I've always been a fan of using the recommended oil weight for an engine, but I know sometimes you can change the weight. I was wondering of some opinions on running 10w30 in my 97 2.2l because it sounds fine when it starts up cold but after it warms up it gets really noisy and clacky (no it's not a knock). Usually in my experience if its clacky it usually does it on a cold start and then goes away when the engine warms. The engine has like 270k and has 5w30 in it now. I guess I'm wondering will running 10w30 help or will it create to much oil pressure or some issue? Thanks.

 

Won't help a bit, 0W-30, 5W-30, and 10W-30 all have the same relative viscosity when warmed up to operating temperature.

 

Actually 10w30 is slightly thicker than 5w30 at operating temp because it thins out to 10 weight instead of 5 weight.

 

Sorry, that's nothing but an urban legend. If the oils thinned out to a different viscosity then they would have different grade numbers.

 

The first number (5w- or 10w-) is the weight when the oil is cold.

The last number is the weight when it's hot.

So those are all 30-weight oils when they are hot.

 

Ok you guys must be joking right? I don't claim to be a master mechanic or anything but most oil designed for most of our cars we drive is thicker when it's cold and thinner when it's hot. So using 5w30 as an example, the first number (5) is how thin it gets at what is to be considered as operating temp and (30) is how thick it gets when it's cold. That's why you should change your oil when its hot because it's thinner and you get more out and more dirt will come out with the oil. That's also why in my 79 Trans Am before I had the motor done I was running 20w50 cause it was clacking so loud when it warmed up cause I was running 10w30. So when you run 20w50 try starting it when it's 0 degrees outside and the starter will barely turn the motor because it's at 50w and not a good thing to do. Im just wondering is it ok to run slightly thicker oil in little engines like Honda 4 cyl?

 

Nope, you've got it backwards.

The xW number is the relative viscosity of a straight weight oil in that same weight when cold (also, but not always, the weight of the base stock). So if an oil is a 5W-XX, when cold (typically calculated at 40°C) it will have the same relative cold viscosity as a straight 5 weight oil.

The second number is the relative viscosity when the oil is warm (typically calculated at 100°C). Said another way, any xW-30 oil, regardless of whether it is 0W-30, 5W-30, 10W-30, or even 20W-30 (if such a grade ever existed), when warm, will have the same relative viscosity as a warm straight 30 weight oil.

Here is a very simplistic explanation: http://en.wikipedia.org/wiki/Motor_oil#Multi-grade

The reason why your TransAm could barely turn over at 0°F is because conventional 20 weight oil (which is the base stock for all 20W-50 oils) is too thick to flow very well at that temperature.

 

Ok so then your saying as the number goes up the oil gets thinner? What I mean is sounds like your saying with 5w30 you start it cold, it's at 5w, then it warms up and becomes 30w? So if I wanted some slightly thicker oil at operating temp I could run 5w20?

 

It sounds like you need a valve adjustment,,provided yours are adjustable

 

Ok I must admit I thought I understood oil but now im 100% confused. I did some googling and I now understand that the first number is the thickness of the oil at cold temp and the second number is the thickness at operating temp. I also know that the higher the number, the thicker the oil. So that's basically saying that the oil thickens as it warms. So this being the case, how is it possible for oil to start out thick and then thin out when it's hot which is what oil does? Also how is it possible for the oil pressure gauge to be higher (meaning thicker oil) on a cold start and then drop pressure when the engine warms? These facts totally conflict each other. Can someone please explain?