Rearend oil weights and MPG

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Slantsix64

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Any of you guys notice an improvement in mileage switching to thinner synthetic oil in the rear axle? I'm currently running straight 140w 8 3/4
 
Wow. This question is right up there with does a waxed car get better mileage also? Good luck on your quest for a answer.
 
Any time you reduce friction you will increase efficiency. Enough to notice....unlikely.
 
140w is HEAVY oil, You should not have a problem seeing an improvement with a syn around 75 weight.
 
Ahhh! Confusions say, “use synthetic in old jalopy and find many a leak.”

80w90 is perfectly fine. Every time I’ve tried synthetic oils in older cars I’ve found every leak magically. Lol!
 
There will be an improvement in MPG using lighter weight gear oil. You'll see a bigger gain in colder climates and shorter trips.
With that said ... I didn't by my Duster as a fuel sipping economy car ...
dirol.gif
 
Ahhh! Confusions say, “use synthetic in old jalopy and find many a leak.”

80w90 is perfectly fine. Every time I’ve tried synthetic oils in older cars I’ve found every leak magically. Lol!
Ok so why does synthetic oil leak and conventional oil doesn’t



Well synthetic oils molecules are are identical in size, where as conventional oil is all over the place.....hence leak and no leak ! ,do not break new gears in on synthetic, 80w90 trusted and true !
 
Any of you guys notice an improvement in mileage switching to thinner synthetic oil in the rear axle? I'm currently running straight 140w 8 3/4

Why would you run 140? Doesn't the manual say 80w90?
 
All my cars run easier/better after being shutoff for 1-2 hrs after a long drive before that.
Warm fluids, 'cold' engine, the difference is noticable (to me in an 'old' daily driven car).
 
Ahhh! Confusions say, “use synthetic in old jalopy and find many a leak.”
^^^^^^^
80w90 is perfectly fine. Every time I’ve tried synthetic oils in older cars I’ve found every leak magically. Lol!
SPELLING ! CONFUSION AND CONFUSCOUS / CONFUSIOUS ?? LOL
 
SPELLING ! CONFUSION AND CONFUSCOUS / CONFUSIOUS ?? LOL

Bob, I did not write the fortune cookie- I’m only repeating what I read at the restaurant.
Last time I go to “Billy Chin’s Chinese food and leather belt emporium.”
Lol! - damn spell check!
 
Bob, I did not write the fortune cookie- I’m only repeating what I read at the restaurant.
Last time I go to “Billy Chin’s Chinese food and leather belt emporium.”
Lol! - damn spell check!

Just kidding , used to know a guy in the A.FORCE that had a million "confuscious" jokes, the guy was a riot !
 
Years back when (ford) switched to synthetic gear lube there were failures. Many failures. Burned up clutches if owner was lucky enough to get it fixed under warranty. Repaired then refilled with conventional oil and friction modifier.

I never considered running synthetic gear oil in my old rigs.
Their job is hard enough, and a lighter lubricant isnt going to help.

I would say 140 would cause higher fuel consumption until oil reaches operating temperature.
Like any heavy oil.

-40 up here, used to run the power wagon in 4 low for a ways before trying to hit the highway.
That ol truck didnt take kindly to
Cold weather.
 
Years back when (ford) switched to synthetic gear lube there were failures. Many failures. Burned up clutches if owner was lucky enough to get it fixed under warranty. Repaired then refilled with conventional oil and friction modifier.

I never considered running synthetic gear oil in my old rigs.
Their job is hard enough, and a lighter lubricant isnt going to help.

I would say 140 would cause higher fuel consumption until oil reaches operating temperature.
Like any heavy oil.

-40 up here, used to run the power wagon in 4 low for a ways before trying to hit the highway.
That ol truck didnt take kindly to
Cold weather.
How many miles does it take for it to reach operating temp?
 
Wow. This question is right up there with does a waxed car get better mileage also? Good luck on your quest for a answer.
I mean it's just a question, squeeze a bottle with thick oil see how much force you have to use to get it out then do the same with thin oil and see how easy it is. My usual driving trips are 10-15 miles around town.
 
It is a crown/pinion and the oil being squeezed through everything it probably doesent take long. I know in extreme cold it only takes a few minutes of driving, to get things loosened up.warmer climates its irrelevant.
 
That's all I had laying around

I gotchya. I've done that with a few things over the years myself. I have to echo the opinions of others on this. If you're looking for a mileage increase, I don't think gear oil is the place. That said, it will hurt nothing to switch to synthetic. I have synthetic to put in the 7.25 in the Valiant, but it's 80w90 like it's supposed to have. I'm not doing it looking for mileage, but for longevity....better cooling, lubrication....all that "hoorah".lol
 
I put synthetic gear oil in the front and rear diffs on my Jeep, I got mayybe 0.5-1 MPG improvement. I didn't do it for fuel economy as much as helping things to last longer and stand up to abuse from occasional off-roading.

I have a 1.5 quart bottle left of the synthetic stuff and 2-3 quarts of conventional, I'm not gonna bother when I swap the 3rd member in my Duster just use the rest of the synth, add friction modifier and top it off with conventional. It doesn't get driven enough for it to matter plus the rotating mass of the 8 3/4" is already huge for a car that size, better gear lube won't do much.
 
never have I used 140 back there; only 75/90 dyno. In my A833 I use 50/50 ATF and 75/90. If you have a slanty then you can use 100% ATF. I only put the EP oil in there to keep my cluster-pin happy with 430 hp.
With an auto, well you have only one choice; but you can put a shift kit in there to reduce your shift-overlap, cuz in your case I am imagining a lotta lotta shifting going on.

10 to 15 mile trips around town means there is no way to make any kind of fuel economy. Especially with a low-compression engine. All you can do is optimize the timing and hope for the best. Around town, I can almost guarantee you will get better mileage with more gear, more than the 2.73s that are often in these old A-bodies. Lord help you if you have 2.45s; those are strictly for hiway cars and 318s!
I would try 3.23s at least. This will make it easier for the engine to get up into the efficiency zone, using less throttle. And the gears following, keep it there. Not until you hit hiway speed will the economy start dropping. And there is an easy cure for that, just slow down. Also, you can optimize the timing for cruise by yanking out the Vcan, making sure it actually still works, and then mod it to bring in a lot more than the feeble 9 or 11 degrees they are often born with; 22 degrees is possible. I think TrailBeast got 24 out of his.
With slantys don't mod the can straight to 24 with numerically low gears; there is a good chance the slanty with 10* initial will detonate at Part Throttle if it sees too much Vcan timing. Take it slow
 
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I clearly noticed a difference in engine torque during cold starts/driving when using a thinner/synthetic engine oil (0w20) in my roller 318.
 
never have I used 140 back there; only 75/90 dyno. In my A833 I use 50/50 ATF and 75/90. If you have a slanty then you can use 100% ATF. I only put the EP oil in there to keep my cluster-pin happy with 430 hp.
With an auto, well you have only one choice; but you can put a shift kit in there to reduce your shift-overlap, cuz in your case I am imagining a lotta lotta shifting going on.

10 to 15 mile trips around town means there is no way to make any kind of fuel economy. Especially with a low-compression engine. All you can do is optimize the timing and hope for the best. Around town, I can almost guarantee you will get better mileage with more gear, more than the 2.73s that are often in these old A-bodies. Lord help you if you have 2.45s; those are strictly for hiway cars and 318s!
I would try 3.23s at least. This will make it easier for the engine to get up into the efficiency zone, using less throttle. And the gears following, keep it there. Not until you hit hiway speed will the economy start dropping. And there is an easy cure for that, just slow down. Also, you can optimize the timing for cruise by yanking out the Vcan, making sure it actually still works, and then mod it to bring in a lot more than the feeble 9 or 11 degrees they are often born with; 22 degrees is possible. I think TrailBeast got 24 out of his.
With slantys don't mod the can straight to 24 with numerically low gears; there is a good chance the slanty with 10* initial will detonate at Part Throttle if it sees too much Vcan timing. Take it slow
A/j the motor is 9:5 compression 3.55 gears 904 shift kit roller camshaft. I'm currently getting 13-14 around town with the 318 in the barracuda I know I can squeeze an extra mile in. I'm at 30 degrees total 18 in the dizzy and 12 initial if I bump up the initial I can hear spark knocking at idle I blame my cheap Ecu box hopefully upgrading to an msd box will allow to run more adnavce with no spark knock.i was als thinking of changing to 3.91s since. Do not do any highway driving
 
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