# Oil for the vehicle



## Ghostmachine (Mar 25, 2020)

Just a question for a 65 Pontiac Grand Prix 389... I know its not a GTO... but thought you all would have good advice... What is the best oil for the engine (389)... I run it a lot during the hot summer of Texas... I here 10-30 weight... Thanks for your comments....


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## Old Man Taylor (May 9, 2011)

Personally I would run 10-40 in the summer, but to be sure I would have to know your bearing clearances..Do you have an oil pressure gauge? That's the best way to tell for sure.


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## Ghostmachine (Mar 25, 2020)

Thank-you....


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## Lemans guy (Oct 14, 2014)

Agree, I use Amsoil 10W-30 ZROD,....it has zinc, therefore the Z supposed to help the cam etc.

As a trivia point we all slang the oil as 30 weight 40 Weight, etc but actually the Society of Automive Engineera (SAE)....uses those designations to describe the Temperature at which the oil flows freely giving good lubrication. The numbers are for ambient temperature,....

A 5W means 5 degrees, the W stands for “Winter” not weight, the 30 or 40 is also temperature. When one used a single designation like 30W it meant that the oil would flow good in themperatures near 30 degrees.

but with advances in oil technology and people driving from Michigan to Florida for example a multi-viscosity oil would do better, so one that was 10W - 40 would flow good at temperatures near 10 degrees and at temperatures near and above 40 degrees.

No such thing as weight in oil, “Winter” is the W.....so the recommendation for the 10W-40 in Texas where it gets hotter than the hinges in hell is a good one!

at least that is my story and I am sticking to it! .......


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## Rlamarche1 (Nov 22, 2016)

I live in the panhandle of Florida and use Shell Rotella 15W-40 in my 64 389.


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## pontrc (Mar 18, 2020)

10W30 with Lucas zinc additive


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## Ghostmachine (Mar 25, 2020)

Lemans guy said:


> Agree, I use Amsoil 10W-30 ZROD,....it has zinc, therefore the Z supposed to help the cam etc.
> 
> As a trivia point we all slang the oil as 30 weight 40 Weight, etc but actually the Society of Automive Engineera (SAE)....uses those designations to describe the Temperature at which the oil flows freely giving good lubrication. The numbers are for ambient temperature,....
> 
> ...


Thanks for the information.....


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## AZTempest (Jun 11, 2019)

In Phoenix were it's 115F summertime temps and doesn't drop below 90F at night I run 20-50 Valvoline racing in my 389 and 326. Used it for years in my 01 Sport Trac and sold it with 320000 miles on it. Great oil for the heat.


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## HiVolts (Jan 27, 2020)

AMSOIL ZROD 20W-50 here, with by pass filter. Butler 461, on original 400 block. Motor likes it and burns less of it here in hot and humid SC..


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## PontiacJim (Dec 29, 2012)

Viscosity of an oil is determined by measuring how long it takes in seconds for 60 cubic centimeters of oil to flow through a small section of tubing. The standard tube is called the Saybolt Universal Viscosometer. The temperature of the oil and the length of the diameter of the tubing are carefully chosen in order to make the test standard.

Tests are run on oil samples at 100, 130, and 210 degrees Fahrenheit. As an example, if an oil has a viscosity which makes it SAE 10 oil when it is cold, chemicals can be added to the point that when the oil is hot it has the viscosity of SAE 30 oil. This blend could be called either SAE 10 or SAE 30, but this does not describe the oil enough. So the oil is called 10W30 where the 10W refers to the viscosity of the oil when cold at 0 degrees Fahrenheit and the 30 refers to the viscosity of the oil when hot at 210 degrees Fahrenheit.

This is how multi-graded viscosity oil came into existence. The multi-grade properties allow for easy starting characteristics of its lower SAE number along with higher temperature lubricating properties (high viscosity and low oil consumption) of its higher SAE numbers.

How oil lubricates the bearings:

When the journal begins to rotate, it starts to rotate along the surface of the bearing which at first has a "boundary layer" of oil between the journal and bearing when the engine is at rest. The journal begins to slip, as it rotates, on the boundary layer of oil. As soon as the journal is rotting fast enough, oil pressure is generated between the journal and bearing. When the pressure is great enough, it lifts the journal up off the bearing and the journal floats on a film of oil. This is called *Hydrodynamic Lubrication*, or *Full Lubrication.* This is what does 95% of the lubricating in a bearing.

Expanding this further, as the journal starts to rotate, it sets up shear forces in the oil which are parallel to the direction of the rotation. But oil has viscosity and doesn't like to be sheared so instead of shearing it is dragged into the converging section between the journal and the bearing. A lot of oil is now being forced into that little space below the journal and it is too viscous to leak out and starts to build up pressure. When the journal reaches a high enough speed, a pressure wedge develops that literally causes the journal to be floated on the viscous liquid film and prevents metal-to-metal contact. In other words, during hydrodynamic lubrication each journal and bearing actually become miniature oil pumps and _the oil pressure generated in the bearings is in no way related to the oil pressure generated by the engine's oil pump!_ The pressure generated by the journal and bearing is much higher than the pressure generated by the oil pump. The only thing the engine oil pump does is to supply sufficient oil to each bearing for hydrodynamic lubrication to take place. This is one reason why you should never lug an engine because you have got to have high speed in a journal before it can support high loads.

In review:

1. It is the viscosity of the oil that enables a journal and bearing to develop it's hydrodynamic oil pressure.
2. Bearings must be loose enough to allow oil to be fed into and create a hydrodynamic wedge.
3. Bearing clearances must be tight enough to keep the oil in the pressure wedge from leaking out the sides of the bearing.
4. The pressure developed in the bearing during hydrodynamic lubrication is not related to the engines oil pump pressure.
5. Avoid subjecting an engine to high loads at low RPM's.


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## Jetzster (Jan 18, 2020)

Great explanation PJ,
the bearing part reminds me of once When I took in a 6 cyl for a old F100 to a rebuildShop,after a week, I picked it up it seemed ok till about 20 min down the freeway, when I started losing oil pressure, it would go back up if I revved it, but would fall off once I didn’t.
After a tow to my house I pulled the pan and Plasti-gaged the bearings only to find two or three didn’t even Crush the thread.I could see a flash lite shine thoughinside the rod cap.
Turned out the shop had sent out the crank and had some ,but not all, of the journals turned the same, and had put the correctly adjusted and numbered bearings in the return box.The shop owner had then decided to let his teenage Son get experienced by putting my 6 back together,apparently with little supervision.
He put the bearings back in randomly,
all Mixed up on the crank.I guess it worked somehow , till the oil got hot enough to
Blow pass the looser bearings, and started dropping the pressure.
Needless to say the great shop owner came, towed it back and had to redo everything all over again, Lots of fun on that one, should’ve checked the tolerances but it was just a kid...this was only the beginning
Of the story, it keeps going..


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## Ghostmachine (Mar 25, 2020)

AZTempest said:


> In Phoenix were it's 115F summertime temps and doesn't drop below 90F at night I run 20-50 Valvoline racing in my 389 and 326. Used it for years in my 01 Sport Trac and sold it with 320000 miles on it. Great oil for the heat.


Thankyou for the information.....


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## tgorby (May 27, 2019)

HiVolts said:


> AMSOIL ZROD 20W-50 here, with by pass filter. Butler 461, on original 400 block. Motor likes it and burns less of it here in hot and humid SC..
> 
> 
> View attachment 134452


I would like more information on that oil bypass system. When you get a chance please email me at [email protected] and I'll let you know what my questions are. Thanks!


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## histoy (May 22, 2019)

I'm using Valvoline VR1 racing oil. It has high zinc & phos. Last year when I bought the car it had 20W50 in the engine, but this year I switched to 10W30. I just use the car for cruising around town and I don't drive it hard. I feel that it came from the factory with 10W30, so that weight should work fine with my driving habits here in Iowa.


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## pontrc (Mar 18, 2020)

You’re right unless you have a race engine 10 30 or 40 with zinc or zinc additive should be fine


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## jsgoatman (Mar 5, 2013)

I also use Valvoline VR1 racing oil, 10W30 in my matching numbers 67. The extra zinc is great! I used to use Shell Rotella with an additive.


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## Ghostmachine (Mar 25, 2020)

jsgoatman said:


> I also use Valvoline VR1 racing oil, 10W30 in my matching numbers 67. The extra zinc is great! I used to use Shell Rotella with an additive.


Thanks


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## Ghostmachine (Mar 25, 2020)

jsgoatman said:


> I also use Valvoline VR1 racing oil, 10W30 in my matching numbers 67. The extra zinc is great! I used to use Shell Rotella with an additive.


Thanks


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## PontiacJim (Dec 29, 2012)

PontiacJim said:


> Viscosity of an oil is determined by measuring how long it takes in seconds for 60 cubic centimeters of oil to flow through a small section of tubing. The standard tube is called the Saybolt Universal Viscosometer. The temperature of the oil and the length of the diameter of the tubing are carefully chosen in order to make the test standard.
> 
> Tests are run on oil samples at 100, 130, and 210 degrees Fahrenheit. As an example, if an oil has a viscosity which makes it SAE 10 oil when it is cold, chemicals can be added to the point that when the oil is hot it has the viscosity of SAE 30 oil. This blend could be called either SAE 10 or SAE 30, but this does not describe the oil enough. So the oil is called 10W30 where the 10W refers to the viscosity of the oil when cold at 0 degrees Fahrenheit and the 30 refers to the viscosity of the oil when hot at 210 degrees Fahrenheit.
> 
> ...


Adding to this post/my reply. I found another oil weight recommendation that may be of help to some. This is based on main bearing clearances for the Pontiac 400/ 3.00" mains engine.

20W-50 for bearing clearances .003"
15W-40 for bearing clearances .002" - .003"
10W-30 or 30 for bearing clearances up to .002"

Of note, with the larger bearing clearances, you want hot idle speeds to be up so as to maintain good oil pressure. This may be 850 RPM or more. If idle engine oil pressures are in the 10-12 pounds at idle, it is too low. 

For rod bearing clearances:
.002" - .0025" for an engine kept to 5,500 RPM's or less.
.0025" - .003" for an engine spinning 5,500 RPM's or more. 

I have also read that a high-performance engine requires .001" - .0015" of bearing clearnace for each inch of journal diameter. Pontiac specified .002" of rod bearing clearance and .0025" of main journal clearance - so this can be a good starting point. Again, each engine build is different as is the engine builder. Things like engine operating RPM's, cylinder pressures, expected load applied to the rotating assembly, outside temperature range, oil pressure, and oil viscosity all can be used to determine bearing clearances - and conversely, bearing clearances can determine oil viscosity.

Just more info to confuse everyone.


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## BearGFR (Aug 25, 2008)

Also, it's important to understand and remember that the test used to determine the "W" (cold) viscosity rating for an oil _IS A DIFFERENT TEST_ than the one that's used to determine the 'hot' viscosity rating.

Described in various places, such as in this excerpt:

_"Kinematic viscosity is a fluid’s resistance to flow and shear due to gravity. If a given lubricant’s viscosity is lower, it will flow faster. For example, if you pour two containers, one filled with water, and the other with syrup, you would notice that the water flows faster due to its lower viscosity. *Additionally, an oil’s high-temperature viscosity grade is determined by its kinematic viscosity. This is where the “30” in 5W-30 synthetic oil comes from.*

Alternatively, there is dynamic viscosity, which is essentially the amount of energy required to move an object through the lubricant. *Dynamic viscosity is measured using the Cold Crank Simulator test, and is used to determine an oil’s low-temperature viscosity grade. This would be the “5W” in Amsoil XL 5W-30 Synthetic Motor Oil."*_

From this link: Oil Viscosity Ratings explained
Also here: Understand Oil Viscosity ratings


ALL oil get's 'thinner' as it gets warmer. *There's no such thing as an oil whose kinematic viscosity increases as it gets warmer.*

Bear


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## Baaad65 (Aug 29, 2019)

Rlamarche1 said:


> I live in the panhandle of Florida and use Shell Rotella 15W-40 in my 64 389.


Me 2 👍


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