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MG MGB Technical - synthetic oil/change intervals

If I switch over to full synthetic oil what should I use for change intervals? Right now I have a GB series engine with about 15K miles since the last full rebuild. I am changing at 1000 mile intervals just because it is my baby. The rest of my family fleet gets 3000 changes.
Carl W French

I suggest that if you do not drive over 3000 miles in 6 months, change the oil and the filter. the 1000 interval seems to frequent, unless of course it's over a long period of time.

rn
RN Lipow

So you are saying the change interval for synthetic oil is three thousand miles? I thought you could have longer change intervals than the usual 3 thousand for standard oil. Just trying to clarify.
Carl W French

Carl-
I've been using Mobil 1 synthetic oil for 25 years. Although its lubricating properties do hold up better over time than petroleum-based oil, one of the major factors regarding how long it can be left in an engine is the filtration system. If you've got a lot of grit in the engine, it mixes with the oil to form a wonderful grinding compound! Always use the finest porosity oil filter you can find and change it regularly. Same goes for your air filters. Another factor is chemical contamination. All sorts of nasty byproducts from the combustion process get into the oil, attacking bearing surfaces. Change the oil every 3,000 miles ant the engine will live a long time. I ran Mobil 1 in my 1978 Caprice Classic for 200,000 miles, changing it every 3,000 miles, and never did anything but a valve job. When I sold it the compression was still within factory specs and it was still giving 22 mpg on the highway.
Steve S.

The load on oil is way less with the new fuels - at least here in Calif. There is very little sulpher in the fuel, there is no lead, and the fuels with additives burn cleaner and produce much less soot. Ring sealing is dramatically superior to a decade ago. Result: the contaminants hitting the oil sump are way reduced. Modern filters and oils are also dramatically superior. GMC tests show that 12,000 mile oil changes under ideal conditions are adequate protection. With synthetic oil the lubrication is stable longer and much better top cylinder lubrication, but there is still the issue of contaminant load.
My '89 Taurus SHO was still running strong with very low oil consumption and excellent performance when my kid ran it into a ditch at 165,000 miles and ended it's career 18 months ago.(I thought) Someone bought the car from the junk yard and repaired the front end and I saw it in town a few days ago. I asked the kid driving it what he had done to the engine and he said nothing and that it ran great. Oil generally 2qts synthetic, 3 qts petroleum (a "no no" to mix, I know) Changes ranged between 5,000 miles and one time 10,000 miles. I remember the "good ole days" when the reliable VW needed an oil change and a valve adjustment every 1,500 miles - some people pushed that to 2500 miles. Points adjusted at 5,000, and plugs at 10,000. The SHO still had original plugs at 165,000. Things have changed.
Barry
Barry Parkinson

Carl, I currently use dino Castrol GTX in my MG; However, I've been using mobil 1 in my Land Rovers for several years. Depending on use, I typically change my syn oil every 5000 miles. I also use high end filters, either K&N or Puralator Pur1. One of the benefits of syn, is that it doesn't break down as easily as dino and good filtration should allow longer time between changes. Check out www.mobil1.com there is a FAQ section.
J Moore

I have been using synthetic oil in daily drivers for years, and change oil and filter at 7,500 miles. I routinely put 200,000 miles on a car, since I drive over 35,000 commuting to work. I still use Castrol 20/50 in my MGs, though, because they were not started on synthetic and i understand that switching a car to synthetic late in the game can cause leaks, or make existing leaks worse (what MG doesn't leak?)
I can attest that synthetic works very well in modern cars (my Volvos hardly wear at all on it), but question it's value in lightly driven MGs (less than 3,000 miles per year). I also change the oil in the MGs every Spring and every Winter (before storage) regardless of the miles driven.

Ira
Ira Spector

I use Mobil-1 synthetic in all my cars. The change interval I use is 5,000 miles or one year, whichever first occurs.
Charles Edwards

I have a new Honda Accord that uses Castrol Synthetic oil and they said to change it every 3000 miles. Therefore, if they recommend this for a new car, then it should be the same for a "new" older engine.
Robert Browning

My wife's Mini S came with synthetic and the first change was due at 10,000 miles. We had it done at 6,000 and it was like pulling teeth to get the dealer to do it before the 10k mark. My '66 B engine has maybe 1000 miles on it and is on it's 3rd oil change with 20/50 Castrol. I'll go to Mobil 1 at 1500 miles and change every 4-5,000 because I run the heck out of it. My 240SX has 147,000+ miles and gets Mobil 1 at 7,000 mile intervals. The Nissan has perfect compression and oil pressure, and uses no oil whatsoever.
David

It is interesting how many different opinions there are on how often to change oil. The oldest car that I own is an 1931 Ford Model A Phaeton. The recommended oil change period is 300 miles. Back then there were dirt roads, no air cleaners on the carb. and a 4.4:1 CR. engine. My newest car is a 2003 Chevy Impala. There is no specified oil change period except for once every 12 calendar months. Otherwise the computer records engine revolutions and engine temperatures and indicates when the oil should be changed. The car is currently 9 months old and has 6,700 miles on it and the computer has not indicated an oil change. I have always changed my vehicles oil every 5,000 miles and I'm gettin a little nervous waiting for the computer to tell me to change the oil. We tend to cling onto what we did in the past and consider that the gospel but things have certainly changed in 72 years. I think that everyone is looking for a one answer fits all with regard to oil type and change frequency and it just isn't there. Modern engineering has changed a lot of things.
Bob

Indeed Bob, but not to worry. My '94 Cadillac ETC NorthStar computer uses 7500 miles as a baseline and adjusts the change interval based on the number of engine start/stop cycles vs mileage. So, sometimes it has gone as high as 10,000 miles.
Edd Weninger

My olds user manual says it may go up to 12,000 miles before the computer says to change. I hear they changed the computer for 2001 and made the max 7,000 miles. The new computers are supposed to go to 12,000 miles under ideal conditions. Supposedly it is an algorithym that includes cold starts, engine rpms, and load level, just about everything except the amount of dust coming in the air cleaner. I expect they will measure that soon too. Cadillac has an aluminum bore. Bad oil would damage that faster than a cast iron block. GMC is probably being conservative.
I've told the story before: In the early 60's we had a salesman who drove a 1959 olds v8. As he was a traveling salesman he put on a lot of miles. The car had just over 60,000 miles. One of the guys at the shop bought the car from him for a good price. After he paid the paid the money and got the keys, the buyer asked how often the oil had been changed. The salesman looked sort of surprised and said "never". The buyer blanched. He changed the oil immediately. I say him driving that car several years later and it was apparently still running fine. I don't think GMC is up to that mileage between changes yet.
Barry
Barry Parkinson

This thread was discussed between 31/07/2003 and 05/08/2003

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