: Cruise Control Curiosity



TulsaVic
04-11-13, 01:18 PM
Now that I'm in hill country I've noticed an unusual behavior with the cruise control. As an example, say it's set at 40 mph and I start going downhill. The car will pick up speed coasting, going well beyond 40 mph (still amazed that my old 2002 Intrepid would downshift to maintain speed but my 2008 Caddy won't). Say it reaches 50 mph. If I "beep" up the cruise setting to 45 mph (I'll get confirmation on the dash that the new speed has been set) and then start going uphill, the car's speed will drop well below 45 mph, as much as 5 - 7 mph below, before the cruise control cuts in and raises the car's speed to the set 45 mph. Anyone else seeing this behavior??

Superjim
04-11-13, 01:22 PM
Nope.. Mine doesn't do that....
If I start downhill... unless it is dang near a mountain... mine maintains speed going downhill.
It lets off of the gas just like I would if I was not on cruise...
I have NEVER noticed mine dropping below the set speed except for maybe one or two mph as it gets to the bottom of the hill and the speed drops off real quick.

MoistCabbage
04-11-13, 02:43 PM
It lets off of the gas just like I would if I was not on cruise...But that won't keep it from accelerating down a steep hill.

Superjim
04-11-13, 05:17 PM
But that won't keep it from accelerating down a steep hill.
I just reread TulsaVic's post...
He said he was using the cruise at 40 mph...
I withdraw my comment as I have never used the cruise at that low of a speed.

My comment applied to speeds at more or less freeway speeds... 50/55 plus.

ffrog
04-11-13, 06:06 PM
Mine will pick up speed going downhill no matter what speed the cruise is set at. At times I have to tap the brake pedal to stay below the speed limit (if that is what I want). There was a thread on this way back, seems as though it was a common problem. I don’t think that it has anything to do with the cruise, as mine will pick up speed even with the cruise off.

Superjim
04-11-13, 06:53 PM
I don't understand your cars... Mine is not like that at all.
When I let off of the gas on mine, it immediately starts slowing down.
I would have to be on a heck of a steep hill before mine would gain any speed... assuming we are talking normal highway/freeway speeds of 55 to 70.

ffrog
04-11-13, 08:18 PM
...
When I let off of the gas on mine, it immediately starts slowing down.
...


Every car that I have driven over the past 50 plus years has also started to slow down when I let up on the gas.
My DTS and DTSs that I have driven as loaners and rentals have maintained their speed (coasting) when I let up on the gas even on fairly level ground. They do slow down, but very slowly compared to others that I have driven. I cannot remember where or when, but I did read complaints of this condition from other owners.

TulsaVic
04-11-13, 11:04 PM
Don't think you understand the situation. I used 40 mph since the max speed limit here in Maine, except for the turnpikes, is typically 50 mph or less. But the situation occurs at any set speed...and it ONLY applies when I push the "plus" to increase the set speed to a level higher than it was, but slower than what the car is actually doing.

With cruise control OFF and driving on a fairly level road, if I take my foot off the accelerator, the car will slow down, though engine braking is pretty minimal. If I'm on a downhill with my foot off the accelerator, it doesn't take much of an incline for the car to pick up speed.

With cruise control ON, if I'm going down a hill, the car would be coasting (I can tell because the instant mpg goes up to 70 mpg) and it's not unusual for the car to speed up as much as 15 mph higher than what the cruise is set to. Keep in mind I'm not talking about Texas hills. I'm talking about New England hills (Not everything is bigger in Texas....). If I don't reset the cruise control, it'll kick in as soon as the speed drops to where it was originally set. It's only when I set a different speed that's higher than where it was, but slower than the down hill coasting speed of the car, that the situation occurs.

Superjim
04-12-13, 12:27 AM
Don't think you understand the situation. I used 40 mph since the max speed limit here in Maine, except for the turnpikes, is typically 50 mph or less. But the situation occurs at any set speed...and it ONLY applies when I push the "plus" to increase the set speed to a level higher than it was, but slower than what the car is actually doing.

With cruise control OFF and driving on a fairly level road, if I take my foot off the accelerator, the car will slow down, though engine braking is pretty minimal. If I'm on a downhill with my foot off the accelerator, it doesn't take much of an incline for the car to pick up speed.

With cruise control ON, if I'm going down a hill, the car would be coasting (I can tell because the instant mpg goes up to 70 mpg) and it's not unusual for the car to speed up as much as 15 mph higher than what the cruise is set to. Keep in mind I'm not talking about Texas hills. I'm talking about New England hills (Not everything is bigger in Texas....). If I don't reset the cruise control, it'll kick in as soon as the speed drops to where it was originally set.
It's only when I set a different speed that's higher than where it was, but slower than the down hill coasting speed of the car, that the situation occurs.

Vic... I will try to check that on my car in the next day or two...
I will find a hill (without a stop sign or traffic light at the bottom) steep enough that the car will speed up faster than the set cruise speed... then I will increase the cruise speed from what it was set at... but lower than my now increased speed and see what happens.

Jim

ffrog
04-12-13, 11:55 AM
...
With cruise control OFF and driving on a fairly level road, if I take my foot off the accelerator, the car will slow down, though engine braking is pretty minimal. If I'm on a downhill with my foot off the accelerator, it doesn't take much of an incline for the car to pick up speed.

With cruise control ON, if I'm going down a hill, the car would be coasting (I can tell because the instant mpg goes up to 70 mpg) and it's not unusual for the car to speed up as much as 15 mph higher than what the cruise is set to.
...


That is exactly what I was attempting to describe, thank you.
I just live with it because I just figured it was the nature of the beast.

grullon10
04-12-13, 01:22 PM
My 06 does the same thing I travel a lot I ct specialy on the merrit for the people that haven't travel I ct the merrit is one of most beatifull road that you could travel on but there is one small problem you drive up and down it is very hilli specialy between exit 39 and 41 I could have my cruise set at 55 when it goes down hill it sped up all the way to 65.

Ozlander
04-18-13, 02:04 PM
My 06 does the coast thing also in 'D'. Set at 65 and it'll go up the 85 if you let it. Shift down the 3rd and it will hold the set speed.

hazcaddy
04-18-13, 04:46 PM
I guess it is a function of the cruise control programming combined with the fact that our cars only have 4 gears. My wife's Mercedes (7 gears) will actually gear down when going downhill with the cruise on, and keep to the "set" speed within 1 mph.

TulsaVic
04-18-13, 11:55 PM
Y'all are still missing the point. My issue has nothing to do with the car picking up speed going downhill.

Screamineagle
04-23-13, 04:07 PM
My '08 does the same thing. Set it at 60, rolling down a hill to 67,68 then bump it up to 65 with the + cruise button on the wheel and it will drop to 62 or 61 before it accelerates to 65.