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DO NOT MIX EP OILS....- OLD WIVES TALE..???


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My '39 Chrysler workshop manual states..

"Under no circumstances should different brand EP oils be mixed".. Is this an old wives tale??

plus..."never top up diff always drain and refill after flushing" (To prevent mixing oils ?)

Also, any opinions on using modern MULTIGRADE EP Diff/gearbox oils ie 90-140 GRADE Etc. in old cars?

Thanks,

Tricky

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On this site are some VERY knowledgeable people about lubricants. I suspect your questions have already been pondered, and although you will find various answers, I believe you will find consensus on many things. As I recall, most recommend against mixing different viscosity ratings. Cleanliness is paramount, as I am sure you know. I mention this because in a very old gearbox, that old gear oil can set up literally almost solid, and the most cruddy seems to be at low points (from settling), or where the lube splashies so that air is in frequent contact. Except for the little breather units, gearboxes are generally sealed units. They sure can get contaminated somehow, though! It is true that some gear oil looks very black, even when new. With an engine or gearbox that was not cared for, and only added to, the lowest part of the housing might have substantial crud that has been there forever, and would stay there forever, providing someone doesn't "stir the s@@@ up", Point here is once you decide to clean it properly, it a requires a truly excellent job of cleaning the whole unit (else you were better off to just top it off). I have seen often, power and gear trains which functioned fine for long periods of time, then had problems almost immediately after someone did the "right" thing and changed the oil. My father was a highly regarded ol school mechanic; he definitely did not believe in mixing brands in a good engine. Some fresh gear oil looks to be dirty-looking, but is not -- just black in color. I think you will receive some better info from others on this forum. They say our worst oils of today are superior to the best of times past. I might add that 90-140 is (or was) used in the gearboxes of gigantic earth moving equipment, and I do not recall any problems attributable to it. Not sure about modern cars, but I believe it did exceptionally well in the vintage and collector car gearboxes, too.

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There are differences and some harm yellow metal so you should keep that in mind.

What’s the difference?

The performance requirements for automotive gear lubricants depend on their intended use.

API Category GL-1 (inactive*) designates the type of service characteristic of manual transmissions operating under such mild conditions of low unit pressures and minimum sliding velocities, that untreated oil may be used satisfactorily. Oxidation and rust inhibitors, defoamers and pour depressants may be used to improve the characteristics of lubricants intended for this service. Friction modifiers and extreme pressure additives shall not be used.

API Category GL-2 (inactive*) designates the type of service characteristic of automotive type worm-gear axles operating under such conditions of load, temperature and sliding velocities, that lubricants satisfactory for API GL-1 service will not suffice.

API Category GL-3 (inactive*) designates the type of service characteristic of manual transmissions and spiral-bevel axles operating under mild to moderate to severe conditions of speed and load. These service conditions require a lubricant having load-carrying capacities greater than those that will satisfy APL GL-1 service, but below the requirements of lubricants satisfying the API GL-4 service.

API Category GL-4 designates the type of service characteristic of spiral-bevel and hypoid gears in automotive axles operated under moderate speeds and loads. These oils may be used in selected manual transmission and transaxle applications.

API Category GL-5 designates the type of service characteristic of gears, particularly hypoids in automotive axles under high-speed and/or low-speed, high-torque conditions. Lubricants qualified under U.S. Military specification MIL-L-2105D (formerly MIL-L-2015C), MIL-PRF-2105E and SAE J2360 satisfy the requirements of the API GL-5 service designation.

API Category GL-6 (inactive*) designates the type of service characteristic of gears designed with a very high pinion offset. Such designs typically require (gear) score protection in excess of that provided by API GL-5 gear oils. The original API GL-6 test equipment is obsolete.

API Category MT-1 designates lubricants intended for non-synchronized manual transmissions used in buses and heavy-duty trucks. Lubricants meeting API MT-1 provide protection against the combination of thermal degradation, component wear, and oil seal deterioration which is not provided by lubricants meeting only the requirements of API GL-4 and API GL-5.

MIL-PRF-2105E this specification released in 1995 combines the performance requirements of its predecessor (MIL-L-2105D) and API MT-1. MIL-PRF-2105E maintains all existing chemical/physical requirements, stationary axle test requirements, field test requirements and data review by the Lubricants Review Institute that were required under MIL-L-2105D. It also adds the stringent oil seal compatibility and thermal durability test requirements under API MT-1. MIL-PRF-2105E has been re-written as SAE Standard J2360.

SAE J2360 standard is a new global quality standard that defines a level of performance equivalent to that defined by MIL-PRF-2105E, a U.S. military standard for approval that was not available to oil blenders in all parts of the world. It includes all of the most recent axle and transmission testing requirements identified in API GL-5, API MT-1, and MIL-PRF-2105E including the need to demonstrate proof-of-performance through rigorous field testing.

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Thanks JF,

Man that's a lot of technical info, but me not being a lubrication chemist leaves me still pondering.

My shop manual says for diffs use EP 80 in winter and EP90 in summer in summer but warns not to mix different brands by topping up etc.

So what modern EP oil do you recommend for my 1939 Hypoid Chrysler diff and is mixing different brands a no no or just fiction.

I'm leaning towards using a modern EP 90 -140 diff oil, (the oil that is currently in the diff is very clean but seems to be very thin ???)

R

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A recent " three o'clock in the morning " concern regarding the effect of EP diff / trany lubricants upon the yellow metals in my old Buick caused me to call the Ask Mobil hot line.

When told of my concern re yellow metals the Mobil rep recommended their Delvac Synthetic Transmission Fluid 50. The product literature available states that it has " substantial advantages over conventional sulphur -phosphorus gear oils " and that it acts as a 90 weight gear oil at the high end of the temperature / viscosity scale.

He also said you needn't flush old lubricants, just drain and fill. I haven't purchased this product yet, and ask if others have any experience or thoughts regarding this product.

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I think the reason was, they were afraid the additive chemicals would clash. But that was a long time ago. Be interested to know if they have solved the problem. In the meantime better not to mix them.

Years ago when I worked in a garage I never heard of this issue. Checking the trans was a standard part of an oil change and lube job. I would top them up with our B/A or Gulf brand lube and never worry about it. Never had a comeback or problem but who knows what happened a few thousand miles down the road. This was in the late 60s.

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G'Day Rusty, Like you have suggested whenever I took a GM or Ford or Mopar car for a service back in 60's 70's, if needed. the service guy would usually just top up the gearbox and diff oils.

No mention or concerns about mixing brands then.

The only trouble I ever had was when one mechanic filled my 203 Peugeot with EP oils which ate away the bronze internal worm gear.

However I still find it hard to believe the general recommendation that you cannot mix EP gear oils. I just can't see why not?? Maybe somebody can explain !!

R

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I think the reason was, they were afraid the additive chemicals would clash. But that was a long time ago. Be interested to know if they have solved the problem. In the meantime better not to mix them.

Years ago when I worked in a garage I never heard of this issue. Checking the trans was a standard part of an oil change and lube job. I would top them up with our B/A or Gulf brand lube and never worry about it. Never had a comeback or problem but who knows what happened a few thousand miles down the road. This was in the late 60s.

Look, as I stated before all manufacturers say no mixing in the owners manual and in the maintenance section of the service manuals, and I don't care from what country, NEW or OLD car. Manufacturers have no skin in the game, because they don't say which brand to use only to continue to use whatever brand you choose and stick to it!

When was a line mechanic we carried one brand of oil only, do you think a dealer is going to carry bulk oil of every kind??? Or go out and buy a brand specific oil for a customer??? So the dealer or gas station or jiffy lube is going to be..... the be all, end all, guy and say you can use anything so he can have customers.

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Here is an interesting web site.

http://www.widman.biz/English/Calculators/Mixtures.html

It provides a calculator for the result of mixing viscosities. It also says in red to NOT mix oils of different brands and formulations. Widman imports oils to Bolivia.

It seems to me that as long as you put in the right formulation (API grade etc.) you can't go too far wrong, as long as you are only topping up. Significant amounts, you are altering the oil towards the top-up oil. Is that what you want?

IMHO the most import thing is to have clean oil of the right formulation in there and enough of it! If you are concerned, change the oil. You will benefit. My vehicles all run noticeably better on fresh oil.

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Look, as I stated before all manufacturers say no mixing in the owners manual and in the maintenance section of the service manuals, and I don't care from what country, NEW or OLD car. Manufacturers have no skin in the game, because they don't say which brand to use only to continue to use whatever brand you choose and stick to it!

When was a line mechanic we carried one brand of oil only, do you think a dealer is going to carry bulk oil of every kind??? Or go out and buy a brand specific oil for a customer??? So the dealer or gas station or jiffy lube is going to be..... the be all, end all, guy and say you can use anything so he can have customers.

I would like to confirm your conspiracy theory and say we were lying but we weren't. We just never heard of this, and never had a problem. In fact we did our best to give our customers good service and help them get long reliable service out of their vehicles.

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The manufacturer recommends the lube it will use at service intervals and hope you heed the manual. They know some oils will not do the job they require or may be harmful and can therefore deny warranty work if the recommendation is not followed. Use whatever you want it's your car and your money. I once worked with bagged 2 part epoxy encapsulate that a box of it got stolen. About an hour later some fool came around asking what kind of oil we had in those bags. He must not have read his manual. We had a good laugh at his folly! We weren't mad at all.

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