EP 90 vs. 80W-90

[bunnspecial]

I'm working through doing a full fluid change on my 1970 MGB. As best as I can tell, the engine oil has been changed regularly but a lot of other fluids seem to have been neglected.

The original specs call for EP 90 in the rear end, along with a(small amount) in the steering rack. The rack is bone dry(thanks to split boots that help retain the oil) and I don't know the status of the rear end-I'm giving the fill and drain plugs regular doses of PB blaster to try and free them up. I've also heard a lot of horror stories advising to remove the fill plug BEFORE removing the drain plug, as more than one person has been caught with an empty transmission or differential and a stuck fill plug.

In any case, the closest I've been able to find locally is 80W-90. Is this a reasonable substitute for EP90? I'm inclined to think it is, but thought I'd be well advised to ask before just blindly filling. Many of he folks on the MG forums still use EP 90, but seem to buy it in 5 gallon drums. Hayne's says 2.25 pints for the rear end and most reference specify "a couple of ounces" for the steering rack, so I'm not particularly inclined to buy what would likely be a lifetime supply of oil for this. I can't say I won't own other MGs in the future, but 5 gallons is still a LOT of oil for use in an infrequent application that calls for so little.

 

[4wheeldog]

The modern iteration of "EP" is GL5. Use GL5 in the rear end. Use GL4, or one of the specialty manual tranny lubes in the tranmission. Redline MT 90 is one of these.

 

[bunnspecial]

Thanks. I'll see if I can hunt down some GL-5.

The transmission actually calls for the same oil as the engine(20W-50) so I'm inclined to stick with that rather than a heavier gear oil unless I see a compelling argument otherwise.

 

[AndyinAL]

20w50 motor oil is thicker than 80w90 gear oil. (Not recommending 80w90 in trans though)

I think you would likely be pleasantly surprised by a manual transmission specific lube in your transmission in terms of shifting and synchro function. 20w50 motor oil I am sure would be fine too!

 

[bunnspecial]

Originally Posted By: AndyinAL

I think you would likely be pleasantly surprised by a manual transmission specific lube in your transmission in terms of shifting and synchro function. 20w50 motor oil I am sure would be fine too!



Thanks. I've heard of folks mixing in some transmission-specific lubes, so am certainly open to either doing that or using only a transmission-specific lube provided it falls in the correct weight.

I'm buying time on the transmission as the 3rd and 4th synchros are on the weak side(3rd grinds a little bit sometimes and 4th always grinds). There are some other issues in this transmission-namely that the speedometer drive gear is stripped and inaccessible without a full tear-down-so will likely drop in a replacement at some point. Good used 4-synchro 4-speed MGB transmissions are under $100 a piece(realistically about $50) and the synchro problem on mine is the exception rather than the norm.

I might also take the opportunity to upgrade to an overdrive transmission, which costs a fair bit more and involves more work but makes for nicer interstate cruising(3500 rpms rather than 4000 at 70mph) and also will easily add $1K to the value of the car. The latter is not a serious concern for me, as I don't have any immediate plans to sell the car, but is nice to know.

 

[stchman]

Originally Posted By: AndyinAL
20w50 motor oil is thicker than 80w90 gear oil. (Not recommending 80w90 in trans though)

I think you would likely be pleasantly surprised by a manual transmission specific lube in your transmission in terms of shifting and synchro function. 20w50 motor oil I am sure would be fine too!



No it is NOT.

Use the fluid that the manufacturer recommends.

 

[Greasymechtech]

Motor oil 50 grade is 16.3-21.9cst
Gear oil 90 grade is 13.5-18.5cst

There is a somw overlap when comparing a 20w50 to a 75w90.

If you use a 20w50 for the manual, pick a motorcycle oil.
There are several 75w90 GL4 specific MT fluids that can be used....like Redline MT90, Amsoil MTG... Ford/GM..

For the differential and steering, any GL5 hypoid Sae90, 75w90, 80w90, and even 75w110 can be used.

 

[zeng]

Originally Posted By: bunnspecial
I'm working through doing a full fluid change on my 1970 MGB. As best as I can tell, the engine oil has been changed regularly but a lot of other fluids seem to have been neglected.

The original specs call for EP 90 in the rear end, along with a(small amount) in the steering rack.




A general category monograde SAE EP 90** pre-SAE J306 in 1970 had a wide viscosity range specification of KV@100C of 13.5 -24.0 cSt.
Then an undesirable scenario arise whereby a low shear-stability EP 90** gear oil would still pass the ASTM/API stay-in-grade tests and got certified.
In order to overcome this predicament and presumbly some other reasons,API/SAE updated J306 and split the single category of SAE EP 90** pre-J306 into two sub-categories as follows :-
a )Monograde SAE 110 of KV@100C of 18.5 - 24.0 cSt, which generally corresponds to AGMA/ANSI gear lubes 5EP /ISO 220 of KV@40C of 198 - 242 cSt ,and
b )Monograde SAE 90 of KV@100C of 13.5- 18.5 cSt , which generally corresponds to AGMA/ANSI gear lubes 4EP /ISO 150 of KV@40C of 135 - 165 cSt ;
in current day 'refined' specifications of SAE J306.



Originally Posted By: bunnspecial
In any case, the closest I've been able to find locally is 80W-90. Is this a reasonable substitute for EP90?


Although current day mineral 80W90 is typically AGMA/ANSI 4EP /ISO 150 , in terms of differential components protection ,is weak against pre-J306 monograde EP 90** as originally spec'ed.
Note: Current day synthetics 75W90 is typically AGMA/ANSI 3EP /ISO 100 of KV@40C of 90 - 110 cSt.


Originally Posted By: bunnspecial
Many of he folks on the MG forums still use EP 90, but ........


For differential components wear protection , I would say both current day monograde SAE 110 in LE 1605 and monograde SAE 90 in LE 1604 are strong candidates.
http://lubetechnologies.com/assets/1601-1610-product-info.pdf

 

[aquariuscsm]

It's possible Redline MT90 in the tranny may help or even stop the gear grind. I'd give it a try since you're wanting to change the fluid.

 

[Silk]

Back in the day we put engine oil in BMC car gearboxes, and EP90 in the J4 van gearbox - same box, different loading.

 

[bunnspecial]

WRT to the transmission oil, some further searching has lead to a LOT of positive reviews in "LBC" gearboxes for Redline MT-90. I've seen comments on it in everything from Spridgets all the way up to Jaguar E-types, and the whole range of cars in between(MGA, MGBs, Triumph Spitfires and TR series, Big Healeys, etc) without any negative comment. Some of these cars, especially the E types and Big Healeys, are getting quite valuable these days. E types are 6 figures on a bad day, and Big Healeys are nearing 6 figures for top condition examples.

In any case, the only negatives I read were in some O/D boxes, where MTL worked better than MT-90.

With that in mind, I just ordered three quarts of MT-90. I had to order it, as no one local seems to sell it. It was painful to plunk down that much on oil(at $17/quart) but if it makes the shifting "slicker than snot" as has been reported I'll be glad to do it.

Now I just need to keep up my daily treatments of PB Blaster on the drain plug so that I can actually get the old oil drained out