High RPMs...thick or thin?

[Gokhan]

Originally Posted by Gokhan
Originally Posted by oghl
Originally Posted by edyvw
And by the way, where is that 15% grade? I lived in CA, so I would like to know.
I think there is a stretch of 6-7% grade at the steepest part of that drive. Nothing close to 15% as far as I can remember. Nothing close to 15% on any of the CA highways that allows 55mph or faster speed.

There are sections of 15% grade (at least one) on I-15 between LA and Las Vegas. The tough one is the one closer to Las Vegas.

OK, you're probably right about 6%. It feels darn steep and most cars can't reach the speed limit though.

http://www.phatpage.org/highways/i15.html

Also, the curvy steep grade near LA turns out to be the deadliest road in US.

https://www.deseretnews.com/user/comments/700012247/I-15-stretch-is-deadliest-road-in-US.html

 

[ZeeOSix]

Originally Posted by Gokhan
Also, in US, we have a lot of hills and deserts. Keeping up with the 75 MPH speed limit on a 15% grade on I-15 between Los Angeles and Las Vegas is no easy task for any car. In addition, US pavement friction coefficients are much higher than the European roads. That's more challenging than cruising on the left lane of a German autobahn as far as the load and temperature stress on the engine are concerned..


The HP required increases as a cubic function with speed due to the combined wind drag and rolling resistance. So going 150+ MPH on the Autobahn is putting a lot of stress on the engine - ie, it's going to be putting out most of it's available power at pretty high PRM to overcome wind drag at those high speeds. That's tough on oil.

 

[Gokhan]

Originally Posted by Shannow
Gokhan
a) The oil temperature rise in the bearings raises the temperature to well above coolant temperature, the heat being transferred from the oil INTO the block and coolant.
b) RPM varies this temperature far far more than load...load has a near negligible effect on temperature rise.
c) both situations the coolant is controlled by a thermostat, so the "heat sink" for the transfer of this heat is largely the same regardless of ambient.
d) As a result, the oil leaving the bearings of the higher speed engine and returning to the sump will be hotter.
d) 0 humidity means nothing to the convective cooling of a radiator.

Did you forget that there is something called the gravity? It sounds like you don't have steep grades in Australia.

You're overlooking the fact that you can't climb a steep grade in overdrive. It's going to be high RPM and high load.

In addition, since the speed is lower, the coolant is going to run a lot hotter.

In fact, you may have lower RPM doing 140 MPH on a flat road than 80 MPH on a steep grade.

I never had cooling issues going full throttle on flat sections but this is not the case when I climb steep hills. So, this is based on real-life experience.

 

[ZeeOSix]

Originally Posted by Gokhan


Those dudes are hamburger if they crash ... no seat belts, and would probably die even if they were wearing seat belts. Nuts for sure.

 

[ZeeOSix]

Originally Posted by Gokhan
You're overlooking the fact that you can't climb a steep grade in overdrive. It's going to be high RPM and high load.


You don't have to down shift and rev the engine to 6000 RPM unless the car has about 50 HP max. I can drive over mountain passes on cruise control and never have to downshift. It all depends on how much low end torque (and hence low end HP) the engine makes and the gearing.

 

[ZeeOSix]

Originally Posted by Gokhan
Originally Posted by edyvw
Dude, get off internet. Get yourself ticket and see the world.
My head started to hurt when I read this.

I've been to several countries in Europe.

So, do you really think that cruising at 140 MPH with an aerodynamic car on a flat stretch of extra-smooth pavement at 60 °F (16 °C, with the wind at the same speed and temperature blowing on your radiator) raises the oil temperature more than climbing a 15% grade at 80 MPH at 110 °F (43 °C) and almost no humidity, not to mention the A/C running?


I would say yes. Go study up on how HP has to increase with speed to overcome aerodynamic drag and rolling resistance. It's a cubic function when those two factors are combines. Even an aerodynamic car needs lots of HP output (and it will be at pretty high RPM too) to go 140+ MPH. More than climbing a steep hill at 80 MPH.

 

[Gokhan]

I did the math. Gravitational power in HP equals to 2.7 times MPH times the weight of the car in thousand pounds times the grade.

We're comparing apples and oranges. It all depends on how powerful the engine is, how fast the speed is, and how steep the grade is. With my car, steep grades are more challenging than full throttle on a flat road.

 

[MNgopher]

I did Eisenhower and Vail passes (among others this summer) and my truck was able to hold fifth gear with a/c running and cruise on. 5th gear is an overdrive gear on my F150. Those are 6% grades at high altitude. (Granted I was cheating with an eco boost, but still)

Lower power vehicles may need to rev, but not all.

 

[Gokhan]

Originally Posted by ZeeOSix
I would say yes. Go study up on how HP has to increase with speed to overcome aerodynamic drag and rolling resistance. It's a cubic function when those two factors are combines. Even an aerodynamic car needs lots of HP output (and it will be at pretty high RPM too) to go 140+ MPH. More than climbing a steep hill at 80 MPH.

Fine but you're still overlooking the cooling effect. They put turn of A/C -- avoid overheating signs on steep grades on I-15 for a reason -- you always see some overheated cars on the shoulder, even newer models. It's not all about HP output.

Enough with this autobahn fascination by the way. Who gets to drive regularly in crazy speeds on autobahns anyway? Recommended speed is 81 MPH from what I read and a few crazies race in the left lane if there is no traffic and speed limit.

 

[OilUzer]

Originally Posted by OVERKILL
Originally Posted by Gokhan


Another German friend of mine was also asking me why the Americans were fascinated with BMWs because we had the much better Cadillac here and everyone in Germany wanted to get one except they couldn't afford it because of auto tariffs around 100%.


Was he intoxicated at the time?


lol
Had a German guy on our soccer team and at half time he drank beer. We used to call it German powerade

 

[Gokhan]

Originally Posted by Gokhan
Originally Posted by Gokhan
Originally Posted by oghl
Originally Posted by edyvw
And by the way, where is that 15% grade? I lived in CA, so I would like to know.
I think there is a stretch of 6-7% grade at the steepest part of that drive. Nothing close to 15% as far as I can remember. Nothing close to 15% on any of the CA highways that allows 55mph or faster speed.
There are sections of 15% grade (at least one) on I-15 between LA and Las Vegas. The tough one is the one closer to Las Vegas.

OK, you're probably right about 6%. It feels darn steep and most cars can't reach the speed limit though.

http://www.phatpage.org/highways/i15.html

Also, the curvy steep grade near LA turns out to be the deadliest road in US.

https://www.deseretnews.com/user/comments/700012247/I-15-stretch-is-deadliest-road-in-US.html

It's called the Baker Grade. Its steepest section is 8%. It goes for almost 20 miles and feels like it'll never end.

 

[ZeeOSix]

Originally Posted by Gokhan
In fact, you may have lower RPM doing 140 MPH on a flat road than 80 MPH on a steep grade.


My Z06 would be revving ~5500 RPM at 140 MPH. At 80 MPH it be revving 3000 RPM. It has enough HP at 3000 RPM to climb any mountain pass I can find where you could actually maintain 80 MPH without shifting down. The oil is going to get hotter doing 140 at 5500 RPM than it would doing 80 going up a grade at 3000 RPM ... mainly from the 2500 RPM difference since solely RPM accounts for the majority what heats up the oil oil from it shearing in the journal bearings.. My bet is the HP output to go 140 on flat ground would probably also be higher than required to go up a steep grade at 80.

 

[Gokhan]

Originally Posted by Gokhan
I did the math. Gravitational power in HP equals to 2.7 times MPH times the weight of the car in thousand pounds times the grade.

We're comparing apples and oranges. It all depends on how powerful the engine is, how fast the speed is, and how steep the grade is. With my car, steep grades are more challenging than full throttle on a flat road.

As a fun exercise, using the formula for an 80,000 lb truck and 8% grade, you get 430 HP gravitational power at 25 MPH, not including air and rolling resistance.

 

[Gokhan]

Originally Posted by ZeeOSix
Originally Posted by Gokhan
In fact, you may have lower RPM doing 140 MPH on a flat road than 80 MPH on a steep grade.


My Z06 would be revving ~5500 RPM at 140 MPH. At 80 MPH it be revving 3000 RPM. It has enough HP at 3000 RPM to climb any mountain pass I can find where you could actually maintain 80 MPH. The oil is going to get hotter doing 140 at 5500 RPM than it would doing 80 going up a grade at 3000 RPM ... mainly from the 2500 RPM difference. My bet is the HP output to go 140 on flat ground would probably be higher than required to go up a steep grade at 80.

If you can climb in overdrive, and I'm sure Z06 can most grades, certainly that's cooler oil and a lot less horsepower. It depends on the engine size and vehicle weight.

See my truck example above.

 

[Shannow]

Cool, now 80,000lb trucks on an 8% grade are pertinent to passenger car engine oils and thin/thick and RPM...

And I get accused of diverting threads.

 

[ZeeOSix]

Originally Posted by Gokhan
Originally Posted by ZeeOSix
Originally Posted by Gokhan
In fact, you may have lower RPM doing 140 MPH on a flat road than 80 MPH on a steep grade.


My Z06 would be revving ~5500 RPM at 140 MPH. At 80 MPH it be revving 3000 RPM. It has enough HP at 3000 RPM to climb any mountain pass I can find where you could actually maintain 80 MPH. The oil is going to get hotter doing 140 at 5500 RPM than it would doing 80 going up a grade at 3000 RPM ... mainly from the 2500 RPM difference. My bet is the HP output to go 140 on flat ground would probably be higher than required to go up a steep grade at 80.

If you can climb in overdrive, and I'm sure Z06 can most grades, certainly that's cooler oil and a lot less horsepower. It depends on the engine size and vehicle weight.

See my truck example above.


The Z06 weighs approx 3300 lbs with me in it. As Shannow said, the majority of the heating of the oil is just from the engine RPM shearing the oil in the journal bearings. There is some heat added to the oil from the combustion in the cylinders, but it's a small part of the whole, especially if the cooling system is efficient at absorbing that combustion heat (which most cooling systems are). If you ran your car down the road at 60 MPH in overdrive and it was revving 1500 RPM the oil would get to X deg F. If you ran the same car down the road at 60 MPH in a gear that made the engine rev 5000 RPM the oil would get noticeably hotter. You're still putting out the same amount of RWHP since you're doing the same 60 MPH. But the oil is being sheared like mad at 5000 RPM and is heating up the bulk temperature of the oil as a result.

 

[ZeeOSix]

double post - deleted.

 

[ZeeOSix]

Originally Posted by Gokhan
Originally Posted by Gokhan
I did the math. Gravitational power in HP equals to 2.7 times MPH times the weight of the car in thousand pounds times the grade.

We're comparing apples and oranges. It all depends on how powerful the engine is, how fast the speed is, and how steep the grade is. With my car, steep grades are more challenging than full throttle on a flat road.

As a fun exercise, using the formula for an 80,000 lb truck and 8% grade, you get 430 HP gravitational power at 25 MPH, not including air and rolling resistance.


So I ran some numbers for the Z06 using your "gravitational power in HP" formula and also an Excel spreadsheet I produced a long time ago for aero and rolling resistance HP calcs, which is pretty accurate.

The Z06 needs 210 HP to go 140 MPH and 67 HP to go 80 MPH on level ground. Cd of the Z06 is 0.30 (pretty aerodynamic as cars go).

The Z06 needs 57 HP extra (the "gravitational HP" only portion) to go 80 MPH up an 8% grade.

So to go up the 8% grade at 80 MPH including the aero and rolling HP it would be 67 + 57 = 124 HP.

That's still 86 HP less than it takes to go 140 MPH on a flat road.

Revs are 5500 RPM at 140 MPH, and 3000 RPM at 80 MPH, using 5th gear.

Do both conditions for an extended period of time, and the oil will be hotter going 140 MPH on flat land vs 80 MPH up an 8% grade.

 

[Gokhan]

Those numbers make sense. By the way, a more precise coefficient in the formula is 2.67.

With my car, hp is limited. I can do about 65 MPH on 8% grade in full power.

It's 5,460 RPM in 3rd gear and 3,760 RPM in 4th gear (OD) at 100 MPH.

One downside of thicker oil is that it will run hotter for the given RPM because of the higher viscous friction.

 

[OilUzer]

How about let's say a car with manual trans. going 35mph on flats or slight down hill @ 2300 rpm vs. doing the same rpm & gear going uphill or slight uphill?
will the heat from the bearings be the same since the same rpm? The temperature in cylinders (combustion) will obviously be much higher going uphill.