Cruise control cannot maintain consistent speed; frequent gear shifts leading to overheating

[A Sober Animal]

I’m about 200 miles into my road trip from Chicago to Denver, and my cruise control is starting to act up. Set at 79, the vehicle is unable to maintain the speed and will vary between 77-81. The engine will frequently switch between gears 5, 6 and 7, resulting in a jolty ride. To make matters worse, this results in the engine overheating.

This same behavior occurs at lower cruise control speeds as well, but does not seem to be as drastic. The only workaround I have found is to shift into manual and keep it in gear 6; however on hills I ended up having to adjust the gear to maintain speed

I have never had issues with my cruise control before, and this is the speed that I almost set it to on long trips. I did have my oil changed and tires rotated on Monday in preparation of this trip.

Has anyone experienced something like this before, and if so, how did you resolve? Wondering if there is any way I can reset the computer or something to see if it will resolve itself. I’ll be wheeling this weekend in the mountains of Colorado, so really hoping to avoid a lengthy trip at a dealership.

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[John VonJeep]

What do you mean when you say the engine is overheating? Is the temp just increasing (which is normal) or is it actually overheating?

 

[A Sober Animal]

What do you mean when you say the engine is overheating? Is the temp just increasing (which is normal) or is it actually overheating?

Actually overheating, but it goes away when I reduce speed.

 

[Wbino]

You need that looked into.
I have the v6 so my experience may differ........

 

[John VonJeep]

Something else is going on. Your cruise isn’t the problem. I suspect that its weird behavior is being caused by a larger problem with the engine or trans.

 

[runningshoes]

Have you tried to replicate the issue at say 65? A +/- 2 mile variance at 79 is not unusual, the gears moving all around is. Had a Sahara with the 2L, and we did a similar trip from Chicago to Ouray and never had that problem. On the steep highway uphills, the gears would drop to 5th in some cases but never jolted or had a "hard" shift.

 

[BruceA78]

I would check your fluid levels ASAP!

 

[A Sober Animal]

So update - I ended up stopping at a dealership a couple of hours after this happened in Iowa. All fluids normal; no codes or anything from the engine. We ended up topping off the coolant for the engine but they honestly had no idea what was going on. Didn’t try to cruise for an hour or so, and magically it’s back working again.

 

[AnnDee4444]

Have you checked other temperatures when this is happening? I would expect the transmission temperature to be highest if this is truly related to the shifting of gears.

Also I bet the "temperature" gauge next to the tachometer will display full red if anything is over-temperature... not just engine temperature.

 

[A Sober Animal]

And day two of our road trip and the issue is back. Cruise control was great for the first two hours, but then the issue came back. I have also noticed that when this happens, the engine has minimal power - I can floor the pedal and the car barely accelerates.

I doubt this is a coolant issue as the levels are all the same they were yesterday and I have no leaking going on under the car. I checked all of my fuses as a last-ditch effort but they were all seated. Going to try resettting the computer next, but I have a feeling this going to be something I need to take to the dealership for.

 

[JimLee]

What's the chances it's de-rating the engine because of turbo temps like on the Diesels?

 

[srt20]

Oil temp hot too? Trans temp? Whats the actual coolant temp?

 

[A Sober Animal]

Coolant will be around 249 when it gives me the warning. Unsure of the trans temp, I want to say around 199, but could be wrong. However, the issue of it heating up is only a final end result that makes me turn off the cruise control. The inconsistent speed takes place for a while before that happens.

What I find odd now is that when this happens, I’ll try to floor it and have no power. I was trying to pass a semi earlier and flooring it wouldn’t even get it past 78. I’m wondering if there’s an issue with the engine getting air or the turbo getting air. I did just stop at a self car wash and using low pressure cleaned the engine bay, and rewashed the front/radiator to see if that helps. I also checked the air filter to make sure nothing was stuck in there and it looked clean.

 

[srt20]

Coolant will be around 249 when it gives me the warning. Unsure of the trans temp, I want to say around 199, but could be wrong. However, the issue of it heating up is only a final end result that makes me turn off the cruise control. The inconsistent speed takes place for a while before that happens.

What I find odd now is that when this happens, I’ll try to floor it and have no power. I was trying to pass a semi earlier and flooring it wouldn’t even get it past 78. I’m wondering if there’s an issue with the engine getting air or the turbo getting air. I did just stop at a self car wash and using low pressure cleaned the engine bay, and rewashed the front/radiator to see if that helps. I also checked the air filter to make sure nothing was stuck in there and it looked clean.

Well the ECU is obviously cutting timing so you dont wreck the engine. I'm surprised the dealer didnt find any codes. But who really knows if they actually checked.
Other than that, it really needs a competent mechanic to diagnose whats happening. Sorry I couldn't help ya more.

 

[GATORB8]

Coolant will be around 249 when it gives me the warning. Unsure of the trans temp, I want to say around 199, but could be wrong. However, the issue of it heating up is only a final end result that makes me turn off the cruise control. The inconsistent speed takes place for a while before that happens.

What I find odd now is that when this happens, I’ll try to floor it and have no power. I was trying to pass a semi earlier and flooring it wouldn’t even get it past 78. I’m wondering if there’s an issue with the engine getting air or the turbo getting air. I did just stop at a self car wash and using low pressure cleaned the engine bay, and rewashed the front/radiator to see if that helps. I also checked the air filter to make sure nothing was stuck in there and it looked clean.

Turbo limp mode may fully open the waste gate, basically bypassing the turbo.
can’t believe it’s not throwing a code when that happens.

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