First impression towing with 6.9 NA
- Thread starter Cubey
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MTKirk
Full Access Member
My freshly rebuilt 6.9 will pull my 4500 lb. travel trailer along all day at 63mph, 3000 rpm, though hills will slow it down. Mileage hauling is between 10 & 12, empty I never really pay attention because it is short trips or plowing snow. I don't mind the 6.9 but my 99 powerstroke is a whole new ball game, waaaay faster and better mileage!
I’m sure mine would but dang do you have to keep yours floored or nearly so? Maybe I’m just expecting too much out of it.
Golden Helmet
Full Access Member
Is your truck 2WD or 4WD? If you're 2WD, it wouldn't be hard for you to find a used 4.10 rear axle and swap it in, that would probably be the most gain for the least money for you. Your engine probably could use a good tune-up too, but the 3.55 gearing isn't helping your NA slug very much.
I know it's not an apples to apples comparison, my truck has an E4ONO and 4.10's, but the last time I towed with it the load was ~6500 pounds and I was still running my very old IP and injectors, and I had no problems maintaining 55 on flat ground or even speeding up to ~70 to pass when needed. It took a few weeks to get up to that 55mph (it's an NA IDI, lower your expectations and enjoy the scenery
), but once it got there it didn't feel like it needed a whole lot of extra throttle to maintain 55, just a bit more than it would need unloaded. It didn't like hills very much though.
I know it's not an apples to apples comparison, my truck has an E4ONO and 4.10's, but the last time I towed with it the load was ~6500 pounds and I was still running my very old IP and injectors, and I had no problems maintaining 55 on flat ground or even speeding up to ~70 to pass when needed. It took a few weeks to get up to that 55mph (it's an NA IDI, lower your expectations and enjoy the scenery
), but once it got there it didn't feel like it needed a whole lot of extra throttle to maintain 55, just a bit more than it would need unloaded. It didn't like hills very much though.Yes RWD. I stupidly paid out the nose for a 3.55 rebuild a year ago.
Supposedly it has a newer IP but who knows. Sellers tell you anything. (A seller of a car with no A/C system told me the A/C would explode if charged, according to her mechanic. Yeah.)
No idea about the injectors age or condition.
I’m used to it not liking hills. Without towing, I could pass the slowest of trucks usually on mountains, doing maybe 30-35 tops but everyone else was passing me. I know that won’t be the case now. I’ll be with those trucks but that’s ok.
I’m just mainly concerned with fairly flat speeds. 55 in a 65+ is less bad than 50. I guess I’ll resume using the diesel kleen I already have and see if that helps any. Once I run out, I might try MMO for a while.
Supposedly it has a newer IP but who knows. Sellers tell you anything. (A seller of a car with no A/C system told me the A/C would explode if charged, according to her mechanic. Yeah.)
No idea about the injectors age or condition.
I’m used to it not liking hills. Without towing, I could pass the slowest of trucks usually on mountains, doing maybe 30-35 tops but everyone else was passing me. I know that won’t be the case now. I’ll be with those trucks but that’s ok.
I’m just mainly concerned with fairly flat speeds. 55 in a 65+ is less bad than 50. I guess I’ll resume using the diesel kleen I already have and see if that helps any. Once I run out, I might try MMO for a while.
I always run diesel Kleen. The low sulfur fuel doesn't have enough lubrication for the older pumps. I also change the filter in spring and fall due to the different fuel blends for the seasons. Probably not needed but I want to make sure it's clean.
Oh? I was running it usually every other tank. The last couple months I got lazy. However the 10mpg City I was getting was during use of it. Plus it had immediately dropped from 11-12 when I put new cheap all terrain tires in place of worn out, mismatched highway tires.
Shadetreemechanic
Full Access Member
I would go ahead and bump the timing a dime's width and see if you notice a difference. Your mileage and power sound down to me.
Ethan Smith
Registered User
Mine was a real dog until i put 10k on it and replaced the racor filter the PO had forgotten about. Id just keep being consistent with her and make sure that fuel system is dialed before you decide anything. 10 thousand miles ago mine was a real slug but after 6 or 7 hundred gallons its gotten a heck of a lot torqier. Is that even a word? 
still ain no pantystroke tho
still ain no pantystroke tho
Josh Oldenburg
Full Access Member
are the 7.3's just as slow?
FordGuy100
Registered User
Yes
Hydro-idi
Full Access Member
There’s not enough of a difference between the 6.9 & 7.3 idi in regards to power output. I’ll take an 85+ 6.9 idi over a 7.3 any day of the week.
One big think many seem to forget, the IDI era trucks (83-94.5) the national speed limit was 55, everywhere, including the interstates. So when the engineers designed these trucks, they designed them to work their best at 55mph and below. That’s why 55 is in the 2000rpm range, since that is the general area of peak torque (an IDI is peak torque in the 1800ish range if I remember correctly). So the truck being able to maintain 55 while pulling a reasonable load was the goal. Yes, the 4.10’s do help, but, they are still shooting for 55. My 88 IDI C-6 4.10 likes 60 and under, yes it will go faster, but, it’s much happier there.
Now, fast forward a few years, and the interstate speed limits have been raised, and in my part of the country, the highest speed limit we have is 70. I know there are some states that have higher, but 70 is a good number ina good part of the country. Now, the engineers are designed the vehicles for working well to 70mph and below. Looking at my 03 6.0 Excursion, it was designed with 70 as the goal, which is why 70 is approximately 2000 rpm... same rpm sweet spot as the IDI, but is geared differently and has more horsepower and more importantly more braking power to handle the increased demand to get to, and stop from 70.
So, take a trailer and hook it to an IDI and it will be happiest at 55, but hook the same trailer to my 6.0, and it will run 70, and be happy doing it. But it was designed to run 70 to begin with. The IDI was not.
Now, fast forward a few years, and the interstate speed limits have been raised, and in my part of the country, the highest speed limit we have is 70. I know there are some states that have higher, but 70 is a good number ina good part of the country. Now, the engineers are designed the vehicles for working well to 70mph and below. Looking at my 03 6.0 Excursion, it was designed with 70 as the goal, which is why 70 is approximately 2000 rpm... same rpm sweet spot as the IDI, but is geared differently and has more horsepower and more importantly more braking power to handle the increased demand to get to, and stop from 70.
So, take a trailer and hook it to an IDI and it will be happiest at 55, but hook the same trailer to my 6.0, and it will run 70, and be happy doing it. But it was designed to run 70 to begin with. The IDI was not.
in kali, 55 is the limit for towing with trailer. you can push 60 and not get hassled. perfect speed for my slugs.
turbo and intercool the truck and you have a new love for it.
hard to justify until you drive one
So true!
I've not done the IC yet, but adding a turbo, getting the fuel system up to ***** and freeing up the exhaust transformed the old mule. Twice a year I tow a 10k+ travel trailer from South Florida to the Catskill mountains of New York. I made one round trip before the turbo. Going through Fancy Gap pass I was in second gear at 28 mph, it sucked! Third gear at 43 mph with the blower, night and day...
My thoughts as well.
When my truck was NA I was getting about the same milage. Since the turbo I'm sure it's gotten better, that is if I could manage to keep my foot out of it! Towing our house trailer, depending upon terrain, it gets 8-11 mpg.
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