5w20 in a 5w30 specd car

[CATERHAM]

We don't have enough info' to give you a definitive answer.
You don't have oil gauges and we don't even know how you drive the car.
That said PYB 5W-20 is a quality product that should provide a sufficient minimum viscosity when the oil is fully hot and the car is driven normally; i.e., you're not driving around all the time with WOT on 100+F days.
If you are at all concerned, save it for the winter months when you simply will not be seeing the same maximum oil temp's.

 

[GMorg]

Well, actually, I posted in response to a different thread. I've never made that mistake before. In any case, I am not saying that anyone should discount any data including HTHSV. In response to the following thread, I was trying to get a new guy started.

https://bobistheoilguy.com/forums/threads/motor-oil-university-confused-me.198328/

 

[Durango]

Originally Posted By: ram_man
So I know 5w30 shears quickly anyway so is it ok to run 5w20 in a 5w30 specd car? I have 5w20 pyb I bought 5 qaurt jugs for 5 bucks a piece.


ram_man,

In my current 01' Durango a fellow from another forum ill advised me to try just what you described from fear of internal bearing damage. I wanted to try/do this in order to increase my MPG due to the gas prices here in California.

By the other spectrum. My old 89' Camry indicated I could use a wide range of oil weights based on the temperature in the area.

I would consult your cars manual and see if you can do this.

Durango

 

[Zako2]

Originally Posted By: 147_Grain
He's basically trying to keep things simple for you and other infrequent visitors until a basic foundation about oils is established.

A 5W-20 oil in the colder winter temps CAN have a similar viscosity as a 5W-30 in the summer.

Oil temperature is the key to viscosity and HT/HS. Driving habits and type of application also make a difference, but the underlying principles are the same.



New cars with modern cooling systems have no problems keeping the water, and probably oil, at the same temperature year round. I keep my eye on the water temperature gauges. In older cars they fluctuate with season. On many new cars they point at the same temp year round.

 

[Zako2]

Originally Posted By: mva

Not long ago typical 5W30 oils sheared down to 5W20 anyway. It is only recent SM and SN formulations that don't seem to shear as much.


One minor flaw in this logic is that the 5W20 also does shear out of grade, specially the conventional variety. In fact, some synthetics do too. By the time you exchange oil, your sheared 5W20 is likely a lot thinner than a sheared 5W30. It probably depends on the engine. If you want to sleep well but still use a 5W20, then switch to a high quality synthetic oil, and take a UOA.

 

[Giorgiz]

Originally Posted By: RamFan
Originally Posted By: Giorgiz
Originally Posted By: GMorg

After you have mastered the kinematic viscosity (KV) issues, the story will change to high temperature high shear viscosity (HTHSV). It is measured at temps above normal engine coolant temps, but it better reflects conditions at lubricated surfaces - bearings, rings, etc. Until the KV story is second nature, I recommend that put the HTHSV on the back burner. However, if you stay here a few months, you will master the HTHSV issues too.


what do you mean when you say that you can overlook hthsv? For example, the Mercedes recommends an oil that is not below 3.5 hthsv, you mean that I can put an oil with 3.0 hthsv and not causing any damage?


Absolutely not. He's saying not to worry about the complexities of oil selection, like HTHSV, for the time being. The number one rule to oil selection is following the manual. Manufacturers spend millions of dollars figuring out which oil should be used and what characteristics an oil should have. In your situation, you should find an oil that meets the minimum requirements set by Mercedes. Once you are more knowledgeable on the subject you can start experimenting with which oils that meet the specifications best suit your wants.


manual prescribes a 20W60 viscosity 0w30 depending on the outside temperature, but always with HTHS not less than 3.5. I have seen that many use lighter oils even in European cars with great satisfaction, that's why I wanted to try 0w30 or 5w30 oil with HTHS around 3.0

 

[Hokiefyd]

Originally Posted By: Zako2
One minor flaw in this logic is that the 5W20 also does shear out of grade, specially the conventional variety.


The acceptable viscosity range for a 20 grade at 100 dec C is 5.60 to 9.29 cSt. Have you seen a UOA for any 20 grade oil that shows a Kv100 of less than 5.6 cSt? I have not. As long as it's at 5.6 cSt or above at 100 deg C, it's still in grade.

From what I've seen, the 5W-20 oils have always stayed in grade pretty well. There may be one or two where a long run has beat them up, but as a group, they all seem pretty good.

 

[CATERHAM]

Originally Posted By: Hokiefyd
Originally Posted By: Zako2
One minor flaw in this logic is that the 5W20 also does shear out of grade, specially the conventional variety.


The acceptable viscosity range for a 20 grade at 100 dec C is 5.60 to 9.29 cSt. Have you seen a UOA for any 20 grade oil that shows a Kv100 of less than 5.6 cSt? I have not. As long as it's at 5.6 cSt or above at 100 deg C, it's still in grade.

From what I've seen, the 5W-20 oils have always stayed in grade pretty well. There may be one or two where a long run has beat them up, but as a group, they all seem pretty good.

That is true in terms of kinematic viscosity and of course the 5W-20 grade is more shear stable than the typical 5W-30.
But since most 20wt oils have the minimum HTHSV of 2.6cP for the grade it doesn't take much actual shear to no longer technically be "in grade".

It should also be noted that the minimum KV100 spec' for the 20wt grade is being raised to 6.9cSt with the introduction of the SAE 16 grade.
Even for the 16 grade the minimum KV100 spec' will be higher at 6.1cSt than the current 5.6cSt for the 20wt.