Need help again - transmission overheating while towing

[15Ram64]

Months ago I joined here to ask about fifth wheel weight and our truck's capabilities. I got a lot of great info and advice. We finally made a decision and purchased a fifth wheel in January. Took it on its maiden voyage Easter weekend. Everything went great. We took it on its second trip this weekend and on the way home, the check engine light came on, then shortly after a message showed up saying "transmission is too hot". So we had to pull over for a bit. One thing to note, we had it in 'tow/haul' mode. Whenever we started going after a red light, the transmission would make a very hard shift at 2500 RPMs. That stopped after the truck cooled down. We made it home safely, but the check engine light was still on.

We have a 2015 2500 Tradesman with the 6.4 hemi. We do have an appointment next week to have it looked at, but wondering if anyone has experience with this issue? Any ideas on what would cause it? We plan on taking it on a long trip next month and I'm concerned.

 

[HDGoose]

What weight is the trailer? What is the pin weight? How was the truck loaded while towing?

 

[15Ram64]

What weight is the trailer? What is the pin weight? How was the truck loaded while towing?

This is what we have.

 

[GsRAM]

I wonder if the transmission thermostat is clogged or stuck partially closed? It's a possibility anyway.

Do you have 3.73 gears? If so, your asking a lot of the 6.4 with a large 5th wheel like that. They are tall and have a lot of wind resistance. How fast were you going on the highway?

The info HD asked is also good. But what is your actual loaded, ready to camp weight? What did you have in the truck bed? Is your truck lifted/oversize tires? Those sort of things detract from towing ability.

Need more information.

 

[crash68]

Post up the CEL code, might give a clue as to what's the problem (most auto parts stores will read them for free).
Which gearing does the truck have 3.73 or 4.10? and how fast are you trying to pull this trailer? We're you climbing a grade when it the high temp happened? What were the ambient conditions when this happened (wind, temp, etc)?

 

[15Ram64]

I wonder if the transmission thermostat is clogged or stuck partially closed? It's a possibility anyway.

Do you have 3.73 gears? If so, your asking a lot of the 6.4 with a large 5th wheel like that. They are tall and have a lot of wind resistance. How fast were you going on the highway?

The info HD asked is also good. But what is your actual loaded, ready to camp weight? What did you have in the truck bed? Is your truck lifted/oversize tires? Those sort of things detract from towing ability.

Need more information.

Yes, 3.73. We really don't know actual weight as the closest scale is several hours away. The truck bed had a stepladder and our dog's kennel. We bought the truck used and I don't believe it's lifted but it has spacers in the front...yes on the oversized tires.

 

[15Ram64]

Post up the CEL code, might give a clue as to what's the problem (most auto parts stores will read them for free).
Which gearing does the truck have 3.73 or 4.10? and how fast are you trying to pull this trailer? We're you climbing a grade when it the high temp happened? What were the ambient conditions when this happened (wind, temp, etc)?

We have 3.73 gears. Hubby was probably traveling around 50 mph, no real steep grades. We were traveling on 301 near Doswell VA (if you're familiar with that area). I think it was in the 80s yesterday.

 

[GsRAM]

Yes, 3.73. We really don't know actual weight as the closest scale is several hours away. The truck bed had a stepladder and our dog's kennel. We bought the truck used and I don't believe it's lifted but it has spacers in the front...yes on the oversized tires.

Your 3.73 gears, plus your oversized tires and a loaded trailer weight, if I had to guess at or over 10k lbs, is a recipe for a 6.4 powered truck to struggle.

With that said, temps in the 80s and no steep grades and doing 50 mph makes me think it's more than just that and you have a mechanical or electrical issue going on.

 

[2003F350]

Your 3.73 gears, plus your oversized tires and a loaded trailer weight, if I had to guess at or over 10k lbs, is a recipe for a 6.4 powered truck to struggle.

With that said, temps in the 80s and no steep grades and doing 50 mph makes me think it's more than just that and you have a mechanical or electrical issue going on.

I agree. While I could see the truck struggling a bit with the 3.73's and oversized tires, it still should have handled it without too much issue. There is definitely more going on here, which is common with a used truck that you don't know the complete history on. If you went to a competent shop, they'll check out everything and make recommendations regarding any repairs. There are a lot of variables to transmission temperature on these trucks, a great many of which really shouldn't be there (like the transmission thermostat - a great way to add a restriction and potential clog that will slaughter a transmission in short order).

Once everything has been diagnosed and fixed, I would also recommend either going back to stock-size tires, or changing your gear ratio, to bring things back into spec and make it pull just a bit better. Tires would be cheaper, gearing will be more permanent. I wouldn't recommend going to 4.11's (even though it's a factory option) because the cost just doesn't justify the return, I would go with 4.56's or 4.88's. The performance would definitely bring things back to, or better than, factory.

 

[15Ram64]

I agree. While I could see the truck struggling a bit with the 3.73's and oversized tires, it still should have handled it without too much issue. There is definitely more going on here, which is common with a used truck that you don't know the complete history on. If you went to a competent shop, they'll check out everything and make recommendations regarding any repairs. There are a lot of variables to transmission temperature on these trucks, a great many of which really shouldn't be there (like the transmission thermostat - a great way to add a restriction and potential clog that will slaughter a transmission in short order).

Once everything has been diagnosed and fixed, I would also recommend either going back to stock-size tires, or changing your gear ratio, to bring things back into spec and make it pull just a bit better. Tires would be cheaper, gearing will be more permanent. I wouldn't recommend going to 4.11's (even though it's a factory option) because the cost just doesn't justify the return, I would go with 4.56's or 4.88's. The performance would definitely bring things back to, or better than, factory.

It handled great our first trip so I was surprised at how it did yesterday. I did TONS of research to make sure we got a fifth wheel that our truck could handle and all of the numbers looked fine. I do know of 5 or 6 others that have the same camper and pull with their hemi and no issues. Upgrading our truck is not in the cards right now. I'm starting to getting really worried that we made a huge mistake.

 

[dhay13]

I agree it sounds like a mechanical issue with the truck. The oversized tires definitely aren't helping either. Your 3.73's are probably closer to 3.50's or so depending on how tall the tires are and that will make the transmission work harder. I towed my step-sons 9300lb camper (CAT scaled) 100 miles with my 2018 with 4.10's and you could barely tell it was back there. It was a bumper pull and flat ground but literally could barely tell it was there. It is a 2021 Grand Design Imagine 3250BH. My son tows his 8000lb TT all over the country with the exact same truck as me and after about 8000 miles of towing has never had a single issue.
Get that trans checked out and like was said, post the codes here so maybe someone can help diagnose it.

 

[2003F350]

It handled great our first trip so I was surprised at how it did yesterday. I did TONS of research to make sure we got a fifth wheel that our truck could handle and all of the numbers looked fine. I do know of 5 or 6 others that have the same camper and pull with their hemi and no issues. Upgrading our truck is not in the cards right now. I'm starting to getting really worried that we made a huge mistake.

Yeah, sometimes stuff just breaks and it's not really something you would notice until you started to work the truck a bit. Hopefully they get it fixed for you quickly.

Since you state that major upgrades like gears aren't in the cards, then I definitely recommend going back to stock-size tires. That will help relieve stress on the transmission and should lower your temps by bringing your effective final drive ratio back to what it should be.

 

[mtnrider]

What size are you tires? I know you said over sized but how over sized are they? They look pretty aggressive in the profile picture. Look to be at least 35's which is going to be hard on the that truck with that trailer and engine/gear ratio combo.

 

[15Ram64]

What size are you tires? I know you said over sized but how over sized are they? They look pretty aggressive in the profile picture. Look to be at least 35's which is going to be hard on the that truck with that trailer and engine/gear ratio combo.

Yep, 35s.

 

[ripping r]

I wonder if the transmission thermostat is clogged or stuck partially closed

this is where i would start. pulling my 10,000 rv in the hills i never see over 160. i deleted mine with the ATS one.

 

[OC455]

Get the transmission cooler/thermostat checked on it. That's probably the reason more than anything.

I agree that going back to the factory tires is better for towing.

I really would like to get a Grand Design 28BH like you have, because it is within specs for my truck.

 

[15Ram64]

Get the transmission cooler/thermostat checked on it. That's probably the reason more than anything.

I agree that going back to the factory tires is better for towing.

I really would like to get a Grand Design 28BH like you have, because it is within specs for my truck.

We really like the 28BH so far.

 

[caulk04]

Service the trans, delete the thermostat and consider going down a little in tire size. Keep an eye on it while towing.

I've noticed that running the AC really pumps a lot of heat into the system, the coolers never see cool air. Dropping the windows and killing the ac could make a noticeable difference in a pinch.

 

[GsRAM]

I agree. While I could see the truck struggling a bit with the 3.73's and oversized tires, it still should have handled it without too much issue. There is definitely more going on here, which is common with a used truck that you don't know the complete history on. If you went to a competent shop, they'll check out everything and make recommendations regarding any repairs. There are a lot of variables to transmission temperature on these trucks, a great many of which really shouldn't be there (like the transmission thermostat - a great way to add a restriction and potential clog that will slaughter a transmission in short order).

Once everything has been diagnosed and fixed, I would also recommend either going back to stock-size tires, or changing your gear ratio, to bring things back into spec and make it pull just a bit better. Tires would be cheaper, gearing will be more permanent. I wouldn't recommend going to 4.11's (even though it's a factory option) because the cost just doesn't justify the return, I would go with 4.56's or 4.88's. The performance would definitely bring things back to, or better than, factory.

This is sound advice if you go back to a stock tire size. If you keep your bigger tires, and elect to regear, consider a 5.13 gear, especially at the weights your pulling. I've heard reports of folks who went with a 4.56 gear on stock tires and wish they would have went with 4.88s

Good luck in getting it ironed out and I hope it's an inexpensive fix.

 

[15Ram64]

Thanks to all for the responses and advice. I'll report back next week after service takes a look at it.