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#1728302 - 01/02/10 11:30 AM Transmission cooler and fuel efficiency.
D_Ville_TX Offline


Registered: 11/20/09
Posts: 29
Loc: Texas
Car here is a 2002 Honda Accord V6 with a 4 speed auto transmission.

I have done some extensive testing and found that an external transmission cooler in serial with the OEM radiator cooler will lower my fuel efficiency.

I am located in Texas, so it never get very cold here, but it will still lower my MPG with 1.5 to 2 MPG.

After adding a Perma-Cool model 1060 oil-thermostat to bypass the external cooler, my fuel efficiency got back to normal.

The OEM cooler is always in the loop, and the external cooler is bypassed until the ATF temp exceeds 180F. The thermostat will only open and send fluid through the external cooler under heavy load in the summer. This time of the year, the fluid temp never got high enough to open the thermostat.

In my case, the thermostat is saving enough fuel to pay for itself in about 10000 miles.

Good info for anyone that has external cooler in a cold climate and would like to save some fuel.

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#1728316 - 01/02/10 11:41 AM Re: Transmission cooler and fuel efficiency. [Re: D_Ville_TX]
JHZR2 Offline



Registered: 12/14/02
Posts: 33783
Loc: New Jersey
What is the basis? Are you claiming that the fluid is cooled down so much that the viscosity goes up and causes more viscous drag?

What kind of "extensive testing" have you performed?

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#1728341 - 01/02/10 12:02 PM Re: Transmission cooler and fuel efficiency. [Re: JHZR2]
gathermewool Offline


Registered: 01/09/09
Posts: 3612
Loc: New England
I'm confused. One cooler showed a drop in mpg while the one you're currently using brought it back to normal (i.e. with out ANY aftermarket cooler?)

Do you tow with your Accord?

Is the cooler upstream or downstream of the radiator cooler?


Edited by gathermewool (01/02/10 12:04 PM)
_________________________
14 Forester XT
GC 0W-30 + Subie blue filter
08 Civic LX (Auto)
VWB 5W-20 + Fram Ultra Guard filter

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#1728354 - 01/02/10 12:14 PM Re: Transmission cooler and fuel efficiency. [Re: gathermewool]
cjhepburn Offline


Registered: 02/24/09
Posts: 251
Loc: Boston
Wait a minute... Is the transmission heat exchanger in the radiator a cooler or a warmer? I thought it brought the transmission UP to operating temperature.


Edited by cjhepburn (01/02/10 12:15 PM)
_________________________
'08 Civic LX, M1 EP 5w-20, 10000 OCI - 98k.
'03 Forester XRS, GC 0w-30, 5000 OCI - 78k

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#1728395 - 01/02/10 12:59 PM Re: Transmission cooler and fuel efficiency. [Re: cjhepburn]
D_Ville_TX Offline


Registered: 11/20/09
Posts: 29
Loc: Texas
Let me clarify.

Normal routing is from transmission to radiator heat-exchanger and back to transmission. This routing will help to heat the fluid initially, and cool it when fluid temp exceeds radiator temp.

Normal way to install an external cooler is:
Fluid from transmission to radiator heat exchanger, and from radiator outlet to external cooler inlet and back to transmission.
This setup lowered my MPG in the winter. I guess the transmission fluid is over-cooled and viscosity stays higher than optimum. Measured temp was max 100F (40C) when at 32F ambient.

My current flow is:
From transmission to radiator. From radiator to thermostat.
The thermostat will send the fluid direct to the transmission if fluid temp is less than 180F. Thermostat will send fluid through the external cooler and back to the transmission when the fluid temp exceeds 180F.

I added external cooler to try to improve the tranny life since I have the 6th gen (bad) transmission. Before the cooler was installed, I measured up to 215F tranny temp in summer stop and go traffic in Dallas TX. After adding the external cooler, this temp dropped about 30 degrees.

Current tranny temp after installing the thermostat went from 100F to 160F when ambient temp is 32F. So I guess the 60 degree increase lowered the viscosity enough to account for the MPG increase.

Im am NOT towing anything.

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#1728823 - 01/02/10 08:51 PM Re: Transmission cooler and fuel efficiency. [Re: D_Ville_TX]
gathermewool Offline


Registered: 01/09/09
Posts: 3612
Loc: New England
I think it's fantastic that you actually know how your equipment operates, and the intended purpose. Good job keeping track, and realize the need for a thermostat during cold-weather operation.

Will you be changing out your tranny fluid at the same interval, still?
_________________________
14 Forester XT
GC 0W-30 + Subie blue filter
08 Civic LX (Auto)
VWB 5W-20 + Fram Ultra Guard filter

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#1729555 - 01/03/10 03:18 PM Re: Transmission cooler and fuel efficiency. [Re: gathermewool]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
"After adding the external cooler, this temp dropped to 30 degrees"
And you state this change from 215??
Something is way wrong, as are the MPG claims.

I think a thermostat is a good idea, if properly set. Cars in cold weather areas could benefit from this.
But in Texas? Once again, something is way wrong here.

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#1729975 - 01/03/10 09:17 PM Re: Transmission cooler and fuel efficiency. [Re: mechtech2]
SecondMonkey Offline


Registered: 10/09/07
Posts: 931
Loc: OR
There is NO POSSIBLE WAY for the average person to determine MPG to within 1-2mpg accuracy. You need CONTROLLED LAB TESTING over thousands of simulated miles, and even then, each and every car is going to be different.

There are literally thousands of other things that could have caused that.
_________________________
"Two things are infinite: the universe and human stupidity; and I'm not sure about the universe." - Albert Einstein

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#1730069 - 01/03/10 11:36 PM Re: Transmission cooler and fuel efficiency. [Re: SecondMonkey]
unDummy Offline


Registered: 02/01/03
Posts: 8756
Loc: RI
And why would we go to DexronVI, MerconSP/LV, Toyota WS,......

Most ATF spec sheets have the temp at 40c(104F) and 100c(212F). Compare yours!

If you don't think a difference between 30-35cst and 6-7cst makes a mpg difference, then you should change the bulb floating over your head. The pumping losses and drag when comparing 35cst to 7cst is MPG wasted.

This temp comparison is great data. Definitely need to make sure your ATF gets up to temp.

Also on some cars, shift points, OD and TC lockup enabled states, can be and are temperature dependent. If the tranny is too cool, it might purposely try to warm itself up causing more MPG loss.

So, the MPG loss is two fold. Fluid is thicker. And transmission is trying to warm up with delayed shifts, delayed TC lockup.....
_________________________
Those who say it cannot be done, should not interrupt the person doing it.
Your automaker lied!
Is this a spelling/grammar forum or BITOG?

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#1730668 - 01/04/10 01:54 PM Re: Transmission cooler and fuel efficiency. [Re: unDummy]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
C'mon now... There are many cars that don't get a 2 MPG drop in winter, with ALL things considered. How would only one factor account for such a massive change?
Many have repeatedly pointed out how manufacturers specifying a 5-20 engine oil only accounts for a portion of a percent in MPG increases.

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