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Roger Frazee

Which Oil is Correct?

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I have been running Valvoline 10W30 in my '47 flathead six since I got it a year ago. It seems that I read somewhere that only non-detergent oils should be used in these engines. Yesterday, I picked up six quarts of 30-weight non-detergent oil (labeled as "lawnmower oil") at Tractor Supply.

I am hesitant to use this oil without checking with the experts on this forum first.

What oil do others use in their old Pontiacs? Will standard multi-viscosity HD oil work, or should I use the non-detergent "lawnmower" oil?

Thanks for your help.

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hi, i bleieve your oil should be a straight 20 weight, the 10w30 is ok if you're going to drive it in cold weather. when my 53 pontiac still had the straight eight in it, and i was living in southern california, i was using regular 30w detergent oil. i don't know about the lawnmower motor oil, so i won't comment on it. it's been said many times that non- detergent oil is ok in these old engines. what is the oil classification on the lawnmower oil ?, do you use a bypass oil filter on the 47 pontiac six ? charles coker, 1953 pontiac tech advisor.

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I normally use Valvoline 10W30 also, and I really like using detergent oil. When regularly driving my old 1963 in the 1980s it was always extra clean when I pulled the valve covers. I would not use the "lawnmower" oil.

The issue with detergent oils in old cars is that an original (not rebuilt) engine can contain old sludge that can be dislodged by the detergent oil. If you have a rebuilt engine and use detergent from the start it will always stay clean inside and IMO this is the better oil.

The other current issue is that oil makers have been reducing zinc content over the last few years and it is thought that wear can result, especially on soild lifter or overhead cam engines. For a low stressed engine like a flathead it is probably not an issue, but just as a precaution I have begun using STP as an additive to help with this. Some have taken to using diesel oil or other industrial oils like your "lawnmower" oil, but I think the wear additives must be different than for a regular car, so I am not comfortable with this. Charles, what do you think? Todd Crews, POCI 1957 Technical Advisor

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hi todd, i wouldn't be comfortable with lawnmower oil in my engine. shell rotella oil has been talked about alot, and i know there's zinc additives on the market. i like the vavoline brand, i really like the kendall brand of motor oil, they used crude oil that has a very low level of ash content in it, quaker state oil does also. ash in motor oils is a major part of what turns into sludge inside the engine. charles coker, 1953 pontiac tech advisor.

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Hi Todd

I guess it all depends on where you live and if you are actually driving the car all year round, only in the summer or just in and out of a trailer. For a 1947 engine I certainly would not be using a 10/30 except if you are regularly driving in sub zero conditions. If you have recently rebuilt the engine and it is CLEAN inside and you are running a modern full flow filter there is nothing wrong with a mild detergent oil. IF you are unsure as to when the engine was last apart and possibly full of sludge, steer clear of modern oils. If you look at the original oil recommendation it probably asks for a straight SAE 30 in summer and a SAE 20 for winter. I would be using a multi-grade 20W-50 from a recognized Antique Car lubrication specialist. There are two or three who advertise in the Antique Automobile. The oil is possibly next to water the cheapest and most important thing that you put in your motor.

Bernie J.

Retired Retail Sales Manager Penrite Oil (Australia).

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I should add here that I have not owned a Pontiac for more than 55 years. I use Penrite HPR 30 in my 1934 Lagonda Rapier all the year round here in South-eastern Australia. These days I rarely rev it over 6,000 rpm.

Bernie J.

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Pontiac1953, to answer your question, the lawnmower oil is rated API SM. I also have some non-detergent 30W oil rated API SA.

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For a 1947 engine I certainly would not be using a 10/30 except if you are regularly driving in sub zero conditions.

I would be using a multi-grade 20W-50 from a recognized Antique Car lubrication specialist.

Interesting, thanks Bernie. Why do you think it should be so heavy and what do you think about my mention of STP? And what is your thought on the diesel oils like Rotella for an old car? Todd C

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hi, i went to a website where they listed all the service grades of motor oil, the sm rating is the highest grade, looks now to be an awfully good oil, sa is the oldest grade, where no performance rating is given, good for low stressed, low performing engines. i guess you're never too old to learn something new. hey torpedo, find out if you can get the api-sm oil in 20w, the w all stands for motor oil tested in cold weather condition. charles coker, 1953 pontiac tech advisor.

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Once it reaches operating temperature a "straight grade" SAE 30 oil is about the same viscosity as a "cold" SAE 10. Products such as "STP" are simply "Viscosity modifiers", that is they assist normal oils to retain their viscosity (thickness) as the operating temperature increases. Ie. they are "oil thickeners".

One of the main differences between a Diesel engine oil and one for a "normal" petrol engine is a higher level of detergent required to cope with the "dirtier" combustion in earlier diesels. I certainly would not recommend using any high-detergent oil in an older engine that has not at least had the sump (oil pan) removed and cleaned out. There is a real danger of sludge and carbon particles blocking the screen on the oil pump pick up thus wrecking the bottom end (especially in a pressure fed crank engine).

Cheap oil = expensive engine rebuild!

Next question....

Bernie J.

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I own my 53 Pontiac since 95 and I always use 10W40 grade detergent oil with no problem with.

I always replace the oil often when it began to turn brown, to avoid sludge causing any problem.

Fitz.

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I read, way back when, the reason to use non detergent motor oil in the early model Pontiacs was because they do not have oil filters. The detergent keeps the particles in suspension so that it gets cleaned out when it passes through the filter. Without a filter you want the heavier particles to drop to the bottom of the oil pan and stay there. My 1940 Pontiac shop manual suggestd SAE 20 to be used from freezing to 110 degrees, straight 20W from +10 to 110, 10w from minus 10 to +70 degrees and (I love this one) 10w plus 10% kerosene from minus 30 to plus 20. They also suggest cleaning the oil pan and screen every 10,000.

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