High RPM Danger in Cruise Control

Short Answer:
Be not Afraid.

Even if you WANTED to, it's impossible for you to over-tach a Prius.
Ever.

Do you want to know why Priuses don't have a tachometer?
Right.
Because they don't need one.
For many cars, I would say that the buzz-kill people who designed the car wanted to remove ANYTHING that would make the driver more connected with the vehicle, and this is true enough in some cases for the Prius.
Examples: Steering, hand brake that isn't, rubber-band CVT, etc....

So.
Our Priuses don't need a tachometer because there is no mechanical connection between your right foot and the engine compartment.
In other words....it's what people sometimes call 'fly-by-wire.'
When you stomp on the accelerator pedal, you're merely sending a polite request to the engine room asking Scotty for more power.
If the squirrels are already running as fast as they can, then instead of a snarky reply in brogue you merely get ignored.

You can.....and I have, placed a heavy object on the accelerator pedal and left the car unattended for a long period of time.
You can.....and I have, placed the car in Neutral and stomped on the accelerator pedal for over a minute without anything much happening in the engine room.

Spoiler Alert:
The transmission (CVT) works the same way.
You can.....and I have placed the car in Reverse while driving on the interstate.
You can.....and I have placed the car into drive while still rolling backwards after backing out of a driveway. (It's just another form of PnG!)


Here's the thing.
Someone wiser than me once said that if you can't drive Priuses like [sic] normal cars, then you're missing the whole point of how seamless the folks in Aichi Japan made the car.
Priuses are a little more fragile than some other cars, but only because of their diminutive ground clearance, and glass-jaw front end.
If you avoid bumping into things, keep the car on paved roads, and avoid deep water on the road, then pretty much everything else will take care of itself.
You should avoid deep water anyway.....
See also: Natural Selection.

Good Luck!

 

It is true that the cruise control "steps down" too much in order to keep speed when a driver can do the same without as much revving. The driver is probably allowing a little more plus and minus time to keep the speed on a steep hill. As a result I might use cruise on relatively flat highways but not hill country roads with fairly steep uphills.

 

As already stated, its completely impossible to over-speed a Prius engine, and there's no reason not to use the speed control and let it scream up those hills. BTW, Raton pass is for pussies - they shouldn't even be allowed to call it a "pass". Red Mountain Pass (US 550) is a "pass".

 

That's true of nearly all recent cars. There's nothing special about the Prius in that respect.

It does need a tachometer, in my opinion. If it had one, you could see how fast it's actually spinning on those grades, instead of being unduly alarmed at "revving" noise that's hard to interpret.

 

See how fast what is spinning?

 

I installed a scan gage ll monitoring rpm, engine temp, I don't use cruise control on steep long upgrades, yes prolong high rpm w high outside temp can cause overheating. That will leads to Mechanical failures! I try to keep rpm below 4,000 on steep upgrades, and watch engine temp normal is around 200 degrees anything above 220+is running hot. Without Gage's your clueless!

 

I hand-fly the steep upgrades. Drive Mode doesn't matter, you are holding speed with your calibrated right foot as opposed to the car doing it via its cruise control logic.

There is no degradation in electric motor output with altitude, while the internal combustion engine typically loses 2-3.5% power per 1000 feet altitude increase due to reduced air density and oxygen content (fuel injected less due to better OAT and MAF sensing, carbureted more). Not used on the Prius, but supercharging or turbocharging or compounding (both) induction air can delay the power lapse rate.

 

There's no reason at all not to use the speed control. Seriously, the system is designed to do exactly what it does. If you do use speed control, it makes no difference what mode you're in - they're all the same when speed control is used. For that matter at highway speeds it really doesn't much matter what mode you're in anyway. There's also no risk of over-heating in a properly functioning system.

 

Hotter temp= low density of air, leaner mixture= higher combustion temp, higher Rpms = higher temps, higher altitude less density engine will run leaner, a/c on , condenser coil heats up , hot air flow thu radiator fins all these conditions will cause overheat no matter what! Why do they blow mass volume of air thu the raditor on dyno???