Diesel Swap questions (Gas mileage, not power)

[BiggSixx1970]

Hello everyone!

I have a 1970 c20 250 I6, sm465 4spd w/granny gear, Eaton full floating rear end, HD rear coil springs. (will post pics when I get them uploaded)

I am looking into a diesel swap this upcoming spring, I am wanting to do this for gas mileage, not to roll coal and blow black smoke everywhere. A lot of people knock the 6.2 Detroit and say its weak and useless, however these people who make the comment are diesel guys that push their engines to the limits, I hear the block isn't as strong but as long as you aren't trying to build a hot-rodder they're solid engines. I have also considered a cummins 4bt (I have my reasons for choosing the 4bt over the 6bt, mostly weight and I just don't need that much power)

I have heard that with the right combination of diesel engine, transmission, and rear end gearing that you can get 20+ mpg, I have even heard guys with 4bt's getting close to 30mpg.

If I were going to swap my 250 for a 6.2 Detroit, what would I need to do to the frame of my pickup? do I need to beef anything up? it is a 3/4 ton after all. I have heard my transmission and rear end are all but indestructible.

What would be suitable for a transmission and rear end gearing to maximize gas mileage?

You may be asking what I intend to do with the 250 I6.. I plan on putting it on a stand and building it up for a turbo and eventually putting it back in when I get the truck closer to restored original condition. I got one with a 250 thinking it would get decent MPG.. turns out I was horribly mistaken, it barely gets over 12mpg on a good day with a fresh tune up, most of that is due to the low farm gears

This pickup is my daily driver so I need any ideas ya'll have to boost my MPG to the max. I live in a very green town in Kansas and we have pumps for bio diesel, and most of the fast food joints will give people they're used oil, so I may or may not burn vegetable oil in the future if I do this diesel swap

Thank you for the advice!

[low'n slow]

might be better off working on the I-6. Change the rear end gears, use an overdrive tranny, fuel injection (throttle body) and the turbo.

Another alternative would be a modern GM V6 and the above.

[SS Tim]

A diesel swap will help your gas consumption. After all you wouldn't be using any gas. It is the amount you might save after paying for a swap (which I fear may prove to be almost irreversible) that is at issue. Not going into the whole miles per pound, or actual B.T.U.s used I think the cost and work for a temporary swap would be break even at Best!
Now 6.2/6.5 are nice swaps but not drop ins. With mid 20s doable. DBear down in TX will I'm sure give some helpful hints. Might need to send him a PM to rattle a response though. If you want mileage and stock you are kind of stuck. If you can live with modifications in your final build there are options. At this point though a good tune an tall rear tires will buy you some cheaply. Finding a set of 3 something gears too unless you are going to a 5/6 speed trans. will also help.

[BiggSixx1970]

Originally Posted by low'n slow

might be better off working on the I-6. Change the rear end gears, use an overdrive tranny, fuel injection (throttle body) and the turbo.

Another alternative would be a modern GM V6 and the above.

My problem is I am taking that straight 6 out and needing something to keep my truck going. Instead of just wanting to throw another I6 in or a small block I wanted to do something different, that's why I chose diesel. I was wanting to build the 250 for all of that at a later point in time.

[BiggSixx1970]

Originally Posted by SS Tim

A diesel swap will help your gas consumption. After all you wouldn't be using any gas. It is the amount you might save after paying for a swap (which I fear may prove to be almost irreversible) that is at issue. Not going into the whole miles per pound, or actual B.T.U.s used I think the cost and work for a temporary swap would be break even at Best!
Now 6.2/6.5 are nice swaps but not drop ins. With mid 20s doable. DBear down in TX will I'm sure give some helpful hints. Might need to send him a PM to rattle a response though. If you want mileage and stock you are kind of stuck. If you can live with modifications in your final build there are options. At this point though a good tune an tall rear tires will buy you some cheaply. Finding a set of 3 something gears too unless you are going to a 5/6 speed trans. will also help.

I am not concerned with breaking even over the period of time the 250 is out. I already have tall (i call 'em "farm skinnies") on the back. And actually if I happen to like the diesel swap and can get the gas mileage and my desired function I might even forgo putting the 250 back in, but that's far down the road.

[SS Tim]

Sounds like you really need to talk to Tommy (DBear). Shoot him a PM with an outline and my name for a phone number. The talk will do you good. I'm thinking there is a diesel in your future that isn't comming back out.

http://67-72chevytrucks.com/vboard/member.php?u=47267

[WIDESIDE72]

I had an 82 suburban with a 6.2 and 340k miles. I parted it out before I got back into 67-72 trucks. I wish i had hing on to that engine! It didn't have a lot of power but was fine empty or lightly loaded and got close to 20 mpg with a 700r4, 4.10's and 33" tall tires. It was the red engine and supposedly had higher nickel content than later black blocks. All o know is it still ran good and didn't use oil even at over 300k. Only problem we had was injector pumps. I was told that there was a rubber or plastic disc that connected the shaft to the impeller and the diesel ate it up. Dad bought the truck with 35k miles and we put three pumps on by 140k til we found a guy that rebuilt the pumps with a brass disc. That pump was still on at 340k!
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[VWBeamer]

Man, I love a diesel. I have a little VW diesel and can routinely get close to 50 mpg, and has way more power than a gas or hybrid car capable of similar economy.

For a truck that is driven a lot, I think a diesel swap is a good idea. Every time I see one at show it's a conversation starter.

As far recouping the money spent, look at what nice trucks with a diesel swap is bringing. They all bring a big premium.

If you look, the 4bts bring more than a 6bt. Just a lot more 6bts out there. Best way...cheapest way to get a good 4bt is to break a an old bread/ frito lay truck. look on craigs list, they go for 2500-4000 around here. The body is aluminum and last I check is worth 1600-2000 scrap.

I had a 6.2 power 1984 1/2 ton truck. Not as slow as you would think. 140 hp. With the OD trans it will get 23-24 highway easy. This will probably be the cheapest and easiest to swap. I believe it will use the factory V-8 engine mount locations, uses standard GM bell housing, etc. Except for the fuel system and vacuum for the brakes, trans, not much different than putting a V8 in.

Lot of the 6.2s on the market, as the army just switched all there 6.2s out for 6.5s, so a lot of surplus engines out there at varying states of repair and prices. Shop, shop and shop some more.

[69GWC]

Man I had a 97 1ton with a 6.5 and never seen over 14mpg from it I might of kept it if it had gotten 20 or more..lol
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[BiggSixx1970]

I have heard about the bread trucks and Frito trucks from doing a little Google-ing. I have found 6.2 Detroits come up on my area craigslist before for anywhere from $400-$1000 (Which is do-able). The 4bt is a lot less common but I have seen them in a similar price range.

My truck is already an manual, but it just doesn't have enough gears.. The last 2 vehicles I have owned have been manual and frankly I like it that way. Can anyone of you tell me about the GM 5 spds? Could I expect good results from a 5 spd swap and putting a higher gearing in the rear end? (some one above said 6 speed but for some reason I'm not thinking a 6 speed out of a Camaro is gonna work with a diesel but I could be wrong.) For the record, I am not interested in a 6.5 turbo, and as much as I would love to just drop a DMAX in the ol' girl I just don't have the money for that (yet hehe). Again I would also like to state I am very interested in the possibility of turning it into an oil burner if I go through with the swap.

I really appreciate the reply's! You have been helpful, I'm pretty much just trying to get as much info as possible trying to weigh out which engine/tranny/gears would be the best. I am not opposed to an auto/od 700r4, I would just rather keep it manual. Also again at a later point in time (like, a couple of years at least) I want to put my rebuilt tubro'ed 250 back in

[MalibuSSwagon]

6.2 diesels seem to be great engines, people report up to 28-30 mpg's with them!

Should bolt in using small block mounts are well.

[special-K]

If you can find a running 6.2 for cheap,then do it. They aren't fast hi-performance motors,but neither is a stock 305 or V6. If you get into fuel injected versions it's better,but don't all those use a computer? Who wants that? If you're getting into a computer,might as well go with a modern V8 that gets 20 or so MPG and have mucho power.
I don't think the 6.2s are so weak. First of all,they have good torque. When you tap the throttle it's instant power. They'll run along at hiway speeds,even up hills. With a whole lot of weigh,you feel a power loss. But,don't you feel that with about anything but a big block? I've had to replace the mechanical injector pumps,but not a chronic problem. The one was at well over 100,000 miles and the other went 200,000 plus a bit. That second one never had anything done to it at all,till I did the pump,injectors,and glow plugs...and that was after it sat a while. The fuel probably was the culprit. It grows algae when it ages and will destroy a pump quick.
I have run these engines since the '80s. I drive three vehicles right now: '72 K2500 350/TH350,'85 Jimmy 6.2/700r4,and '92K3500 6.5TD/NV4500. So,most of the time I'm running these diesels. I am seriously debating whether to swap a 6.2 into my '72 with a 4L80E I have left over from my retired '91 Suburban. Yeah,it has an ECM and yeah,it's kinda hanging me up. Maybe if I found another NV4500 I'd go for it for sure. My intentions were to put the 4L80E in the Jimmy,but the 700r4 does just fine. It sure is nice to have a good old big tough 4wd with big tires that's practical to drive in this day and age.

[Lemield]

I have a 1971 K20 with a 6.2 diesel in it. 4 speed with a Ranger overdrive. It's great. I love it. I bought the truck from a dealer after the 85 year old original owner traded it in so I have no details on the conversion. It's pretty sweet though....

[special-K]

And that truck helps me along with deciding on my swap. I think about that one a lot. I drive along in my '85 Jimmy and think how cool it would be if my '72 K2500 ran along (and sounded) like that. Not to mention economy. The same when I drive my '92 K3500. Then,when I drive my '72 K2500,I think how cool it would be if it ran and sounded like those trucks. I have friends roll their eyes,but I don't care. I even still have the Suburban here with big gas tank and all associated parts,even hydro-boost brakes. Just need the engine...and money to buy with.

[WIDESIDE72]

The NV4500 5 speeds are bullet proof. They put them behind a lot of engines. Just be sure to use only the specified synthetic oil. The last one I had was in a 93 GMC K2500 with are rebuilt TBI 350 and Vortec heads. It was one of the last years to have the super deep 1st gear. It was great for creeping and taking off from a dead stop with super heavy loads. I towed a 67 MF 2200 Industrial tractor/ loader with it with it wih no trouble. I think it and the trailer weighed around 10k lbs, so not super heavy. The truck and tranny had 205k on when I sold it and it ran and shifted great still.

93 was the last year of the mechanical injected 6.2 diesel. I bought a 94 c2500 and was going to swap it into the 93 k2500 before I insalled the rebuilt 350 but decided it was too much hassle since it was computerized.
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[WIDESIDE72]

My uncle had an 83 3/4 ton Suburban 6.2 diesel he bought new and bought a Banks Sidewinder turbo onsoon thereafter. It had about the same power as a 350 with better mileage. There is a used kit for sale local. I have
heard if bad luck installing one on a used high mileage engine due to ring seal, though. I would look into this kit if it weren't for two things:

1. Don't have the $$$
2. Don't have a truck with a 6.2 to put it on
http://austin.craigslist.org/pts/3177615113.html
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[WIDESIDE72]

Originally Posted by Lemield

I have a 1971 K20 with a 6.2 diesel in it. 4 speed with a Ranger overdrive. It's great. I love it. I bought the truck from a dealer after the 85 year old original owner traded it in so I have no details on the conversion. It's pretty sweet though....

That is a nice truck and swap! Any idea if they used the 82- 87 exhaust manifolds or the 88- later? I can't tell by looking anymore but wonder if it's possible to see part numbers through the clutter.
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[Lemield]

Originally Posted by WIDESIDE72

That is a nice truck and swap! Any idea if they used the 82- 87 exhaust manifolds or the 88- later? I can't tell by looking anymore but wonder if it's possible to see part numbers through the clutter.
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I can try to take a better picture for you....but I have no idea....I do know the conversion was done around 1982-83 so I assume the manifolds are the early ones.....

[Mr onetwo]

Dude, this is just my opinion,but I would find an old 1980's 5 cylinder iron Mercedes Diesel with an automatic.Those motors will realistically go for 3 to 4 hundred thousand miles and will slip right in.You will get over 30MPG...just make sure you get a turbo model.

[special-K]

I've been through three NV4500s in two different trucks. Two had just over 100k on them. They are great,but no match for the good old truck 4spds. One was in a '95 K3500. I swapped the electronic (DS4) pump with the mechanical (DB2) pump in that one. Actually,that was the pump that came on the 300hp Peninsular Marine crate engine I installed.

[SS Tim]

These guys have a lot of information on the NV4500 and the NV5600. Actually they have a LOT of information period.
http://www.quad4x4.com/

[walterbolton]

there is nothing wrong with the 6.2 diesel. every one bad mouths the injector pumps saying that they are too expensive too replace, i did mine for $300 exchange so its about the same price as a carb, big deal. the only thing i didnt like was my 1985 3/4 ton had 4:10 rears and granny 4 and high gear was too tall and 2nd was too low. later i got a 81 1/4 ton with a 6.2 and a 700r4 and loved it, got 24+ mpg and would run every bit of the speedometer until the governor hung wide open at a stop sign, one heck of a sight to see a 81 chevy diesel burning the back tires off and turning 5500 rpm before wiping the engine out

[special-K]

Originally Posted by Mr onetwo

Dude, this is just my opinion,but I would find an old 1980's 5 cylinder iron Mercedes Diesel with an automatic.Those motors will realistically go for 3 to 4 hundred thousand miles and will slip right in.You will get over 30MPG...just make sure you get a turbo model.

Those will slip right in?? I'll have to check with a friend who specializes in adapting those into Jeeps. They slip in with the adapter kit he makes and sells. He's working on other adapter kits for a couple other vehicles. Nothing as big as a GM Truck,though. He has one on a stand he runs as a demo. It has 260,000 on it and needs valve guides.

[Lemield]

Originally Posted by special-K

Those will slip right in?? I'll have to check with a friend who specializes in adapting those into Jeeps. They slip in with the adapter kit he makes and sells. He's working on other adapter kits for a couple other vehicles. Nothing as big as a GM Truck,though. He has one on a stand he runs as a demo. It has 260,000 on it and needs valve guides.

Hey Tim...don't mean to hijack this thread but I am interested in putting a diesel engine in my 1949 Willys Jeep...maybe your friend can help guide me in the right direction???

[special-K]

His name is Nathan Koch. I'm acquainted with him by setting up side by side at Carlisle Trucks these past two years. A very sharp and nice guy. His adapters are probably limited to later Jeep transmissions,but who knows? See what he says. My name is Tim.
EDIT: He does mention Willys
www.mercedesdiesel4x4.com