towing in OD vs Drive, rpms, temps?

[dieselrealtor]

I just bought a 98 Terry, approx. 6500 lb dry weight, towing it home my temps (ambient 85) kept going to 200-210, fan clutch would engauge around 190-195 (all according to gauge). Empty running temps are around 190.

The truck (as far as I know) is still bone stock, 373, new design cooling system, clean radiator & trans coolers.

Also, what rpms are best for towing around 7000-7500 lbs for max fuel economy? :D

[rjschoolcraft]

You should run in OD anywhere your truck has the power to pull your trailer. When in stock trim, my temperatures (egt, and coolant) would climb badly when in 3rd. At high rpms, the computer cuts boost back way too much causing the temps to rise.

[damork]

I've towed in OD and drive and usually keep it in OD unless downshifting is needed. As long as boost, tranny, water, and pyro temps are all where they belong I see no problem using OD.

[dieselrealtor]

what speed/rpms will give the best fuel economy?

[HowieE]

In your part of the country there is no reason for your temperatures to rise pulling that trailer unless something is wrong. My first guess is look at the radiator and condenser for clogging. Most people just look in through the grill and walk away. Remove the grill and seperate the engine and trans cooler from the face of the condenser, that will give some idea of whats inside the fins.
If you want to see what I am taling about before you remove the grill take a look at my site.
You should make sure you get an EGT guage installed before towing and consider a Turbo Master to retain the boost you want while towing.

[computer monkey]

Take the radiator to a shop to get rodded. My 98 was 25% plugged according to them.

[HammerWerf]

I just had my radiator rodded out. The shop said that a "slime layer" was building up inside the tubes. Took the oportunity to switch to lower temp thermostats. The engine temp, by the guage, runs at the same temp on 105f days now as it did on 96f days before the cleaning. Good investment as I am going to be towing a 28ft trailer on vacation.

HammerWerf

[Keith Richards]

The best economy with my 4.10 geared truck is about 55mph period.I would imagine yours to be at 60,to 65.Obviously in Od.Happy towing!

[damork]

With respect to the best mileage, you might look at the torque curves for the 6.5. IIRC, the peak torque is about 1800 rpm and that is usually where I get my best economy.

I also get slightly better economy running hotter thermostats like 195's, but stay with the 180's presently - did it to see if PMD life would be better. Probably will move back to 195's now that the PMD/FSD is remote now.

[dieselrealtor]

OK, finally got new tstats, put them in today, pulled the top shroud & radiator brackets off, could not believe the ammount of leaves, feathers? tongue.gif , grass & other junk at the bottom of the radiator with the oil cooler & condensor clean as a pin.

I was also suprised to find out that this is an aluminum radiator with plastic tanks. Advance Auto Parts has a brass radiator, anyone have recomendations on radiator replacement?

gonna pull the camper on about a 90 minute trip this weekend :D , that should give me an idea of how it will do.

Thanks for the tips!

[Diesel Dan]

When I'm towing I'll run 3rd 'till about 55-60 then after that switch too OD. Stock tires and 4.10s will keep the rpm around 2600 in 3rd. What I shoot for is keeping engine rpm at or above 2000 when in OD.

Have a 8.5' real-lite truck camper and pull my '98 dodge(7K+) on the car trailer. Figure that is around 11K that I'm pulling. The fan clutch will kick on at times, generally pulling a hill and with the a/c on.

I had to pull the trans when I first got the truck for a slipping torque converter. Installed an aftermarket converter, trans-go 4L80E HD2 kit and mobil 1 synthetic fluid. Now I can be pulling a hill loaded, in 3rd, and when the converter comes in it'll be firm and pull the motor down 150-200 rpm.

These are shorter Michigan hills, not east/west coast hills however.

[CareyWeber]

Originally posted by Keith Richards:
The best economy with my 4.10 geared truck is about 55mph period.I would imagine yours to be at 60,to 65.Obviously in Od.Happy towing! Keith,

Wha t do you get for MPG loaded and empty @ 55mph?

I have never been able to drive 55mph empty to check mine @ 55.

Carey

[dstoops]

Gearing is important. When I ordered my truck GM said to order 3.73 to tow a heavy trailer. I can pull a 12,000 lb. liquid fertilizer tank 400+ miles a day in OD (It will downshift on the gentle hills). I'm thinking that I should have ordered 3.43's or similar so that I could run OD when empty and direct when loaded. As it is with all the mods I've made it averages 16-17 mpg in mixed driving pulling some kind of trailer half the time. (I have 2 flatbed's and a dump trailer as well). I think my average would improve with the higher gear. So far I have run the standard 245-75 tires but I'm thinking of going to 265-70 or 265-75's next time. I'd be interested in hearing any thoughts on going to a 265 tire, especially as it relates to load capacity

[Marty Lau]

Originally posted by diesel realtor:
what speed/rpms will give the best fuel economy? 1800-1900 RPM should do the job, if I remember when I had 3:73 1900-1950 RPM I got about 63 mph in OD. My truck tows best at 65 mph it running at peak tourque RPM and down shifts the least if I try and tow faster it starts shifting down more and MPG drops off a bunch.

[LanduytG]

I pull my 26 ft 5th wheel in OD all the time and I gross at 16K. The only time I pull it into 3rd is if it can't make up its mind where it wants to be. I have 170K miles on the original trans with Amsoil ATF and extrenal filter which I change ever 10K or so. As far as economy I like to run it 1800-1900. Thats right in the fat of the torque curve. But I can never seem to run that slow. My normal speed is 70 and I get 10-11 mpg. It really does not seem to change much. The truck and trail have been all over the US and has always done well.

Greg

[tanker]

For the best MPG's the lower the engine RPM's the better the MPG, towing or not. ;) As Greg, and Damork stated above 1800-1900 rpms is ideal, for max torque on this engine. I tow above that most times, and yes mpg's fall off quickly.
I have been towing in OD since new, and now have over 150,000 miles on the original transmission.
I do use Amsoil synthetic fluid, and change it about once each season. I have also added two additional transmission coolers, one which has a built in thermostat/fan and is 12-Volt. You should run a transmission temp gauge along with a pyrometer/boost gauge. 4L80E transmissions are not cheap, and you will get unreal temps when towing whenever the converter is unlocked, like when pulling a hill. This heat is also transferred to the engine cooling system via the factory trans-cooler in the radiator. This will then cause higher engine and higher exhaust temps, which can translate into head gasket and or cylinder head failure's. (been there :eek: )
Keep things as cool as possible, and all will be fine. smile.gif

[dieselrealtor]

Took the camper for a short "shake down" camping weekend. No interstate driving , quite a bit of curves, hills & stop lights (252 to 31 south to columbus, fyi for the hoosiers out there).

We got 8.75 mpg, it seemed to run the best around 1850-1900 rpm, around 62 mph. Didn't really have the opportunity to try any faster to see how it would pull up the hills starting at a higher speed.

Temps only breifly went up to 210 while climbing & accelerating, then cooled back down to around 190-195 quickly.

Can't wait to take it on a real trip! :D

[jspringator]

I got better milage with my Jayco Eagle (9,000 lbs) than I did with my 7000 lb trailer because I couldn't go as fast. On hills, I give it all the throttle it can take without downshifting.

[markrinker]

Good idea on replacing the radiator at this point. Personally, I don't re-rod anything with plastic tanks. Before your next trip in summer temps (or any trip in the mountains) I'd add the Kennedy fan and clutch. A huge improvement for the investment.

Yesterday, I towed 6,500lbs (truck #2) one way during the heat of the day. Temps hit low 90's. Average water temps were 180-185, EGTs 650-700 (downtube) running 65-70mph. On the return, I had 4.5 tons of hay (large wind drag) plus trailer for a total of 11,000lbs in tow. EGTs stayed about 800-850. Hills no issue. 9-10mpg average for 650 miles.

Once you do exhaust and gauges, a Heath Turbo-Master and/or chip won't be far behind. You won't believe what a towing machine your 'burb will become!

[Marty Lau]

Originally posted by diesel realtor:
there).

We got 8.75 mpg, it seemed to run the best around 1850-1900 rpm, around 62 mph. Didn't really have the opportunity to try any faster to see how it would pull up the hills starting at a higher speed.
Can't wait to take it on a real trip! :D I have found if you cruise with your RPM's above 2000 RPM the truck will start down shift much more to keep the higher speed with the cruise on, now if you drive manual you can pickup speed as you approach a hill but keep a light enough throttle so as to keep it from down shift as long as posible for best MPG. at about 1900 RPM your in the "sweet spot".