I have a 1991 4WD F150 5.0L 302 V8 with extended cab and really do like it (insert laugh here). It has served me well and never left me stranded after 215,000 miles. The only repairs I’ve made have been warranted considering the mileage.
My situation is: I now have a horse and my truck just can’t handle pulling the trailer and horse. I would prefer to keep my truck since I know all the history, don’t like buying used and chancing getting someone else’s headache, and (most important) cannot afford a new 3/4 or 1 ton truck.
So the question is: can I put a new larger engine in my truck to make it do what I need without major modifications and expense? Willing to upgrade engine and tow package to the tune of $5000-ish.
In a word, no not really. Engine swaps really stopped being practical with computerized fuel injection and emissions systems. Even swapping in an engine that was originally available for your truck will probably be prohibitively expensive. Also in many areas, they’re not legal for newer vehicles.
How bad is your truck really? I would expect the 5.0 to strain a bit, especially if it’s an automatic, but it seems to me it should be capable of hauling a small-ish horse trailer. Maybe you should get a compression test to see if your engine is just worn out-- maybe a rebuild would get you enough horses back to haul yours comfortably.
Have you checked the tow capacity of your current truck in its configuration? They do produce lightweight horse trailers made of aluminum.
Maybe tow capacity is greater, my sister was using a 2000 Toyota Tundra 4wd extracab which is essentially a 1/2 ton pickup to pull a single horse and her modern lighter trailer. She had a quality aftermarket hitch installed with sway bars. The engine did not strain whatsoever as long she kept overdrive off (requirement). I understand 215k maybe the issue. I would check condition of current motor and your hitch system.
Regardless of what engine you install (yes, you can upgrade), you will still have a light duty pickup. There is a lot more to towing capacity than the engine. You would be better off selling it and putting the money toward something more heavy duty, if that’s what you really need (see the advice in the other replies about lighter trailers).
What is the weight of your trailer? If it?s within the towing capacity of the truck, and if the body and frame are solid I would keep it, and just put in a new engine. Your existing engine is likely pretty worn out. You may have to have the rear end and trany rebuilt at some point, but that could be a few years away.
Another option if your existing engine is still in good shape is to re-gear the differentials to lower gears. This will cost around $300-$400/axle at most independent shops.
Have the horse pull the trailer??
I’ll bet he’s got low gears already with the 4WD. rockymtcrispy could start in 4WD low and switch to 2WD on the fly if starting required that low a gear. Since the truck is old, it might just make sense to continue to drive it until it breaks down for good. Ford claims that the truck can tow up to 7500 lbs even with the 6-cyl.
Forget the truck and ride the horse.
I have another thought. Out here I sometimes see these rack structures in the back of pickups that basically make your bed into a horse-sized cage. I don’t really know much about horses, and maybe these are only for moving them around a ranch, but for one horse something like that would probably work and it would eliminate the weight of the trailer.
Nothing wrong with buying a used truck that’s heavier than horse doody. Ten year old ones go for about what you should be willing to pay. I like having a spare vehicle to drive while I figure out what’s wrong with my primary one. It’s a lot safer for the other drivers and pedestrians.