A few comments which may or may not help your confusion:

• Oil is a viscous liquid; the more it is refined, the more pure it gets and the "thinner" it gets.
• The same oil at any given level of refinement also gets "thinner" the warmer it gets. Think about wax, at room temperature it is a solid, however, as it warms it becomes quite runny.
• Conventional motor oil has a huge number of petroleum byproducts still in suspension (some of which might even be considered wax), even fresh out of the bottle, and it is those "impurities" which cause the oil to thicken when cold and thin when warm.
• There are two ways to make an oil which doesn't thin as much as any other oil of a similar "cold" viscosity, 1) imbue the oil with additives called Viscosity Improvers, or 2) start with a more pure base stock (think synthetic oil).

As for your oil pressure gauge, it sounds like you're kind of confusing pressure with flow. Think of a jar of molasses; put it in the refrigerator for a while and it can become so thick pouring it out would take hours. If you were trying to pump that same cold molasses through a small hole the pressure required would be quite high just to move a small amount through said hole. Now warm that same molasses up to say 150°F, it becomes so fluid you could literally pour the entire jar out in a few seconds; if you were to pump it out through our same small hole, even a modest amount of pressure would easily evacuate the entire jar in a very short period of time.

The above is exactly the same dynamic in your car engine. If you were to fill your crankcase with say a straight 5 weight oil, it would start as the same weight as a 5W-30, but it would thin out so much once it got warm as to be useless at protecting your engine from harm. If you were to instead fill your crankcase with a straight 30 weight oil, starting, especially in cold weather (think your TransAm) would be quite difficult, however, once the oil warmed up, it would be perfect until you shut the engine off and it cooled down again.

One more thing; when you said "the higher the number the thicker the oil", you forgot one key element, "at any given temperature". So, "at any given temperature", a straight 5 weight oil will be much thinner than a straight 30 weight oil, however, if you compare a cold straight 5 weight to a sample of straight 30 weight when at operating temperature, the 30 weight will be much-MUCH thinner.

 

Motor oil gets less viscous as it heats up.

What is confusing you about motor oil (0W-0 in this example) is that the viscosity of 0W on the left side does not equal the viscosity of 0 on the right.

For 0W-20 motor oil:

0W part: The motor oil has the same viscosity as 0 straight oil at low temperatures (-35 and -40 C for the 0 grade).

20 part: The motor oil has the same viscosity as 20 straight oil at 100 C.

 

Ok so your saying the first number and the second number are based off of different scales? That would help explain some confusion and probably cause more. Also, can you please talk in ferenhieght for me. Thanks.

 

Ok clearly there's something major I'm missing. About the oil pressure gauge thing, I've seen tons of oil pressure gauges tons of times and they are always high when you start on a cold engine so I totally understand the difference between pressure and flow and I totally get your example, which begs the question, why with 5w30 is it thicker on a cold start if it's supposed to be 5 weight and then it's supposed to get thicker and become 30w, but the oil pressure drops when it gets thicker? Are the two numbers based off of different scales or something? I'm starting to think that?

 

I think I get it. Thanks guys! Oh well, I spent like the last six hours researching oil online and learned a bunch of things. I'll just stick with 5w30. I think I just need better oil or synthetic. ...or yeah that valve adjustment. I'm glad I figured this out by just after 1am so I can get some sleep cause I'm sure I would've stayed up all night thinking about this.

 

One scale, a cold straight 5 weight will always be thicker than a hot straight 30 weight.

 

Suggest, put the different oil in your car and see if it helps.
The world learns from experience; that's the way we advance.
and is an affordable test for you.

 

Shipo, JimBlake and PAHonda are giving you the straight info. All these oil scales are relative.





Viscosity of a petroleum oil drops dramatically as temperature increases so the relationship
of 'weight/grade', temperature and viscosity is not steady. ... very much a sliding scale.
All should agree: a 5 or 10 weight oil at 32F will have much higher viscosity (more resistance to flow) than a 30 weight oil at 212F.



10W - 30 oil viscosity. Standard ratings detail, my understanding.
W behind the 1st number says the measurement is performed at the freezing point of water (32F)

10W - says the (COLD) viscosity is no higher (no more thick, no more resistant to flow) than standard 10 weight oil.
This specifies a maximum relative cold viscosity measured at 32F.

Second number - 30 says the measurement is performed at the boiling point of water (212F).
- 30 says the (HOT) viscosity is no lower than that of standard 30 weight oil at 212F.
This specifies a minimum relative hot viscosity measured at 212F.


Odd-ball. If there is a W after the second number that means the oil does not have a minimum hot viscosity spec at all,
and the oil is a special winter only oil. One company (Pennzoil?) used to sell a 20-20W.

 

The W number is determined from a different test /viscosity than the second number. The second number is at 212F.

Uhoh is not right on the W number. It is not at 32F. Google SAE J300 and look at a chart.

-40 C = -40 F. 100C = 212F.

 

I completely understand guys. My problem was up until now I always assumed that a straight weight oil always had the same static thickness hot or cold, even though I have never owned a car that took a straight weight oil or worked on a car that took straight weight oil or probably never even picked up a container containing straight weight oil. I get it now and totally learned something. I'm sure you guys can understand why things did not add up for me. Thanks for taking the time to explain