Best oil for My Slant 6

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Mopar Pearl

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Hey All,
Need suggestions for the best oil for my 1966 Plymouth, Valiant 200. Slant 6.
I had all the specs written down in a note book but some how I have lost it.
Any help would be appreciated.
Thank you,
Mopar Pearl
 
Rug_Trucker said:
15-40 Valvoline diesel was what I was running in my 198. High detergent, plenty-0-zinc.
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Diesel oil is not really a good oil for gasoline engines. Additive package is not correct. A stock slant six engine in "normally" serviceable condition, needs noting other than a reasonable quality 10w-30 conventional oil.
 
Charrlie_S said:
Diesel oil is not really a good oil for gasoline engines. Additive package is not correct. A stock slant six engine in "normally" serviceable condition, needs noting other than a reasonable quality 10w-30 conventional oil.
Click to expand...

My Buicks............@89K my 2005 3.8 Lesabre started getting 10-30 semi synthetic Rotella presently has 264K.

My 1997 3.8 Lesabre had 150K when I bought it. Went to 10-30 Rotella. 256K on it will get many more when I get a new transmission.

Neither use oil beyond factor norm. The '97 leaks more than it burns which ain't much.

My 93 Corolla started it's diet of 10-30 Rotella @142K it made it to 264K and it T-boned a Chevy Astro van. We will never know how man miles it could go..............:rolleyes:
 
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Rug_Trucker said:
My Buicks............@89K my 2005 3.8 Lesabre started getting 10-30 semi synthetic Rotella presently has 259K.

My 1997 3.8 Lesabre had 150K when I bought it. Went to 10-30 Rotella. 256K on it will get many more when I get a new transmission.

Neither use oil beyond factor norm. The '97 leaks more than it burns which ain't much.

My 93 Corolla started it's diet of 10-30 Rotella @142K it made it to 264K and it T-boned a Chevy Astro van. We will never know how man miles it could go..............:rolleyes:
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Hey, use whatever you want. Hell I used Quaker State for umpteen years back in the '70's and'80's. Everyone said it was garbage and would sludge up my engine. But Quaker State sponsored my stock eliminator car. Never had a problem. But time and technology change, and I am not an expert, but Lake Speed is, so I will defer to him.
PS: I had a boss at one time. Whenever he tried to get someone to change the way they were doing something, and they said "that's the way we have always done it". He would reply "So you've been doing it wrong for X number of years, don't you think it is time to do it right"?
 
Charrlie_S said:
Hey, use whatever you want. Hell I used Quaker State for umpteen years back in the '70's and'80's. Everyone said it was garbage and would sludge up my engine. But Quaker State sponsored my stock eliminator car. Never had a problem. But time and technology change, and I am not an expert, but Lake Speed is, so I will defer to him.
PS: I had a boss at one time. Whenever he tried to get someone to change the way they were doing something, and they said "that's the way we have always done it". He would reply "So you've been doing it wrong for X number of years, don't you think it is time to do it right"?
Click to expand...
:rofl:
 
Charrlie_S said:
Hey, use whatever you want. Hell I used Quaker State for umpteen years back in the '70's and'80's. Everyone said it was garbage and would sludge up my engine. But Quaker State sponsored my stock eliminator car. Never had a problem. But time and technology change, and I am not an expert, but Lake Speed is, so I will defer to him.
PS: I had a boss at one time. Whenever he tried to get someone to change the way they were doing something, and they said "that's the way we have always done it". He would reply "So you've been doing it wrong for X number of years, don't you think it is time to do it right"?
Click to expand...
He likes to add drama. Direct injected engines, you know the ones getting a shot from the cylinder wall is what he's talking about. At low speeds putting around town they need a special oil that has additives that resists oil dilution. I did my research on that stuff when I was buying oil from my ex-GF's 2.0 DI turbo Camaro.

We are talking about a carb'd slant 6 here.
 

Mopar Pearl said:
Need suggestions for the best oil for my 1966 Plymouth, Valiant 200. Slant 6.
Click to expand...

Read the links from this post, then put in five quarts of a reputable brand of 10W-30 oil and a good quality filter as specified here.

It will also be a good idea to service the oil pressure relief valve to make sure it's doing its job, as described in these two threads: thread 1, thread 2.
 
Rug_Trucker said:
He likes to add drama. Direct injected engines, you know the ones getting a shot from the cylinder wall is what he's talking about. At low speeds putting around town they need a special oil that has additives that resists oil dilution. I did my research on that stuff when I was buying oil from my ex-GF's 2.0 DI turbo Camaro.

We are talking about a carb'd slant 6 here.
Click to expand...

With all due respect, trust me, Charlie knows the slant 6. lol
 
We are talking about a minutia of wear here. I read the charts. Unbelievably small amounts of wear that aren't going to make a difference in an engine going the distance that is was designed to do.

For the Quaker State? There was gobs of goo in my oil pan with 24K on my 72 Duster. Gobs of that paraffin based Quaker State like the sticker on the inside of the door jam said. 2002 10/30 Valvoline couldn't dissolve that glop.
 
There is a reason that SAE certs gas and diesel oils differently. They basically cost the same, should use the correct oil for the application. My brother knows an oil chemist that worked for Chevron in the SF bay refinery. Not he has his own brand oil. I was talking to him last summer, as asked about running Delo 400 in gas engines. So it’s not recommend… not like you put gas engine oil in a diesel…
 
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Scody21 said:
There is a reason that SAE certs gas and diesel oils differently. They basically cost the same, should use the correct oil for the application. My brother knows an oil chemist that worked for Chevron in the SF bay refinery. Not he has his own brand oil. I was talking to him last summer, as asked about running Delo 400 in gas engines. So it’s not recommend…
Click to expand...
The dramatic pic of the detonated piston in the video was a direct injected engine. It's to draw your attention to the video in hopes of seeing destruction=more views. Yes it is a valid thing.

My actual use and abuse over 100K's of use in my Buicks. It's not been a problem. They are still alive and will be for a long-long time. They aren't direct injected and neither is the slant. No oil smoke, no clogged converters from too much ZDDP. Very clean inside the valve covers.
 
Penn grade(Brad Penn) has a good zinc oil for our mopars. Shaeffer oil is another good choice. VR-1 of course is also a great oil.
 
Check your owners Manuel for viscosity. It's based on the temp. in your area. Valvoline VR1. I have been using Lucas Hot Rod and Classic 10w40 in my Slant for about 10 years now, and it seems really good.
 
Here's the skinny we got about Quaker State oil at an oil conference when I worked at a local auto parts chain when I was a kid in the very early 80s. In fact, it MIGHT have been 1980. We had all kinda oil reps giving us their shpeels. Whether this has a drop of truth to it, I don't know, but this is what we were TOLD. They said there is a certain kind of bacteria that can set up in the refining process if it is processed incorrectly and that's what happened to *** number of barrels of Quaker State and a few other brands at that time. The bacteria causes the oil to sludge. At least that's the story we got. Who knows what's true or not?
 
If you wanna go further on down the rabbit hole, see here and here.

If you'd rather stay on the surface of the planet and avoid all that digging, well…the answer's not sexy and doesn't involve conspiracy theories or hunting down and paying for special brands of oil with special additives…it's easy and simple and inexpensive (good brand of 10W30, good filter).

Here's what the factory said in '66:

Screenshot 2025-04-28 at 14.43.05.jpg


And here's what they said in '73:

Screenshot 2025-04-28 at 14.44.13.jpg


Some aspects of these recommendations wound up being not so wise in the long run (10W40, for a lot of years, was considerably more sludge-prone than 10W30…10W50 even more so, and it's been absent from the mass market for many years). But look how the recommendations are more permissive than restrictive. They don't call for a higher viscosity oil for cars used in hotter climates, for example.
 
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