Towing and temperature issues

[lectric74]

I have an 12 Yukon XL 5.3 with all the heavy duty trailer options (JL1, K5L, KNP, Z82, 8k rating), and I tow a 24' camp trailer that weighs in at about 4500, give or take, with a WD hitch. Towing down to my house this last weekend I noticed that with the A/C running (94 outside), that my engine temp would climb to the 3/4 mark, and trans temp was about 220 at the highest, averaging around 210. I could turn the A/C off for a bit, get hot in the truck, then turn it back on and the coolant temp would drop for a while to 210, with trans about the same, but would creep up slowly.

Question is, before I tow a bit longer this weekend, is there anything I can do to help keep that temp lower that isn't going to cost a lot? It already has a heavy duty trans cooler, radiator, oil cooler, and the 2 speed cooling fans, but is there anything I can do to help that temp stay a bit lower. The trip this weekend has a few fairly steep hills to climb, and I'm leaving earlier in the day so it will be cooler, but anything else that might help? Any additives to the cooling system that might help keep that temp a bit lower? Anything I need to check? Outside of towing the Yukon has been absolutely flawless, even with 219k on the clock, so I'm hoping this isn't a serious issue, but want to ask.

 

[swathdiver]

I have an 12 Yukon XL 5.3 with all the heavy duty trailer options (JL1, K5L, KNP, Z82, 8k rating), and I tow a 24' camp trailer that weighs in at about 4500, give or take, with a WD hitch. Towing down to my house this last weekend I noticed that with the A/C running (94 outside), that my engine temp would climb to the 3/4 mark, and trans temp was about 220 at the highest, averaging around 210. I could turn the A/C off for a bit, get hot in the truck, then turn it back on and the coolant temp would drop for a while to 210, with trans about the same, but would creep up slowly.

Question is, before I tow a bit longer this weekend, is there anything I can do to help keep that temp lower that isn't going to cost a lot? It already has a heavy duty trans cooler, radiator, oil cooler, and the 2 speed cooling fans, but is there anything I can do to help that temp stay a bit lower. The trip this weekend has a few fairly steep hills to climb, and I'm leaving earlier in the day so it will be cooler, but anything else that might help? Any additives to the cooling system that might help keep that temp a bit lower? Anything I need to check? Outside of towing the Yukon has been absolutely flawless, even with 219k on the clock, so I'm hoping this isn't a serious issue, but want to ask.

Hi Jason, are you asking about the transmission or coolant temps or both? As for the engine cooling system, make sure the fluid is less than 5 years old and still the right mixture. The transmission fluid has a service life too that is visible with a scan tool as a percentage but if you've recently changed it, those temps are fine.

GM doesn't consider the transmission temp hot until it gets up into the 260s.

The ECT gauge on the dash is purposely designed not to move around much and at normal cruise, the temperature is actually lower than it shows, around 195. If the temps begin to climb past 210, it will then show a more accurate reading. This was done so as not to alarm the driver (such as soccer moms) as the temperature moved throughout its designed operating range.

If you head into the hills, stick her in 4th gear, that's what the shop manual says is the preferred gear for towing, this spins the motor to cool the engine proper while towing and 4K rpms is nothing to these LS motors. My guess is that you were towing in 5th or 6th when the coolant got that hot?

 

[lectric74]

I was in Tow/Haul mode with the trans typically staying in 5th, but I will switch over to manual, especially on the hills, and kick it down to 4th. I was more concerned with trans temps, as that's quite a bit higher than I see under typical conditions, but glad to hear it isn't as bad as I thought.

Water temp did stay in the "normal" range, I will have to watch with Torque to see what the actual temp is when I'm towing. It's just a bit nerve wracking to see it at the 3/4 mark (255 is what that would typically mean on the gauge), and I wasn't sure if this was something to be concerned with.

No idea on coolant age, as I only bought this last month, but I'll add a coolant flush to the list of things to do. It likely won't be before this weekend, so I may try something like Water Wetter to try to keep it a bit cooler, without having to do a full flush that I don't have time to do. I still have front/rear diff fluids to do, trans flush, transfer case drain/fill, and a few other minor things like replacing the screen and oil pressure sensor, as it reads low and triggered the SES.

Thank you swathdiver!

 

[swathdiver]

I was in Tow/Haul mode with the trans typically staying in 5th, but I will switch over to manual, especially on the hills, and kick it down to 4th. I was more concerned with trans temps, as that's quite a bit higher than I see under typical conditions, but glad to hear it isn't as bad as I thought.

Water temp did stay in the "normal" range, I will have to watch with Torque to see what the actual temp is when I'm towing. It's just a bit nerve wracking to see it at the 3/4 mark (255 is what that would typically mean on the gauge), and I wasn't sure if this was something to be concerned with.

No idea on coolant age, as I only bought this last month, but I'll add a coolant flush to the list of things to do. It likely won't be before this weekend, so I may try something like Water Wetter to try to keep it a bit cooler, without having to do a full flush that I don't have time to do. I still have front/rear diff fluids to do, trans flush, transfer case drain/fill, and a few other minor things like replacing the screen and oil pressure sensor, as it reads low and triggered the SES.

Thank you swathdiver!

My pleasure sir! She'll run a whole lot nicer with fresh fluids in the drive train. Good luck and let us know how she tows and grab a pic or two of the whole set up if you can.

 

[lectric74]

I can say towing it home was about 92 miles, and she towed like it wasn't there. Trailer braking was solid once I got the gain adjusted to my liking, and it was easily able to hold 65-70 even with a bit of a headwind. My Dakota with a 6 spd. manual and 4.7 was a chore to even maintain 60, typically in third if there was a head wind, fourth if not, but never into 5th or 6th unless it was downhill, then it wouldn't be shifted up anyway, and always getting passed on hills by semi trucks. I'll try to get some pictures, where I store the trailer at home I can't get a shot, but I should be able to get one at the campground we are staying in.

 

[97audia4]

I have had the temp go up to about 225/ 230 but it has always gone back down while towing and never above that . It seemed to cycle while in tow haul mode . This was 5000 lbs extra height enclosed trailer

 

[lectric74]

I will watch it using my OBDII reader and Torque this weekend when I'm towing. This trip is 180 miles each way, and has a few fairly steep grades to climb, but I think I'll be ok. I do have a new oil pressure sending unit and the filter that I'm going to replace tomorrow, that should resolve the low oil pressure readings that have been popping up lately and tripped the SES. The Yukon has 219k miles, so I'm sure that filter is the real issue, but I'm not about to replace the screen without doing the sending unit.

I'll have to do a bit of research on logging things, so I can log the entire trip and see what the temps are really running. ECT appears to be staying in the normal range, but I'm still adding a bit of Water Wetter to help keep it a bit cooler until I can get a full flush done.

 

[97audia4]

There is also a pressure relief valve on the expansion tank. I had mine go bad, didnt notice it until it actually started to leak coolant ever so slowly that could be lowering the psi of the cooling system pressure and making it less effective.

 

[lectric74]

There is also a pressure relief valve on the expansion tank. I had mine go bad, didnt notice it until it actually started to leak coolant ever so slowly that could be lowering the psi of the cooling system pressure and making it less effective.

Where is this valve located? I'd like to check it out.

Trip went well, overall engine temps peaked at 240, according to Torque, with trans peaking at 220. Outside of that, which I don't like 240 on a gas engine, everything worked exactly as expected. I did not add any additives, I'm going to focus on getting a flush done in the next week or so, after I get the trailer hauled back to my property for the rest of the summer. No pics, things were hectic and I forgot, but I will get pics when I haul the trailer up this weekend.

 

[97audia4]

Where is this valve located? I'd like to check it out.

Trip went well, overall engine temps peaked at 240, according to Torque, with trans peaking at 220. Outside of that, which I don't like 240 on a gas engine, everything worked exactly as expected. I did not add any additives, I'm going to focus on getting a flush done in the next week or so, after I get the trailer hauled back to my property for the rest of the summer. No pics, things were hectic and I forgot, but I will get pics when I haul the trailer up this weekend.

On the bottle of the tank near the bracket for the air box. Its a small hole, I would go for a drive and get the car hot and look under the bottle where the fender liner is you will see drips. I never noticed it until I shook the bottle and saw it start to drip.

 

[lectric74]

I will check that out later this week when I have some time off. Thank you!

 

[thompsoj22]

ok so not trying to highjack but just got back from a trip to mammoth lakes ca. 190 miles from Ridgecrest ca at 2500 ft. to mammoth 8,000 ft. with an evil 14 mile 6% grade from bishop to crowley lake, avg temp 98f until you hit crowley lake than 78f. I have an 08 yukon denali xl 6.2 with 135,000 miles and tow an approx 4,750lb travel trailer. I recently changed the "holy grail of grills" out for the standard Silverado/tahoe grill with the lateral bars and there is no doubt about it that the "Denali holy grill" restricts ram air effect! seriously prior to installing the different grill the trans temp would not drop when decending a grade? my thought is that when decending and throttle off the coolant temp drops and turns off the electric fans and without suffecient ram air the trans cooler is stuck in "stale air"? with the new grill the trans never exceded 207 on the grade and averaged 175 on the flats. Stock trans cooler, is it possible that design engineers sacraficed performance for their perception of a luxury grill?

 

[Larryjb]

Does everyone let their engine coolant rise to 220/240 when towing? At what point would you turn off the AC and open the windows?

My 2008 Explorer with the 6 speed kept the coolant below the 212, even going up the Grapevine in CA in August. I was quite impressed. My Tahoe would rise, but I don't have exact engine coolant temperatures. This was on the Coquihalla where you don't have ANYWHERE to pull over and people are coming up that hill at 80 mph easy. That would not be a fun place to break down. At least the Grapevine had some shoulder to pull over to.

 

[swathdiver]

...is it possible that design engineers sacraficed performance for their perception of a luxury grill?

You'd think all the grills were flow tested, even the accessory ones.

 

[thompsoj22]

You'd think all the grills were flow tested, even the accessory ones.

im sure your correct, my guess is the volume is sufficient to supply air for the fans at all speeds but ram air speed/volume is diminished when the fans are off.

 

[thompsoj22]

im sure your correct, my guess is the volume is sufficient to supply air for the fans at all speeds but ram air speed/volume is diminished when the fans are off.

Also as i look at the photo i think ill miss the OEM look so i might get another emblem and run the original grill in the winter.

 

[swathdiver]

Mine came with the black one, would be cool to light up GMC in red but that's a no no with the po po.

 

[lectric74]

Does everyone let their engine coolant rise to 220/240 when towing? At what point would you turn off the AC and open the windows?

My 2008 Explorer with the 6 speed kept the coolant below the 212, even going up the Grapevine in CA in August. I was quite impressed. My Tahoe would rise, but I don't have exact engine coolant temperatures. This was on the Coquihalla where you don't have ANYWHERE to pull over and people are coming up that hill at 80 mph easy. That would not be a fun place to break down. At least the Grapevine had some shoulder to pull over to.

It was what really started this conversation. As for me, now that I know approximately what the temp is based on gauge position, I tend to turn the A/C off for a short time once it climbs to ~230, let the temp drop, then turn it back on. Usually the ECT drops quickly once the A/C stops, but fans stay steady. I'm hopeful that a good coolant flush will resolve these higher temps as the truck has 220k, and it may be about due for a water pump and thermostat. It might also benefit from a good flush through the radiator to help clean out all the bugs and debris that builds up and reduces flow.

As for the grill, I'm guessing the Holy Grail grill has the round holes as mine has more of an oval hole in the chrome grill. Either way, my emblem is gone as yours was and I'm honestly thinking the black grill looks better. May give that a shot to see how temps do, but I likely won't tow my trailer again until Sep when I bring it back down from my property. By then temps will below the steady 95-100 that I was towing in last weekend and this weekend. Temps seem to climb when towing steady, even across relatively flat land, at higher speed, while once I drop into town it will quickly drop to the normal range I see when not towing.

I managed to get a pic this weekend, not hooked up but gives a good idea.

 

[swathdiver]

It was what really started this conversation. As for me, now that I know approximately what the temp is based on gauge position, I tend to turn the A/C off for a short time once it climbs to ~230, let the temp drop, then turn it back on. Usually the ECT drops quickly once the A/C stops, but fans stay steady. I'm hopeful that a good coolant flush will resolve these higher temps as the truck has 220k, and it may be about due for a water pump and thermostat. It might also benefit from a good flush through the radiator to help clean out all the bugs and debris that builds up and reduces flow.

As for the grill, I'm guessing the Holy Grail grill has the round holes as mine has more of an oval hole in the chrome grill. Either way, my emblem is gone as yours was and I'm honestly thinking the black grill looks better. May give that a shot to see how temps do, but I likely won't tow my trailer again until Sep when I bring it back down from my property. By then temps will below the steady 95-100 that I was towing in last weekend and this weekend. Temps seem to climb when towing steady, even across relatively flat land, at higher speed, while once I drop into town it will quickly drop to the normal range I see when not towing.

I managed to get a pic this weekend, not hooked up but gives a good idea.

View attachment 226833

Nice! You might just want to replace the radiator with those miles on it. DO NOT get an aftermarket radiator as they do not have the built in restrictors that keep the temperature in check.

Transmission was 160 tonight on the way home, a little hotter than previously, but it was still 90 out and quite humid. Closest photo I took was last June, 92 degrees outside and 156 @ 76 MPH.

It was 99-100 for nearly the whole run south, hot!

 

[lectric74]

Nice! You might just want to replace the radiator with those miles on it. DO NOT get an aftermarket radiator as they do not have the built in restrictors that keep the temperature in check.

Transmission was 160 tonight on the way home, a little hotter than previously, but it was still 90 out and quite humid. Closest photo I took was last June, 92 degrees outside and 156 @ 76 MPH.

It was 99-100 for nearly the whole run south, hot!

It appears the trans isn't much to worry about, it never climbs above 220, and already has the heavy duty external cooler, but I may look at replacing all three, radiator, trans cooler and oil cooler, to help ensure longevity. Of course now I need to consider how long the engine may last having had AFM active all it's life. The list of maintenance items just keeps growing, but the wife loves the ride and comfort, and I don't miss all the manual shifting of the previous truck.