"20W-50 is too heavy for that small engine"

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This is a recent topic from an MG site. The standard go-to grade in MGs and a lot of other old British cars for a long time has been 20W-50. The manuals list about a dozen different possible grades depending on expected operating conditions, but 20W-50 is the go-to all around grade. With concerns over ZDDP, many of us now have switched to oils specifically indicated to be high in it(Brad Penn, Amsoil, and VR-1 are all favorites) but that's another discussion/argument. Recently, there was a thread where someone's arguing that their mechanic is very adamant about how these "small engines" are "harmed" but oil as heavy as 20W-50, and that 10W-40 or lighter should be used instead. The member, BTW, is base out of Florida. Of course, a lot of less than charitable discussion has ensued, but I'm wondering what the thoughts on here are.
 
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The engine being small has nothing to do with the oil grade. But a heavier oil will demand more energy out the engine, so o low hp engine will suffer more. Maybe he was referring to this aspect.
 
20W-50 is the go to grade for most European classics until the 1980s, for a reason, it simply works. Also helps reduce leakage and oil consumption... And as you said, a high level of ZDDP is good aswell.
 
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Funny, the owner's manual and factory service manual for my Midget calls for 20W-50. Ran 10W-30 in it once (it's on the chart for winter), but in summer the oil pressure gauge was drooping noticeably at idle. As Yoda would say, "Size matters not".
 
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Originally Posted by maxdustington
Originally Posted by LeoStrop
But a heavier oil will demand more energy out the engine, so o low hp engine will suffer more. Maybe he was referring to this aspect.
Pseudoscience.
The difference in pumping power of different viscosities is a calculable tax on the engine. Once warm the differences are small but still measurable. In cold weather (ie, not Florida) it is enough to prevent engines from starting. So just what part are you calling Pseudoscience?
 
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Originally Posted by maxdustington
Originally Posted by LeoStrop
But a heavier oil will demand more energy out the engine, so o low hp engine will suffer more. Maybe he was referring to this aspect.
Pseudoscience.
Physics is real, a higher viscosity oil will require more energy to pump and will cause more internal drag. Why do you think automakers are specifying lower grades to improve fuel economy?
 
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Former British Leyland cars; MG, Triumps, older Jaguars engines had tolerances that I would say are not as precise as those found in engines today. The 4 cylinder push rod SU side draft carb engines was technology that was used for a long time in various models of those makes. A thicker oil like 20w50 would be fine to use especially in warmer climates IMHO.
 
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I used Mobil1 5w-30 in my '70 MGB-GT back in the late 70's. Mobil's 5w-30 didn't sell very well back then because everyone used 10w-30 and it was to "light". They, eventually, had to come out with a 10w-30. Any ways, it ran great from the East coast to the West coast and back (with no consumption).
 
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"This is a recent topic from an MG site. " In your signature you list 1970 MG MGB Roadster-Valvoline VR-1 20W-50 50 years of proof. Starting with the manufacturer..and ending with what is in your sump now. "their mechanic is very adamant about how these "small engines" are "harmed" Has your engine been "harmed"?
 
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I always ran 10W-40 in my MGB as well as everything else we owned up to 1997. A 10W-40 should be just fine in any of these low specific output engines, especially since they usually had oil coolers, without regard to BL's grade recommendations. The 20W-50 grade was widely recommended for a variety of Euro cars up through my old e36 of the mid nineties, for which it was the recommended grade for ambients >84F. For the record, my old BMW gets 10W-40 almost all of the time with occasional fills of M1 15W-50 or Delvac 1300 15W-40. If I ran an old Euro or Brit car and didn't trust a PCMO 10W-40, a HDEO 15W-40 might be just the ticket and many owners of old Euro cars use these oils.
 
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Originally Posted by bunnspecial
This is a recent topic from an MG site. The standard go-to grade in MGs and a lot of other old British cars for a long time has been 20W-50. The manuals list about a dozen different possible grades depending on expected operating conditions, but 20W-50 is the go-to all around grade. With concerns over ZDDP, many of us now have switched to oils specifically indicated to be high in it(Brad Penn, Amsoil, and VR-1 are all favorites) but that's another discussion/argument. Recently, there was a thread where someone's arguing that their mechanic is very adamant about how these "small engines" are "harmed" but oil as heavy as 20W-50, and that 10W-40 or lighter should be used instead. The member, BTW, is base out of Florida. Of course, a lot of less than charitable discussion has ensued, but I'm wondering what the thoughts on here are.
Apparently, I've been doing it wrong for the past ~30 years.... Though I have gone to M1 15w-50 for most of the older toys.
 

SR5

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These old Brit cars have run on 20W50 for years without damage. If I had to select a second option it would be a 15W40 HDEO like Rotella or Delo.
 
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20w-50 is what went into my 31 year old Alfa Romeo until I sold it two years ago. The funny thing is that most British cars grew up on Castrol. I few years back when Castrol reduced the zinc and phosphorus levels in its GTX conventional oil, they followed it up with a Castrol Classic label. But it was very hard to find, and it may only be available in the UK. Try Kendall GT-1 Competition 20w-50 for some of the highest zinc and phosphorus levels you'll find.
 
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In something like a basic lawnmower that is splash-lubed, I could see it maybe not being as good for it since it is thicker and may not be "splashed" where it needs to be? Probably doesn't matter but just my thinking.
 
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1800cc is a small engine ? My 650 motorcycle is smaller than that and hasn't been ''harmed.'' These engines haven't always used 20W-50, that was brought in specifically for the fwd versions. We used to have 10w-30 in our bulk tanks in the early '70's, and everything got it, including mini's 1100's and 1800's. We didn't differentiate between oil require for a Mini or Morris Minor, Landcrab or MGB. Austin Marina ? Is that a badge job for the US ? Did you get a Morris Maxi ?
 

bunnspecial

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Thanks everyone for confirming what I thought-that it was ludicrous. With that said, I have been know to run Delo 15W-40 when I thought I would be driving in low temperatures. I know there's plenty of ZDDP in it, and it makes the initial "bump" from the starter quite a bit easier than 20W-50 when temperatures get down into the 30s(F).
Originally Posted by Silk
Austin Marina ? Is that a badge job for the US ? Did you get a Morris Maxi ?
It's a left hand drive version of what was sold in the UK and elsewhere as the Morris Marina-i.e. the 70s corporate BL parts-bin-rush-a-product out the door car. The US ones are a bit interesting. They were only sold here in the 73, 74, and 75 m/ys. The US market didn't get a lot of options on them, but all were decently trimmed(vs. what was all was available)-we only had the 18V low compression 1.8L(same as the MGB of the same age) with a single HIF6 carb and of course the requisite smog gear. All had power assisted front disks. Our only options, aside from color, were either an auto or a manual(most were manual-mine is a bit uncommon in that it's a power-sucking slushbox BW35 auto), and either 4 door or a 2 door hatchback-looking thing that's not actually a hatchback. In typical BL parts-bin fashion, the 2-door uses the same doors as the 4 door, so it gives the overall side profile of the car a bit of a strange look. Under the pretext of making a 75-horsepower, 3000lb car seem "sporty", the 2 door is badged as a "GT" and has a tachometer. Oh, the 74 and 75 US market ones also got comically large, blocky chrome bumpers. I've never actually taken a good look at them, but it would surprise me if-to comply with the 5 mph impact regulations, they're a solid block of rubber with a chrome plated steel shell. The couple of thousand imported to the US were so widely loved that they've been saved in huge numbers-there are about 20 remaining.
 
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