I'm thinking seriously about ditching my 460 and going with a 12 valve Cummins. My reasoning, I like driving my truck, but I cannot afford to drive it much except for using it for the truck chores I purchased it for - gathering firewood, etc. It is an 85' DRW crew cab 4x4 F350. Here is my build thread to give you a little bit of an idea https://www.ford-trucks.com/forums/1...1985-f350.html

My truck has low mileage and is in very good condition. If I could squeeze 20 mpg out of it, empty, maybe 13 or so towing, I can justify the cost and hassle of the swap based on fuel savings. We have a 7.3l Excursion that is my wife's daily. We both like diesel's, but the Ex is 2WD and is not usable half the year (snow). My wife and I both enjoy driving the truck, we have discussed replacing our bumper pull travel trailer with a fifth wheel, need a truck for that. I can't justify buying yet another vehicle, we already have four and only two drivers. I can't really afford a newer truck anyway, especially a diesel.

I'm after feedback and comments from those who have performed this swap. Any problem areas? Stuff I should budget for that is not obvious? Are you happy with the conversion?

I would most likely purchase a running and driving 89 - 98' Dodge so I have all of the little bits and pieces. I'm seeing trucks in the $4 - $6k range. My thoughts are I can grab the engine, intercooler, etc and then recoup some of my Dodge investment in parting the truck out.

I have a 460 ZF5 that I would use for the swap. I have been doing a bunch of research but have not came to any great conclusions on which brand of motor mounts and trans adapter to use. I would most likely freshen up the 5.9, with new gaskets, etc before install. I need to be careful with this to not get in over my head financially. From what I have read, I'm comfortable with the mechanical part of the swap.

 

One other bit of info; my 460 has recently developed a knock. I'm not sure what it is yet, thinking it might even be clutch related as it does not do it under heavy load, only mid-rpm cruise. I have not written it off yet, I need to figure out what the knock is. But, I may need to rebuild or replace the 460 - another reason I'm seriously considering the diesel re-power.

 

Not done yet, but under way with a 12V swap.

A few things I can toss out. Auto World mounts seem to be HIGHLY regarded by those who have used them. I am going to try making my own, if they don't work out well, I'll get the auto world mounts.
DeStroked engine/trans adapters seem to be preferred over the DCS adapters, but either will work. I have no personal experience with either, but my boss bought his adapter from DCS, and a customer used the destroked plate. They both work, but the boss said DCS was a pain to deal with, but that was a couple years back. They may changed their ways.
A/C can be a bit tricky. The factory A/C box can cause issues fitting the turbo. There are ways around it, but they aren't always cheap. I don't have factory A/C, so mine shouldn't be a problem.
The dodge A/C compressor location can be an issue. I haven't got that far yet......

What gearing is in your axles? 3.55 is a better match for a Cummins than 4.10.

 

I haven't done a Cummins swap, but do the math. It's really hard to justify a diesel swap as a cost savings. Assuming 20 mpg on $4.40/gal diesel for the Cummins and 10 mpg on $3.50/gal gas for the 460, it takes about 7,700 miles to recover every $1000 you have into the swap (assuming all other operating costs are equal). MAYBE you can do it for $5000 (38,000 mile payback). But I'd guess it'll be more like $10,000 - $15,000 (77,000 - 115,000 mile payback). Hard to justify that from a cost perspective.

On the other hand, if you really want a diesel and you really like your current truck and you really want a (probably multi-year) project, then go for it. I'm trying to justify doing one myself some day. But cost is not the way to do it.

 

Thanks for the feedback. I would like to keep my AC, do you know if I can use the Dodge compressor with my system? What are the fixes for the AC box clearance problems.

I'm running 4:10's. I would like to see how these work out but would re gear if necessary. I may have access to a Gear Vendors over drive, though I'm not sure of it's condition and the cost for the adapter as it is currently on a GM vehicle. In reality, most of my driving is on mountain highways with 55-65 MPH speed limit, the 4:10's might be okay, especially when towing.

 

I'm thinking I can do the Cummins swap for around $5k - $6k. If I do not swap it, I may need to rebuild my 460, that would be around $2.5k, if not more, to do a good job at it. That leaves me with a difference of around $3k. Diesel is $3.72 where I live, the price has been fairly stable, gas has not and is currently $3.59. At these prices and assuming 10k per year, and 9 mpg vs 18 mpg, I would save $1900 per year with the swap.

I do want a diesel, that plays into it. I tend to keep a hold of vehicles for 10 - 15 years (except my commuters which I wear out quicker). With the cost of new or newer trucks (gas or diesel) being ridiculous, it is easier for me to justify throwing some money at this old truck.

 

I faced a lot of the same issues. The 300 ran great, not getting away with oil, great oil pressure all that good stuff. But, it developed a mid-level rattle, most likely from a busted piston skirt and/or wrist pin issue.
I could have torn the 300 apart and fixed it, but I scored a good deal on a low mile 89 Cummins, and I've always wanted another diesel. I had a VW diesel years ago. $10/week for fuel, vs $10/day in the truck I had at time, and the car only cost me $25/week in payments.

The current price of gas, without ethanol, is slightly higher than diesel. Ethanol blend is ~$.25/gal cheaper than diesel, but I don't like running it, particularly in something that isn't driven frequently since the fuel tends to degrade much faster.

The 300 struggled to get much more than 12 MPG (C6). I'm betting the diesel will top that, even towing. Likely be in low-mid 20's or better empty.

Right now, I'm at about $2K invested in the swap. The 300 was rebuilt by the PO a couple years before I bought it, in 1997. They spent $1800 (in mid-90's money) to rebuild it right.......
Obviously, I've owned the truck many years, and have no plans of replacing it any time soon. If it comes down to needing to replace it, it will be with another of the same style, so I can swap the drivetrain over to it.

 

Some "light" reading on the subject, by someone that has done plenty of these swaps.

1980-1997 Ford F-250+ | Diesel Conversion Specialists

 

Thanks for the continued feedback and the link. I'm going to keep researching and watching for 12 valve trucks for sale in my area and make a decision on what to do. Cummins truck seem very popular. If I find a good truck to yank the motor from and change my mind I'm sure I could resale it without too much issue.