Where to find information on dynamic viscosities?

[kilou]

Hello,

I'd like to compare cold flow abilities of 2 gearoils (both 75W). I can only find informations on cinematic viscosities at 40°C and 100°C but I cannot find the informations on dynamic viscosities although this is the main value that determines the cold index W!

The gearoils I'm interested in are:

-TransElf TRJ 75W80 GL5 (Elf)
-Gear 300 75W90 GL5 (Motul)

I've contacted both Elf and Motul and they cannot give me this information (they do not know where to find it..............).

Does anybody knows where I may find this info?

Additionally, I'm interested in this topic because I'd like to know if a 75W90 oil (Motul) may have better cold weather abilities than a 75W80 oil (Elf). I know both are 75W but people from Redline told me that any 75W90 will remain thicker when cold compared to a 75W80......and this is true for cinematic viscosities. But I suspect that the 75W90 from Motul (pour point: -60°C) would flow better than the 75W80 from Elf (pour point: -40°C) even if it has a higher viscosity at 40°C. What do you think?

 

[KobaltBlau]

I don't know this area too well, but in my experience pour points are a good indicator of low temperature performance. Gearsets do tend to warm up even in fairly cold ambient temperatures.

What is your application: what vehicle, type of use, and ambient temperatures?

 

[Titanium_Alloy]

kilou,

You're actually on a right track. Redline is telling the truth - if both oils 75W-90 and 75W-80 have approximately the same formulation 75W-80 will flow better when cold. Below 0C viscosity at 40C and 100C doesn't really matter because base oil comes into play.

For example:

Viscosities of the following oils at -40C are

- Mobil 1 75W-90 viscosity 130000 cP.
- Redline 75W-90 viscosity 110000 cP (if I'm not mistaken).
- Regular Amsoil 75W-90 viscosity 75000 cP.
- Amsoil Series 2000 viscosity 75W-90 35000 cP.

However, all these oils have approximately the same viscosity at 40C and 100C.

I suggest just going with whatever your car recommends. If it calls for 75W-90 - Motul seems like an excellent choice if you need low temperature performance. On the other hand if it calls for 75W-80 - Elf would work just fine especially if it's synthetic (you didn't mention if it is synthetic or not). If your car gives a choice of what to use 75W-90 or 75W-80 I would go with Motul since it has lower pour point.

Regards,

 

[kilou]

Thanks for your replies.

Actually my car (European Volvo S40 with a manual Renault gearbox) calls for a very specific oil: 75W80 API-GL5.

I know I MUST use a GL5 oil in that gearbox but I must use specific GL5 formulation since I have brass synchronizer rings and some GL5 are corrosive for these.

Both Elf and Motul oils match the GL5 specification but my car specifically calls for a 75W80, not a 75W90. However I suppose that using a 75W90 instead of the 75W80 should not be a problem at operating temperature.

The problem is really down to the cold temperatures. The Elf 75W80 oil is "only" a semi-synthetic oil with a pour point of -40°C while 100% synthetic Motul Gear 300 75W90 has a pour point as low as -60°C!!!!! So I strongly believe that the Motul would flow better in cold weather compared to the Elf.

As you said, the viscosity at 40°C is not determinant for cold weather

For example Redline MTL is certified to be (now) a 70W80 although it has a viscosity of 56.2 cSt at 40°C. However the Elf TRJ which is a 75W80 has a lower viscosity (47cSt) at this temperature! But I suppose that the Redline stuff would yet flow really better when the gearbox is cold.

This is why now I'm really interested in the possibility to use a full synthetic 75W90 instead of a semi-synthetic 75W80 oil.

NB: Forgot to mention that I have all those "troubles" because I cannot find a 100% synthetic 75W80 oil WITH GL5 and MIL-L-2105D certifications available in Europe....... All 100% synthetic oils with GL5 certifications seems to occur as 75W90 only.

 

[KobaltBlau]

I am surprised it needs a GL-5. Is there a hypoid gear set in there? it seems that the S40 should have a normal style FWD transaxle.

 

[tdi-rick]

GL 5 spec is common for Peugeot, Citroen, Renault, Alfa......

Kilou, I know Redline is hard to find and expensive in Europe, however, have you asked them about their SuperLight or Light Shockproof ?
They claim the SuperLight is equivalent to a 70w-90, with the internal fluid friction of an ATF.

quote:

---

LightWeight Gear Oil - a 75W/80W GL-5 gear oil designed to lubricate transmissions and transaxles which recommend 80W GL-5 gear oils. It has excellent low- temperature flow which allows easier shifting when cold. Also has good synchro compatibility. May be used to obtain maximum power transfer in racing differentials which do not see high temperatures.
SuperLight Gear Oil - a 70W/75W GL-5 gear oil with the viscosity of an ATF. This is used when temperatures are not high and when the maximum power output is
required such as in qualifying laps.

---

Rick.

 

[kilou]

quote:

---

Originally posted by tdi-rick:
Kilou, I know Redline is hard to find and expensive in Europe, however, have you asked them about their SuperLight or Light Shockproof ?
They claim the SuperLight is equivalent to a 70w-90, with the internal fluid friction of an ATF.

---

Yes I've yet asked them but they say it wont be very good since these oils are too slippery as they are designed speciffically for rear axles. For gearbox they "only recommend" me the 75W90NS as this is a GL5 oil which does is is speciffically designed to be non slippery (the only one of their GL5 oils). Unfortunately it's a 75W90.......and yes it's too expensive in Europe.

As grades are specified following SAE tests, do you think that SAE records all the values for each oil that is tested with their methods? Maybe they may have thus the dynamic viscosity of the Motul Gear 300?

 

[tdi-rick]

strange, as I was talking to the Redline importer here only yesterday, and his recommendation in WRX and Porsche transaxles is Shockproof.
He says it isn't as slippery as their standard LSD gear oils, and will actually cause low speed chatter in a LSD. He claims very good synchro compatibilty, and I have heard of a number of WRX owners using it to overcome synchro issues.

BTW, that quote I used comes directly out of the Redline catalogue.

PS, Motul make a 75w-80, but it looks like a mineral, or at best, semi synth.

 

[kilou]

Some news from a friend who tried Motul Gear 300 75W90 in his tranny calling for a 75W80 oil.

The purpose of the trial was to know if a full synthetic 75W90 oil with a low pour point and a low dynamic viscosity could provide better shift change when compared to a synthetic blend 75W80.

Tested car: Renault Laguna (french car)
First some comparison:

Previous oil
------------
TransElf TRX 75W80 (synthetic blend)
API GL5
40° viscosity: 47 cSt
100°C viscosity: 8.5 cSt
pour point -40°C
dynamic viscosity: unknown

New oil
-------
Motul Gear 300 (full synthetic ester based)
API GL5
40° viscosity: 72 cSt
100°C viscosity: 15 cSt
pour point: -60°C
dynamic viscosity: 49 cP at -40°C

As the dynamic viscosity is determining the cold grade index, we thought the Gear 300 (dynamic viscosity in the lower range of the 75W index) may provide significantly improved gear change when cold. It was false!
Basically my friend felt more difficulties to shift up and down with 2nd and forth gear when compared to old TransElf TRJ 75W80. The only thing that was noticeable is a quieter gearbox on highway probably due to the grade 90 rather than 80 but cold shifting performance were worse with the 75W90 full synthetic when compared to the 75W80 synthetic blend.

All in all, this seems to argue that the cinematic viscosity at 40°C is the main thing to look at when one is interested in cold shifting abilities (here cold means when you start the car in the morning but NOT when the outside temperature is very cold). In very cold weather, of course the pour point is very important but we were particulary interested in how the gearbox operates right after the car is started and for the first few miles.

In conclusion for our application, the 75W80 even semisynthetic remains better than a full synthetic 75W90 for cold shifting abilities due to its lower 40°C cinematic viscosity!