OD on or off? - Page 2 - Fiberglass RV


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Old 05-11-2011, 02:08 PM   #15
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I bought a ScanGauge II just for the transmission temperature function. It plugs into your vehicle’s OBDII port and displays the data you vehicle collects…easier than adding another sensor.

From memory, my Chev runs around 185-190f both towing in 3rd and not towing in D (OD).
I don’t run in 3rd while not towing.
If I forget and put it in 4 while towing it’s gotten up to 223f before I noticed and kicked it back down to 3. Once I down shift the temp eventually returned to normal

I haven’t checked how much running in 3 impacts MPG, but I don’t seem to be hitting gas stations much more often….
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Old 05-11-2011, 02:46 PM   #16
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My 99 Silverado (4.8 V8 Auto 2WD)when towing my 13' Scamp, runs about 180-190 degrees on flat ground. Get about 16 MPG when towing.
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Old 05-11-2011, 02:51 PM   #17
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My 99 Silverado (4.8 V8 Auto 2WD)when towing my 13' Scamp, runs about 180-190 degrees on flat ground. Get about 16 MPG when towing.
In our heavy duty Ford Bounder transmission Ford recommends changing transmission fluid every 25,000 miles. I do it even though it never looks burnt, always a nice pink.

Norm
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Old 05-11-2011, 08:52 PM   #18
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I have Scan Gauge II on my truck.I have it set to read water temp,transmission temp,volts and MPG.
ScanGaugeII - Trip Computers + Digital Gauges + Scan Tool
I would buy one of these if I could be sure it would give the transmission temps for my '08 Highlander. From what I've read (not much but some), it appears that the device does not give this info for all vehicles with OBD2 port, only some vehicles. Something to do with cracking codes from various car mfrs I guess.
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Old 05-11-2011, 09:00 PM   #19
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I just bought the $59 version of the scan gauge, I let you know how it works.

Norm
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Old 05-11-2011, 09:20 PM   #20
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What does it say to do in your owners manual?

-- Dan Meyer
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Old 05-18-2011, 09:24 PM   #21
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FWIW: I pull my 16' medium-heavy Scamp with a 2005 Forester, which has a 2.5L normally-aspirated engine and a manual transmission, and if I'm driving 65 or so (like I usually do on the interstate), I can leave in 5th almost all the time, unless I'm climbing a steepish interstate-type hill (which is to say, a minor one), where I downshift and/or let the speed drop as needed.

If I'm on a non-interstate with, say, a 55mph limit, I find myself downshifting to 4th quite a bit more, because not only can the hills be steeper, but at 55mph I'm not as far into the power curve as I am at 65. I think even if interstate and non-interstate hills were comparably steep, the power curve thing would in my case still dictate more downshifting than the interstate does.

Now the disclaimer - I have no idea whether the gear ratio on an automatic OD is comparable to that of a manual 5th gear, so all this may not apply so much to an automatic, but I hope it's at least some useful perspective.

(Just in case anybody's interested, I get about 21mpg at 65mph on slightly-hilly Minnesota interstates with no significant head or tailwinds. Is this typical for a TV in this class?)
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Old 05-26-2011, 03:34 PM   #22
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You want to run no overdrive with an auto unless it's flat in most cases. The thing about an auto vs 5spd is pretty simple - with a 5spd if you don't have enough power to pull up the hill you slow down.. with an auto you get a certain degree of slip due to the torque converter, aka, slushbox. This causes your heat to build quite rapidly... but you don't slow down.

The vast majority of people driving on the road have no idea what overdrive is or does.. your standard gear ratios across the gears in your tranny are all reduction gears of various levels from the engine.. meaning the engine rotates 10 times and the output from the tranny rotates 5 times or 6 times or 1 time etc etc depending on what gear you are in. This allows an engine to pull considerably more weight than what it could do directly. There is more reduction in your transfercase (if 4wd, most vehicles are 1:1 high range but there are a few that have a small amount of reduction in high range too, such as 1.2:1 for instance) as well as a comparably large amount in the diffs.. Diffs range from 3~:1 to 5:1~. When you get a 'tow package' on a vehicle it's going to include things like lower gears in the diffs, tranny coolers, oil coolers, rear swaybars etc..

Anyway, off topic. Overdrive does the opposite of what every other gear does - it drives the output of the tranny FASTER than the output of the motor. So, for every 10 rotations you could get 12 output rotations. This is VERY hard on the tranny if it's an auto, and it's under load.

Long story short, take it out of overdrive unless you like paying your mechanic to rebuild your tranny. Your mechanic buddy told you to leave it off ALL the time because he doesn't like rebuilding trannies and doesn't care about your fuel economy.
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Old 05-26-2011, 05:26 PM   #23
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With a Scangauge or an Ultagauge it is easy to see if your transmission is slipping.

Put your transmission in Overdrive.

Set your gauge to display RPM and MPH. Drive at on a flat stretch and see what the mph and RPM are at a specific speed. For example on my car at 60 mph the RPM might equate to 2500 RPM.

If my transmission's in OD and the engine's spinning at something greater than 2500 RPM at 60 MPH my transmission is slipping.

Norm

These gauges are accurate versus your tachometer.

Norm

I'm not an automatic guy but I assume this is true for any gear.

It seems it would provide good feedback to the driver.
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