Does synthetic oil result in lower revs?

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263
Location
LA, CA
I just switched from dyno 10w-30 oil to M1 5w-30 this past weekend. Today was the first time I was able to drive it fast on a freeway, and I immediately noticed that the tach was only at 3K RPM at 80 mph. Prior to the switch, 3K RPM only yielded 70 mph. Is this normal? I didn't expect this, but if it helps with my gas economy, it's certainly welcome.
 

Al

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19,256
Location
Elizabethtown, Pa
Oil can't change the gea ratio. Auto trannies have a positive "lockup" it sounds like perhaps your's was not locked up before switching to synthetic.
 

DaveInLA

Thread starter
Messages
263
Location
LA, CA
quote:
Originally posted by Al: Oil can't change the gea ratio. Auto trannies have a positive "lockup" it sounds like perhaps your's was not locked up before switching to synthetic.
I'm not sure I follow. What do you mean by "lockup"? I do have an auto tranny, and I've been driving it the same as before, nothing different. I always leave it in O/D (top gear). Can this be bad?
 
Messages
1,294
Location
Western Washington
quote:
Originally posted by Al: Oil can't change the gea ratio. Auto trannies have a positive "lockup" it sounds like perhaps your's was not locked up before switching to synthetic.
My mom's Plymouth Voyager does not have a lock up tranny. I hate it, you lose a lot of power through it, and when you're coasting down a hill, in gear, and you take your foot off the gas, the engine drops to idle. Driving without a lockup torque converter is horrible! I'll bet that's the situation we've got here.
 
Most modern auto trannys are built such that they connect (lock-up) the engine to the axle/drive-line in top gear (O/D in your case). This is so there is no slippage and power loss in the tranny. When this occurs there is usually a drop in engine RPMs. Running with the selector lever in "O/D" all the time is fine, as long as you're not pulling a trailer or other extremely heavy load.
 

DaveInLA

Thread starter
Messages
263
Location
LA, CA
My car is relatively new (2002 Nissan Altima 2.5) so the lock-up thing probably wouldn't be a concern. The car drives fine, and despite what Mobil 1 says on the jug of oil, so far my fuel economy has been exactly the same. Anyway, I'm starting to wonder if I read the RPMs right. My other car is 3K at 70 mph (1989 325is, stick) for sure, and maybe I confused the two cars (unlikely).
 
Messages
39,805
Location
Pottstown, PA
quote:
My mom's Plymouth Voyager does not have a lock up tranny. I hate it, you lose a lot of power through it, and when you're coasting down a hill, in gear, and you take your foot off the gas, the engine drops to idle. Driving without a lockup torque converter is horrible!
Then your mom must have an old one ..or one with a rebuilt trans in it. A lock up torgue converter does nothing for gas mileage per se'. I mainly reduces heat. Your gas mileage is "load" related. The same gas can be consumed at 1800 rpm or at 2000 rpm under the same load. It DOES allow for a very high stall torque converter to be installed (better low end response) without all the related heat from turbine to impeller differential while cruising. This also allows a 4 banger or smaller V6 to simulate low end without being over consuming at cruising that would normally require a bigger engine.
 

DaveInLA

Thread starter
Messages
263
Location
LA, CA
I just checked with other people with my car... 3K rpm is 70 mph. Now it's 80 for me. I wonder if something happened to my speedometer? Again, all this is right after I switched to syntethic oil.
 
Messages
231
Location
So Cal
Sorry, there is no way changing to synthetic or a different viscosity or any other "change" in oil would account for this. Either you got the 2 cars mixed up, or you have some real unfortunate luck and this is nothing more than a coincidence. Darryl [Cheers!]
 
Messages
1,294
Location
Western Washington
quote:
Originally posted by Gary Allan:
quote:
My mom's Plymouth Voyager does not have a lock up tranny. I hate it, you lose a lot of power through it, and when you're coasting down a hill, in gear, and you take your foot off the gas, the engine drops to idle. Driving without a lockup torque converter is horrible!
Then your mom must have an old one ..or one with a rebuilt trans in it. A lock up torgue converter does nothing for gas mileage per se'. I mainly reduces heat. Your gas mileage is "load" related. The same gas can be consumed at 1800 rpm or at 2000 rpm under the same load. It DOES allow for a very high stall torque converter to be installed (better low end response) without all the related heat from turbine to impeller differential while cruising. This also allows a 4 banger or smaller V6 to simulate low end without being over consuming at cruising that would normally require a bigger engine.

I believe that it's a 97 or 98.
 
Messages
4,872
Location
MN
quote:
Originally posted by Gary Allan:
quote:
My mom's Plymouth Voyager does not have a lock up tranny. I hate it, you lose a lot of power through it, and when you're coasting down a hill, in gear, and you take your foot off the gas, the engine drops to idle. Driving without a lockup torque converter is horrible!
Then your mom must have an old one ..or one with a rebuilt trans in it. A lock up torgue converter does nothing for gas mileage per se'. I mainly reduces heat. Your gas mileage is "load" related. The same gas can be consumed at 1800 rpm or at 2000 rpm under the same load. It DOES allow for a very high stall torque converter to be installed (better low end response) without all the related heat from turbine to impeller differential while cruising. This also allows a 4 banger or smaller V6 to simulate low end without being over consuming at cruising that would normally require a bigger engine.

Any loss of torque converter slip will result in better efficiency and therefor gas mileage. The TC slip is one of the main reasons automatics get worse gas mileage than manuals. -T
 
Messages
44
Location
Ann Arbor, Michigan
quote:
Originally posted by T-Keith:
quote:
Originally posted by Gary Allan:
quote:
My mom's Plymouth Voyager does not have a lock up tranny. I hate it, you lose a lot of power through it, and when you're coasting down a hill, in gear, and you take your foot off the gas, the engine drops to idle. Driving without a lockup torque converter is horrible!
Then your mom must have an old one ..or one with a rebuilt trans in it. A lock up torgue converter does nothing for gas mileage per se'. I mainly reduces heat. Your gas mileage is "load" related. The same gas can be consumed at 1800 rpm or at 2000 rpm under the same load. It DOES allow for a very high stall torque converter to be installed (better low end response) without all the related heat from turbine to impeller differential while cruising. This also allows a 4 banger or smaller V6 to simulate low end without being over consuming at cruising that would normally require a bigger engine.

Any loss of torque converter slip will result in better efficiency and therefor gas mileage. The TC slip is one of the main reasons automatics get worse gas mileage than manuals. -T

I would have to agree with you there. Without the lock-up TC, there is still slippage between the impeller and turbine. When it locks up, they're at the exact same speed and this will increase mileage because the engine is not running faster than the input shaft anymore.
 
Messages
1,412
Location
Falls Church VA
DaveinLA-- Believe it or not, your observation isn't that unusual after a change to synthetic. I'm not exactly sure how to explain it, but the stuff really does work better. If you haven't changed your automatic transmission over, try that. Might see a bit of mileage increase, too.
 
Messages
1,487
Location
Indiana
quote:
Originally posted by Dick in Falls Church: DaveinLA-- Believe it or not, your observation isn't that unusual after a change to synthetic. I'm not exactly sure how to explain it, but the stuff really does work better.
Sorry guys, there's no way that synthetic oil changes the vehicle gear ratio. And the rpm difference he quotes is not enough to be overdrive vs direct ratio either. The only possibility here is error or somehow converter lock is now working and it didn't before.
 
Messages
2,703
Location
Lincoln, NE
Assuming all other things equal (trans at operating temp so the converter will lock up, ect), I don't see how changing the kind of oil you're running would account for it either.
 
Messages
5,785
Location
Dixie
On older hydraulic transmissions that don't have lockup torque convertors, you may notice less slippage with a synthetic ATF.... My 1990 Audi 100, three speed, Vw sourced transmission slips a bit less with the Amsoil synthetic ATF installed and the shifting is a bit more positive/direct as well. This transmission originally called for a Dexron II type fluid, although VW/Audi have been making their own special ATF fluid since about 1995 or so. Tooslick www.lubedealer.com/Dixie_Synthetics
 
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