Engine revs up on long down hill
 

When I come off our hill, about 1.5 miles, and I have it in L at the bottom the engine will rev up to 3-4k while I come to a stop. If I pop it into D then it goes right to 1k or shuts off.

Also do the MMH come stock with a block heater? I did not know my truck did till I found the 110 plug tucked behind the battery.

Thanks
TC

Re: Engine revs up on long down hill
 

I would be interested in the answer to this as well. When I was going down the steep trail I reported earlier the ICE would pop on to "charge" when I was riding the breaks down. I think this might have been response to dropping ICE temperature but it was disconcerting anyway.

Re: Engine revs up on long down hill
 

No this has nothing to do with the warming up the engine or charging. The battery is full by the bottom of the hill and soon as I pop it in D it goes right to 1K or off so it must be warm too.

Re: Engine revs up on long down hill
 

The ICE will fire up on a long downhill when you exceed 40mph (that is the upper mph limit), the engine temperature (cylinder head temperature) drops around or below 124 degrees and when your hybrid battery state of charge (SOC) exceeds a certain %--normally the hybrid battery SOC is kept between 40-60% for the 2005-07 models while the 08 may be allowed 35-65%. :D

Re: Engine revs up on long down hill
 

I have noticed the same thing, it will rev to 3-4000 RPM while slowing from a long downhill, and then if stopped for a light it continues to rev while stopped. Shifting out of L gets it to idle normally. Seems strange. phil

Re: Engine revs up on long down hill
 

Right know all that and that is normal. What I am talking about is a high rev 3-4k rpms. If you come to a stop at the bottom of a hill it will stay at the high rev until you put it in D. Now when it does rev, you do not accelerate or anything like that, it just revs.

Re: Engine revs up on long down hill
 

The short version is, when the battery is "full" there is no where to send the regen wattage. So the traction motor makes wattage ( slowing you ) and sends it to the generator instead of the battery. The generator motor is what "starts" your car every time you turn the key. So with all that extra wattage, the generator spins up the ICE, basically just as a big air compressor, to dissipate the load.

This is your "low gear" engine brake, in a round about way.

Actually it is very clever, totally normal, and totally designed to do that.
All fuel is shut off when this happens also.
:shade: -John

Re: Engine revs up on long down hill
 

The high revving is normal. When you are going downhill in L, the car is using regenerative braking to use the car's kinetic energy to spin the generator. Sinning the generator causes resistance which helps slow the car down. The energy has to go somewhere and until it gets full, it goes to the battery. Once the battery is full, the energy still has to go somewhere so it is used to spin the other motor which spins the ICE. The ICE is actually off in that no fuel is fed, but the energy required for the second electric motor to overcome the resistance of spinning the cylinders uses all the excess energy created by the generator. Seems a bit of a waste, but the brakes turn all that kinetic energy into head so at least you recaptured some of it, and you are saving wear on the brake pads.
Hope this helps,

rcomeau

Re: Engine revs up on long down hill
 

Thanks guys that makes sense.

Ok so 2nd part of OP is there a cold plug or block heater?

Re: Engine revs up on long down hill
 

An engine block heater is an option, for additional cost in most states.

You can DIY for about $170 or have a dealer put one in for ~$300.
Price is for 3 parts, plug, block heater, battery warmer.
If you skip the battery warmer, cut price in half.

It should be listed on the window sticker if yours comes with one.

This will help people who have short drives at low speeds after a cold start most. If you go from a cold start to a freeway right away, it's not such a great help. -John

Example: on a 10 mile drive at 15 degrees F in the city, the block heater takes 20 cents of power, and saves 30 cents of gas, because it lets you use EV mode more. If you go right to speeds over 40 miles per hour, EV is not allowed, and you might not "get your 20 cents" of power back in the form of gas savings. Of course the heater and defroster works quicker.
;)