Ohh shit another motor oil thread...

[AdrenalineS14]

Ok ok ok sorry guys but bare with me on this, so ive been told that i should run 15w 50 or 20w 50 motor oil on a built sr20det mind you i live in dry hot heat Arizona and its starting to get HOT! I'm currently using mobil 1 10w 30 which i guess is okay but just wanted to know the pro's on why i should run thicker oil, im seeing and hearing that with thinner weight oils when up to temp tend to "water down" causing more risk of spinning bearings idk? So i need help on this matter, im anal about car maintenance, and im always looking out for the best for my car and wanna do what i can to help it last as long as I can, so lets here some facts and logical explanations on why i should switch over or hell maybe 10w 30 "IS" okay idk. I do daily my car and tend to change my oil more frequent than normal too.

[4x4le]

First number is how thick it is cold, 2nd number is how thick it is hot (cant remember the cold and hot test temperatures).

Supposedly anything over 0 is usually thicker than you need for startup in most cases and 30-40-50 for the 2nd is the choice you need to make for oil temp, bearing clearance and oil pressure.

Often higher 2nd numbers are associated with higher first numbers because its cheaper to produce because of the thicker base used, less additaves are needed to keep it thick hot.

There is a website called bobtheoilguy or something like that with lots more information than this but thats what i got from it.
I tend to stick with 5-40 5-50 and 0-50 and track my car in tennessee weather.

[KiLLeR2001]

I'm in Florida. I use 10w-40.

[Croustibat]

How to chose your oil 101:

0.5/ dont listen to anyone telling you to use xxWxx grade because they do use that. You dont have the same engine, mods, condition, use and may not live with the same weather.

1/ get the manufacturer requirements regarding oil pressure and temps (for nissans, that is in their workshop manual). There are usually 3 requirements:

hot minimum pressure at idle;
hot minimum pressure at 3000rpm;
hot maximum pressure at 3000rpm.

2/ use different oils from a reliable source ( forget unbranded oils as their composition changes depending on the supplier) until you reach these requirements;

3/ ???

4/ profit.

As you can see, oil grade depends on "hot" definition. This in turns depends on the weather and what you do with your car, but it basically is the temp the engine reaches when being used. On a track car it can be 110-120°C. On a regular car it is more like 90-100°. If your oil does not reach 90°C then you have a problem, because it should and your engine is designed for that.

the step 1 assumes your oil pump is working well, and your engine is in ok conditions.

reasons why you need some oil pressure, but still are better with the lowest pressure:

1/the more pressure, the less flow. Less flow means less cooling, and believe it or not, the engine oil is used way more than the "water cooling system" to cool critical areas. Because oil can reache a much higher temp. Using a thicker oil does just that : more pressure, at the expense of flow.

2/ you still need a bit of pressure for all of these main ends, big ends, cams and turbo bearings.


The biggest problem people are facing when chosing their oil is that their oil pump is old, and does already not provide enough flow / pressure, which can easily been controled when reading idle pressure. Any new oil should be able to maintain enough pressure at idle... if it does not, then its oil pump change time, and not "thicker oil time" (because you then get even less flow, signing your engines death )


I know that because i asked myself that question some times ago, when i had to use 10w60 to get the pressure requirements right, and that oil did cost a lot, while lasting not long at all. Just a fast hill climb would make my oil temp to skyrocket to 120°, and i needed some cooldown driving to let that heat go away, standing still was not enough.

So i ended up changing the pumps and making a global overhaul of the engine. The water pump was like new, i just changed it because i did not trust the bearing (that and it was cheap and easy to do it now the engine was out). The oil pump was worn. Headgasket was changed too.

Now i use 10w50 and can track my car not even forcing electric fans on when it is 40°C. Oil temp reaches 110°C max, but that is at the worse time of the day, it was around 100° most of the time. And the car got a 40HP increase at the same time (bigger turbocharger, free exhaust and so on).

I also just change oil once in a while, when pressure readings go lower than it should, or temps rise abnormally (which is how you know your oil needs a change).

Now i am also inclined in using only 100% synthetic (blended is just mineral with maybe 5% syntethic oil in it, dont be fooled), because it just is better and lasts longer. But to each their own.

[4x4le]

I think one thing you brought up is the true key: The oil pressure/temperature relation ship.
You will come to know what to expect from your car and when it detours from that the oil is loosing its intended characteristics.

You are also correct about higher pressure caused by thicker oil will = less flow. Basic fluid dynamics. A very true statement. Dont however get confused that higher pressures always equal less total flow of oil. At given set engine speeds when comparing oils (which is what this thread is about so the context is absolutely correct) the higher the pressure, the less that oil is flowing given the oil is at the same temperature.

With that said, there are other things to consider in built motors when deciding on oil as well. Im not disagreeing with anything, just adding some further insight.
When bearing clearances are loosened up intentionally a thicker oil may be needed in order to create enough pressure. The looser clearances will however allow for more flow vs std. clearances.
Also, doing things such as blocking off oil squirters will increase pressure and flow and at a lower oil temperature due to less heat transfering from your pistons to the oil, this is at the cost of your pistons running at a higher temperature. Not necessarly a bad thing, some fuels do a good enough job cooling the pistons and have a high enough flash point the oil squirters are redundant anyways.
So deciding on an oil, take into account what is done to the engine and how hard your driving it.
Also keep in mind that with multi viscosity oils that the further apart the 2 numbers are, the more additives there are to break down which CAN render is bad or needing changed sooner. The benefit to it is its typically better for your engine on cold starts
and the higher number (of your choice after your testing) is suited for your engine at the temperatures and speeds you operate your engine at.

With higher first numbers which are almost always higher than needed, your giving up a certain amount of protection at startup in favor of potentially longer oil live (provided the oil brand and quality have charastics of lasting long).

With that said
Rotella 5w40 is good oil, lasts long and is cheap enough to change frequently making it a favorite of many (including myself)
Mobil 1 makes many different multi viscosity oils. Just watch your temps and pressures. In my daily driver which I NEVER drive hard I get around 8k mile oil changes using mobil 5w30 but it is a low milage engine. Oil analysis are nice! Oil still looks almost new, almost a transparent brown barely darkend. The car is turbod from the factory too. (not a nissan)

Oils like eneos offer a 0w50. You will need to cough up some money for it, probably have to order it, may not need the 50 on the top end, but if you do need it may be well worth it because of its superior thinness at startup. Very good oil and should last well. I would not run an oil this expensive without doing analysis as well to find out when its good and when its bad for sure. Similar brands of high end oils like redline and amsoil

I would stay away from royal purple. Just search about the hype and horror stories.

[Kingtal0n]

The most important thing that was mentioned and often overlooked is that the increase in pressure results in a loss of flow. Use the thinnest oil you can get away with while, as was mentioned, "maintaining the manufacturer's recommended oil pressure".

Using too thick of an oil may cause serious problems, including oil pump failure, and engine bearing wear.



a pin prick of organic chemistry:
the fundamental properties of carbon chains involved with lubrication;
Generally, oil is composed of carbon chains, saturated with hydrogen. Just like gasoline, except the chains are (much) longer.

What I just described is straight oil. ("Conventional motor oil is made up of an inconsistent mixture of long and short chains of carbon and hydrogen atoms.")-BOBISTHEOILGUY
The oils on the shelves that change weight with heat, are not all straight chains of carbons- they may contain hydrophilic and hydrophobic regions, and additives, that assist with the structure of the carbon chains. As temperature increases, kinetic energy from that heat allows the carbon chains to change shape (generally straighten), since the energy of molecular motions tends to disrupt the temporary hydrogen/electrophilic bonding regions of those compounds... that alters the oil's weight and properties. Chemists then define the oil based on the properties while at a specific temperatures, as was already mentioned, the temperature is the key to an oil's characteristics at that time.


Some reading:
film strength... - Bob Is The Oil Guy

Exactly How Does Multi Viscosity Oil Work? - TractorByNet.com

[trickey1991]

Amsoil 5W40 RB20DET