Thin vs Thick Discussion

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1,442
Location
Sarasota, Florida
Let’s use top gear:

Let’s go racing. I will discuss driving in traffic jams in the Florida summer as well as racing in Sebring though there is little to no commonality. People lump these two driving situations together but there is little overlap.

On the race track one usually uses all the BHP their engine can give them. You briefly step on the brakes for the corner then put the pedal to the metal the rest of the time. Your oil will get up to 302 F, but your cooling system is around 212 F. The engine produces tremendous heat but can only pass it off so fast to the cooling system. There is a lot of air moving past the cooling radiator so the antifreeze / coolant is able to get rid of the extra heat from this part of the system with relative ease. Much of the engine cooling is performed by the oil system.

The temperature of oil on your gauge is not actually as hot as it really gets. This temperature is an average with oil from different parts of the motor. Some parts are hotter than others. It is said that some of the oil gets as hot as 400 or 500 F in these racing situations.

In an earlier section I said that thicker oils are usually needed in racing situations but not necessarily. Remember that a major function of oil is to cool the inside of your engine. In ASTM D 4485 3.1.4: “Terminology: Engine oil- a liquid that reduces friction and wear between moving parts within an engine, and also serves as a coolant.” Since the oil with a viscosity of 10 cS at 212 F thins to a viscosity of 3 cS at 302 F we will get some more flow. The pressure will go down some as well. This is OK as long as we have a minimum of pressure to move the oil.

This increased flow will result in increased cooling by the oil. This is a good thing. You would probably want more oil flow in these situations and you get it. The hotter oil thins and this increases flow. This is because the pump does not reach its pop off relief pressure. I will show you how this works later. The higher flow works harder to separate the engine parts that are under very high stress. It all works out for the better. Higher revving engines need thinner oils. You do not necessarily need to go to a thicker oil while racing. Only experimentation will tell.

The best way to figure out what viscosity of oil you need is to drive the car in the conditions you will use. Then use the oil viscosity that gives you 10 PSI per 1,000 RPM under those circumstances. For some reason very few people are not able to get this simple principal correct.

These same rules apply to engines of any age, loose or tight. Just because your engine is old does not mean it needs a thicker oil. It will need a thicker oil only if it is overly worn, whether new or old. Yet the same principals of 10 PSI per 1,000 RPM still apply. In all cases you need to try different grade oils and see what happens. Then choose the correct viscosity.

I used 0W-20 in my Ferrari 575 Maranello. It had over 5,000 miles on the clock. There will be a day (my estimate is 100,000 miles) when one will have to go to a 0W-30. In the future one will have to increase the viscosity to a 0W-40, then a 0W-50, maybe. You should use whatever it takes to get 75 PSI at 6,000 RPM during the lifetime of the engine. This formula works in all situations.

Some people have tried this and occasionally get a somewhat low oil pressure while at idle. This is fine. There is no stress on parts at idle, the smallest oil flow will do the trick. It is at higher RPM where more BHP is produced. This is where we need the flow. Remember that Ferrari uses 75 PSI at 6,000 RPM as the place to test your oil viscosity needs. If your oil gives this value under your driving conditions then your lubrication system has been optimized.

Do not go 5,000 miles with the same oil if you are racing your car. You should change the oil every 1 or 2,000 miles. If you drive your car only around town then you need to change the oil for that situation. Use racing oil on the track and urban oil around town. The best situation as described by Ferrari is to use the 0W-40 around town and the 10W-60 “racing oil” on the track. It has to be that “hot” track though. A compromise situation would be to use the 5W-40 for both but this may not be optimal. Certainly, if you are just an urban driver as me use the 0W-40 or even a thinner oil as I do in my Maranello. Again, I used the 0W-20 grade.

FYI. The Formula 1 cars that run at 15,000 RPM and higher use straight 5 and 10 and 20 grade oils.

Now let me discuss what people think is a similar situation to racing. That is hot summer traffic jam driving. Your car should be able to handle this. If you have problems then you have a problem with your car, most likely in need of a cooling system overhaul.

When you drive that car down the road mid-winter in upstate New York or mid-summer in Florida the engine and oil temperatures will be around 212 F. But your Florida vacation is suddenly altered by a hurricane. You have to get out of Tampa, but so do a million other people. It is now 95 F and you are in a snarl. Everyone thinks they need a thicker oil for this situation. This is false.

Your engine is not producing much heat at low RPM and low BHP output. The production of heat is relatively slow. It can easily be transmitted to your cooling system. The problem is that your cooling system has trouble getting rid of the heat. The oil and the coolant will slowly rise in temperature. They both rise together. The increase is no big deal for your oil. It goes to 220, then 230 F. The problem is that the cooling system can only handle heat up to 230 F. After that you overheat the cooling system and the car must be shut off. The oil never got that hot, It was just that the water got a little hotter than its system design.

You now see that overheating in traffic is a cooling system problem and not an oil system problem. Do not change to a thicker oil based on your traffic situation.

AEHaas
 
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4WD

Messages
17,387
Location
Texas
Flow does not increase because oil thins … pressure can decrease slightly while flow is fixed to the pump RPM and what is regulated by the PRV.
Pressure is not flow … most modern vehicles have variable output ECM controlled pump “systems“ …
In the table of truths of what parameters impact circulating pressure - viscosity is at the bottom …
Exotic cars are interesting … but I doubt 5% of the members here have one.
 
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2,507
Location
South Carolina
Interesting. The specified oil pressure requirements for the two cycle Detroit Diesels was 4psi at idle (500rpm) and 30psi at high rpm (2250). Most heathy engines I tested ran 10psi at idle and 40-50psi at high rpm. The Detroit Diesel oil pump, and oiling system, was designed for flow and they determined these pressures would deliver the required flow.
 

BeerCan

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1,852
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FL
The best way to figure out what viscosity of oil you need is to drive the car in the conditions you will use. Then use the oil viscosity that gives you 10 PSI per 1,000 RPM under those circumstances. For some reason very few people are not able to get this simple principal correct.
I think for 99% of drivers the best way to get the viscosity they need is to look in the owners manual.
 

OVERKILL

$100 Site Donor 2021
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46,489
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Ontario, Canada
Interesting. The specified oil pressure requirements for the two cycle Detroit Diesels was 4psi at idle (500rpm) and 30psi at high rpm (2250). Most heathy engines I tested ran 10psi at idle and 40-50psi at high rpm. The Detroit Diesel oil pump, and oiling system, was designed for flow and they determined these pressures would deliver the required flow.

The 10psi per 1,000RPM rule was just a rough rule of thumb for the Small Block Chevy for guys who were building them, why it is being applied universally here is yet another reason why these threads keep getting locked. They are full of incorrect information and personal opinion being presented as fact.

Applying the above logic more broadly, my wife's truck produces ~32psi hot at ~800RPM on a 0w-20. FCA spec's a 5w-20. They didn't spec 5w-20 so that I'd have 10psi at idle and 30psi at 3,000RPM, they spec'd it because their internal testing under the anticipated usage profile confirmed that it was a safe choice under the anticipated operating conditions the vehicle was to experience. Tossing 0w-8 in the pan to try and drop my oil pressure down would likely result in a rod leaving the party through the side of the block and I doubt the author here would be willing to foot the bill for that experiment.

This is the reason that when Honda started going below 0w-20, chasing 0w-16, 0w-12 and 0w-8, they made mechanical changes to the engines, such as wider bearings, which would be necessarily more tolerant of the reduced MOFT provided by the lower viscosity lubricant.
 
Messages
2,347
Location
WA
Regarding 10 psi per 1K rpm:
that ratio is not universal.
I think I posted in another thread that my car service manual shows:
V8 @3000 RPM: 43-85 PSI.

also not trying to be mean but curious who are these "people"? (refer to the quote below).
I've never heard or seen anyone comparing the two (city vs. race) driving conditions!!!


"I will discuss driving in traffic jams in the Florida summer as well as racing in Sebring though there is little to no commonality. People lump these two driving situations together but there is little overlap.
 
Messages
20
Location
New York City
Since owning my 1st car back in 1987, a 1986 Mercury Capri, then a 1981 Toyota Cressida, to a 1998 Chevy Cavalier to my current 1998 Volvo S70 non turbo, I have pretty much used 10w40 for all these cars throughout their lifetimes. 10w40 has a bad reputation today for being too thick, too many polymers etc but it has never done any kind of damage to my engines. The Chevy Cavalier which I purchased new in 1998 lasted 474,000 on the original engine on a combination of 5w30 until about 325k then switched it to 10w40. The other vehicles have been 10w40 exclusively. I like 10w40. It is a much maligned weight oil but I have used it for 34 years with great results. My Volvo runs either Formula Shell or Pennzoil YB in 10w40 and doesn't burn a drop in a 4K oil change interval. That car right now just turned 196K miles.
 
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18,145
Location
Upper Midwest
Since owning my 1st car back in 1987, a 1986 Mercury Capri, then a 1981 Toyota Cressida, to a 1998 Chevy Cavalier to my current 1998 Volvo S70 non turbo, I have pretty much used 10w40 for all these cars throughout their lifetimes. 10w40 has a bad reputation today for being too thick, too many polymers etc but it has never done any kind of damage to my engines. The Chevy Cavalier which I purchased new in 1998 lasted 474,000 on the original engine on a combination of 5w30 until about 325k then switched it to 10w40. The other vehicles have been 10w40 exclusively. I like 10w40. It is a much maligned weight oil but I have used it for 34 years with great results. My Volvo runs either Formula Shell or Pennzoil YB in 10w40 and doesn't burn a drop in a 4K oil change interval. That car right now just turned 196K miles.
Your success doesn't have anything to do with the winter rating of that grade. And today's wider-spread multi-viscosity oils have far superior VII in them than did the early ones, and superior base stocks have reduced the need for them to some extent.
 
Messages
20
Location
New York City
Your success doesn't have anything to do with the winter rating of that grade. And today's wider-spread multi-viscosity oils have far superior VII in them than did the early ones, and superior base stocks have reduced the need for them to some extent.
Excellent point Kschachn! Motor oils are getting better all the time. In the 80's, VII was a problem but today it is truly a thing of the past. I'll continue to use 10w40 for as long as it's available.
 
Messages
2,347
Location
WA
Excellent point Kschachn! Motor oils are getting better all the time. In the 80's, VII was a problem but today it is truly a thing of the past. I'll continue to use 10w40 for as long as it's available.

I think 10W40's of old days are being replaced with the 0W40's ...

Sounds like if you want to buy any good xW40 oil without having to do extensive research, you have to stick with 0W and the other magic word is EURO.

Tell the waitress, I would like to have some 0W-40 and side of Euro and/or HTHS please! That would taste good any in any restaurant like the standard cheese burger. Don't risk any other unknown food when out of town. :alien:
 
Messages
769
Do thicker oils protect the timing chain system better? I'm sure this has been discussed/asked here before but God knows I cant remember haha:D
Probably not. The real problem is the engine itself and how bad it trashes the oil during an OCI. Some engines are easy on oils, others aren't. As a result, the timing chain experiences additional wear and tear from high heat, soot, and other crud, like burned up VII polymers. So the correct answer is: it depends. When I think timing chain, I think bicycle chain. All it needs to stay healthy is clean oil and no additional contaminants.
 
Messages
769
The best way to figure out what viscosity of oil you need is to drive the car in the conditions you will use. Then use the oil viscosity that gives you 10 PSI per 1,000 RPM under those circumstances. For some reason very few people are not able to get this simple principal correct.
bang1.gif


I used 0W-20 in my Ferrari 575 Maranello. It had over 5,000 miles on the clock. There will be a day (my estimate is 100,000 miles) when one will have to go to a 0W-30. In the future one will have to increase the viscosity to a 0W-40, then a 0W-50, maybe. You should use whatever it takes to get 75 PSI at 6,000 RPM during the lifetime of the engine. This formula works in all situations.
bang2.gif


Much of the engine cooling is performed by the oil system.
You now see that overheating in traffic is a cooling system problem and not an oil system problem.
bang3.gif


Do not change to a thicker oil based on your traffic situation.
motul.png


I will discuss driving in traffic jams in the Florida summer as well as racing in Sebring though there is little to no commonality. People lump these two driving situations together but there is little overlap.
sean.jpeg


Now let me discuss what people think is a similar situation to racing. That is hot summer traffic jam driving. Your car should be able to handle this. If you have problems then you have a problem with your car, most likely in need of a cooling system overhaul.
Much of the engine cooling is performed by the oil system.
lumberg.jpeg


When you drive that car down the road mid-winter in upstate New York or mid-summer in Florida the engine and oil temperatures will be around 212 F. But your Florida vacation is suddenly altered by a hurricane. You have to get out of Tampa, but so do a million other people. It is now 95 F and you are in a snarl. Everyone thinks they need a thicker oil for this situation. This is false.
justgo.gif
 
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