Towing a toyhauler in mountains and 85.5 octane

mikeyk101 · June 26, 2022

I think I just learned a valuable lesson. I have towed through the mountains pulling my toyhauler before through the elevations in places like Tennessee, Arkansas, etc... and have always put "regular" gas in it. It is a 5.3l with a 6l80 trans with new updated thermostat and 3.42 rear end. The toyhauler is a 25' and is probably in the range of 6200lbs loaded. The regular I've put in has always been 87 octane.

Fast forward to yesterday. My journey put me going down 16 in Wyoming from Buffalo as I was headed to Cody but I need to get fuel before I started into the Big Horn Mountains. So without thinking, I put in "regular" gas which I always do but happen to notice it's 85.5 octane. I was low and think I put in about 22 gallons. And with the obvious current gas pricing, I have always gone with the cheapest that worked. So now I head out of Buffalo and start the uphill climb. It's a pretty serious grade that seems to be neverending. I want to say it was a 6-7% grade that went on for miles. As I'm climbing, it seems to lack power. I have to mash the accelerator to the floor and even drop the shifter from "D" to "M" which is a trick I've used many times before to help maintain speeds up grades. Usually in situations like this, I dont even need to have to have the accelerator fully floored and can sometimes even drop back a bit on the accelerator and still keep up the speed.

This time was different. I was able to maintain a speed of maybe 55-60mph but it was struggling. I had my Bluetooth OBD11 reader connected and was monitoring the oil, cooling, and trans temps. I saw all of them steadily climbing. IIRC, several miles into this climb, I get a message that the air conditioning was being turned off because of engine heat. Eventually the coolant temp hit 260⁰ and a warning to let the engine idle to cool it off. I believe the trans temp got right around the 240⁰ mark as well.

Unfortunately, I had wanted to pull over before it got that high but there were no pulloffs to do this. Luckily when that last warning came on, I did just reach one and pulled over and let it idle. Coolant temp dropped as well as trans temp too. After coolant got down to about 220⁰, I pulled back out. The grade continued upward for a bit more but I got through it. I did hit a couple more uphill grades but coolant never got back up to 260⁰ again. I did find myself with accelerator all the way to the floor and could maintain speed but not accelerate any more. Once out of the Big Horns, the coolant and trans temps never got anywhere near the levels they did in the mountains but I definitely noticed a lack of power. I'm pretty convinced that most of the problems were because of using the 85.5 octane gas.

I think it would have gone much better if I had gone with 87 octane. I will find out if I'm correct in about 2 days as I make the journey back east. Not quite sure what route I am taking though but strong possibility it will end up taking me back through the Big Horns.

KARNUT · June 26, 2022

6 hours ago, mikeyk101 said:

I think I just learned a valuable lesson. I have towed through the mountains pulling my toyhauler before through the elevations in places like Tennessee, Arkansas, etc... and have always put "regular" gas in it. It is a 5.3l with a 6l80 trans with new updated thermostat and 3.42 rear end. The toyhauler is a 25' and is probably in the range of 6200lbs loaded. The regular I've put in has always been 87 octane.

Fast forward to yesterday. My journey put me going down 16 in Wyoming from Buffalo as I was headed to Cody but I need to get fuel before I started into the Big Horn Mountains. So without thinking, I put in "regular" gas which I always do but happen to notice it's 85.5 octane. I was low and think I put in about 22 gallons. And with the obvious current gas pricing, I have always gone with the cheapest that worked. So now I head out of Buffalo and start the uphill climb. It's a pretty serious grade that seems to be neverending. I want to say it was a 6-7% grade that went on for miles. As I'm climbing, it seems to lack power. I have to mash the accelerator to the floor and even drop the shifter from "D" to "M" which is a trick I've used many times before to help maintain speeds up grades. Usually in situations like this, I dont even need to have to have the accelerator fully floored and can sometimes even drop back a bit on the accelerator and still keep up the speed.

This time was different. I was able to maintain a speed of maybe 55-60mph but it was struggling. I had my Bluetooth OBD11 reader connected and was monitoring the oil, cooling, and trans temps. I saw all of them steadily climbing. IIRC, several miles into this climb, I get a message that the air conditioning was being turned off because of engine heat. Eventually the coolant temp hit 260⁰ and a warning to let the engine idle to cool it off. I believe the trans temp got right around the 240⁰ mark as well.

Unfortunately, I had wanted to pull over before it got that high but there were no pulloffs to do this. Luckily when that last warning came on, I did just reach one and pulled over and let it idle. Coolant temp dropped as well as trans temp too. After coolant got down to about 220⁰, I pulled back out. The grade continued upward for a bit more but I got through it. I did hit a couple more uphill grades but coolant never got back up to 260⁰ again. I did find myself with accelerator all the way to the floor and could maintain speed but not accelerate any more. Once out of the Big Horns, the coolant and trans temps never got anywhere near the levels they did in the mountains but I definitely noticed a lack of power. I'm pretty convinced that most of the problems were because of using the 85.5 octane gas.

I think it would have gone much better if I had gone with 87 octane. I will find out if I'm correct in about 2 days as I make the journey back east. Not quite sure what route I am taking though but strong possibility it will end up taking me back through the Big Horns.

Tow-haul mode is probably where your transmission should have been in. You don’t say where your RPMs were or what gear you where in. In my many years of pulling heavy I’ve never had an engine over heating problem. So that’s puzzling. The gas situation your engine going to pull timing with lower octane. The higher you go you’ll lose power. And lastly depending on how old your truck is even if it’s a year old. Your radiator could be restricted from bugs.

Edited June 26, 2022 by KARNUT

diyer2 · June 26, 2022

I run 85 octane, our regular here in Colorado except when towing, then 87. It's possible you got some bad gas. Premium 91 here does not make a difference.

Get your foot out of it rising temps tells me it's struggling, slow down, lower gear for higher rpms moves more coolant.

Edited June 26, 2022 by diyer2

mikeyk101 · June 26, 2022

1 hour ago, KARNUT said:

Tow-haul mode is probably where your transmission should have been in. You don’t say where your RPMs were or what gear you where in. In my many years of pulling heavy I’ve never had an engine over heating problem. So that’s puzzling. The gas situation your engine going to pull timing with lower octane. The higher you go you’ll lose power. And lastly depending on how old your truck is even if it’s a year old. Your radiator could be restricted from bugs.

I did forget to mention I always used the tow-haul when towing it. The RPM's ended up going into the upper 4k and lower 5k. I honestly don't know what gear it was in while in "D" but we where traveling in the 55-60mph range. I found out that the highest elevation on this highway is at 9677 feet. My truck is a 2016 and has almost 70,000 miles. And surprisingly, I did check for bugs in front of condenser prior to this trip and gave it a good rinsing. I did a more thorough cleaning of it at the end of last summer.

KARNUT · June 26, 2022

11 minutes ago, mikeyk101 said:

I did forget to mention I always used the tow-haul when towing it. The RPM's ended up going into the upper 4k and lower 5k. I honestly don't know what gear it was in while in "D" but we where traveling in the 55-60mph range. I found out that the highest elevation on this highway is at 9677 feet. My truck is a 2016 and has almost 70,000 miles. And surprisingly, I did check for bugs in front of condenser prior to this trip and gave it a good rinsing. I did a more thorough cleaning of it at the end of last summer.

Ok gas and altitude is in play. It’s spinning too high for too long. I would usually keep mine around 3500 - 4000 on a long pull. You need more gear if this your usual stomping ground’s running these altitudes. First I’d use higher octane gas to see if that helps. 4000-5000 RPMs are pass through RPMs not sustained RPMS very long is why your building heat.

diyer2 · June 26, 2022

Rinsing from the front through the grill? You just pushed the bug bodies into the cooling fins IMO. I remove the grill and clean with a radiator comb, or zip tie a piece of window screen the the grill. When I pull long steep grades I try to keep rpms 2500- 3500 by selecting the proper gear, speed doesn't matter. If you have to go the speed limit, diesel IMO.

mikeyk101 · June 26, 2022

2 hours ago, diyer2 said:

I run 85 octane, our regular here in Colorado except when towing, then 87. It's possible you got some bad gas. Premium 91 here does not make a difference.

Get your foot out of it rising temps tells me it's struggling, slow down, lower gear for higher rpms moves more coolant.

Bad gas could have been a possibility too. The thing about this road is that when leaving Buffalo, you are at city speeds and it goes almost right into the climb so there isnt much chance to build up speed. Yes, I probably should have let my foot off the gas a bit more and just let it slow down but was traveling with and behind another couple that was just towing a much lighter 6x12 enclosed V nose cargo trailer with their pickup. In the past, I had always been able to at least maintain the speeds without too much of a struggle but I guess never tackled a mountain route of this magnitude. The other couple were going just under speed limit so I figured I would be ok too. This part of 16 climbs for quite a few miles without any downhill runs. I couldn't find exactly how long the first part does this but it is many miles. After that first loooong climb, it then starts a more reasonable up and down until you exit the mountains. On the rest of the Big Horn mountain road, it did just fine. Temps would rise and fall but never got back up to what it was on that first part. Once out of that mountain range, temps were normal. But it did seem to lack the regular power I'm used to on the flatter terrain. I'm just glad my route took me down 16 instead of WY-14 or even 14A as I have been told that those are even a more difficult highway to tackle while towing.

mikeyk101 · June 26, 2022

2 minutes ago, KARNUT said:

Ok gas and altitude is in play. It’s spinning too high for too long. I would usually keep mine around 3500 - 4000 on a long pull. You need more gear if this your usual stomping ground’s running these altitudes. First I’d use higher octane gas to see if that helps. 4000-5000 RPMs are pass through RPMs not sustained RPMS very long is why your building heat.

Not a regular drive luckily. Usually a lot flatter but even in places with grades like I mentioned, they are not the ungodly long distance that this one was so more up and downs. I agree with you and @diyer2that the stupid choice of octane was a big factor. After tomorrow, I will be headed back east towards home at a more leisurely pace and not sure what route I will be taking but won't go any lower than my usual 87 octane especially when towing.

mikeyk101 · June 26, 2022

9 minutes ago, diyer2 said:

Rinsing from the front through the grill? You just pushed the bug bodies into the cooling fins IMO. I remove the grill and clean with a radiator comb, or zip tie a piece of window screen the the grill. When I pull long steep grades I try to keep rpms 2500- 3500 by selecting the proper gear, speed doesn't matter. If you have to go the speed limit, diesel IMO.

The cleaning at end of summer was much more thorough and bugs are not a big problem in the part of Wisconsin where I stay. A good rinsing is usually enough but I have a lot of time after this trip to do it again and check.

KARNUT · June 26, 2022

3 minutes ago, mikeyk101 said:

Not a regular drive luckily. Usually a lot flatter but even in places with grades like I mentioned, they are not the ungodly long distance that this one was so more up and downs. I agree with you and @diyer2that the stupid choice of octane was a big factor. After tomorrow, I will be headed back east towards home at a more leisurely pace and not sure what route I will be taking but won't go any lower than my usual 87 octane especially when towing.

It’ll probably be a good idea to change the transmission fluid after your trip.

mikeyk101 · June 26, 2022

15 minutes ago, diyer2 said:

Rinsing from the front through the grill? You just pushed the bug bodies into the cooling fins IMO. I remove the grill and clean with a radiator comb, or zip tie a piece of window screen the the grill. When I pull long steep grades I try to keep rpms 2500- 3500 by selecting the proper gear, speed doesn't matter. If you have to go the speed limit, diesel IMO.

That is a most excellent suggestion about switching to a diesel but I only make a couple trips a year towing the toyhauler so I can't quite justify the switch right now. The truck is long paid off and regular use doesn't require the extra umph a diesel would give me. That coupled with the recent cost of diesel fuel, I will be staying with the gasser for now.

mikeyk101 · June 26, 2022

Well looks like tomorrow I will find out. I fired up my Garmin RV GPS and plotted possible routes to my next destination of Devils Tower. One route puts me up in Billings Montana and taking I-90 to 212 over. The other route puts me back through the Big Horns again on 16 and then pick up I-90 over to 14 just past Gillette. Billings route is 374 miles and route through Big Horns is 315 miles. 315 miles beats 374...

mikeyk101 · June 28, 2022

Those Big Horn Mountains really are something else.

So I began the eastward trek today. With full tank of 87 octane, I again started up into these mountains again on 16. The first part was again a serious grade but no signs to say what the percent was. This time I kept it in the 50mph range and never went much over 4k rpms. I didnt try to maintain speed and let it drop when it needed to. Luckily very little traffic and never really held anyone up. By maybe 5 miles up, I got the warning of the air conditioner being shut down because of engine heat and by this time the coolant was at 258⁰. Luckily I was already looking for a pullout and one was right there when this happened. I stopped and let it cool down. From then on, I just kept the AC off and opened the windows instead just to be safe. When I started off again, at times the coolant would get back to the 250⁰ range but then a couple down hill sections helped it cool down again. I was able to make it all the way to Buffalo without having to stop again. It mostly stayed in the 230⁰ range. Interestingly enough one of the longer flat runs, it actually cooled down to just under 180⁰. I thought that was a bit odd. That didn't happen on the way west.

Before I hit Buffalo, there was a sign that said there were 5 downhill grades of 8%. After that sign and the first downhill grade, there was another sign with the number of approching grades dropping. But it looks like that initial westward climb was 8%. I tried to calculate how long it was and it looked like maybe 5 miles or just over. So that did put the engine to a real test.

Based on what happened heading east, I don't think I can put the blame completely on the 85.5 octane I used the first time through. The first time through, I know I may have been going a little faster and running the rpms a lot higher for as long as I did. I didnt do that this second time. I know the trailer brakes weren't sticking because I have a TPMS system that also shows the temperature of each tire. All maintained roughly the same pressure and temp. And there was no smell or smoke coming from them. Same with truck tire pressure. All were about same and no smell or smoke. Not quite sure what to be looking at but sure seems like something is off.

Edited June 28, 2022 by mikeyk101

swathdiver · June 28, 2022

Tow in 4th for maximum cooling. At the rpms and speeds you mentioned, with stock tires and 3.42 gears, that tells me you were running that mountain in 2nd gear.

Quit being a cheap skate and put some high octane gas in that thing when you want to hump over them mountains.