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MG TD TF 1500 - Differential Gear Oil

Not long ago a customer questioned me about the use of Mobile 1 75w90 GL5 synthetic in our cars rear ends. I've done quite a bit of research and the best explanation I've found is at,266128 Although it's for Corvairs it has the information we need and is a great read.

I am correcting my installation document to read :

" Any GL4 rated oil around 75-90 will work. Sta-Lube Hypoid SAE 85/90 hypoid api/gl-4 is one commonly used and is available at NAPA. Using a synthetic oil will risk higher leakage in the axle tube joints, seals, and filler and drain plugs."

Dave Clark Arizona

When I read the article, my takeway is that you should use GL 5 in the axle, since it is especially made for hypoid gears with high pressure load as in the diff.
On the other hand you should NOT use GL 5 in the transmission because of the brass in the synchromesh.
Rgds Mike
Mike Fritsch

The differential gears have brass thrust washers. They set the lash on the carrier gears.
Dave Clark Arizona

ok, that may be a reason to be careful, then. I would think that plugs and seals should not be a problem, since they don´t carry any load and don´t move.

Rgds, Mike
Mike Fritsch

I received an email from Doug Grimm, one of my conversion customers that just happens to be "in the trade" and is a "Certified Lubrication Specialist ". Doug doesn'twork for Chevron but does market for them as a lubricant consultant. He actually works for Holtzman Oil Corp. who is a Chevron jobber. This is a long read and might be more than you want to know but I find it very interesting.

Dave, you have done a lot of solid work here on your explanation of GL4 & GL5. The only thing I can add is an explanation of why Synthetic oils seem to leak out easier than mineral oils.
If Viton seals are used for the axles and rear end there should be no leakage issue. Synthetics have much less aromatic rings than mineral oils. The reduced aromatics dry out the common buna seals over a period of time. Aromatics are natural in mineral oils and what keeps seals soft and pliable. With reduced aromatic compounds in synthetic oils leakage is much more common particularly when a mineral oil was changed out for a synthetic oil on a vehicle with many miles on it. I've had customers purchase a used vehicle with say 80,000 miles and switch it to synthetic oil thinking they were doing the right thing only to find front and rear main seals weeping oil a few weeks after the change. If and engine or a rear end the result is the same. Most engine and rear end manufacturers today use viton seals reducing the possibility of seals losing their pliability over extended periods of time using synthetic oils.

I'd also like to add Chevron has a line of gear oils called Delo Gear ESI oil. Delo Gear ESI utilizes borate compounds and eliminates zinc and sulfur-phosphorous as additives. This products has 5 times the film strength of mineral and synthetic oils and reduces wear dramatically. It is priced between mineral and synthetic gear oils. My MGTD seems to be very happy on Chevron Delo Gear ESI 80w-90 in both the rear end and transmission. Chevron has a wonderful research and development facility in Richmond, Ca. where this product was developed.

Another thing I'd like to mention. The word "synthetic" is truly a play on words today. Let the "buyer beware". As a lubricant specialist I understand what is going on in the market place. The majority of the driving public do not. Chevron developed Group ll and Group lll lubricant technology many years ago. Group ll and Group lll are severely hydro treated mineral oils taking the majority of the contaminants out and making them very pure and by doing so raise V.I. (viscosity index) making these products mimic synthetics. In 1999 Mobil had the only true full PAO synthetic. Mobil sued Castrol for calling Castrols product synthetic when it wasn't a pure PAO synthetic. It went through the courts and Mobil lost the battle which allowed the word "synthetic" to be used in marketing oils even if the amount of synthetic base oil in the product was very low....sometimes as low as 3% but the manufacturer was still allowed to call it synthetic. This has added so much confusion to the public and some people who don't understand just purchase seeing the word synthetic on the container. Group ll and Group lll products are excellent but not up to par to a 100% PAO synthetic which is getting almost impossible to find. I understand that even Mobil 1 is now a blend of Group ll and PAO. By blending Group ll or Group lll oils with PAO any oil company can reduce manufacturing cost and increase margin. Where I've started to see an issue is customer complaints from people trying to increase drain intervals (or just follow OEM recommendations). Let use Toyota for example. If I use Mobil 1 0w - 20 motor oil Toyota says I can change the oil out every 10,000 miles. Customers are complaining of starting to use oil at the 6,000 to 7,000 miles.When additives are depleted oil usage increases. If we were getting 100% PAO oils today we would be able to achieve 10,000 miles in my opinion. 100% PAO oils are very stable and temperature resistant. We all have to keep in mind that it is the additives that are doing the work in motor oils for the most part. Increasing the amount of PAO in and oils certainly helps maintain the integrity of a oil. Motor oils are typically 15% to 20% additives and the balance base oil. Base oil is simply the carrier for the additives except where PAO's are concerned. PAO has a natural lubricity (slipperyness) that Group ll and Group lll do not so where there is a blend of Group ll and PAO offered you get and inherent better product in my opinion. The problem is no manufacturer has to disclose the amount of PAO (if any) in the oil they are selling. Many are just using Group ll and calling them synthetic. There is a group of people (me included) pushing SAE and API to pass laws making manufacturers disclose the contents and percentages of synthetics in each container. Unfortunately the oil companies are making so much money manipulating the word synthetic and have such strong lobby groups in Washington that I'm not sure it's going to happen.
Dave, this is a very misunderstood part of the oil business and I hope what I said makes sense to you. It is very complicated. Until we pass the laws that allow the public to understand what they are buying this will continue. I've included the explanation chart that I use to explain synthetics to customers.

Group l - These oils are commonly called solvent refined base oils because nearly all of them are manufactured using solvent extraction and solvent dewaxing. WW II technology.

Group ll - These oils are hydroprocessed which give them significantly lower levels of impurities than Group l base oils. They are considered synthetic by many people.

Group lll - These oils are also hydroprocessed but have significantly higher V.I. than Group ll base oils. They are now generally regarded as "synthetic" in the USA.

Group IV - Polyalphaolefin (PAO) are manufactured from olefins, a specific type of chemical feedstock. They predate Group lll base oils and are sometimes referred to as traditional synthetics.

Group V - This category is a catch all for all other base oils not included in categories l thru lV. It includes low VI base oils like naphthenic base oils (also called pale oils) and high VI non-PAO synthetics like esters.

Regards, Doug

Dave Clark Arizona

mga twin camr jumping in guys but I
J Hughes

Redline MT 90 is the best gearbox oil I have come across. Use it on my Jag MK2 and MG TF. Chose it after a lot of research. Do a search on the archives for it and you will find many others using it.

If you can't get it then yes EP 90 with a GL4 formulation is safe to use with yellow metals.

I would use a 90 weight oil over an 80 weight.


D Moore

Many thanks Dave. As it's synthetic have you had oil leak issues?
J Hughes

Thanks Dave for the great article that you submitted from Doug Grimm on "SYNTHETIC OILS" and so called "synthetic oils".
I know I will have to read it a few?? times.
In fact I will be printing out a copy for my hard file.
I have used Redline MT90 in my standard 5.125 gearbox, but did not notice any difference. Although, my TD only has about 50,000 Kil.
I am now installing a High Gear, 5 speed gearbox for better cruising speed on the freeways with a 4.55 rear end.

Hard to say on the increase on leaks. Yes I have some. Increased - couldn't tell you I am afraid. Had some before and after :-)

D Moore

I'm another fervent supporter of Redline MT90 which I've bee using (and changed, I must add) since I installed my 4.3 CWP in 2006.

Also in my gearbox.

Absolutely no issues, including no leaks.

Gord Clark
Rockburn, Qué.
Gord Clark

This thread was discussed between 19/09/2015 and 24/09/2015

MG TD TF 1500 index

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