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MG MGB Technical - engine oil

what type of engine oil do people use in their cars mine is a 1969 18GG engine with 21,000 miles from new,I have been using castrol magnetec 10/40 in it any coments or opinions also how many miles to the pint would you expect to get
andy tilney


i also tried modern oils one one of my B's and came back to 20W50 as it was recommandet by the factory.
For not starting a discussion upon thinking and beleving, here is a semi sientific explanation upon differnet grades of engine oil and why to use what grade:

Just have a look there and you will find the right quality for your B too. It is easy.

Hope this helps


thanks Ralph i will have a look did you notice any difference in oil consumption with modern oils to 20/50 mineral oils also what would you expect to get to a pint/ltr
andy tilney

Hi Alan
I use Duckhams 20/50, I used to use GTX when it was 20/50 but stopped when they changed it. Only complaint, Duckhams has gone up 50% in price in the last cou[ple of years.
R. Algie


i do not remember the exakt grade but think it was a 10W40 wight i used and as it has been some two or three years ago i tried it and when i changed to TEXACO 20w50 (bought it in a 40 litre barrel, normaly used by motor bike service points here) i soon had a much lower oil consumption than before. My engine is rebuilt to the specs of stage 6, as described in the Special Tuning Manual, so sometimes it is also reved to 6800 rpm, until the ignition limiter cuts it off. In this engine i have to refill aproxemately 1 litre on 1K kilometers / 750 miles. On a stock 18G... or 18V... i would not calculate more than half a litre for 1K kilometers, as my other 1977 RB GT (the shopping car) does only burn one litre between the regular changes of oil and filter at 5000K kilomerter intervals.

On the V8 i tried 10W40 but also changed back to 20W50. This engine is an almost stock SD1 block with only modified heads, induction system, carb and exhaust manifolds. I just change oil once a year on this engine (4-6K kilometers) and there is no top up necessary in betwen the changes and there is no fuel smell too, if i check the dip stick.

With the 1800 ccm B-Series engine, you should allways remember, that the capabilities of modern syntetic oils are no real benefits for this type of historic construction, as these oils tend to penetrate through the gasket material used on this old modells and avoid the built up of deposits that help to seal the pistons, a point that was considered by the designers of the old BMC A- and B-series engines!

BTW, BMC and BL used the 20W50 for the gearboxes too, as some of their internals might suffer when using EP80or90.

Hope this helps


I have to say my car is very tolerant of oils. I have run it on semi synthetics down to 15W/40 and also 20/50 "classic" oils without any problems while maintaining good oil pressure.
Stan Best

With the refomulation of just about all of our past favorites, I now use Valvoline VR1 racing oil 20/50. It is has adequate levels of ZDDP (Zinc). Price is not all that bad, around $3.00 per quart.

Not sure how much reformulation has taken over in Europe. In the U.S., Very few oils now have the zinc we should have for our flat lifter engines.

Especially important if you are rebuilding an engine.

The 4-cylinder was fine when GTX changed from 15W/50 to 15W/40 but the V8 showed lower hot idle oil pressure which I wasn't happy with. So I changed that to Halfords 15W/50, then couldn't see much point in continuing to pay more for GTX in the roadster, so changed that over to Halfords as well.
Paul Hunt 2

I recently switched over to Castrol motorcycle oil which still has the higher zinc concentration. It holds a higher pressure across the entire rpm range regardless of the temperature. It is available in 10/40 and 20/50. I'm using the 20/50 and am quite pleased with the results. Ray

I have returned to mineral 20w50 after experimenting with other oils. It feels and sounds right, somehow! My 3 main engine use about 0,5 liters in 1k kilometres (one pint in about 600 miles?). When I used 10w40 oil consumption was about twice as high.

I now use Comma Sonic 20w50, because it it easily available here and because it has 0,15% of both zinc and phosphorous.


thanks for your input Tore it is very interesting to hear that your oil consumption was twice as much when you used a 10/40 instead of a 20/50 i think this may be my problem on a 3,000 mile trip this summer to austria i used 4 Liters of 10/40in 10 days many thanks andy
andy tilney

I agree with Bruce C. of Wisconsin and his choice of Valvoline VR1 racing oil 20w/50. It has it right on the label that it contains ZDDP.

I did use Castrol 20w/50. However, Castrol has not updated their MSDS in several years (and they don't respond to email requests for updates!) and since many formulators have eliminated ZDDP from their oils as of 1/1/07, there is now a big question in my mind on whether or not Castrol contains that additive.

If I had an engine with a new cam and lifters, I'd sure have second thoughts about using Castrol. Not so with Valvoline VR1 racing oil.
Tom Fisher


I use GTX 15W/40, always have done. Mine's a high compression, big valve, long cam job. It runs high revs (although 6800rpm is pushing it a bit as it runs out of steam before 6000...!). Doesn't use a single drop.



Actually, my consumption figures are based on a very pleasant trip to Cumbria and Yorkshire last summer, and a similar trip to Scotland this year, with 10w40 and 20w50 in the sump respectively. I was a little shocked by the oil consumption last summer, with long distances and much motorway driving, but at least I checked the oil level every day. A fellow MGB owner with an engine that "never uses any oil" tried some kind of semi-synthetic oil on the same trip, and had terrible bearing ratte when we climbed Hardnott Pass. He then found the dip stick was practically dry! He too is back on mineral 20w50 now :-)


Based on a number of articles I have read there is reason to believe that the ZDDP - or zinc/phosphorous - problem is much more serious in the US than in Europe. Your choice of oils is probably very sensible. Anyway I think none of us should use oil from manufacturers that refuse to give us technical information about their products!



i run a 'hairy cam' and use flat top pistons, HIF 6 (not HS6), large valves and the ST dizzy, lightened crank, fly, con rods, pistons (everything ballanced), close ratio gearbox and all the other stuff for performance. This engine and the car it is in are realy just for fun only and it is more plesure to drive it than to drive my GTV8 and it is capable for equal speeds although the V8 is faster in every situation, it is simply the torque that makes it a winner. At 120 MpH with the works hartop fitted, it feels safer than the V8 at equal speed, although the suspension and the tyres on both the cars are uprated the same way. Concerning driving fun, i never ever had a more amasing car than this 4 cyl. B with stage tuning, it is still my favorite and i think there have bees some ambitious MX5 an Z3 drivers who drove their cars to the workshop and have it checked after beeing out performed by am old black MGB with an old driver with grey hair and glaces.
This car always makes me smile and i should have built it in the late 1970's allready, not in 2001. I simply did not know what i could have missed...



In my experience 10W/40 will leak from seals whereas 15W/50 won't, which will contribute to higher consumption of course. Also long distances at 70+ results in noticeably higher consumption than slower and more varied driving, both on 15W/50.
Paul Hunt 2

All this worry about using exactly what the factory recommended is absurd - this is British Leyland we're talking about :)

The oil available when our cars were built was lousy. Just lousy. Engines used to last 80,000 miles. Remember this when looking at what they recommended back in the day.

I'm running full synthetic 5w-30.

I'll say it again: I'm running full synthetic 5w-30. No joke. I switched to this oil in 2003 - I broke in my new engine on the lousiest oil I could find from the dollar store, then switched to full synth when it was broken in. The results are nothing short of joyous. Low friction = long lasting smoothness, power, and economy.

I drive the car daily. I commute to work in it. My commute is half an hour each way, assuming the traffic is good. I've been doing this for four years. I easily drive it 10-15,000 miles every year. No problems. None. I leak more oil than I burn, and it isn't much. Holding a constant 70-80mph for a couple hours won't burn any appreciable amount of oil. I literally don't even check my oil but every week or two, and maybe add a pint every month or so. The tappets are fine, my valves stay adjusted, no problem. This is after years of driving! Any oil-related failure would surely have happened by now!

All this anecdotal evidence of harm done by modern oil is bunk. The fact is, any time an engine fails, the builder needs to come up with a reason why. Oil, right? If oil's the cause, then all cars running that oil would die, including mine, right? Could it simply be that the engine builder screwed up? Can we really ignore the possibility that an engine part was simply faulty? Defective engines happen, and it's not the oil's fault, folks.

I bet my new engine on lightweight synthetic oil and now, almost 50,000 miles later, with no appreciable oil burning or loss of power, I think it's safe to say I won the bet.

Take it for what you will. Drive and enjoy :)

My motor is built similar to Ralph's. I stand with Bruce and Tom using VR-1. Too much research out there to ignore for me. I am curious about the Zink level in Castrol motercycle oil.
Steve Meline


Of course synthetic 5w30 is, generally speaking, far superior to mineral 20w50. I use 5w30 in my everyday Citroen, and expect that engine to last as long as I care to drive the car. But that does not mean it is neccesarily better for my MGB engine.

I am not surprised that your engine is running well on 5w30, but you do have the advantage of regularly driving long distances. That is of course most healthy for any engine.

As to the factory reccomendations: Even the cheapest modern mineral oil is far superior to the oils of the sixties and seventies, not to mention the pre-multigrade fifties, so under favourable circumstances like your engine has I would expect any decent modern oil to perform well. If, of course, it has the amount of zinc and phosphorous needed in our old flat tappet engines.

My ī63 MGB has the original 3 main engine, and as many of you know this engine does not have a proper oil seal at the rear bearing. I find thin oil is leaking out at an alarming rate.

There is also the question of what oil clings best to the mechanical parts of an engine that is only run every now and then. Some sources, like Crane cams, suggest that a mineral oil is a better choice for engines that are stored for long periods, and also that it gives a better rotation of the valve lifters.

I donīt know. But there sure are a lot of factors to consider.



Just so there is yet another voice heard from on this continuing questions... Here's my 2 cents.

In my other cars (typically Japanesse 4 cyl) since the 70s, I've used different synthetics with very good results. That's all I use - in the Japanese cars. I do not use the extended mileage feature, I change every 5k w/filter. I typicaly go 150k at least with each car before trading it in, without ever having an engine problem.

However, in my MG I use Castrol 20/50 GTX since I used to use other Castrol in motorcycles, yes even the british one, and several prior responses to this question frequently default back to Castrol as a reliable oil.

I will add that I've recently introduced 1 qt of synthetic in with the Castrol 20/50 with only a very slight drop in oil pressure - I'm doing this more to slowly help clean out engine than to thin oil.

And a final note: For those with a Checker Auto store near them, one can buy Castrol GTX for $1.99/qt on sale plus an additional $1 back from rebate, which brings it down to $1 a qt this week. Coupon was in major city sunday papers. And I've purchased Synthetics for near this price too when watching for sales w/rebates.

Personally, I've always held that oil is oil (but I have my favorites) but to go the distance it is more important to change oil more frequently w/ a good quality filter, than to worry about which brand oil to use.

R.W Anderson

I don't know about your MGB engines, but when Rivergate rebuilt my 1275 midget engine several years ago, they told me to run 10W30 in it. A couple weeks ago I figured that, since cold weather was coming fast, I would put in 5W30 Castrol GTX this time around. Took it down to Mobile and back afterwards, about 2005-mile round trip, down on Friday, back on Sunday, and did not use any appreciable amount of oil and the oil pressure gauge still reports 65psi at speed and 40psi at idle. Yes, I had the usual bottle of STP in there as well. As I said, the rebuild was geared to tighter tolerances than stock.
David "it doesn't do anything to help the rust, however" Lieb
David Lieb


Go talk to the folks at Delta Cam in Tacoma. They have reground a couple of my MG cams and when they report seeing significant wear on new cams from new oils without zink, I tend to listen.


Motorcycle oils usually have higher zddP levels than even Diesel oils, also more shear stable and usually have a higher ester content (and expensive). zddP is also an anti rust additive.

Most oil companies will buy in the additive package which is tailored to the type of oil blend being used (3 Groups of mineral oil) PAO and Esters.

Although Magnatec advertise polar molecules basically ester oil this is a very low % compared to a race oil which can use 15-20% ester content. Redline has a very high undisclosed ester content and normally high in zddP.

Keith Ansell has had a lot to say about this in recent months. His concern is about ZDDP - or the lack of it in the new formulation of Castrol GTX. The Castrol GTX we get over here in the Colonies is no longer the Castrol we've extolled for generations. The name is on the bottle, but at the bottom on the back, you'll see that it is now a product of BP.

If I understand correctly, Keith's concern is mostly for engines still in break-in. Modern slippery oils keep the lifters (followers) from rotating, causing premature wear problems.

My engine was broken in on the old Castrol 20/50 and it seems fine after about 35,000 miles. It does use/leak a bit of oil - perhaps a pint in 1,000 miles, more when driving long distances at 70+ mph in high temperatures. I just switched to Valvoline VR1 20/50 and I'm a little surprised as the consumption went up slightly. But this is based on one change after an 11,000-mile summer of long hard driving. It's possible that my consumption would have gone up a little anyway, and it's also possible that it's leaking a little more for reasons having nothing to do with the oil. And it's also possible that this observation was a fluke.

Allen Bachelder

The resulting trend of decreasing phosphorus is as a direct result of observations that modern engines, with lower spring pressures and lighter vavletrain, including multiple intake and exhaust valves, seems to require only .03% Ph to prevent wear. It was further documented that by increasing to 180 lbs of spring pressure with a .03% ZDP resulted in 267 mil of wear where with .05% ZDP concentration tests resulted in 26 mil of wear. That same .05% oil with just 205 lbs of pressure resulted in 153 mil of wear, requiring .095% ZDP to reduce wear, resulting in just 16 mil. The ZDP requirements of a motor oil are directly proportional to valvetrain spring pressure.

The European ACEA A1, A2, A3, B2, B3, and B4 classifications plate a cap on P levels at 0.10-0.12%. Additionally, ACEA A2 and A3 sequences require higher high-temperature high-shear (HTHS) viscosities, stay in grade sheer stability, and tighter limits on evaporative loss, high temperature oxidation, and piston varnish. This makes oils meeting these ACEA standards that much better, especially since wear limits are much more stringent for valve train wear, 1/6th to 1/4th the wear allowed in the sequences for API's SM standard. A minimum 3.5 cSt @ 150C HTHS viscosity is a good measure of the protection any given motor oil provides. For the JASO JPI-5S-36 test procedure, a high temperature high shear viscosity of 2.9 mPa s min is required with shear stability performance less than that required of the ACEA sequences, so it's best to look for an ACEA A2 or A3 xxW40 in addition to any other classifications for a motor oil.
Paul Wiley

According to

"% zinc is the amount of zinc used as an extreme pressure, anti- wear additive. The zinc is only used when there is actual metal to metal contact in the engine. Hopefully the oil will do its job and this will rarely occur, but if it does, the zinc compounds react with the metal to prevent scuffing and wear. A level of .11% is enough to protect an automobile engine for the extended oil drain interval, under normal use. Those of you with high reving, air cooled motorcycles or turbo charged cars or bikes might want to look at the oils with the higher zinc content. More doesn't give you better protection, it gives you longer protection if the rate of metal to metal contact is abnormally high."

It quotes GTX as having 0.12% zinc, whereas Mobil 1 for example has none. This could tie up with the non-synthetic versions of GTX being recommended by the manufacturers for 'older' and 'high-mileage' engines (i.e those with some wear and larger clearances when new) and synthetics like Mobil 1 being recommended for modern injection engines (i.e. close tolerance aka tight bearings and little wear). I doubt any of us are going to put enough mileage onto one engine to come to any conclusion, and certainly not multiple engines and extreme conditions. As such I take the manufactuers recommendations over individuals.
Paul Hunt 2

P Not Z

Mobil use "zddp" many forms some work better with moly.

Synthetics are less thick when cold but less thin hot, minerals use additives to mimic synthetic performance.
These are typically pour point depressants and viscosity improvers (plastic). A 20W50 mineral is only that out of can, in use it will shear.

Zddp is multi purpose anti oxidant corrosion wear, EP is a term usually used for gear oil.

Z relates to temp/pressure of p if using "zddp", Z free oil still uses P, check Fuchs Titan for Zinc free oil.

Because of US energy conserving requirements US oils can be light on zddp and testing is biased towards around town with a full broken in cam.

In UK an HTHS of 3.5 and above is fine, so at least a 40 (unless heavily ester based), if using in winter a 20W is a bit thick for good cold flow and oil temps will be low so a 10W40. Synthetics at 0W40 give better cold flow but the oil pump is still happy with a mineral 10W/15W with UK cold extremes.
Paul Wiley

A warning to those using valvolines street version racing oil (VR1). I've come across a few different things that corroborate the ZDDP ppm does not meet the minimum required. Either purchase the race only version of valvolines oil, purchase another brand, or add that ZDDP additive I posted above.

This thread was discussed between 10/11/2007 and 30/11/2007

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