Castrol Syntorq 75W-85 Vs Mobil LS 74W-90

[97fatboy]

SRT tranny calls for Castrol Syntorq 75W-85. I have been to 4 auto parts stores and all I can find is Mobil 1-Synthetic Gear Lubricant LS 75W-90. What is the difference? Is it a comparable product-or apples to oranges?

 

[Tom F&L GoR]

Castrol Syntorq is actually 75W-85W, which means that at -40C both products are similar viscosity, but at 100C the Castrol has a minimum of 11 cSt, while the Mobil has a minumum of 13.5 cSt. Basically the Mobil is thicker when hot.

This is a very small image, but shows the label.

Mobil product is API Service MT-1 and GL-5, which is non-synchro transmissions and shock loaded differentials.

Castrol product is API Service GL-4, which sounds "lesser" service because it's not for high speed and shock loaded differentials and therefore doesn't have the highly aggressive Extreme Pressure additives that GL-5 oils do. These EP additives attack yellow metals (copper, bronze, brass) which are your synchros.

Gear oil specs do not necessarily get better with higher numbers and letters like engine oil does. The gear oil specs are just "different" for different applications.

Castrol is available from Dodge as 4874459 and from GM as 12346190. If the dealer prices make you gag, at least look for similar viscosity in a synthetic meeting GL-4 and not GL-5.

 

[Steve-Indy]

Thanks, Tom!!! From a pricing viewpoint, last time (last summer) that I bought Mopar's Synthetic Manual Transmission Lubricant, I paid $15/qt.(slight VCA discount). About three years ago I bought GM's Synthetic Manual Transmission Fluid for $20/qt. from the local Chev. dealer (no VCA discount!!!).

 

[Tom F&L GoR]

I have to replace a transmission rear seal and was going to get some just in case I needed to add. GM now costs $33/qt.

 

[VIPER BAZ UK]

Tom we can only get these two here in the UK....
Mine has been running the Valvoline..

Castrol SMX S 75w-85 Fully Synthetic Manual Transmission Fluid

lubricants, engine and car care products, Valvoline Europe

 

[97fatboy]

Thanks, I guess I need to hold off and visit the local Dodge dealer to get get some. I ran the circuit of parts stores today trying to find it.

 

[Tom F&L GoR]

Tom we can only get these two here in the UK....
Mine has been running the Valvoline..

Castrol SMX S 75w-85 Fully Synthetic Manual Transmission Fluid

lubricants, engine and car care products, Valvoline Europe

In trying to find more about US Castrol Syntorq, I did come across references to the Castrol SMX being the same as Syntorq (but I didn't save that link.) It is GL-4, which is correct. At 10.74 (US$15.21) the price is not bad!

The Valvoline GL-4 is obviously "GL-4".

Either would seem an appropriate choice, other than a visit to the dealership.

 

[Vman455]

Tom, do you know why the Castrol Syntorq only seems to be available from dealers? I looked just about everywhere (including online) last year and couldn't find it anywhere except my local Dodge dealer, branded as a Mopar product.

 

[Tom F&L GoR]

It's not unusual for transmission fluids and differential fluids to be developed with an OEM. Most people treat them as fill for life anyway. So aftermarket sales will be low and the only way for the lubricant marketer to make any money is to get the OEM to sell it for them.

Castrol Syntorq can be found at 4x4 truck online stores.

 

[eucharistos]

Castrol Syntorq is actually 75W-85W, which means that at -40C both products are similar viscosity, but at 100C the Castrol has a minimum of 11 cSt, while the Mobil has a minumum of 13.5 cSt. Basically the Mobil is thicker when hot.

This is a very small image, but shows the label.

Mobil product is API Service MT-1 and GL-5, which is non-synchro transmissions and shock loaded differentials.

Castrol product is API Service GL-4, which sounds "lesser" service because it's not for high speed and shock loaded differentials and therefore doesn't have the highly aggressive Extreme Pressure additives that GL-5 oils do. These EP additives attack yellow metals (copper, bronze, brass) which are your synchros.

Gear oil specs do not necessarily get better with higher numbers and letters like engine oil does. The gear oil specs are just "different" for different applications.

Castrol is available from Dodge as 4874459 and from GM as 12346190. If the dealer prices make you gag, at least look for similar viscosity in a synthetic meeting GL-4 and not GL-5.

good info as always tom, thanks

 

[TexasPettey]

I'm in the middle of this search myself, with no luch on the Syntorque. I've found two aftermarket fluids that seem to meet the requirements.

Amsoil sells a Synthetic 75W-90 Transmission & Transaxle Gear Lube that is GL-4 & GL-5. They call it out as a direct replacement for the GM & Mopar part numbers. It's $12/quart. Unfortunately, Amsoil doesn't seem to be common in the local part stores. It's order from the web only.

Royal Purple sells a 75W-90 Gear Lube that claims to be GL-5 & GL-4 classified. They make some marketing noise about their additives being less coorosive, thus meeting GL-4 and GL-5. It's $12/quart and is all over the local stores. Not to mention that, it's made here in TX!

The RP has a limited slip additive mixed in the bottle. I called RP, and they said that it wouldn't have any effect on the transmission. It was an interesting discussion, as they knew Hennessey and asked why Viper guys run gear lube in the tranny when the Vette guys all run ATF.

Tom, would you agree that the limited slip additive shouldn't have an effect on the tranny?

 

[vp97]

Syntorque is hard to find. You might want to try a local manual transmission shop, thats where I found it when I used to use it. I have had my tranny rebuilt by GForce a couple of years ago and they said to use Mobil 1 ATF.

 

[Tom F&L GoR]

Tom, would you agree that the limited slip additive shouldn't have an effect on the tranny?

No. Limited slip additive is a friction modifier for clutch plates. Whether it affects shifting or not (i.e. synchro engagement) depends on whether the operating temperature of the synchro, the synchro face material and the temperature at which the LS additive becomes effective.

Syntorq 75W-85W 2 qts/$35 NV4500 Parts

 

[Kevan]

Tom- does the GL-4 or GL-5 rating(?) have anything to do with the pre-2000 T-56 transmissions having paper (not kevlar) blocking rings?

And just to check the summary:
GL-4 = Good for trans.; Bad for diff.
GL-5 = Bad for trans.; Good for diff.
Correct?

 

[Steve 00RT/10]

I'm in the middle of this search myself, with no luch on the Syntorque. I've found two aftermarket fluids that seem to meet the requirements.

Amsoil sells a Synthetic 75W-90 Transmission & Transaxle Gear Lube that is GL-4 & GL-5. They call it out as a direct replacement for the GM & Mopar part numbers. It's $12/quart. Unfortunately, Amsoil doesn't seem to be common in the local part stores. It's order from the web only.

Royal Purple sells a 75W-90 Gear Lube that claims to be GL-5 & GL-4 classified. They make some marketing noise about their additives being less coorosive, thus meeting GL-4 and GL-5. It's $12/quart and is all over the local stores. Not to mention that, it's made here in TX!

The RP has a limited slip additive mixed in the bottle. I called RP, and they said that it wouldn't have any effect on the transmission. It was an interesting discussion, as they knew Hennessey and asked why Viper guys run gear lube in the tranny when the Vette guys all run ATF.

Tom, would you agree that the limited slip additive shouldn't have an effect on the tranny?

As you may know -- I've been using the Amsoil lubes since buying our 1st car new in 2000. 83K miles on the car now. I've been running the tranny lube for almost 70K miles and the rear end lube for over 50k. The differential lube is in a 3.45 set up which spins faster than stock (creating more heat) in the small Dana case. I use analysis and change them out every 3yrs/30K or so. Always comes back good to go more. While completely unscientific, IMO, the Amsoil tranny lube runs cooler than the OEM Castrol based on the heat transfer up the MGW short shifter. Our car sees track miles, xcrosses, and lots of parade idling in hot weather.

Steve

 

[Tom F&L GoR]

Tom- does the GL-4 or GL-5 rating(?) have anything to do with the pre-2000 T-56 transmissions having paper (not kevlar) blocking rings?

And just to check the summary:
GL-4 = Good for trans.; Bad for diff.
GL-5 = Bad for trans.; Good for diff.
Correct?

I think the "not kevlar" ended sooner than 2000. I "combined" 3 moderately used T-56s into the one in the car now. I know I have the newer style rings and I know none of the three transmissions were as new as 2000, so the "paper" had to end sooner. Chuck Tator will know.

"I think" the history is the early T-56 used ATF with paper, then newer T-56s used ATF with kevlar, then newest were GL-4 with kevlar. Complainers of NGR could switch from ATF to GL-4. I assumed this was OK only for the kevlar cars. The early paper cars are supposed to stay with ATF. Chuck Tator will know.

GL-4 could be the spec for some differentials, probably older and probably lighter duty. After all, "GL" means Gear Lubricant. But I think from here on, it is a good rule.

 

[Kevan]

Thanks for the info, Tom.
I appreciate it.

Just so everyone knows, my source for the paper/kevlar switch-over comes from both T-56rebuilds.com and from the tech I spoke with at Tremec.
BUT...as with anything, there are oddballs out there.