Seattle to Detroit - "Flattest" Route?

So my husband, my daughter and I will be driving from Seattle to Detroit this August. My husband has a 1986 F350 Utility Truck that will be towing a 35' Travel Trailer.

Flat lands - No problem.
But his truck struggles uphill, and downhill curvy roads are just a little scary towing that much weight.

I'm looking for the best route to get cross-country while avoiding uphill/downhill. Basically the best way to get through the mountains.

Time isn't an issue. We are planning on making a 2-3 week trip out of this.

Thanks in advance for your help!

Welcome to RTA!

There really isn't a way to avoid mountains, but I-90 to I-94 through Minneapolis is going to be the least strenuous.

As a note - a 35 footer is way above the maximum ratings for a F-350 of that vintage.

Thanks GLC,

From what I've seen, the max towing capacity increases if you have electric trailer brakes installed (which we do), is that correct information?

Also it's not the original engine, just the body. The engine was replaced brand new in 2005.

(Not sure if that changes anything either... But I guess I should have been more specific about truck specs in my OP)

I meant to hit the "reply" button so you would get a notification... Oops 😳

GLC is much more knowledgeable about the details of towing capacities, but it sounds to me like your description of the tow itself kind of answers the question. If it's a real struggle to go up hill, and it's scary coming back down, that's should be a big red flag that you're trying to do too much with too little vehicle.

GLC is correct on the route recommendation, I-90/I-94 would be the best choice. You'll still have to climb a 6,300 ft. mountain pass, but there really isn't a better option. The only route that would be lower would require you to go all the way down to I-10 - where you'd still have a 5,000 ft. pass in Arizona - and would have multiple mountain passes to deal with heading down the coast (not to mention, several extra days of driving).

Electric brakes do not increase the towing capacity, but they are mandatory in all states for a trailer that size.

Which engine and transmission does the truck have? Is it single or dual rear wheel (dualie)? How much does the trailer weigh, loaded up for the road? Is it a 5th wheel/gooseneck or conventional bumper pull?

It's not just the brakes or engine that defines towing capacity - it's also the transmission, chassis, axles, and tires. An F-350 is a strong truck, but it's 30 years old!

Engine is a 351W, truck is a dually, trailer is attached to a 2" Pintle hitch. Transmission was just replaced about a month ago - but I'm not sure exactly what transmission it is.

That's all the stats I know, but when my husband gets home I'll have him tell me the rest and I'll post it here.

Thanks a lot guys, I really appreciate the help.

Ok, transmission is a C6 automatic, it's a service truck (with rear boxes), tires are 215/85/r15

So what would you recommend pulling it with? What kind of truck would pull this?

I would not have "no go" type reservations about towing a 35' TT with a 1986 F350 which has a new(er) engine, but I would want to be comfortable that:


The TT has good electric brakes and they're actuated by a good quality brake controller unit in the cab of the truck. You need a breakaway connection, too. With a TT of that length, brakes and breakaway are likely mandatory in all of the Lower 48 states.

The truck's cooling system is up to snuff: fresh coolant, thermostat, and upper and lower radiator hoses. If the hoses are > 2-3 years old, I'd replace them as a matter of course. If the radiator itself is old, I'd strongly consider replacing it.

Often overlooked is the automatic transmission service interval. Towing in general, and in particular all-day towing, and in particular towing up long grades, can cause an automatic transmission to build up heat to the point of destruction of the transmission. At the very least, I'd want to have a full system ATF flush and refill, a new internal filter, and a high-quality transmission cooler installed. If the F350 already has an automatic transmission cooling system (my 2002 F350 has one from the factory), all you'd need is the flush/refill/filter. If a transmission cooler is installed, I'd consider the additional cost of a transmission temp gauge installation. I'd watch that gauge like a hawk on the grades. Heat is the only real enemy of an automatic transmission, and if you can manage it by watching it closely, you'll likely win.

Of course, the truck's brakes need to be in good shape.

As to "flatness", I-90 is essentially the only logical option. Once you get east of Snoqualmie Pass outside of Seattle, you have Lookout Pass (4,500'), Homestake Pass (6,300'), a "false pass" just west of Bozeman (5,000'), and finally Bozeman Pass (east of Bozeman, topping out at 5,700') to climb and descend. From central ID all the way through Billings, MT, I-90 runs along rivers, excepting the noted passes. That means it's as flat as can be. You'll have some long grades between Billings and Rapid City, SD, but you'll only be picking up and losing 1,000' to 1,500' at most, and there aren't that many of them anyway. The passes will be slow on the upside, regardless of tow vehicle, with a 35' TT as your tow. Just camp out in the right lane with the tractor-trailers, turn on your emergency flashers, gear down to 2nd, and hold your rpms as steady as the ascent and weight will let you, watching the gauges all the way. If your old F350 is properly prepared, you should be fine.

I'll guess your truck's hitch is a 2" reciever hitch, not a pintle hitch. I don't know that I've ever seen a TT with a pintle hitch. Pintle hitches are more often seen on utility trailers which haul Bobcats and similar heavy equipment. Assuming the truck has a 2" receiver hitch, examine it carefully to assure it's a Category IV or V, and know what the weight of your TT is to assure it fits within the rated Category of your truck's receiver hitch and drawbar.

Foy

That poor little 351 is going to have a real hard time climbing the mountains, you will probably be down in low gear doing 20 mph. As Foy said, the C6 will need an auxiliary cooler with its own fan. As far as the rest of the truck goes, it will handle it.

With a C6, I would not gear it down to 2 when climbing as that is a true manual second gear and it won't downshift to low, I'd leave it in D. However, 2 will be useful on the downgrades to save the brakes.

With that kind of load, the ideal truck at those altitudes would have a turbo diesel.

I wouldn't go via Rapid City, I'd take I-94 through eastern MT and ND, it's considerably flatter than I-90.

These guys know their stuff, and I agree with all of them regarding what you're towing with. My husband and I once had a 1993 Ford truck -- it was an F-350, dually, Automatic transmission. It was also a diesel. However, we wrecked a transmission on one of our first long trips with it, exactly as was described above. We drove our last 300 miles with the O4D light flashing, and stopped a lot. Earlier in the trip, we had come down Monarch Pass in CO with smoking brakes. We were lucky we didn't burn them out and have a wreck! After that trip, we had to have the transmission rebuilt, and we had the mechanic add something called a "slip kit" which kept the tranny from slipping a lot. When that mechanic was done, we took it to a diesel guy in San Marcos, who added a tranny cooler, the tranny and exhaust gauges, and a PacBrake to it. BTW, we were towing a 27' 5W trailer. I'm telling this story because I don't want you to have the same ending to your vacation as we did.


Donna