Multi-grade Motor Oil

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Money Pit

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Does it matter if I use a multigrade oil or a single grade oil like 30W? I've only had my slant for about a year. It seems like after I changed the oil with 10W-40 I see small puddles of oil. It looks like it's coming from the rear main. I checked with the auto parts store, they said I would have to special order the single grade oil. I live in Calif so the cold weather isn't a problem. May be it's just time for a new rear main. Thanks
 
The oil isn't going to make it leak. You need a new seal.

Do people actually run straight weight oil anymore? If so, why?
 
roccodart440 said:
The oil isn't going to make it leak. You need a new seal.

Do people actually run straight weight oil anymore? If so, why?
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roccodart440 said:
The oil isn't going to make it leak. You need a new seal.

Do people actually run straight weight oil anymore? If so, why?
Click to expand...
I was watching the show Roadkill. They were saying some older cars need the heavier grade oil due to bearing clearances. I know a lot of small garden equip (4 stroke) require the heavier oil. Thanks
 
Money Pit said:
I was watching the show Roadkill. They were saying some older cars need the heavier grade oil due to bearing clearances. I know a lot of small garden equip (4 stroke) require the heavier oil. Thanks
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Then you run a heavier grade oil, not a straight weight.

"It is perfectly fine to use SAE 30 oil in place of the 10W30, as long as you never let the oil get below degrees 50C"
 
As mentioned above, the older engines were manufactured to much looser tolerances then modern engines. The multi viscosity oils like 10w40 means that the oil viscosity (thickness) is 10w when the engine is cold and thickens to 40 when at operating temperature. Obviously if the engine has been rebuilt, the tolerances are probably tighter then the original build was.
Oil Types, Weights & Viscosity FAQ - Valvoline®
 
roccodart440 said:
Then you run a heavier grade oil, not a straight weight.

"It is perfectly fine to use SAE 30 oil in place of the 10W30, as long as you never let the oil get below degrees 50C"
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I live in so cal. We complain when it gets into the 60s.
 
Doesent actually get thicker,it remains as thick as 40w at operating temp. The explanation was close, it doesent get any thicker than 10w in the cold and doesent get any thinner than 40w when its hot.
The styrene molecules in the oil expand as oil heats up.
Try a farm supply for single grade oil. Or order in a case.
Not all motor oils are the same. The most expensive isnt always the answer either.
I had a car that quit using oil when i switched to mopar oil. Just sayin...
 
Tooljunkie said:
Doesent actually get thicker,it remains as thick as 40w at operating temp. The explanation was close, it doesent get any thicker than 10w in the cold and doesent get any thinner than 40w when its hot.
The styrene molecules in the oil expand as oil heats up.
Try a farm supply for single grade oil. Or order in a case.
Not all motor oils are the same. The most expensive isnt always the answer either.
I had a car that quit using oil when i switched to mopar oil. Just sayin...
Click to expand...

10w 40 for example, flows like 10 weight when cold, but supposed to protect like 40 weight when hot. No thickening , if anything it will get thinner when hot. Still supposed to protect like 40 weight tho.
 
famous bob said:
10w 40 for example, flows like 10 weight when cold, but supposed to protect like 40 weight when hot. No thickening , if anything it will get thinner when hot. Still supposed to protect like 40 weight tho.
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All great info. Thanks
 
More important is to look for an oil w/ high zinc to protect your flat solid lifters from wear. You can find that in either "high mileage" oils or "diesel" oils (CJ rating, Rotella, etc). Many classic owners use diesel oil since it is higher quality. The main difference is more detergents to suspend the higher carbon one gets in a diesel (from blow-by).

Re your oil leak, you can change the rear seal from below, w/ engine in the car. But, not a job for someone w/ little experience and few tools. You need to loosen the motor mounts and jack the engine up 1-2" to get clearance to slide the oil pan past the K-frame. You also need a Pitman arm puller to unbolt the steering cross-link from the gearbox to drop it down. The seal is in an aluminum bracket which bolts to the block. Same PN for 426 Hemi engines.
 
Used to be some of the single weight oils didn't have the additive package, detergents, etc.

I used to run Rotella diesel but apparently they dropped the zinc content a few years ago. A slant six cam and springs aren't very aggressive but I'm not taking any chances on wiping out my 225. I now use Lucas Hot Rod oil, 10w-30 in my old junks. High zinc content and it's about $36 at the local Summit store.
You should be ok with 10w-30 or 40 in CA.
 
Money Pit said:
All great info. Thanks
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The "high mileage" oils also have a seal conditioner that can slow or even stop leaks from old seals that hardened up.
That is what I would try first if I had to put off the seal replacement.
(Castrol 20/50 high mileage) is what I would use in it if I were in that position.
 
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