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MG MGB Technical - Running oil pressure differences between drivers h

To all,

I thought I would add this post for the benefit of archives, and because it has clarified for me differences I have seen in past threads on recommended normal running oil pressures.

I have acquired a copy of the MGB driver’s handbook supplied at the time with cars here (1969 version – British Motor Corporation Limited). There are differences in the General Data section from an earlier version I have which came when I bought my car. That version (M.G. Car Company Limited) carries a printers mark suggesting a date of Feb 1964. Both originated from Nuffield Press. Both describe features of cars with pre MK11 electrics even though the later version was printed during the MK11 distribution period here and is clearly updated in wording and layout from the earlier one. Local production of CKD MGBs ceased at the end of 1972.

In the 1964 version running oil pressure is given as “between 30 and 80 lb./sq. in.”

In the 1969 version the figures are “50 to 80 lb./sq. in.”

Interestingly, I have two service manuals for the MGB. One from British Leyland (1970) and another from Leyland Australia (1976). Both give the latter figures above for MGBs from the 18G/GA onwards.

Given the nature of engine changes in that period of years I can’t imagine the reason was other than that the factory had reason to change its thinking on the subject based upon experience as these cars were showing up for service/warranty.

This may have more relevance to people with the early cars or with a motor of that period fitted to a later car.

This sort of thing must make assembling data for contemporary publication rather interesting!

Roger T


Just posted this on another thread but oils available at time may play a part, as PRV would limit max.

I did my Engineering training - six years - with BMC - in NZ and in England (Stewart & Ardern, "The Vale" Acton - 1962-63)

The export prototype Mini was my first development project in NZ in 1959
The tragedy of BMC was the lack of funds for refinement and, in the end funds were taken from the very viable Leyland Trucks Division to support the cash hole in the Car Division. However that was long ago and far away

oil changes on the Mini were done at 1000 miles without fail - but they leaked SO much anyway it probably didn't matter much!
The OCI for other BMC engines was 3k miles max. and Castrolite (20w-20) or Castrol XL (20w-30) were the most common lubricants. Mobiloil Special 10w-30, or BP Visco-static were "not good" in these engines in the 1950-60s!

It is also interesting to note that engine life in cold and hot climates is very similar if the Manufacturers servicing advice is adhered too. Therefore, similar cars starting from a base low (cold) of -25C and +25C will almost always have the same engine life other factors being the same. Does this suggest that the design of the cooling system (for quick warm-up) and the Engineer's designed core temperature have much to do with the engine's ultimate life?

When the Mini came out in 1959 a specially formulated oil was required Duckhams 20w-50. It was the first "heavy" multigrade - 10w-30s had been out for years. You could use the same oil viscosity today in the same engine without an issue of course. We used 10w-30 20w-20, 20w-30, 20w-50 and mono HD oils in BMC "A" "B" and "C" series engines around the world in various markets without problems - as you could today. We got very good engine life at that time.
The '74 MGB I sold a couple of years ago ran well on 15w-50 and 5w-40 synthetics - the 5w-40 wasn't in the Handbook but met the original viscosity "intent" of the Handbook
The engine felt better on the 5w-40 though

the "intent" with the B series engines was to run as I recall 20-20W (Castrolite) or 20w-30 Castrol XL. We also used HD30 oils such as Delo etc. Later this included 20w-50 as these oils became available. We used 10w-30 too and had exceptional engine life with all of these mineral oils if the car was serviced reasonably well. I know of one doing well over 300k miles without work (except for a water pump as I recall)

The availability of synthetic oils changed all this
Paul Wiley

My 1976 Leyland Workshop manual quotes "50 to 80 running, 10 to 25 idling", even for the early 18G engine. In my experience the pressures quoted are probably hot, as mine idles at about 60 when first started, and only gets down to 25 when fully hot. 60 is also the consistent running pressure, hot or cold.
Paul Hunt 2

This thread was discussed between 21/09/2006 and 22/09/2006

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