Slight performance decrease

[A_User55555]

A few weeks ago, I noticed a slight performance decrease in my 2011 DTS. When I first bought it with 80K miles, I could lightly press the accelerator pedal and next thing I know, I'm going 80MPH.

Now when I do the same thing, I still pick up speed, but I feel not as much as before. I have to push slightly harder. When I did a WOT, I got the impression that the car accelerated a bit slower than before. The car now has 90K miles on it. No codes or anything.

I run Mobil 93 Gas and changed the oil and filter 1K miles ago.

Now last weekend I installed new Tires on my DTS. I noticed that after this, my MPG went down a few gallons. It also seems like the car "brakes" a little by itself. Ill be on a flat road then turn off cruise control. Ill then feel the car decelerating faster than it did before. This is because of the rolling resistance of the new tires right?

 

[OVERKILL]

Sounds like you could have a stuck brake calliper. Do any of the wheels feel hot after a drive?

 

[A_User55555]

I'll have to check. When I bought the car last April, All the brake calipers were painted by the dealer. So I figured they probably greased the caliper pins. All the rotors were resurfaced and the front pads were replaced. I saw grease put on the edges of the pads too so things are less likely to be stuck.

If it were a dragging caliper, would one wheel feel significantly hotter than the other or just slightly more warm?

 

[Kestas]

I check for stuck brakes by rolling ever so slowly in neutral. If there was a problem, the car would stop relatively abruptly.

 

[OVERKILL]

Originally Posted by A_User55555
I'll have to check. When I bought the car last April, All the brake calipers were painted by the dealer. So I figured they probably greased the caliper pins. All the rotors were resurfaced and the front pads were replaced. I saw grease put on the edges of the pads too so things are less likely to be stuck.

If it were a dragging caliper, would one wheel feel significantly hotter than the other or just slightly more warm?


Yes, if you have one dragging it will be significantly warmer than the others.

 

[Eddie]

The new tires may not be as low rolling resistance as the original. The new tires might be slightly larger in circumference. Ed

 

[eljefino]

Originally Posted by Kestas
I check for stuck brakes by rolling ever so slowly in neutral. If there was a problem, the car would stop relatively abruptly.


Best trick is to toss it in neutral while going up a very slight hill at 5 mph. Let the car coast to a stop then reverse. If you have a dragging brake you'll feel it at the moment of direction reversal. Do this after driving so the wheel bearing grease etc is thinned out.

 

[MONKEYMAN]

Tires do make a difference. I just replaced OEM NPriz AH8 on my Elantra with Continental True Contact. I have the opposite problem you are reporting. My car is going at higher speed faster than before. Roll resistance does make a difference.

Have you checked the tire pressure? The tire shops I use never set the correct tire pressure even when I ask them.

 

[krismoriah72]

Winter blend gasoline?

 

[A_User55555]

Slight update. I still feel this lack of performance. But it is intermittent. I did a couple of tests a few days ago. I started driving the car on long stretch of road when I felt like the performance issue wasn't there. I then pressed the brakes firmly, let go then got back up to speed. I did this a couple of times, but not enough to make the brakes super super hot.

I got the impression that after I let go of the brake pedal, the car took longer than usual to get up to speed. When I pulled into a parking lot, The front rotor was too hot to touch, and It looked like the outside edge of the rotor had some slight discoloration but its hard to tell. Note that the rotors felt hot because I did a lot of firm braking over a short period of time.

Other times before I leave for a drive, Ill push the brake pedal hard and let go, but I don't notice any difference in acceleration.


I then continued my driving and when I stopped to put gas, the rim was cool to the touch, and the front rotor felt warm to the touch. The rotors and rims have never been too hot to touch unless I do a lot of severe braking.



If one of the caliper pins were sticking a little bit, would it cause the rotor to be too hot to touch all the time? Or can brakes still drag where the car will slow down, but the rotors and pads won't get too hot.