Anyone regret using synthetic fluids
Melting Slicks
Joined: Sep 2004
Posts: 3,226
Likes: 670
From: Northeast
No regrets changing to Mobil 1 full synthetic 75W/90 gear oil in the BorgWarner 4spd. Zero issues.
Much easier & smoother shifting than with conventional gear oil. Especially in cold weather here in the Northeast. Been over 12 years
Thousands of miles, trips to the drag strip, it has worked in my M21.
Much easier & smoother shifting than with conventional gear oil. Especially in cold weather here in the Northeast. Been over 12 years
Thousands of miles, trips to the drag strip, it has worked in my M21.
Race Director
Joined: Nov 2006
Posts: 13,246
Likes: 7,837
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
Yes. Put full syn in my super T10 about 10 years ago. Made second gear synchro useless. Crashing and grinding into gear. up or down. 3rd wasn't much better. Drained trans. Let it sit with plug out for 24 hours to get it all out.
Put dino gear oil back in. Been shifting fine now for the last 10 years. The syn was to slippery. Synchro's didn't grab.
NEVER again.
Put dino gear oil back in. Been shifting fine now for the last 10 years. The syn was to slippery. Synchro's didn't grab.
NEVER again.
Race Director
Joined: Mar 2017
Posts: 11,953
Likes: 4,508
From: Virginia
Yes. Put full syn in my super T10 about 10 years ago. Made second gear synchro useless. Crashing and grinding into gear. up or down. 3rd wasn't much better. Drained trans. Let it sit with plug out for 24 hours to get it all out.
Put dino gear oil back in. Been shifting fine now for the last 10 years. The syn was to slippery. Synchro's didn't grab.
NEVER again.
Put dino gear oil back in. Been shifting fine now for the last 10 years. The syn was to slippery. Synchro's didn't grab.
NEVER again.
Le Mans Master
Joined: May 2002
Posts: 5,086
Likes: 786
From: Lebanon Township New Jersey
I've been using Valvoline full synthetic trans fluid in my TH350 for years. It is subjected to severe duty on the drag strip plus street driving with no problems. I do change the fluid and filter once a year.
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Thread Starter
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
I am sold on syth engine oil and remember the "leaks" oil when switching complaints.
I have a 2004-r I am going to rebuild, upgrade and I am hesitant to go synth.
This comes from using a few quarts in an old th350 that used standard type 3 dex for its entire life.
I noticed a subtle change in shifting and feel.
Le Mans Master
Joined: May 2002
Posts: 5,086
Likes: 786
From: Lebanon Township New Jersey
was the tb350 built/redone before using synth?
I am sold on syth engine oil and remember the "leaks" oil when switching complaints.
I have a 2004-r I am going to rebuild, upgrade and I am hesitant to go synth.
This comes from using a few quarts in an old th350 that used standard type 3 dex for its entire life.
I noticed a subtle change in shifting and feel.
I am sold on syth engine oil and remember the "leaks" oil when switching complaints.
I have a 2004-r I am going to rebuild, upgrade and I am hesitant to go synth.
This comes from using a few quarts in an old th350 that used standard type 3 dex for its entire life.
I noticed a subtle change in shifting and feel.
Melting Slicks
Joined: Jun 2016
Posts: 2,979
Likes: 332
From: Woodinville WA
Why?
(You can't drop a bomb like that without explanation!) ;-)
I went with Penzoil Platinum Full Synthetic 10w30 which is ILSAC GF-6, but only because I found it a tiny bit cheaper than Castrol Edge 10W30 which is also ILSAC GF-6.
-I'll happily use either one.
I bought Amsoil synthetic for my 4L60e, but I'm tired of paying the Amsoil tax and looking for something else when I refill it (radiator swap.))
Synthetic wheel bearing grease seems like a no brainer to me.
I also use Motul DOT 5.1 brake fluid; I like all the benefits of modern fluids science.
Differential is the only place where I'm scared of synthetic...
I've seen too many people complain about slippage and I honestly don't understand what's required, it's one place where I'd LIKE to embrace modern synthetics, but I just see too many threads where it caused issues and going back to a more OEM fluid and the original GM additives solved the issue to try to experiment here on my own car... (Plus I don't feel like I fully understand differentials, so naturally more fear there...)
Adam
(You can't drop a bomb like that without explanation!) ;-)
I went with Penzoil Platinum Full Synthetic 10w30 which is ILSAC GF-6, but only because I found it a tiny bit cheaper than Castrol Edge 10W30 which is also ILSAC GF-6.
-I'll happily use either one.
I bought Amsoil synthetic for my 4L60e, but I'm tired of paying the Amsoil tax and looking for something else when I refill it (radiator swap.))
Synthetic wheel bearing grease seems like a no brainer to me.
I also use Motul DOT 5.1 brake fluid; I like all the benefits of modern fluids science.
Differential is the only place where I'm scared of synthetic...
I've seen too many people complain about slippage and I honestly don't understand what's required, it's one place where I'd LIKE to embrace modern synthetics, but I just see too many threads where it caused issues and going back to a more OEM fluid and the original GM additives solved the issue to try to experiment here on my own car... (Plus I don't feel like I fully understand differentials, so naturally more fear there...)
Adam
Race Director
Joined: Mar 2017
Posts: 11,953
Likes: 4,508
From: Virginia
The explanation is backed by many anectdotes. The GL-5 will eat the syncros and "yellow metal alloys" in your transmission.
https://bobistheoilguy.com/forums/th...ar-oil.119570/
I use the same Red Line GL-4 in my manual transmission and C3 differentials. The car seems to shift better. I haven't run into the "too slippy" issue that @4-vettes mentioned.
On every car I've tried, synthetic gear oil leads to smoother shifting, and in one case a lower transmission temperature. Just be sure to use the specified rating.
https://bobistheoilguy.com/forums/th...ar-oil.119570/
I use the same Red Line GL-4 in my manual transmission and C3 differentials. The car seems to shift better. I haven't run into the "too slippy" issue that @4-vettes mentioned.
On every car I've tried, synthetic gear oil leads to smoother shifting, and in one case a lower transmission temperature. Just be sure to use the specified rating.
Race Director
Joined: Nov 2006
Posts: 13,246
Likes: 7,837
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
I do not remember the brand from 10 years ago.
I have however read numerous times others have had this issue. Perhaps it's the difference between GL4 and GL5.
I do not know. I know my modem 6 speed loves the synthetic. My old 4 speed does not.
I have however read numerous times others have had this issue. Perhaps it's the difference between GL4 and GL5.
I do not know. I know my modem 6 speed loves the synthetic. My old 4 speed does not.
Racer
Joined: Nov 2019
Posts: 336
Likes: 173
From: Canadian living in southern France
I worked in the heavy truck industry for a lot of my time, and I can tell you this. When I retired in '05, as far as I recall, every Eaton and Rockwell transmission, and all diffs were filled from the factory with synthetic lubricants. And these vehicles had l-o-n-g warranties.
Safety Car
Joined: Jul 2005
Posts: 3,694
Likes: 833
From: WI
I've had a few manual transmissions I have rebuilt where certain synthetic gear lube's affected synchronizer friction (i.e. shifting), but others which were unaffected. In those cases I went back to dino-lube. But otherwise, no regrets. I've been using walmart synthetic gear lube for over 22 years in all my vehicles' diffs, and various synthetic motor oils in cars/trucks.
My John Deere garden tractor have been using Mobil 1 for 20+ years, and I mow a lot of grass. Engine still functions great. Doesn't use any oil at all. Briggs Vanguard. Every year for the last 10 years I keep saying I should replace it, but there hasn't been a compelling reason.
My John Deere garden tractor have been using Mobil 1 for 20+ years, and I mow a lot of grass. Engine still functions great. Doesn't use any oil at all. Briggs Vanguard. Every year for the last 10 years I keep saying I should replace it, but there hasn't been a compelling reason.
Burning Brakes
Joined: Aug 2013
Posts: 1,071
Likes: 322
From: palm springs ca
Well,
I mix a bit of STP with the required oil in the dif and trans and never had a problem.
Now mixing or additives are probably a NO NO. but I used to get STP by the gallon for 3.50 if I brought the container.
Still use it.
Dom
I mix a bit of STP with the required oil in the dif and trans and never had a problem.
Now mixing or additives are probably a NO NO. but I used to get STP by the gallon for 3.50 if I brought the container.
Still use it.
Dom
Melting Slicks
Joined: Jun 2016
Posts: 2,979
Likes: 332
From: Woodinville WA
The explanation is backed by many anectdotes. The GL-5 will eat the syncros and "yellow metal alloys" in your transmission.
https://bobistheoilguy.com/forums/th...ar-oil.119570/
I use the same Red Line GL-4 in my manual transmission and C3 differentials. The car seems to shift better. I haven't run into the "too slippy" issue that @4-vettes mentioned.
On every car I've tried, synthetic gear oil leads to smoother shifting, and in one case a lower transmission temperature. Just be sure to use the specified rating.
https://bobistheoilguy.com/forums/th...ar-oil.119570/
I use the same Red Line GL-4 in my manual transmission and C3 differentials. The car seems to shift better. I haven't run into the "too slippy" issue that @4-vettes mentioned.
On every car I've tried, synthetic gear oil leads to smoother shifting, and in one case a lower transmission temperature. Just be sure to use the specified rating.
Adam
Thread Starter
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
After putting 3 qts in a th350 that lived its life with dexron 3 I noticed some "feel" changes.
It shifts quicker.
It will kickdown with little thottle.
Seems the stall rpms have increased?
Definitely different from such a little amount of syn overall?
I am worried about clutch and band slippage.
It shifts quicker.
It will kickdown with little thottle.
Seems the stall rpms have increased?
Definitely different from such a little amount of syn overall?
I am worried about clutch and band slippage.