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What grade of oil?


coolp51d
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Hi everyone,

I'm sure you get this all the time, but I would like opinions on what grade of oil to use.

The car is a 1953 Chrysler Windsor Deluxe with a 265ci flathead six and engine fed torque converter. I've been using straight SAE 30, but I'm wondering if a multigrade would be better for my engine. Does anyone have thoughts on a 15W-40 or 20W-50? My oil pressure gets fairly low when I come to a stop after driving at 60mph for a while, and I'm wondering if a different oil would help me out.

Thanks in advance,

Thomas

P.S. I'm new to this forum so feel free to direct me to a different section if there is more information there!

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You could try 15W40 or 20W50 and see what happens. 30 is thickest the factory recommends, and then only for temps above 32F.

What is your oil pressure? Factory specs call for 50 pounds at 30MPH or above. They do not give pressure readings at idle but 15 pounds is usual.

Low oil pressure is an indicator of engine wear and could mean an overhaul is due.

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Hi, I am using Shell Rotella T 15 W 40 in my Flat Head 6, oil pressure 50 to 55 psi on highway, 45 around town, 30 to 40 at an idle when hot.

This is a decent oil, still has 1250 PPM of Zinc additive, these are Canada specs.

I also throw in a little Lucas oil stabilizer, although it's probably not necessary.

I am sure I would have lower reading if I used 5 W 30 oil or straight 20.......

Edited by fred (see edit history)
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My oil pressure is about 7-10psi at idle after I drive at highway speeds. At speed, I'm getting around 50. Sounds like I don't have much to worry about if that idle pressure is acceptable. Also, I'm planning on doing a main/rod bearing job...I'm starting to get a clicking knock when I load the engine going uphill. Maybe that will boost my hot oil pressure. Thanks for the responses!

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  • 3 weeks later...

Chrysler's engine oil recommendations have not changed very much from the 1930s to the 1970s. See the following page for more information:

Chrysler Oil Recommendations

There is no need to run a higher viscosity than what is necessary as it will just reduce power and fuel economy. If you're in a warm climate, a 15W-40 HDEO should work fine but a 10W-30 should be suitable year-round. Excessively thick oils tend to run hotter than thinner viscosities. A 5W-30 oil will have a higher Viscosity Index than a straight 30-weight oil and will therefore keeps its viscosity over a wider temperature range. Even though a 5W-30 oil will flow better at cold temperatures, it will also be thicker at higher temperatures. The second number (30) in 0W-30, 5W-30, and 10W-30 means that all have the hot viscosity of a 30-weight oil. 0W-30 oils (being synthetic) will be the best at not thinning-out with higher oil temperatures.

As for additives, there is no need for more than what already comes in the oil. Lucas is good for causing foamy oil and at making high profits for the company (See The Story With Additives).

Edited by fraso
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I have a 1951 Chrysler owner's manual and it recommends "heavy duty" or detergent oil, just coming in then. It also says it is not necessary to use thick oil like they used to, thin oil lubricates better and should be used. This may refer to multi grade oils just coming into use then.

I would use 10W30 unless I had a pressure problem due to a worn motor, then I would use 15W40. Straight 30 and "good ol' thick oil" is not needed and not recommended.

In fact, since 10W30 was the default choice in all garages in the fifties and sixties chances are your car never used anything else. Until it turned into an "antique" and some rube said "all them old antique cars use straight 30 oil".

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A conventional (mineral oil) 10W-30 multigrade oil is a 10W oil with an added VII (Viscosity Index Improver additive) to give it the hot viscosity of a 30-weight oil. A VII is a polymer additive that causes oil to become relatively thicker (thins out less) with increasing temperature. The problem with VIIs is that they can shear down with use so that a 10W-30 might perform like a 10W-20 after some time in service . This is the reason that straight SAE 30 oils are commonly recommended in air-cooled engines like the ones found in lawnmowers.

However, straight 30-weight oils generally have a lower VI (Viscosity Index) than multigrade oils (like 10W-30), which means that, although they don't shear down, they also become relatively thinner with increasing temperature and relatively thicker with decreasing temperature. Modern multigrade oils are more refined (Group II & higher), which means they are require less VIIs and consequently more shear-stable (10W-30 engine oils are quite shear-stable nowadays). Synthetic oils (Group III, IV, V) use minimal or no VIIs to meet viscosity grade requirements. Group I (Solvent-Refined) oils were the norm in the old days so any modern API-certified oil is an improvement over what your car would have used when it was new.

Technical specs for engine oils aren't always very informative. The Esso XD-3 Extra data sheet is better than most and shows the following for 30 weight oils:

  • SAE 0W-30, VI=176, 100°C viscosity = 12.2 cSt
  • SAE 5W-30, VI=163, 100°C viscosity = 11.0 cSt
  • SAE 10W-30, VI=148, 100°C viscosity = 12.0 cSt
  • SAE 30, VI=108, 100°C viscosity = 12.0 cSt

Also, I believe that detergent oils started coming out in the 1930s (see Engine Oil Guide, p3). See the following report about the use of detergent vs non-detergent in a modern engine: Impact of Low Quality Oils on Engine Wear and Sludge Deposits. Modern Heavy Duty Engine Oils have additives to keep engines clean and minimize flat tappet wear.

Edited by fraso
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