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MG MGB Technical - Gearbox oil - don't use high-mileage formulation


I'll bet the majority of you know this already, but . . .

I was working on my '72 GT this weekend, replacing the overdrive filter. I knew that the transmission oil had to be a specific type, so I referenced my manual and and found Castrol GTX 20W50 recommended.

I had some. I used it. Hey! The overdrive doesn't work! (I tested it while the car was in the air). I knew I should check first the thing that I had done last; so I popped out the filler plug, only to allow lots of foamy brown/green stuff to pour out. I double-checked the oil, and it was the "special high-mileage formulation". A-HA! Replaced with non-special formulation, overdrive still didn't work. Checked the oil, still a little foamy. Thought I'd change it again, just to try to make sure that the newest oil wasn't diluted with remanants of the old; and it worked. There you go! Note to self: pay attention to detail . . .

Phil

PS: I'll bet I've got the (internally) cleanest gearbox around, by this point.
Phil Jones

I *knew* I was doing the right thing by never touching my gearbox oil other than to check the level ...
Paul Hunt 2

I had exactly the same problem with Millers 20/50 Classic Trans. Cured by using Penrite Gear Oil 30.
j soutar

Modern oils are now manufactured without the same ingrediants of only a couple of years ago. Unless you have a very old case of Castrol 20W-50, don't use what is sold now. For the same price you can get Red Line racing oil that will protect your engine and gearbox.
Dave Shively

I've used standard auto trans fluid for my overdrive trans and it works just great. It's made for gears not engines. I don't know why anyone modernly uses engine oil in a trans. The extreme pressure ingredients (zinc) in new catalytic convertor friendly oil is missing, unless you use a 15-40 commercial diesel engine oil.
Barry
Barry Parkinson

There has been a number of threads on this oil spec question. I believe if your 20w/50 oil is SJ or even SL it will be OK, but the new SM oil must not be used in the engine or gearbox.

Tore
Tore

I have always understood that regular gear oil should not be used in our gearboxes as it will not protect the bronze bearings, true?

The Wiz

Funny, the works V8 had a filling with gearbox oil while the 1800 had engine oil in the gearbox in this period. On my 1800 roadster i have changed to gearbox oil without any signs of problems within the last three years since changed.

May be in the time the cars were introduced, it was easier for the workshops to use engine oil for both, engine and gearbox and the wights of 20W50 are very close to EP80's.

Ralph

Ralph

Gear oil (EP) is OK if it is APL 4 and not APL 5 - it is the latter that attacks the bronze.

Triumph gearboxes use EP 80/90 oil while MG use engine oil - both have ODs so who knows why.

Rover recommended ATF in the LT77 manual gearbox and it is OK in MG gearboxes & ODs too - it just tends to find all the oil leaks!
Chris at Octarine Services

Barry- As I understand it, oil is your passion. What exactly did you use in your OD box then? And the recommended #9 Type AT specified in the Ford Sierra 5 speed conversion is how better and why?
I've been doing Royal Purple and Redline iterations in everything, diff, gearbox, engine, with no apparent problems, but have I erred
Why in the world would they market a bronze attacking oil called APL-5? Vic
vem myers

I use a good grade of 20w-50 Motorcycle oil and have had not any problems in almost 20 yrs. Why "motorcycle" oil? It simply has different molecular shear strength additives than regular motor oil as many bikes use a common sump for both the engine AND the gearbox. Over time bikers have found that this formulation could withstand the stresses of both engine use and gearbox peculiarities. Don't know what Chris thinks of this (I respect his opinion), but in my O/D box it has done a fine job at minimizing the amount of metallic sediment at each draining. FWIW.
Bob Muenchausen

GL4 has lower levels of the Sulfur-Phosphorous (S-P) additive package, so less interaction with brass and bronze. However, most additive packages now contain "inactive" sulfur which do not allow the sulfur to interact.

ATF is a 5W20 so good cold weather properties very little ZDDP which is an anti wear additive but has EP dditives S-P.

A box will shear a mineral 20W50 in next to no time so 20 or 30 weight oil work without issue.

A Bike oil is designed for a hostile environment and the Mobil V twin contains a greater ester content and higher ZDDP than their PCMO.
Paul Wiley

Not being a Petro engineer, Paul, what does that mean as relates to bike oil?
Bob Muenchausen

the gl5 oil has sulfer. sulfer is a superb extreme pressure lubricant. Differentials need gl5 oils. The problem is that sulfer is corrosive to copper/brass materials so you can't use it in a trans with brass synchros.

I'm really no expert on oils, What I've learned is from reading and curiosity. It irritates me that the chemistry of lubrication is radically superior and in some products, different, than it was 40 years ago - yet everyone trys to stick with a factory reccomendation that was "eccentric" in some cases even then and is certainly out dated today.

Greases for instance are far superior to 1965. For some odd reason no one worries about original grease. About the most unchanged lubricant would be the gl5 gear oil used in the differential.

What is so special about "shock oil"? A good non foaming auto trans oil is superior to the reccomended oil. If your shocks are too soft put some thicker oil in. The new oil will keep your seals fat, provide better lube and are more stable than the orig stuff.

Why 20-50 engine oil? Modern 10-40 oil will withstand heat and maintain viscosity better than any 20-50 would in the 60's and 70's, and turn out more horsepower than the 20-50.

Lower friction, more resistance to shearing and better buffers result in better lubrication and long life. The modern car runs on 4 liters of oil with an engine that has an operating temp of 210f. We think that same oil would be inadequate for the B engine. The modern turbo engine is putting out up to 2 hp per cubic inch and we think the oil spec's for that engine is not suitable for an MGB engine that puts out about .75 hp per cubic inch by today's rating standards.

One problem with modern lubes is the changes that have been made to protect the catalytic convertor - mainly the omission of zinc additives. Various substitutes are used but none meet or exceed zinc for Extreme Pressure lube.(mainly needed for valve train) Diesel engine oil is used in engines with no cat converter. The fleet owners are very sensitive to reliability. Even though the oil is also rated for passenger engines it contains substantial amounts of zinc. I'll guarantee you that if zddp or some other additive were equal or superior,the new EP additive would replace zinc in Diesel engine lube.

Most modern engines no longer have flat tappets - or push rods and lifters - for that matter. The manufacturers have found more reliablity by getting away from flat tappet systems. So far roller cam kits for MGBs are rather expensive. The flat tappet engine in a US MGB with no overdrive, cruising on the freeway at 78 mph is running well over 4,000 rpm -- it needs every bit of "extreme" lube it can get.

I recognize that to some extent this is a philosphical issue. Some want to be genuine and original and some have fun modifying their "B" and adding modern parts.

I'm in the latter camp with my '67 GT, and have alloy wheels, modified cam, flat top pistons, alloy head, electronic ignition, Nissan transmission, alloy flywheel, electronic tach & speedometer, Fiero seats, geared starter, 210f thermostat, modern alternator, plastic rear springs, etc.

I have fun fixing and driving. I've put about 10,000 miles on my car in the last 12 months. By modern standards my car is pretty slow. Compared to stock it is a much better performing car and lots more fun to drive on the road than it was. In 5th gear at 70 mph and 3000 rpm the cam is really "on" - a little nudge on the throttle and I'm over 80.

Barry

Ps After I rebuilt then engine, I ran the engine on 10-30 for a while. At idle when hot, the oil pressure dropped real low. I had to pull the engine after about 3000 miles because the head wasn't getting enough oil to the valve train. Turns out the rear cam bearing was incorrectly installed by the machinist cutting off the oil flow to the head. The main and con-rod bearings looked just great - like new- as did the lifters and cam. I was using and am still using a standard size crank with 127,000 miles before I rebuilt the engine. - now more like 140,000 miles. The oil pump is orginal with a replacement gear kit. Probably if I had run 20-50 oil, so little of it would have squeezed through to the head that I would have had catastrophic rocker arm failure.

So much for my rambling
Barry Parkinson

There is a concurrent thread in the Triumph BBS on "overdrive Oil?" http://www.british-cars.co.uk/cgi-bin/gen5?runprog=trbbs&mode=thread&access=&subject=1009&source=T&thread=2007042514175432584

Why should the MG and Triumph handbooks have such different recommendations - as far as I can see the OD units are the same/?. A contributor to the Triumph thread swears by Valvoline 20/50 racing oil. Since I have just replaced my TR6 clutch I have to decide which oil to use in the gearbox/OD. Don't post to the Triumph thread via my link - you will appear as me!

With thanks,

Barry
75 TR6
former 73 MGB
B.J. Quartermaine

I tend to strongly agree with Barry P. about modern lubricants as well as many other things we are offered today but choose not to use, for whatever reasons.

In the intervening years since our cars were made, a good many things have advanced in their chemistry, metalurgy, or manufacturing processes, and I think it pays to at the least, be aware of them, even if we choose not to use them. Also, I believe that some of the confusion about why parts, especially, sometimes no longer look the same for the same function, probably has as much to do with a manufacturer's choice of process (modern vs. as original) and tooling as any desire to thwart our intentions for originality. I think that function sometimes overides appearance and complete originality if a manufacturer, including an OE one, looks at his balance sheet for a small run item. And, in today's world, liability thresholds are probably higher than they were 40-50 yrs ago and those can influence choices of materials, design, and manufacture.

As for lubricants, having had some experience with changes in industrial types, I have made choices for synthetics and other newer formulations simply because the evidence of their superiority was strongly indicated by our actual experiences with them. Of course, we had no thought about maintaining our chillers and HVAC gear with OE type lubricants, just making sure that the lubes we used exceeded their standards and provided greater longevity than what we had used before.

That is a little different mindset than in the automotive restoration world, where some pre-WW2 drivers still look for castor bean oil and others of us take the owner's manuals and shop manuals as set in stone.

My guess is that if we were to look at the types of lubricants chosen for the latest MGs, it would reflect modern demands and the stresses on materials of modern choice. Most of these well exceed what our cars face, and because that is often true, they can provide better protection in forms which contradict manuals written from a materials base that simply did not exist 40 yrs ago.

A good example is the controversy today about ZDDP. The choice of metalurgy and other standards has moved on and so have the products on the shelves of our suppliers. In a case like that, we have to either find existing oils that work for what we have, or "retro-fit" our oils with additives to replace what is no longer needed. In the case of many other products like wheel bearing grease or chassis lubes, the newer formulations simply far exceed the performance of what we had before to a point where there is not much point looking for something that does not perform as well.

And to Barry Q., thanks for a different view about this subject!!
Bob Muenchausen

Not just the works V8s, but all factory V8s, had gear oil in the gearbox and OD as opposed to engine oil of the 4-cylinder cars. Because of that one can only assume that both are equally as effective/not damaging. The requirements for the V8 gearbox and rear axle are identical (SAE90 hypoid for temps above -10C), even though most manufacturers have slightly different products specified.

10/40 has a significantly thinner consistency than 20/50, or 15/50, and will leak more readily. That may well be enough to tip the balance towards 20/50. 0/5 synthetic is even 'better' viscosity and losses wise, but I would never use it in my MGBs. In the UK oils are loosely classified into 'older/high mileage', 'injection' and 'modern' categories. There are also differences between markets, Castrol GTX is still talked about in terms of 20W/50 in America, but changed to 15W/50 in the UK donkey's years ago. It's since changed to 15W/40 which gives lower hot idle pressures which was why I stopped using it.
Paul Hunt 2

This thread was discussed between 23/04/2007 and 27/04/2007

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