Any downsides to thicker oil?

[il_signore97]

Originally Posted By: Jim Allen
Has anyone seen any oil pressure comparisons for oils of a similar kinetic viscosity but differing HTHS?



That would be a neat test, but probably hard to replicate exacting conditions for all of the runs.



Just out of curiosity, I looked up the oil pressure specs for my Altima in the service manual. It accepts 30 or 40 grade oils as per the manual, and lists the following blanket specs:

Hot engine, hot oil:

Idle: >14 psi
2000 RPM: 48 psi

The bypass valve opens between 70-75 psi, and with a minimum of 50 psi at 2,000 RPM, it's very hard to believe that my oil pump won't be in relief mode well before redline (which is 6700 rpm). Given this info, I should be bypassing by about 4,000-4,500 rpm on hot oil as per the recommended grade.

It seems to me that most commuter cars are designed this way. Perhaps the extra flow attained by using a thinner oil (thus increasing the RPM at which bypass occurs) is not necessary. I'm sure manufacturers would test to make sure flow rates under all operating conditions are adequate.


Talking about all this stuff makes me think of one of my buddies who lives 35 min north of me. In the winter time, it's not uncommon for it to be -30C or lower at his place. His cars sit outside all night. He does use 0W30 oil in all except for his Benz (5W40), but when he starts them up in the morning, his foot is planted and he's redlining them cold or hot. No concern for the engines. All of his vehicles have very high mileage on them and seem to run just fine. Obviously, oil flow is terrible at those super low temperatures, and the pump is probably bypassing at idle speed let alone driving. But still his engines live on. He has 450,000 km on his 2002 Grand Prix GTP, 360,000 km on his GM 4.3L V6 (Safari), 280,000 km on his 98 Mercedes S500, and 350,000 km on his 93 Taurus SHO. His long gone 3.5L Intrepid was on conventional 5W30 it's whole life and lived to see 600,000 km before he scraped it for the GTP. Yes he drives a lot.

We must be splitting hairs here with thin/thick oil discussions!

 

[21Rouge]

Originally Posted By: il_signore97
We must be splitting hairs here with thin/thick oil discussions!


I have no doubt this is true in very many cases. There are have been several UOAs that have come across this forum in which the oil seems like it might be too thick for the application but the wear #s show just fine or more than fine. Ah found one: This is an example of an almost 10 year old Prelude using an 0W40 HDEO:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1948378&page=1

Really how much better wear #s could be obtained using say an...xW20 in this engine?

 

[river_rat]

Originally Posted By: il_signore97
We must be splitting hairs here with thin/thick oil discussions!

Sure, but it makes good discussion.
Before the internet, I would have no idea that there was a guy who redlined his cold engines in winter with whatever oil, and get high mileage out of all of them.
Since BITOG I've learned engines usually aren't that sensitive to oil, and that pretty much any namebrand oil is pretty good nowadays. Good for peace of mind.

 

[CATERHAM]

Originally Posted By: Shannow

The biggest downside is the myth that you're providing more lubrication protection with a thicker oil.


A thicker oil will always have a thicker oil film under all operating conditions, and thus greater parts seperation between the bearing and journals.

Whether you need it or not is another matter


At operating temps there are few deletarious of running a thinker oil than required.
The problem is at start-up. With thick oil the risk of cavitation damage to the rings and bearings if an engined is rev'd too high is very real. It's not an uncommon problem with high end sports cars that spec' very heavy oil. I've witnessed complete engine failure at the track on a number of occations usually with some yahoo running heavy 50wt race oil on a cool day and reving the snot out of his stone cold engine.

 

[CATERHAM]

Originally Posted By: il_signore97

Has anyone seen any oil pressure comparisons for oils of a similar kinetic viscosity but differing HTHS?



That would be a neat test, but probably hard to replicate exacting conditions for all of the runs.



Actually it's very easy test to replicate but in addition to an accurate oil pressure gauge you need a oil temp' gauge as well.
Then it's simply a matter of comparing oil's at the same rpm and oil temperature.
In a car so equipped, not only can you compare the actual operational viscosities of different oils but also the on going condition of your current oil fill. If the oil starts to shear to will know the moment it happens.

 

[CATERHAM]

Originally Posted By: 21Rouge
Originally Posted By: il_signore97
We must be splitting hairs here with thin/thick oil discussions!


I have no doubt this is true in very many cases. There are have been several UOAs that have come across this forum in which the oil seems like it might be too thick for the application but the wear #s show just fine or more than fine. Ah found one: This is an example of an almost 10 year old Prelude using an 0W40 HDEO:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1948378&page=1

Really how much better wear #s could be obtained using say an...xW20 in this engine?

Rouge21 you've got it completely backwards.

Forget about better wear numbers with a 20wt oil, you want to run the lightest oil that gives you the same wear numbers.
With all the disadvantages of running a heavier oil than necessary; i.e., sluggish engine response, reduced power, lower fuel economy etc, it's just plan illogical to run a thicker oil than necessary.

 

[Jaymus]

I think I lost mpg in my wife's 2001 Eclipse GS 2.4 SOHC 4 cyl going from GC 0W-30 to RTS 5W-40. Going from GTX 10W-30 to RTS 5W-40 made my '86 F150 5.0 EFI run better and rev easier.

10W-40 GTX made it sluggish on the other hand in the high RPM. I think it depends on how quick the oil can get to operating temperature after that experience. According to my oil pressure gauge, GTX 10W-40 took longer to thin down than RTS 5W-40. Quite a big difference in time, too. Talking 15 minutes or more to get to the same psi at idle after driving.

 

[CATERHAM]

The 10W-40 is simply a heavier oil than it's 5W-40 counterpart at all temperatures, but more so when it's cold.

 

[21Rouge]

Originally Posted By: CATERHAM
Originally Posted By: 21Rouge
Originally Posted By: il_signore97
We must be splitting hairs here with thin/thick oil discussions!


I have no doubt this is true in very many cases. There are have been several UOAs that have come across this forum in which the oil seems like it might be too thick for the application but the wear #s show just fine or more than fine. Ah found one: This is an example of an almost 10 year old Prelude using an 0W40 HDEO:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1948378&page=1

Really how much better wear #s could be obtained using say an...xW20 in this engine?

Rouge21 you've got it completely backwards.

Forget about better wear numbers with a 20wt oil, you want to run the lightest oil that gives you the same wear numbers.
With all the disadvantages of running a heavier oil than necessary; i.e., sluggish engine response, reduced power, lower fuel economy etc, it's just plan illogical to run a thicker oil than necessary.


No Caterham I do know your catchy mantra i.e. the oil should be as thin as possible and just as thick as necessary and related to this I do realize the possible disadvantages of running a heavier oil (as you have mentioned above) but purely from a wear stand point, as shown in a UOA, it may well be difficult to distinguish between a thick and thin oil in an application.

 

[Shuttler]

Originally Posted By: CATERHAM
At operating temps there are few deletarious of running a thinker oil than required.

Pernicious usage of misspelled adjective discredits your thesis

 

[bruce381]

less mileage

 

[Jaymus]

Originally Posted By: CATERHAM
The 10W-40 is simply a heavier oil than it's 5W-40 counterpart at all temperatures, but more so when it's cold.


Depends. One brand may have a 5W-40 that's thicker at 100C than another brand's 10W-40. Especially when comparing RTS 5W-40 to GTX 10W-40.

I know a year ago, and it may still hold the same, but Mobil1 5W-30 was thicker than Mobil1 10W-30 at operating temperature. Oil weight ratings give a base idea, they don't come close to telling the real story of the oil.

 

[CATERHAM]

Originally Posted By: Jaymus
Originally Posted By: CATERHAM
The 10W-40 is simply a heavier oil than it's 5W-40 counterpart at all temperatures, but more so when it's cold.


Depends. One brand may have a 5W-40 that's thicker at 100C than another brand's 10W-40. Especially when comparing RTS 5W-40 to GTX 10W-40.

I know a year ago, and it may still hold the same, but Mobil1 5W-30 was thicker than Mobil1 10W-30 at operating temperature. Oil weight ratings give a base idea, they don't come close to telling the real story of the oil.


I was of course referring to your specific Castrol case in hand.

You're mistaken about M1 30wt's.
Your making the classic error of looking at the Kvis 100C spec and ignoring the more relevant HTHS vis.
Yes the 10W-30 has a 100C Kvis of only 10.0 cSt but it's HTHS vis is 3.14 cP which is higher than for their 5W-30 grade.
5W-30's Kvis of 11.3 cSt but it's HTHS vis is 3.09 cP.
And their most fuel efficient and lightest 30wt is the 0W-30 with a Kvis of 11.0 cSt and a low HTHS vis of 2.99 cP.

As I believe has been discussed in this thread, the oil with the higher HTHS vis will have the higher operational viscosity even at normal operating temps regardless of it's Kvis 100C spec.

In terms of fuel economy, since the HTHS vis correlates more closely with actual operational viscosity than the Kvis 100C spec', true to form, their most fuel efficient 30wt (0W-30) has the lowest HTHS vis although not the lowest Kvis 100C spec.

 

[CATERHAM]

Originally Posted By: Shuttler
Originally Posted By: CATERHAM
At operating temps there are few deletarious of running a thinker oil than required.

Pernicious usage of misspelled adjective discredits your thesis


I'm glad someone caught that.
I meant to say "deleterious effects"

 

[CATERHAM]

Originally Posted By: 21Rouge
Originally Posted By: CATERHAM
Originally Posted By: 21Rouge
Originally Posted By: il_signore97
We must be splitting hairs here with thin/thick oil discussions!


I have no doubt this is true in very many cases. There are have been several UOAs that have come across this forum in which the oil seems like it might be too thick for the application but the wear #s show just fine or more than fine. Ah found one: This is an example of an almost 10 year old Prelude using an 0W40 HDEO:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1948378&page=1

Really how much better wear #s could be obtained using say an...xW20 in this engine?

Rouge21 you've got it completely backwards.

Forget about better wear numbers with a 20wt oil, you want to run the lightest oil that gives you the same wear numbers.
With all the disadvantages of running a heavier oil than necessary; i.e., sluggish engine response, reduced power, lower fuel economy etc, it's just plan illogical to run a thicker oil than necessary.


No Caterham I do know your catchy mantra i.e. the oil should be as thin as possible and just as thick as necessary and related to this I do realize the possible disadvantages of running a heavier oil (as you have mentioned above) but purely from a wear stand point, as shown in a UOA, it may well be difficult to distinguish between a thick and thin oil in an application.



The truth is most commuter passenger vehicles are very tolerant of the oil grade used in non temperature extreme applications.
And yes you can get good UOA with a wide range of oil grades.

What I'm poking fun at, is your assertion (which you may not realize you've made) that it is somehow okay to use a thicker oil than necessary. In fact you've qualified the disadvantages I mentioned as "possible disadvantages" which implies that you're not 100% convinced they are real. And therefore psychologically you are simply more comfortable running a heavier oil than is required.

So that is why I say your argument is illogical. But please don't take offense, I still think you're a great guy!

 

[Steve S]

Originally Posted By: CATERHAM
Originally Posted By: Shannow

The biggest downside is the myth that you're providing more lubrication protection with a thicker oil.


A thicker oil will always have a thicker oil film under all operating conditions, and thus greater parts seperation between the bearing and journals.

Whether you need it or not is another matter


At operating temps there are few deletarious of running a thinker oil than required.
The problem is at start-up. With thick oil the risk of cavitation damage to the rings and bearings if an engined is rev'd too high is very real. It's not an uncommon problem with high end sports cars that spec' very heavy oil. I've witnessed complete engine failure at the track on a number of occations usually with some yahoo running heavy 50wt race oil on a cool day and reving the snot out of his stone cold engine.
Kinda seperates the men from the boys.

 

[Steve S]

Originally Posted By: StevieC
My engine is spec'ed up to 20w50 depending on the temperature but seems to feel the best with 5w20 as stated on the oil cap and in the owners manual.

I don't get why thicker would be better...
Get in your car on a really hot day with the a/c on and the car full of luggage and people get on the open road and run it lets say you are on the autobahn type of highway and then see what happens to the ability of a 5w-20 protects as compared to a 20w-50 oil. 5w-20 works great in engines specd for it because of oil coolers and maybe some other tweaks and most likley the engines do not run loaded for hours on end. that is the same reason most poeple will never see any advantage in the use of syn oil because they never load the engine long enough. It is not a thick is better .It should be is thicker needed?

 

[znode]

Well in a well designed engine, the 20w will stay a 20w in the almost all conditions and the film will still hold.

The question is, what is the condition and the engine, and how often do you see such conditions that will break film? And even if you try to preserve the film, is it a good idea for the rest of the engine?

Say you optimize for the large grinding surfaces like the piston ring with a thicker oil, nothing says you still won't be hurting the hotter and higher tolerance parts that needs a thin oil to cool, such as tiny oil holes in a turbocharger.

This is why you stick with as "as thick as necessary", because thin is always preferred.

 

[21Rouge]

Originally Posted By: 21Rouge

There are have been several UOAs that have come across this forum in which the oil seems like it might be too thick for the application but the wear #s show just fine or more than fine. Ah found one: This is an example of an almost 10 year old Prelude using an 0W40 HDEO:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1948378&page=1

Really how much better wear #s could be obtained using say an...xW20 in this engine?

Originally Posted By: CATERHAM

Forget about better wear numbers with a 20wt oil, you want to run the lightest oil that gives you the same wear numbers.
With all the disadvantages of running a heavier oil than necessary; i.e., sluggish engine response, reduced power, lower fuel economy etc, it's just plan illogical to run a thicker oil than necessary.


Originally Posted By: 21Rouge
No Caterham I do know your catchy mantra i.e. the oil should be as thin as possible and just as thick as necessary and related to this I do realize the possible disadvantages of running a heavier oil (as you have mentioned above) but purely from a wear stand point, as shown in a UOA, it may well be difficult to distinguish between a thick and thin oil in an application.


Originally Posted By: CATERHAM

And yes you can get good UOA with a wide range of oil grades.

What I'm poking fun at, is your assertion (which you may not realize you've made) that it is somehow okay to use a thicker oil than necessary. In fact you've qualified the disadvantages I mentioned as "possible disadvantages" which implies that you're not 100% convinced they are real. And therefore psychologically you are simply more comfortable running a heavier oil than is required.


Yikes Caterham! Add Psychologist to your resume

as I think you are correct in that I/others may feel "more comfortable" to run a heavier oil (than is specified in the owners manual). But there may be (good) reasons for this deviant behaviour. For example wrt to the Honda Prelude I referenced above (using a 40 wt), the owner wished to remedy his excessive oil consumption that he was experiencing when running a lighter oil. The result was lower consumption with a UOA still showing good wear #s.

For me running a heavier oil (but maybe technically, still the same grade as spec'd i.e. 30 wt) makes sense as previous UOAs on this engine showed excessive shearing due to fuel dilution. So starting with a more robust and heavier oil is justified as it may stand up i.e. resist shearing better than the OEM spec'd oil.

Originally Posted By: CATERHAM
But please don't take offense, I still think you're a great guy!


Thanks Caterham. I do still feel the love

.

 

[CourierDriver]

All oil will run off ur cylinder walls, test this out, pour some oil on piece of metal and brush it around , then set the metal up outside and in the sun, it will be gone in 2 or 3 days at least, it doesn't hang around gang, if it does, its thin, not like u got 1/8 inch of oil hanging onto ur cylinders the next day, but it aint a big deal, never lost an engine anyway for that, have any of u. Even my beloved MMO in the long run aint gonna save, lol.