Does synthetic oil for cars get thicker as it warms up?

Some very curious answers here. All oils get "thinner" and less resistant to flow as the temperature increases, multi viscosity oil or not.

Synthetic oils flow easier when cold ( but are still many times "thicker" than hot ) and have a higher "flash" point, that is the temperature at which they begin to cook off and cause sludge. In terms of viscosity, take a look at any oil's data sheet. The data sheet will list kinematic viscosity hot at 100 C and cold at 40 degrees C.

For example 0W-20 Mobil 1 synthetic has kinematic viscosity hot at 8.7 and cold 44.8 compare that to conventional oil Valvoline 5W-20, which is 8.5 hot and 50 cold.

Note the similar viscosity hot, they have to be similar otherwise they would not be rated 20 weight oils.

Just for fun, a straight grade 30 weight oil will have a kinematic viscosity of about 12 when hot but a whopping 90-120 when cold. Now you can see the reason for multi grade oils. They flow and protect the engine after a cold start.

The differences are, the synthetic has a higher flash point, lower pour point, resistance to being broken down.

Some of the answers on here are moronic. You've got people that don't understand or know anything about motor oil trying to answer this question with garbage information because they themselves don't actually know anything. First off, motor oil comes in GRADES, not weights. The word 'weight' should be totally forgotten when referring to oil all together. It has no place in a conversation about oil. The numbers in the oil title like 5w30 can be looked at like this- What you need to understand is any oil that ends in 30 is a 30 grade oil when hot. This hot grade is measured at 212 degrees and that is how the grade of the oil is determined. Any 30 grade oil whether it is a 0w30, 5w30, 10w30 or straight grade 30 is ALL a 30 grade oil when HOT. The first number in the oil title is NOT an oil grade. It is a number that tells you how thick the oil gets when it has cooled. It is NOT a viscosity or grade. The HIGHER this first number the thicker the oil gets when it's cold. SO, a 10w30 will get thicker when cold versus a 0w30. A 5w30 should be thinner than a 10w30 when cold but a smidge thicker than a 0w30 when cold. But, these first numbers really only come into play in very cold temps like below zero. All oil when cool is MUCH thicker than when it's warm or hot. The VISCOSITY of the oil is told in the second number in the title of the oil. This is the grade. A 5w20 will be a little thinner than a 5w30 at 212 degrees. A 5w40 will be a bit thicker in viscosity than a 5w30 at 212 degrees. Depending on your climate you can choose from a few different grades of oil. Usually your car oil fill cap will tell you which oil to run. For those who live in extremely cold climates, a 0w oil is a good way to go. 0w oils can be used in any climate but are great for cars that must start in very cold weather. Remember, a 0w30 is the same grade when hot as a 10w30. It's just the 0w doesn't get quite as thick when it cools or it's very cold out. So if your vehicle requires 5w20 and you live in MN, a 0w20 might be a good idea.

No oil gets thicker when it gets hot. It gets thinner. Multi viscosity oils are designed to not get as thick when cold, to help prevent lack of lubrication on start- up. For example, 10w30 oil has a viscosity of what straight 10w would have when cold, and what 30w would when hot. This does not mean it gets thicker, but rather that it is more resistant to change, or more stable. When you drain oil out of a warm motor, it is thinner than when you drain it out of a cold motor.

good grief oil is given two viscosity numbers. one for hot other for cold.

the first number is for hot hence an oil claiming 5W40 as an example is thicker when cold at 40 ( this being time taken to flow ) than same oil when hot now flowing at just 5.

ALL Oils get thicker when chilled. ALL fluids thin or have faster flow rate when hotter . eg lava is molten rock, when cooler but still in lava state will flow slowly . when hotter ( and brighter) will flow very much quicker.

common result of physics. look at tar experiment in museums.

Then you need to find some better car guys. All motor oil increases in viscosity when it gets hotter. That's what it's suppose to do.

Hornchurchmale is a complete phony. 30 seconds of research will tell you how oil viscosity changes with temperature. And, anybody who knows anything at all about engines knows that the oil needs to be thinner when cold and thicker when hot.

1. The viscosity of multi-weight oil does get more resistant to flow as it gets hotter. It doesn't matter if the oil is conventional type of full synthetic. Why else would it be rated as 0W-20, 5W-20 or 5W-30?

#2. Advise your non-mechanic buddies to read what "polymers" do in multi-viscosity motor oil. Also read how an oil viscometer (flow tester) works.

no

Multi viscosity oil,is designed to ACT like thicker oil as it warms up in lubricating abilities

it does not actually get thicker

There are 2 types of motor oil: "straight-weight" and "multi-viscosity".

Straight-weight oils have a single number, like "SAE 30" or "SAE 40" on the bottle. These oils do NOT get thicker or more viscous as they warm up. In fact, in warmer climates these oils become THINNER when warm.

Multi-viscosity oils have 2 numbers, like "10W-30" or "20W-50" on the bottle. These oils DO "thicken" (become more viscous) as they heat up.

it,s not true ! any mechanic will tell you that oil gets thinner as the engine gets hot ! that guy that said that don,t know what he,s talking about ! there is no oil that gets thick when the engine gets hot !

That guy needs to put down the crack pipe.