Oil Grade Effect on Starting Cranking Speed

[RalphVa]

I used to have a whole lot of calculations of lube oil properties and other stuff in Visual Basic Applications (VBA) that were used in Excel. It was one of my hobbies as a chemical engineer working in the lube process business.

Found my backup and put together a VBA module with stuff I needed. I then calculated the relative cold engine rotation speeds for various grades of oil.

Here they are?

Grade -20 F 0 F 10 F
15w40 10 20 27
10w40 16 29 37
10w30 17 32 42
0w30 22 38 48

I just took a base of 10 rpm at -20 F, which is not necessary what you see on a real tractor engine.

Rotation speeds is a function of the Sq Rt of the cranking oil viscosity. The oil against the bearings at startup is the effect.

In addition, there are also effects of how long it takes the oil pump to get suction and to supply pressurized oil to the upper parts of the engine. These times are probably gonna be pretty much relative to the cranking speed, but probably more pronounced at very low temperatures.

You do not need to switch from xxx40 to xxx30 from summer to winter. 0w30, 5w30 and 10w30 are all good year round based on millions of VW diesel miles all over the globe with no engine failures due to oil problems. If your owners manual says 10w30, as many do, 0w30 or 5w30 can be used as well and are better, especially at lower temps.

Ralph

 

[Bavarian]

The same can be continued into the transmission. Since the kind of transmissions trend away from a mechanical dry clutch to hydrostatic or hydraulic power reverser, the starter has to turn the transmission while cranking the engine. Pushing in the clutch pedal if there is one, is useless. Most of them are hydraulic oprated and require hydraulic pressure. That is built up when the engine is running. The cranking speed of the starter is too slow to build up pressure.

 

[Texasmark]

I used to have a whole lot of calculations of lube oil properties and other stuff in Visual Basic Applications (VBA) that were used in Excel. It was one of my hobbies as a chemical engineer working in the lube process business.

Found my backup and put together a VBA module with stuff I needed. I then calculated the relative cold engine rotation speeds for various grades of oil.

Here they are?

Grade -20 F 0 F 10 F
15w40 10 20 27
10w40 16 29 37
10w30 17 32 42
0w30 22 38 48

I just took a base of 10 rpm at -20 F, which is not necessary what you see on a real tractor engine.

Rotation speeds is a function of the Sq Rt of the cranking oil viscosity. The oil against the bearings at startup is the effect.

In addition, there are also effects of how long it takes the oil pump to get suction and to supply pressurized oil to the upper parts of the engine. These times are probably gonna be pretty much relative to the cranking speed, but probably more pronounced at very low temperatures.

You do not need to switch from xxx40 to xxx30 from summer to winter. 0w30, 5w30 and 10w30 are all good year round based on millions of VW diesel miles all over the globe with no engine failures due to oil problems. If your owners manual says 10w30, as many do, 0w30 or 5w30 can be used as well and are better, especially at lower temps.

Ralph

Thanks for thaking the time to show that.

Mobil 1 mentions it on their container that 0wxxx covers warranty requirements for 5wxxx and 10wxxx multi vis oils. Everywhere you read about engine wear driven by lack of lube, it's always on startup. Having been a heavy oil guy most of my life, I bought a 2009 Dodge Hemi 1500 with the 4-8-4. engine. They were animate about using 0w-20 (or Mobil 1 0w-20) for that matter. They even molded the caution in the oil fill cap. Said the 4-8-4 wouldn't work with heavy oil.

One of my misconceptions, not being an engine designer, was my first vehicles, well worn past prime since I couldn't afford anything decent, you'd follow the oil pressure gauge under different driving conditions, temps, and all that. I didn't realize that some engines are designed for high pressure with a popoff valve to maintain a constant pressure, and others were high volume pumps and pressure varied as a function of temp and rpm.

 

[LouNY]

Nice information, I'll be sticking with the 5w-40 synthetic I have been running.

 

[RalphVa]

One responder on the green tractor forum where I posted this as well mentioned that he is using 0w40. I put M1 0w40 properties (185 VI!) in and calculated the starting viscosity. Much lower than any of the other oils I looked at.

So, if you want your 40w at operating temperature and nice low vis at starting temperature, 0w40 is the way to go. VW experience says 40w in diesels is not needed. I read somewhere that Ferrari might even be using 10w in its racing engines. Why? Protection against overpressure at start of races with colder engines. I'd have to check this one out some more.

Ralph

 

[LindenBruce]

Just anecdotal, But I had an 89 ChevyK2500 with a small block once. When I rebuilt the engine I used a High Volume oil pump. In winter on really cold days, when I first started the engine and finally rolled onto the roadway, the pressure relief would pop open as indicated by a drop in oil pressure. Pressure would climb to nearly 80PSI then drop to 40ish. Once the oil warmed up pressure would hold around 55-60psi. B.

 

[RalphVa]

Most engines have oversized oil pumps, e.g. run at relief valve pressure. I've only owned 2 or 3 engines where the oil pressure actually cycled up and down with rpm. Got one now with the Miata. Actually, its oil pressure gauge is a computer simulation, but it fluctuates just like the one we had straight off the sensor in our Alfa Duetto Spider.

Engine cranking speed is also an indicator of how fast the oil pump might get suction. In code weather, it could be several seconds before it gets suction AFTER the engine starts, e.g. starving upper valve train and bearings of oil. A 0wxx oil is about the only one that will instantly get oil to the oil pump. Other oils have to have the oil pump to sit there and warm up the oil by its not being pump before it will warm enough to flow into the pump.

Ralph

 

[Cougsfan]

I used to have a whole lot of calculations of lube oil properties and other stuff in Visual Basic Applications (VBA) that were used in Excel. It was one of my hobbies as a chemical engineer working in the lube process business.

Found my backup and put together a VBA module with stuff I needed. I then calculated the relative cold engine rotation speeds for various grades of oil.

Here they are?

Grade -20 F 0 F 10 F
15w40 10 20 27
10w40 16 29 37
10w30 17 32 42
0w30 22 38 48

I just took a base of 10 rpm at -20 F, which is not necessary what you see on a real tractor engine.

Rotation speeds is a function of the Sq Rt of the cranking oil viscosity. The oil against the bearings at startup is the effect.

In addition, there are also effects of how long it takes the oil pump to get suction and to supply pressurized oil to the upper parts of the engine. These times are probably gonna be pretty much relative to the cranking speed, but probably more pronounced at very low temperatures.

You do not need to switch from xxx40 to xxx30 from summer to winter. 0w30, 5w30 and 10w30 are all good year round based on millions of VW diesel miles all over the globe with no engine failures due to oil problems. If your owners manual says 10w30, as many do, 0w30 or 5w30 can be used as well and are better, especially at lower temps.

Ralph

Excuse the high viscosity of the fluids in my brain, but could you explain your results a little clearer? What does the "10 20 27" represent after the 15w40 oil? You say you calculated the cold rotation speeds, so are you showing rpms at -20,0 &10 degrees F?

 

[LouNY]

That's kind of how I read it,
I wish that he had included numbers for 5w-40.

 

[RalphVa]

Excuse the high viscosity of the fluids in my brain, but could you explain your results a little clearer? What does the "10 20 27" represent after the 15w40 oil? You say you calculated the cold rotation speeds, so are you showing rpms at -20,0 &10 degrees F?

The numbers are relative (not actual) cranking speeds based on cranking speed being relative to the square root of viscosity in one study that I found. I just took the 15w40, the most viscous at cranking temp, at my base = 10. Probably not too far from actual. Bet the actual crankiing speed of 15w40 at -20 F might be pretty close to 10 rpm.


Ralph