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MG MGB Technical - Recommended Fluids & Intervals?

I'd like opinions on types of oil to use. I've only had my 80 B for about a year. This spring, I changed the oil using the correct weight traditional motor oil. However, should I be using synthetic oil instead? The car does start to feel tired after 50 miles or so, and I wonder if a synthetic oil is better for older engines. As for the gearbox, how often should it be changed, and how big of a task is it? Thanks.
CRH Hoebel

I use Castrol GTX 20/50 and change it every 3000 miles. Synthetic is not necessary, our cars don't generate enough heat or stress to break down traditional oils in less than 3000 miles.

The gearbox is an interesting question, I just checked out 79 handbook, it says to check the oil every 12000 miles but says nothing about changing it. Personally, I would change the oil when I first bought the car and then not worry about it, I guess it wouldn't hurt to change it every 50,000 miles or so.

I have found that a gearbox is generally capable of going for well over 100,000 miles with the factory oil, regular top-ups but no changes.
The Wiz

Thanks. As a rule I always have changed the oil in my cars every 3000 miles. Like most British cars (so I've been told) it leaks a little (only about enough to make a fifty cent piece sized mark on the ground each night). Not bad for a 25 year old car. However, when I changed the oil for the first time, there was no leak for a few weeks. I figured the viscosity of the new oil kept it from seeping through where ever it does.

As for the gearbox, since the history of the car is uncertain, checking it might be a good idea. Does the filler/level plug on the side of the gearbox pull off or screw off? Thanks.
CRH Hoebel

It unscrews.
The Wiz

If you want to change the gearbox oil, its not a big deal. There's a drain plug in the bottom - unscrew it, let the oil drain out, put it back in, unscrew the the filler plug on the side, and fill it with oil until it is level with with the plug hole. Actually, you might want to remove the filler plug first - the oil might drain faster.

There is a lot in the archives about what to use in the gearbox, but the consensus, and what the workshop manual says, is 20w/50, just like your engine.

If you have the Bentley manual, it will show you how to clean the filters on the gearbox too. I haven't done it, so I'll let someone else talk about how much fun that may be.

Another level you might want to check is the differential. If you're facing the differential from the rear, there's a plug you remove, and fill it with Castrol 80w/90 gear oil. Fill it until it is level with the bottom of the plug hole, just like the gear box. You'll have to make a tool to remove the plug - there's a square depression in the middle. I think I used a 5/8" bolt, and ground it down until it was flat on 4 sides and the size of the depression - then I inserted it into the plug, and turned it with a socket wrench.

I believe checking fluid levels is the easiest thing I can do to keep my car running, so I change the oil and filter every 3000 miles, and check the gearbox and differential every other oil change. Maybe I'm being obsessive, but I'd rather be safe than sorry.

John
John English

I didn't think to mention the differential, Autozone and Advance Auto Parts both sell a tool for undoing drain plugs with the square hole, they sell one with eight different sizes on it - worth every penny.
The Wiz

Some of the later rear differential plugs may be of the recessed, hex type. I have two cars, on converted from wire wheels using an 80 disc wheel axle, and a 79 which have the hex headed plugs. But, after a minimum of 25 years it is hard to say what is perfectly correct.

All of the comments on lubricants are in line with what I use. I use the Valvoline 85W-90 Gear Oil because it is easily available here. Castrol motor oils are commonly available, but their other problems are not. The Valvoline works fine as would any other "name brand" gear lube.

Chassis lube is any good quality chassis grease. I have both the larger pump style grease gun and one of the shorter, one handed versions. The short gun has a straight, metal tube going to the grease fitting connection, the larger gun has a rubber flex hose going to the connector. Both get used when changing the oil and lubing the chassis.

For the transmission, either one of the oil bottle pump attachments or a suction gun work well. I have two of the oil pumps, one for the transmission and one for the rear end. After use, each goes into its own one gallon ziplock style bag which keeps it clean until the next use.

Les
Les Bengtson

The car does start to feel tired after 50 miles or so

Dashpots ? - Ignition gap? - fuel octane ? - binding brake ?


RMW

Synthetic oil can be used but tends to clean up deposits left by a mineral oil and leaks may occur. Synthetics are also expensive if not extending OCIs.
Mobil have a new range of oils based on OCIs
Mineral 5k
Semi 7.5k
Synth 15k

The zinc anti wear additive is also being reduced in modern oils to suit modern cars and consequently the latest oils may not be the optimum choice.

Older cars also tend to have periods of non use so oils with high anti corrosion additives may be more suitable.

Paul
Paul

To add to the questions. WHat about thenew "High-Milage" oils? Is this just another sales ploy or do they add things to this blend that would be better for older- high mileage cars?

I did not find a significant price difference between standard castrol 20/50 and their high mileage oil.
Bruce Cunha

Bruce,
These are Data sheets for Castrol and HM

http://home.comcast.net/~dsmphotos/cgtx.jpg
http://home.comcast.net/~dsmphotos/himile.jpg

Zinc is higher with HM and also HTHS (Oversimplified viscosity at 150c bearing temps rather than sump).

There is perhaps something extra for seals.


These oils perhaps help with a higher mileage vehicle.
Another one of Castrols interesting oils is Magnatec (need to click on Magnatec link) called start up in US
http://add-on.castrol.com.au/magnatecgilchrist/

Although Castrol and Sales ploys go together the mineral based "synthetic" may also be a good choice for older vehicles.

Paul
Paul

Only thing I'd add on the gearbox oil change in a car for the first time by a new owner is to make sure the filler plug DOES remove before unscrewing the drain plug.

I would hate to find I had a drained box and a siezed filler plug.

Regards
Roger
Roger T

Excellent point Roger.
For the rear diff I bought a cheap 1/2 inch rachet wrench from a local discount store and ground it down a bit until it was a perfect fit. It is now labeled and stored as yet another specialty tool for the MGB.
Lewis

Don't forget to replace the oil drain washer when changing the oil. Buy a few and store them, they are cheap. As for the car feeling "tired" after fifty miles, that doesn't sound like an oil related problem.
John

This thread was discussed between 28/08/2005 and 29/08/2005

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