i am buying a 97 f250 heavy duty super cab 4wd with a 7.5l v8. it has a3.55 li. m slp axle. can anyonetell me if it is ok to tow in low range? i am a bit worried that the 3.55 axle ratio is bit low and may result in overheating the tranny. towed boat is about 6k. i would like to install a transmission oil temp gage. anyone know where i can find info on this proceedure?

 

You shouldn't have any problems with your trany overheating pulling only 6K. Now if your load is over 10k and your pulling mountain passes, then you could have transmission heating problems.

A trans temp gauge is always a good idea.

 

That BW transfer case has a low range of better than 2:1. That means that the engine will run at too high of an rpm if you select the low range. 6K lbs is not much on a trailer, and that truck can pull it suprisingly well.
You mentioned the gear ratio, but did not mention tire size. This will have the greatest effect on the overall ratio. If you are running anywhere near stock size tires you wont need the lower gears, but if you have 40's or 44's you my consider changing the gears in the axles to something that will bring the truck back into the right rpm range where it belongs.
As for running that thing in low range on the street, it will only do it if you have manual hubs. If they are autos or even semi autos, you will be putting power to the ground, and it will not do well, and you will tear it up. As a matter of fact, even with the hubs unlocked, you will be spinning the front end and even though you will not hurt it that way, you will probably get some pretty nasty vibrations, and much noise from the case. That can't be good for very long.
Bottom line, if you need lower differential gears, it is best to get them replaced with the right ratio.

 

You should be able to pull that load in regular 2Hi without any problem, provided it isn't some radical lift setup with huge tires. We've used a truck like yours as a backup here on the ranch for years without any trouble. It's pretty much stock except for the trailer wiring and the transmission cooler.

The biggest problem with the 3.55 axle trucks from that era is that they don't usually have a transmission cooler installed. When we bought our 1992 F-250, the 3.55 axle locked us out of the trailer towing package. In those days, I'm pretty sure no trailer tow meant no transmission cooler. We retrofitted the factory cooler to the truck and had the lines made up at NAPA. If you're going to tow, I'd check and see if there's one on there. If not, you should consider putting one in.

 

You truck shouldn't have a problem towing that. I may suggest putting it in low when pulling the boat out of the lake and up the ramp, just to take some stain off the tranny. But i would not pull it in low on the street. Really you don't need to go over 25 or 30 in low if that fast.

I occasionally pull our 5000 lb. correct craft with my f150 with the 300 with no problems. Didn't even have a problem pulling out of the lake. We normally pull it with a 6.0 4x4 f250 king ranch

So unless your on a really steep slick ramp i would keep it in 2hi. But defiantly do not run in low on the street. It will tear up your truck, extra wear and you don't need it.

Hope you have fun.