Transmission Excessive Heat Light

I’ve got a 2005 4.7L 4x4 Dakota with 170,000 miles. Bought it used last year. Since I bought it, I’ve replaced the water pump, all coil packs/plugs/wires and a few other regular maintenance details. I drive 40 miles to work through the mountains. At about the 20 mile mark, the heat light for the transmission comes on and about 5 miles later, goes off. What is causing this and is it something I need to be worried about?

Yes. You should worry.

Heat is what kills transmissions.

Check the condition/odor of the transmission fluid.


Would old fluid cause that or could it be something more serious?

Old worn out transmission fluid can cause slipping and an overheating transmission.


You should make it your first priority, as in get a competent mechanic’s advice asap. Do you have or can your rent another vehicle until you know more? Is this a new problem or has it been occurring since you got the vehicle? Can you associate it with something that has changed (your route, load, ambient air temperature)? Have you checked both the ATF level and condition (color, smell)? Does driving in a different gear help?

It only happens on my way to work, so highway driving in the mountains at about 70 mph. It only started happening last week, I can probably get it into the mechanic next week. Its an automatic so the only gear I could shift to when it’s happening on the highway is 2nd, no way to test it shifting changes anything without shredding the transmission. Would adding fresh fluid buy me any time? Is there an easy way to drain some or do I have to do a full flush? If the fluid is okay, what else could be causing the issue? How much is this going to cost me, best case worst case, is what I’m trying to get at.

There may be a restriction in the transmission cooler, does this truck have the tow package with auxiliary cooler? You might consider replacing the radiator to be sure that the transmission cooler is working properly and performing a transmission service.

  1. The fact that it’s a new event suggests something is changing for the worse, possibly in a hurry.

  2. Worst case is a transmission rebuild or replacement, easily several thousand $$ or more, more likely the longer you keep driving it. Suggest you park it until diagnosed by a qualified shop, the shop may offer a loaner or discounted rental which is excellent insurance at this stage. If you don’t have one, consult Car Talks “Mechanics Files” for recommended shops. If the shop is far away, tow it.

  3. Best case is the fluid just needs topping off, or replacement. It should be easy to check the level at home (there is a specific procedure, should be instructions in owners manual or a mechanic can do it) - do this today. If below the limit add a quarter or half qt. at a time, recheck, don’t over fill (low-to-full may be just 1pt., if over full have the excess sucked out). If a change is needed take it to a qualified independent shop or dealership (not a chain, they’re often not well trained, might do anything, and often try to sell unneeded services). Use the approved fluid - vehicles are very specific and the wrong fluid can do damage. Transmissions seldom need after market additives - possible exception is for a minor leak and consult a Dodge dealer about what’s safe for that.

  4. There are other potential causes, some easily corrected and relatively inexpensive, if addressed asap.

  5. Does the transmission have a locking torque converter that should be disengaged while driving in the mountains? (Owners manual is your source.) One thing that overheats and wears transmissions is excessive shifting which can happen in the hills, so it may be better to go down a gear or two and control the shifting yourself. (See owners manual). Learn what the transmission actually does when you put the shifter in “2nd” (owners manual), at higher speeds it may just shift down one gear such as from 5th (I believe your’s is a 5 sp.) to 4th, or from 4th to 3rd, working its way down as appropriate for your current speed. Most (maybe all) modern automatics won’t drop into too low a gear for the speed when shifted to 2nd. Learn the maximum speeds for each gear (owners manual).

  6. The fact that this just started happening is a big red flag (see Items 1 and 2). Take it seriously, best wishes, and let us know the outcome.

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truck has 545rfe trans.
3 rd gear is 1:00
4th is 0.75
5th is 0.67

A full transmission service (including a pan drop, drain, replace the filter, sieve the old fluid & inspect for metal debris, and refill if that’s possible) and checking for a restriction in the trans cooling lines that run through the radiator is the common-sense first thing to do. From what I see there’s a chance your truck sports a separate air-to-fluid trans cooler, located in front of the radiator. If so, that should be checked also. Verifying the radiator fins aren’t plugged up with bug debris, and that the radiator fans are working is common sense too.

New symptom! Light came in this morning, I switched to neutral for as long as I could safely coast on the highway. When I put it in neutral, the light turned off. I put it back in drive and it never came back on.

There’s no new information there, transmissions heat up when they’re working (but normally don’t overheat) and cool down when coasting.

You should be concerned about why it’s overheating in the first place, and sufficiently concerned to get it into a shop. Your problem may be relatively inexpensive to fix at this point but become very expensive very soon, especially given your 80mi. commute.

Hey all, thanks for the insight. Took it in, fluid was broken down. For those who felt I wasn’t taking it as seriously as I should have, I was. I don’t have the means to rent a car or drop everything (including work) to go to a shop. I got it done

Broken down fluid suggests that your vehicle hasn’t enjoyed routine fluid inspections and changes (this didn’t happen over night, it likely aged your transmission some and left too long it could have ruined it). If you haven’t already done so suggest that you either verify the condition of or replace the other fluids and the belts and do any other maintenance or adjustments the manufacturer recommends. It might pay off in the long run to consult with a good independent mechanic (or dealership) to set up a fluids/inspection/maintenance schedule as letting things go can cause much woe. Preventative maintenance is cheaper in the long run, and easier to budget for than break downs. Also review how to properly use your automatic transmission to reduce excessive shifting while driving in mountains, in an earlier remark you appeared to have an misconception about that. Enjoy your truck.

Thanks. Since I bought the truck last year, I’ve replaced the water pump (new coolant, new belts), full brake job including calipers (new brake fluid) and the power steering lines (new fluid). Now that the transmission fluid is done, other than blinker fluid I should be good. I do VERY regular maintenance on my vehicles because I’m very aware of the long term savings. I know what repairs are coming in the next 6 months and what I plan to change before they wear. As for excessive shifting in the mountains, I maintain a speed of 65, never use cruise and avoid hard acceleration to prevent downshifting at high speeds. That’s how I was told to drive out here. If that’s incorrect, please let me know because I do not want to damage my truck.

Sounds like you’re off to a good start with the maintenance. When hills are sufficiently steep there are several reasons why you may want to hold the transmission in a lower gear gear than it would select automatically. a) if the throttle response is sluggish going up hill you can shift down a gear or two into a higher rpm range that provides more torque or “climbing power” - the rpm for peak torque may be listed in the owners manual or available on-line, but when pulling a large load you can feel from the throttle response when you’re near it. When the vehicle has sufficient power you won’t need to go as high as the the torque peak, but if it’s struggling to maintain speed such as with a full load on a steep hill at high elevation, etc., one would select an rpm somewhat above the peak torque rpm, maybe 500-1000 rpm higher, so that when the load increases and the vehicle slows more torque becomes available to arrest the decline in speed. Keep an eye on the coolant temperature and the transmission temp. light when pulling large loads. b) if you find yourself using the brakes frequently or for long periods while going down hills, you can reduce brake wear, the risk of disk warping, and the chances of brake fade or outright failure due to overheating by shifting down to obtain more engine braking - try it one step at a time and watch the tachometer to confirm rpms don’t go too high, but modern electronically controlled automatic transmissions should protect themselves from shifting down too far (but with a manual transmission it’s all on the driver to prevent this by not selecting too low a gear). Depending on your transmission details, you might accomplish this by by first locking it out of overdrive (if it has that mode) and/or by shifting the selector to one position down from drive, or it may have a manual shift mode where you can select a gear up or down one step at a time. c) If you find the transmission shifting up and down frequently on it’s own while in hills you can reduce this by shifting down one or two gears to get the engine to turn at higher rpms, an example might be going into the 3000-4000rpm range rather than the sub-to low-2000rpm range you might see in “Drive”, just enough to reduce the frequent shifting or whatever seems proper for the situation. The above may be covered in the owners’ manual and If you have any concerns best to review this with your mechanic rather than taking it from a stranger. Best wishes.

OP, you were getting a warning for excessive heat in the transmission, apparently due to broken down fluid letting the transmission slip, and changing the fluid and filter solved this and the warning light no longer appears? I’m a little surprised that worked. I’ve always been told that once the fluid is left in long enough to allow the transmission to slip, the damage is done and new fluid won’t help. Just curious. So no more warning lights showing up?

Hopefully, they put in the proper fluid, which is ATF+4. Anything else, and transmission problems are likely to reappear.

It’s a Dodge. Transmission problems are likely to reappear anyway. :grimacing:

I have nothing against Dodges, I had a 1998 Ram and liked it. But man, that particular truck ate transmissions like a fat man eats fried chicken. I changed the fluid and filter every 30k miles since new (I think it was ATF +3 back then), but it failed at 130k, the rebuild failed at 170k, and I sold it at 190k. I think if I had it to do over, I would’ve had a factory reman unit installed when it failed the first time. To be fair, it never shifted exactly right after the first rebuild. Transmission trouble is the worst.

Yeah, I was a little surprised it worked too but no, not a single warning light since. I’m sure damage has been done, I just need it to get me through one more winter in the mountains. At 170000, I know she doesn’t have much left. Who knows what the previous owner did to her.