[DigitalGriffin]

I was driving my wife's Prius the other day and I noticed how the engine is constantly cycling on and off.

I know from my engineering experience that the vast majority of engine wear actually occurs at startup since the oil is not in the vital places it needs to be. (Oil settles to the pan when the engine isn't running.)

So my question is this: How does the Prius keep from prematurely wearing out? Does it keep the oil pump running even after the engine is off?

I wonder if this is why Toyota doesn't recommend synthetics as these oils tend to be more free flowing and would drain away from critical parts faster when the oil isn't being pumped...hmmmmm.....

Anyone?

 

[KTPhil]

No oil pump runs when the ICE is off.

Yes, wear occurs right after startup, but not simply because of a lack of oil on wear surfaces. It is from force being applied to wear surfaces before pressure maintains the sheet of lubricatant on those surfaces. By spinning up the ICE before providing ignition (and the resultant forces) this wear is almost eliminated.

 

[Jonnycat26]

Yes, wear occurs right after startup, but not simply because of a lack of oil on wear surfaces. It is from force being applied to wear surfaces before pressure maintains the sheet of lubricatant on those surfaces. By spinning up the ICE before providing ignition (and the resultant forces) this wear is almost eliminated.

That's not entirely true. Any metal on metal contact is going to create wear.

 

[KTPhil]

Yes, but there is oil remaining even after sitting overnight. It doesn't take much when the forces are so light.

 

[Jonnycat26]

Yes, but there is oil remaining even after sitting overnight. It doesn't take much when the forces are so light.

The Honda engines have an electric oil pump to keep lubrication going even when the engine is off, not sure about the Escape Hybrid. And that film of thin oil sitting on the engine isn't going to be enough to protect it at 1,000rpm.

A lot of other cars even keep the oil pump going for a minute or two after the car is shut off!

 

[kirby]

I recall reading that a lot of the wear caused in starting an engine is from the force created when the piston is forced to move at full force under the pressure of the expanding gases from zero to full speed when there is almost no lubrication. In the Prius the engine is already turning at 600 rpm BEFORE any fuel or spark is introduced so that you don't have the sudden forces on a "dry" engine -- this should reduce wear to a minimum.

Further, the engine physically turns much less per mile that a conventional engine so total friction over time should be less.

 

[RSnyder]

The first start of a trip causes far less wear on a Prius engine than on a traditional car's engine. The additional starts on the Prius engine cause a bit more wear. But probably not enough to equal that nasty start that traditional cars must endure. So over all, the Prius engine accumulates less wear even though it starts more frequently.

 

[KTPhil]

The mechanical oil pump in the Prius starts pumping as soon as the ICE is spun. So by the time it hits 1000 rpm there is full oil pressure.

A conventional ICE spins at 200-500 rpm for several seconds, under irregular spark, with fuel washing the cylinder walls. Yet somehow those conventional engines last for 1-200,000 miles. The Prius ICE, with its lack of spark and fuel until it is up to speed (all the while with the oil pump running) will experience much less start-up wear.

 

[jeromep]

Toyota has never recommended against synthetics. In fact you would be hard pressed to find a manufacturer that does. So long as the oil used is the correct weight and is meets at least the minimum API grade which the manufacturer specifies, there is no issue with synthetics. One exception is the rotary engine in the RX8, but that is a special situation.

In addition to the way the ICE is spun up and ignited, the engine also is equipped with piston rings which were designed to reduce friction and enhance fuel economy this leads to other benefits associated with the topic of this thread. However, even without the more modern piston rings, the oil pump brings the entire oil system up to pressure in a fraction of a second, long before fuel and spark are introduced to the engine.

Compare this to a conventional vehicle which is being spun at 100-200 rpm with spark and fuel invading the cylinders and no oil pressure there when spark actually catches.

Think of the Prius engine just before ignition as a reciprocating air compressor. When they start, the oil is usually in the sump, however the oil pump system comes to speed and psi is generated before forces act significantly against the pistons.

 

[c4]

Because the oil pump is run off the driveshaft, there is oil pressure whenever the ICE is spinning, regardless of whether the ignition and fuel is being introduced.. In other words, whenever the MGs spin the ICE for starting or in the occasional high-speed EV modes where the ICE is off but is spun to prevent MG overspeed, there is oil pressure to the engine.. The pump is a trocoid design which retains oil inside its impeller cavities when stopped, so there is pretty much instant oil pressure as soon as the drive shaft is spun.