1979 MGB oil change interval

I have a 1979 MGB. 95,000 or so. No issues and I am an old diesel engineer mechanic from a previous career with Caterpillar. We all know we can change or should change the oil on newer cars when the change oil light comes on. 50000 - 10,0000 based on the type of oil even. My question is for those antique cars we drive around in Sundays. In my past profession we would change the oil in Diesel engines generators, once a year regardless of hours run. We were instructed to tell the owner, conventional oil degrades even though the oil has few hours. I run a high mileage synthetic in my 1979 MGB and have for 4 years now. Runs great, good oil pressure hot and cold. If I am only putting 1000 miles a year on synthetic oils can I run 5 years totaling 5000 miles. Right now I change the oil and filter once a years regardless. Oh and one more thing - your drop down menu for model has not choices anddoes not work for MG so I had to change to Morgan the make to submit the question.

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That is the proper thing to do . As you are a mechanic I am surprised you even have to ask this question . And modern vehicles that have the oil life monitors still have mileage and time ( in months) listed in the owner manual.

Hmm… Ya I get it, but do synthetics breakdown like conventional? I have not heard one way or the other from the manufactures of said products only hearsay or opinion from those who think they are wise.

Why would you ask about synthetic oil ? That MGB was not designed for synthetic oil . And if you have a newer vehicle the manual will specify what to use , what more do you need to know .
Just go to oil manufactures web sites and you will find all you need to know.

I don’t think the breaking down of the oil is the issue

It’s getting all the other contaminants and moisture out.


I have started some research. Started with the MG on line chat space. History shows a wide difference of opinion. Have yet to see anything from manufactures suggesting one way or the other. For me, my engine is clean Inside and out being a restored beauty. Running high mileage synthetics and a load pressure at around 45-50psi at 55mph. Idle pressure is around 20-25. I have noticed no additional leakage and trust me MG’s leak-weep what have you. I did see where some have said engine ok for synthetics but traditional oil for the overdrive / transmission. Yes in MG’s you use 20/50 oil in the trans / overdrive. My guess is oil makers are not going to advise one way or the other. The question remains.

If I had a classic I assume it is wintered, every fall before sitting for the winter I would do regardless of synthetic or old dino oil. If driven year round I would do spring and fall, better too many than not enough imhop.

Synthetic oils are best used in high temperature applications like turbocharged engines or where low viscosity oils are required. Couple that with the low mileage, and IMO, you should use mineral oil of the proper viscosity. Your car, your choice.

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Reed, I would suggest you look carefully at the type of synthetic oil you are using. Modern oils do not have enough ZDDP additives to keep an engine with a flat tappet cam happy. Modern engines use roller cams and rockers almost exclusively so zinc snd sulfer additives have been greatly reduced.

There are additives you can use or many folks use diesel spec motor oil because it contains more ZDDP than auto oils. Or racing oils. Both are certainly is available in 20W50


A lot of modern cars still use flat tappet lifters and do fine with the new oils, but the metallurgy on those old engines and the manufacturing techniques are completely different. You do need the higher ZDDP amd MoS2 because of the metallurgy, not the flat tappets.

But there are some newer oils are using new additives that work just as good so a quality synthetic is OK. Most important thing is that you use the recommended weight. A 79 MGB probably recommends 10w30 but you need to verify that with your owners manual.

An annual oil change after only 1000 miles may be overkill, but what is this vehicle worth to you? Is it worth the cost of an annual oil change to you to keep it in top shape? If it were mine, I’d do the annual oil change and never look back. I think you can get a ZDDP additive if you really want one.

Name two that still do. I can’t think of even one.

Toyota 2.5L, Nissan 2.5L. Most direct cam actuated valves use them.

I stand corrected with respect to the Nissan. Direct acting on the 2.5 and the V8 as well. And the V6, too.

No so for the 2.5 Toyota as they list a roller rocker arm for the 2017 Camry 2.5l


The 1.8L Toyota was a direct acting bucket type (flat tappet) in 2003. Maybe they changed that too.

You are only going to get opinion on this matter, who would fund research on the use of modern synthetic oil on a 41 year old MG. My opinion is that I would use 15W40 diesel for the zinc. I have no evidence to back up my opinion.

I would not experiment with lubricants or hydraulic fluids for British vehicles. They got their bad reputation by being serviced like American vehicles. My 1960 Austin Healey Sprite Mk 1, 1960 MGA Roadster, 1962 MGA Coupe, and 1967 MGB Roadster required 30 weight motor oil for engine, transmission, and lever action shock absorbers. Lockheed Girling hydraulic fluid for hydraulic systems. I’m guessing a 1979 MGB could use 10/30 engine oil. Many vehicles were using it by the 1970s.

Spell Check sucks in Google Chrome!

These cars specified oil like 10W-30 because that’s what was for sale. There was no synthetic, or 20W-50 or 0W-20. What MG said in the 70’s is hardly relevant to today’s marketplace. In my view the biggest concern is water condensation from humidity, and that depends a lot on where you live. If you park the car all winter and it sits for 4-6 months, I’d change the oil in the spring, and get rid of the condensate that formed all winter.

If you are restoring a car to be period correct, fine, use old oil standards and old brake fluids, etc. And bias ply or Michelin X steel belted radials. If you want to drive the car safely it’s time to do some homework.

20W50 oil was available before 1979.

Consider the lousy oil that was available back then, API category SC, today we have API service category SN, SN Plus and SP.

My old Dodge used API category SJ oil and called for oil changes every 4 months/3,000 miles. With modern engine oil I change once a year/5,000 miles.