPG and better 0-60 performance than will a lockup converter, everything else equal.

 

[Joe Rappa]

I know there are 2 types of converters. Actually there are additional types as well, including a dual pitch converter used by Buick some years ago. I've been building transmissions for 15 years now. The reason lockup converters make more heat than non lockup ones is the higher stall speed(more slippage). This allows the engine to reach a higher speed when starting from a stop, and it creates greater torque multiplication(as high as 3:1). The down side is high heat production. If VW is using a very tight converter(one with a low stall speed) then slippage is minimal. Mileage increase under lockup will also be minimal as well as heat production.
To say mileage increase is "puffery" is a mistake. I've witnessed on my own car as I stated before.
Joe Rappa

[This message has been edited by Joe Rappa (edited February 05, 2000).]

 

[JeffT]

A lock-up torque converter doesn't give even 1 more MPG than a non locking converter. And under cetain driving conditions a lock-up converter may even give a little poorer mpg.

Read the literature or manuals they always say something like "slight" or "somewhat" improved MPG. If the increase in MPG was at least 1 or 2 or 3 mpg wouldn't they say so????

[This message has been edited by JeffT (edited February 07, 2000).]

 

[Ric Woodruff]

Drive ANY car/van/suv, whatever, with an onboard computer that calculates instantaneous MPG. What you will see is that the absolute best MPG physically possible (steady state) is just AFTER the auto transmission has shifted to the highest gear and the torque converter clutch has engaged - period - no ifs, no ands, no buts!

 

[Ric Woodruff]

The simple fact is that an automatic's MPG is inherently lower because of energy loss due to slippage & heating of the transmission fluid (you may know that automatics ALWAYS route the transmission fluid thru the radiator to cool it, otherwise it would burn up. Manuals don't have any type of cooling because there is no heating).

If you compared the MPG of:

a) a car with manual transmission

b) the same car with auto w/ lockup torque converter

c) same as b) but with lockup forced OFF,

and the same three cars ran at identical RPM's at highway speeds, you will find that a) and b) get identical MPG, while c) gets lower MPG at any given highway speed.

 

[SkyPup]

Super HOT Topic!

One key point to remember to bring it all back home:

HEAT KILLS AUTOMATIC TRANSMISSIONS!!!

Stuff that up your soot pipe and smoke on it.

 

[ThinkDiesel]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Ric Woodruff:
Drive ANY car/van/suv, whatever, with an onboard computer that calculates instantaneous MPG. What you will see is that the absolute best MPG physically possible (steady state) is just AFTER the auto transmission has shifted to the highest gear and the torque converter clutch has engaged - period - no ifs, no ands, no buts!<HR></BLOCKQUOTE>

That's been my experience too, for what it's worth, Ric. Saw that phenomenon in both an auto Subaru and my mother's Volvo XC w/ auto.