Why Different Oil Viscosities?

[J.P.G.]

Hello all,

 

I drive a 1946 Plymouth Deluxe, and absolutely love it. But admittedly, I've always pined for the Chrysler New Yorker of the same year. I intend to own one in addition eventually, so I read up on any information I can get about them. Having procured an original owners manual, I noticed something unexpected. The book calls for SAE 20 oil to be used in the crankcase on the eight cylinder models at normal temperature. My Plymouth calls for SAE 30.

 

So, why the difference? They're pretty comparable engines, or so I understand. Further, do any of you Chrysler owners use SAE 20?

 

Many thanks in advance, and all the best,

 

J.P.G.

[desoto1939]

might want to check the manual again.but the lower weight oil might be recommended for winter time and the 30 weight might be for summer driving.

 

Rich Hartung

[Dodgeb4ya]

I looked in the service book and intro of the 1946 Chrysler's..... yep 20W above 32 degree's ....

I use 30W  in my straight 8 cars.... always have.

[Dodgeb4ya]

Chrysler six cylinder engines state 20W too..

[captden29]

10w 30, detergent conventional.i have been around the dial using different oils. now i buy whatever is on sale. were the weights rated differently in 1946? maybe a 20w was thinner or thicker.    capt den

[BobDeSoto]

straight 30 - non detergent

 

[desoto1939]

back when our cars were produced most cars used straight weight conventional lubrication motor oil such as 20w and or 30w.  These would have been non-detergent type of oils.

 

As the engine technology progresses the engines then were made with better specs and then the multi-viscosity oils came into use such 10w/40 10w/30  The first number refered to the weight or thickness of the oil when the temperature was cold in winter so the oil is thnner in cold weather so the oil will flow when the engine is first stated in winter time. the 2nd number refers to the weight in summer time so the oil is thicker becsue of the heat so the oil can be thicker to stick to the  piston cylinders and stillhave coatingpropertires.  Also when the detergent oils came in to use then the use of full oil filters and the spin on style and also the canister filters became standard equipment on cars and truck.

 

If you have a car that has always been run on straight weight oil then stay with the straight weight oil because if you go with a multi viscosity oil it will start to clean the crankcase and dislodge the sediment in the oil pans and can cause issue.

This is my understanding of car motor oil  and now we have bended and full synthetic oil for our modern car/trucks

 

Rich Hartung

Desoto1939@aol.com

[sser2]

Upscale models had better engine tolerances from the factory than bottom of the line, hence lighter weight oil.

[thisoldtruck]

My thought is, if you have an engine that has a sludge problem, it's time to pull it out of the truck/car and take it apart and clean and check EVERYTHING!  Replace what's worn, which I'm sure there will be plenty that's worn.