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MG MGB Technical - 20w50 oil

hi 79mgb
20w50, it seems, is the recomended motor oil for my mgb.
but, in winter weather (no garage ) the car wont start,
i have to connect my battery charger to start.
so, why must i use 20w50? if i use monograde 30 i start.
will i really damage my engine if i use mono30 year round ?
i'm to old to change oil twice a year, 20w50 sommer, 30 in the winter.
i really would like to hear comments on oil usage.

john sutter

John. The Brits used single weight oil for a number of years with the BMC engines. No, there is nothing wrong with using a straight 30 weight oil in your engine. Nor, would there be a problem using a 10W-30 multi-grade oil in your car during the winter. The 20W-50 was the last of the oil recommendations made, but the factory also noted that other grades of oil might be needed under different conditions. The 20W-50 (and 20W-40 or straight 40 weight) oil was recommended for "Tropical and temperate down to 5 deg C (41 deg F.)" while 10W-30 (in one brand 10W-40) was recommended for "Extreme cold temperatures between 5 deg C(41 deg F) and -12 deg C (10 deg F)". You should hurt nothing by using a good quality 10W-30 oil in the winter. Switching to a somewhat heavier oil for summer driving is an option, but, if you maintain good oil pressure with a straight 30 weight oil, (or a straight 40 weight) I would allow the oil pressure gauge to provide my guidance. Back in the 60's we mostly used straight 30 weight oil in the American performance cars and either 30 or 40 weight oil in the Brit sports cars.

Les Bengtson

John I use a 10/60 Penrite classic light all year round, made for our cars and and has all the good stuff inc the highest ZDDP for cam and lifter protection. Denis

Nothing at all wrong with using a straight 30 grade oil and as Les says provided that you can maintain a good oil pressure it will be fine. The only downside is that your engine might use slightly more oil than with a 20/50 but that is a small price to pay
Iain MacKintosh

Why won't start? Does it crank but not fire? Not crank? Or what?

There is absolutely no reason why car filled with 20W/50 should have starting problems, unless there is something else wrong. I've always used it in my cars right from when this technology was current, on cars parked outside covered in snow and the doors frozen shut, and not had problems.

However 20W/50 is the recommended oil for temps above -10C or 15F - along with 10W/40 and 10W/50.

For temps in the range 10C to -20C or 50F to -5F it's 10W/30, 10W/40 and 10W/50, and when all temps are below -10C or 15F it's 5W/20 and 5W/30.

So maybe you need a lighter grade for all year round use, the problem with those is that leaks can become more apparent.

I wouldn't use straight 30, it's not going to give the protection of 10W or 20W in winter, nor 40 or 50 in summer. There is a very good reason why multi-grades supplanted straight grades. It's said 30wt is good for running in as it helps the rings and bores bed in, especially compared to modern synthetics, but that implies accelerated wear and I wouldn't want that.
Paul Hunt

Oils have moved on a bit since straight grades, in fact even during the MGB's early production life multi-grades came in, by 1979 multi-grade were the order of the day

but oils have also move on since 1979

as has been said 30 mono isn't a good idea it won't give good very cold weather protection and will make the car even harder to start for you in winter

30 mono isn't good for summer use either

the 10w/60 Penrite classic or equivalent depending on what you get out your way is a good choice - personally I'm unconvinced by the ZDDP scare stories but it's in there if you buy into such stuff

- now this bit will frighten many so a warning here -
I've been using synthetic Mobil 1 10w-60 (Extended Life) and only doing one oil change a year now

when I had my previous Spridget and MGBs I was told that using Mobil 1 then it would ruin my engines, rot my teeth and steal my good looks but despite many, many 10s of thousands of miles of use over many years the engines remained in very good order (and I've still got my teeth and good looks)

the people who told me these things were normally the people that either never used their cars or had very low annual mileage

yes it is a little thinner but consumption (and leaks) are still very moderate on my midget

I was concerned about the 60 figure as I don't want drag on my engine but I was told that it quickly wears in to the 50 bracket so in effect a 10w-50

Paul makes a very good point the engine should still start even if it takes a while and is reluctant so you may have another problem too

like you my car is outside 24/7, 365/6 and is actually used during the winter and it was it reluctance to during a spell of very cold weather that reminded me to move away from 20w/50 classic oil as my engine was well run in by then

here are some differing views on oils (including Paul's), if you or anyone else is interested -

below a chart to show how wide the bands are

Nigel Atkins

This thread was discussed on 02/05/2014

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