Why do some people use 10W-40 and 5W-50?

[TechnoLoGs]

What re some reasons 10W-40 is a "go to" oil for some, and 5W-50 is considered "better" if you arent against buying that $8 Castrol bottle when it can be found? *cough*cough* Advance *cough *Autozone

I had an older BMW I put Castrol 5W-50 in, also some 10W-40 or even 20W-50. Truthfully, they all did about the same. Was that overkill? (Inline-6, 2.7L) - HOT summer. 105 degrees! Driven all day.. consumed some oil..

 

[aquariuscsm]

I`ve tried different oils,and the 40-50 weights definitely feel better under wot acceleration and alot of hard/fast driving. Alot of VG30DE/TT builders recommend 15/20W50.

If WM would ever start carrying Syntec 5W50 I`d give it a try,but I`ll never pay $10 for a quart of oil.

 

[Maxima97]

10W40 20W50 oil are high HTHS oil. For towing and wot, it helps. But they are not energy conserve oil, for highway cruiser, it is not recommended weight. I am using 5W30 Maxlife for my VQ3.0 year around. I recently bought some 10W40 Maxlife at discount prices. I am figuring out mix it 50/50 with Valvoline Durablend 5W30.

 

[Kruse]

My brother has one truck that we use 10W-40 oil in. It's a '71 Ford F600 grain truck with a 390 that we use in places that we can't get the semi grain truck to. It has high mileage, the engine is loose, it runs at fairly high RPM, and we usually run it when temperatures are 100° or close to it during harvest. So it's a beater and we usually beat the thing.
THAT, and the fact I bought some Kendall GT 10W-40 on sale a few years ago and it's really a no-brainer.
I don't use 10W-40 in anything else.

 

[miniac007]

10W40 is THE European standard oil like 10W30 in USA.

So if you use european oil or read a manual from an european car, 10w40 is the in the mid-range oil between dino 15w40 and synth 0W/5W-XX.

In europe, 99% of the people ignore what HTHS is, but use 10W40 as standard as specified in car manual...

 

[Johnny2Bad]

I believe that if you are using conventional oil, you should avoid "extra" viscosity than what your motor needs or the OEM recommends, because they have a higher and more expensive additive package, and additive packages are depleted during engine operation.

In essence used oil over time reverts to it's base oil viscosity with time and mileage. A simpler oil (say, 10w30, 20W-40, etc) needs fewer viscosity improvers and costs less.

Considering the complex viscosity oil is slowly reverting to something more like 10w30 over time, you may as well save the money and buy the cheaper 10w30 in the first place.

With synthetics you can use "extra" viscosity as they rely much less on additive packages to achieve the label's viscosity rating.

Having said all that you should still choose viscosity based on the engine's requirements and local weather.

The European preference for higher warm viscosity is I believe related to the requirement in Europe to meet High Pressure High Temperature (HPHT) standards, which the API does not mandate, but does have an approved test for.

It's basically viscosity at roughly 100F higher operating temp than the API standard. In other words, your 40WT oil must meet 40WT standards in Europe while an API oil can be rated at 40WT but not meet 40WT at 300+F.

 

[andyd]

I run 20w50 in my 528es, It is the recommended viscosity. When it gets cold, I switch to 10w40 or just dump in a pint of MMO. Thin oil is for MPG, not protection.

 

[fdcg27]

Because some engines seem to need these oils, based upon original OM recommendations as well as UOA results.
For example, a 10W-40 is a daringly thin oil for my old 318i in summer weather, according to the temp/visc chart in the OM.
Now, fuel dilution as well as the long allowable OCIs for those who follow the BMW MM probably have something to do with the thick oil recommendation.
Fuel dilution of 2.9% alone brought the Nextgen Maxlife I had UOAed after a little over 4K down to a thirty, so starting with a thirty might result in too thin an oil over a typical OCI.
I've also run M1 15W-50 in this engine, and it seemed perfectly fine with it, even averaging over 30 mpg for the 6K I used this oil.

 

[KCJeep]

I favor "thick" 30 grades for my Jeep, so I find 10w40 quite useful. My next OCI will be 5qts of PYB 10w40 with a quart of PYB 5w20. This will yield a thick 30 grade with a much higher VI than most 10w30's.

I can do the same thing blending it 50/50 or a bit more with 5w30.

I remember in the 70's just about everybody ran 10w40 in most everything. That is no longer true, but most engines will still run just fine on it.

 

[aquariuscsm]

Originally Posted By: andyd
Thin oil is for MPG, not protection.


This. Thin oil is for fuel economy and thick oil is for protection. It's all a give and take.

 

[CATERHAM]

It is only suitable for older engines and even then probably still unnecessarily heavy unless the engine is well worn.

Of course the easiest way to determine whether you need to run anything heavier than a 30wt is with an oil pressure gauge.

Porsche for example no longer spec's has scraped all 10W-XX and heavier oils that it once specified before the advent of synthetic oils and now it's 0W/5W-40 for all models going back to the early '80's.

That said, there are still lots of old school guys that still think heavy low viscosity index oils provides more protection and they will take that notion to their graves.

 

[vinu_neuro]

Originally Posted By: CATERHAM
I
Porsche for example no longer spec's has scraped all 10W-XX and heavier oils that it once specified before the advent of synthetic oils and now it's 0W/5W-40 for all models going back to the early '80's.



Porsche still specs 50wt oils.

 

[crinkles]

My camry runs like a dog on NextGen 15w40.

Spark plugs are due though in 3000 miles. Maybe they are not happy.