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toolman53

Straight 8 Recemended oil weight

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The 51,52 Buick reference manual recommends using heavy weight 10w.oil, would I be harming the motor by using 10w40 for year round use? When refilling the oil do I fill the oil canister as well? This is my first oil change in this ole gal and I`m being cautious as it`s not typical of what I`m used to. The manual also specs 5 1/2 quarts w/ filter,am I correct on this?

Thanks for any advise in advance, Toolman53

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I would reccomend a single weight detergent oil that has enuff zinc in it to protect your valves, lifters and cam shaft. Suggest you get Shell Rotella 30 weight and fill the oil filter can with oil after putting in the filter. Use a new gasket. I'd try four quarts in the crankcase, and fill the filter, then after running the engine, check the dipstick. 5 1/2 quarts sounds about right.

If you are not aware of the zinc problem, please research it. If you dont know how, just get on here and ask for more details.

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Hi Toolman53,

I have owned my 1951 Roadmaster for six years. I live in Colorado Springs where the weather allows you to drive from mid-April through most of October. I change my oil at the start of the driving season and at the end. I use Castrol 10w50 as my engine can get a little warm and I like using an oil with a little more body. I also throw in some Marvel Mystery Oil right before I change it as I think it helps with sludge build-up. If your engine has not been rebuilt, you may want to pass on the MMO.

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I increased my oil pressure in the '39 Buick I have with some wear on it by 10 pounds by using Shell 20w50. In the rebuilt engine I use 10w40 Shell.....the most modern Shell Oil. I tried the Rotella on advice and it didn't do anything for the oil pressure.

What you have to worry about is sludge in the oil pan and oil pump screen. If you drop the oil pan and clean everything out, then you can use multi-weight modern high deterrgent oil with good results. Straight 30w loses viscosity when it gets hot and you lose oil pressure, or I always have. I don't use 10w30 in any old straight 8 with significant miles on it anymore, only 10w40. I did use 10w30 in the rebuilt engine for about the first 20,000 miles on the advice of the builder and in more norther climate.

Edited by Dynaflash8 (see edit history)

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First of all I`d like to thank all of you for your timely responses and all the information that you have shared. As the Reference Manual suggested,using heavy weight oil 10w30 or40,I think that is the way to go.I was hesitant on the heavy oil because of the cars age and the climate here, but it appears that it`s being used in typical climates. For now I will pass on the Marvel Mystery Oil.

Happy Motoring,Toolman53

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Hi Toolman53,

I've been adding 1/2 oz. per gallon gas Marvel Mystery Oil as an antedote to E10 gas eating fuel line components.

I've been using 10W30 with good oil pressure, but it drops a little at idle. Maybe I'll try the 10W40 next time.

On the oil filter canister; I made the mistake of not tightening the lid retaining bolt enough...lost 4 qts. in 15 miles! It covered the entire engine, soaked the hood insulation and was even running out the port holes and down the right side of the car!

So make sure that top bolt is good and tight.

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Hi 1950 SuperBuick,

I did my first oil change a few weeks back,after reading different posts I decided to use 10w 40. So far the oil pressure remains the same, even at idle. A lot of this is quite new to me since I`ve only had her 2 months. I`m hesitant about adding any treatments at this time since it is origonal and I have the fear of loosening up deposits.I have only been burning regular gas in her without any additives as well. So far I think I`ve been lucky with the way she runs, it was sitting for quite a few years. Thanks for the info,Toolman53

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I would reccomend a single weight detergent oil that has enuff zinc in it to protect your valves, lifters and cam shaft....If you are not aware of the zinc problem, please research it. If you dont know how, just get on here and ask for more details.

This is sure to ruffle some feathers, but the so-called "zinc problem" is a myth. Many folks in the hobby are running around wringing their hands over something they know nothing about due to a number of mis-informed magazine and internet articles. These stories--usually based on anecdotal evidence with no factual basis---have resulted in a cottage industry for oil and oil additives that is playing on our fears in order to take our hard-earned dollars.

Rather than drag this post down with a side-bar on zinc, I started a new thread in the BCA General section. If you really think there is a "zinc issue", I urge you to read that thread.

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I just gotta tell ya, that 10weight is NOT heavy oil. 10 is the thinnest lightest weight oil. As the numbers go up so goes the weight of the oil. I thought someone might fill you in, but alas,no one has. A 10-30 oil is a 10 weight oil with the lubricity of a 30 weight.

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yea I was wondering why everyone was saying 10w, thats WAY too thin for any old engine. Good way to wear it out! I have 20w-50 and even thats a little thin. So I'm going to a straight 30w.

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I noticed absolutely no change in oil pressure between 10W30, 15W40, and straight 30W oil. The only difference I noticed was that the engine turned over harder when cold with straight 30W. Buick recommended 20W when new, but that's only because multi-weights didn't exist. As soon as they did--Buick recommended them. 10W30 is recommended in my '65 Skylark's owner's manual.

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10w and 20w is only at start up, and the oil mysteriously builds up to the top number. I tried using straight 30w and when the car got hot, the oil thinned and the oil pressure went into the basement. I used 10w-30 for years in a rebuilt engine as recommended by the rebuilder (39 Buick sedan). Now that the engine is 44 years old and 20,000 down the road and I'm in Florida I'm still using 10w-30 but contemplating 20w-50. This car still idles at 15 pounds and runs at 45 pounds hot, which is the recommended numbers. The car (39 Buick convertible) that lost oil pressure on 30w still has the same engine 35 years later and I do use 20w-50 in it. It carries 35-40 pounds at 50 hot and 10-15 pounds at idle hot. I gained 5 pounds oil pressure all around on the convertible by shifting to Shell high mileage 20w-50 last year. I have no idea why.

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"In single grade oils, the lower the number, the better it flows at cold temperatures. Likewise, the higher the number, the thicker the oil. In regard to multigrade oils, the first number in the code, such as 10W in SAE 10W-30, means that the oil can still be pumped by the engine at a temperature as low as a single grade 10W oil. A 5W, like in SAE 5W-30, can be pumped at an even lower temperature, and a 0W, like in SAE 0W-30, will pump at the lowest tested temperatures. The W in the designation is commonly thought to represent weight, but in fact stands for Winter. The second number, 30, indicates how well the oil will flow when heated to 100C/212F or higher."

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With respect to straight-weight motor oils, as they are not OEM spec by anybody any more, they are NOT "SM" rated oils, usually no higher than "SL" (which should still have enough zddp to satisfy many users).

The recommendation on Rotella T multi-weight would be for higher levels of zddp due to its diesel-main-design-orientation nature rather than building oil pressure per se.

In the earlier days of 10W-30 multi-weights, they were known to "shear" down to about a 10W-20 rating as the miles of use grew. This was in the early days of the various "chemistries" that make multi-viscosity oils work (early-mid 1960s). The viscosity ratings are "a range of actual flow values" rather than a hard & fast situation. Therefore, you can have "thick" 30 oils and thin 30 oils, just depending upon which part of the spec range the particular brand oil might test out. Same with multi-weights, too.

On older engines, my gut suspicion is that to try normal 30 oil first (in ambient temps generally at 32 degrees F or above), to get a baseline of how things act. With no multi-viscosity chemistry, the "straight weight" oils are the most stable, viscosity-wise. Once that baseline of oil and engine performance have been done, then you might venture off into 10W-40 land or even 20W-50 land if desired. From the number of miles that many of these cars might be driven, that could take a while. If the engine is reasonably fresh and internallly "in-spec), then 10W-30 might be tried.

Oil pressure at idle used to be considered a good judge of an engine's health, back when many salvage yard engines were purchased rather than repair what you had. In reality, ANY oil pressure at idle is sufficient to keep things lubricated (especially with solid lifter motors)--at least that's what my 1950 Plymouth service manual says. If there's sufficient oil to keep the bearings quiet, that's the "min spec" for what is needed, rather than something higher for the particular motor. Even the old "10psi/1000rpm" rule of oil pressure for engines has been reduced somewhat in our more fuel-use-conscious times.

Generally, though, as long as the main bearings and rod bearings are in spec, oil pressure should be good too--by observation. But for the oil to get there, internal passages and such need to be clean and open. On some of the used cars I've bought, I did an oil and filter changes, then added one pint of Stewart-Warner Alemite CD2 to the oil. When it got one quart low, I'd put another pint in. With it got low again, I'd change it. That seemed to work well, but then most of them have been reasonably well taken care of. Still, what I could see through the oil filler cap was clean. Then I'd use Castrol GTX and things progressed from there.

Just some thoughts,

NTX5467

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