Should I swap to a 6.2/6.5?

[dyeager535]

This has been a long time coming. I'm more concerned about range than most anything else with the truck. I should have built it as a Diesel in the first place, honestly.

The most I tow is (and this is high) 3000lbs, and that is flat ground scrap runs, which I do maybe twice a year. Trailer weighs 500lbs, I use it perhaps 10 times a year total, 1500lb average weight. Only mountain/hill use truck sees loaded down is hunting season, and that's up and down once.

Truck runs right about 2200RPM @ 65MPH as-is, and I don't cruise over that MPH. My thinking is that the final drive ratio is about right for a diesel now. I do enjoy a nice burst to pass someone, but I could learn to live without that if I had to.

I might put 5000 miles on it per year. And that's probably higher than reality, I never pay attention to how far I go. It's so little that I don't put gas in it before I park it, so I don't end up with bad gas.

I'll "lose" quite a bit of money trying to get rid of all my spare TPI/gas engine parts. I've got a LOT of spares I picked up because the price was right. It's money already spent, so I'm not really losing anything that isn't already gone, but I would not look forward to knowing I'm taking a loss on brand new stuff, let alone tossing it because there is no demand. With the LS stuff getting so popular, I'd probably be dreaming to think I could get $750 for the complete TPI motor out of the truck now, even if someone could test drive it first.

Judging by Craigslist and my location, pretty sure a .mil 6.2 could be found pretty easily, and I saw a 6.2 running/driving Suburban for $1200. Not sure if more power is what I need if I'm worried about best economy. Of course, by the way most people take care of stuff, I'll need a new radiator at least, and I'm betting the huge ones are still $400+.

It doesn't sound like there is any pro or con between the 6.5 and 6.2 in terms of durability. Both had issues apparently, but I would think a low mileage 6.2 would be pretty likely to last my lifetime.

Economy I'm unsure of, I assume the 6.5 uses more fuel. I'm not scared of electronics, but again, unless there is a marked gain in reliability or economy with a later 6.5, probably not worth a tradeoff in range.

I've driven 6.2 equipped rigs a fair number of times, but they weren't a manual, I wasn't towing or climbing hills, and/or they weren't one of these trucks. Gearing is different, weight is different, etc.

My thought process is that the 6.2/6.5 swap is pretty much a bolt in with a donor rig, and I will get 28% better MPG than I do now, if the engine will do an honest 25MPG, which I've heard is possible with the right setup.

What do any of you diesel owners past or present think?

 

[blazinzuk]

I don't know if 25 mpg is possible or not. I have only driven a couple of stock 6.2s. I think a turbo is the only way to go.

I get about 18 mpg with mine but 6" of lift 4.56s and 37s. I bet I would get close to 20 with a turbo cause my foot wouldn't be in it all of the time.

There is lots of info out there about best years etc.

 

[dyeager535]

I read a fair bit, but as with everything, not sure what of it I can believe. Economy seems to be the tough one though. There are a lot of people that can't drive, and there are an equal number it seems that can't calculate mileage, so even if I could find some numbers to compare between the two, who knows how valid they are?

I believe it was tRusty that said he got 25MPG out of one of these with the SM465. The diesel economy would have to be significantly better than the gas variant in my truck to make the swap worth it. At 25MPG and a 31 gallon tank that's 750 miles (factoring in dead tank area), nearly 200 miles more than what I can get on my best day with gas.

 

[blazinzuk]

I know one thing for sure. Altitude kills these engines. Way way more than a gas engine.

I agree with mileage who knows. I have gotten as high as 21 and as low as 16. I have actually gotten lower but that's my high and low with no trailer.


Right now gas is about 30% lower priced than diesel. So for me I would need to achieve around 13.5 mpg from a gas motor to claim the same monetary cost.

I know a guy with a 5.3 tuned for economy. Dead bone stock with headers, 4.56s and 37s getting 16 mpg. That's his average over a couple thousand miles.

When I add a turbo I expect mileage to increase to a consistent 20 mpg seems like a 2 mpg boost is the norm.

 

[Russell]

I've had a couple Detroit diesels over the years. One was a NA 6.2L in an 83 K10 regular cab long box with an NV3500 5 speed manual transmission, NP208 transfer case, 3.07 gears and 35s. My top speed was 60mph with the pedal on the floor in 4th gear and I got about 10 or 12 MPG. If I shifted into 5th on anything but a downslope I lost speed. Better gearing would have done that truck a lot of good but I bet that NA 6.2L still wouldn't have been able to get out of it's own way even then. My 96 4.3L Vortec V6 truck with an NV3500 kicked it's butt in every way including acceleration, towing and even fuel economy.

Another was a 6.2L that I'd added a GM-3 turbo to in my old 83 K5. I had the same NV3500 5 speed manual transmission behind it with an NP241 transfer case, 1 ton axles with 4.10 gears and 37" tires. It got me around 15 mpg on the highway at 62mph and steadily dropped off with any increase in speed. The power was alright with the better gearing and the turbo but it was still far from quick. I'd put it on the same level as a stock smogger 350 / SM465 truck.

Penny was a factory 6.5L truck with a 4l80e transmission and an NP241. I ran her around a bit bone stock and saw around 18 mpg with her with really quite decent power. On the same level as a TBI 350. You could pass people on the highway if you had some room and could see what was coming. When I did the solid axle swap and put her on 37s with 5.13 gears the mileage dropped to around 14 but she was quite peppy with the excessive gearing but tach'd out on the highway pretty quickly.

As much as I love the 6.x engines, I don't think I'll ever run one again. They were good at getting decent fuel economy in their time vs their gas counterparts but there are modern gas engines that make considerably more power and similar fuel economy without the added hassles of old school diesel ownership such as poor cold starting performance, fuel additive, extra maintenance requirements etc.

When you consider the cost of buying a mechanically sound 6.2L, the installation costs, added fuel costs and the additional maintenance costs later on down the road I suspect you'll find it will be years before you even break even with a swap like this.

If you want to do the swap because you love diesel, I'm the last one who will tell you not to. Diesel runs through my veins too. Don't do it if you are just looking for better fuel economy and cheaper operation of your vehicle. You can swap a 295hp 4.8L LS in and get better fuel economy with modern fuel injection and still be able to pass people on the highway if that is your only goal.

 

[dyeager535]

Definitely not doing it for cost savings. Realized long ago I don't drive this thing enough to ever break even from any changes made. If I make changes now, normally it's because it's something cool I'd like to do. With the diesel though, it would add fuel commonality amongst the group I hunt with, which is important, and my range would theoretically go up as well.

I'd have to go back and compare the ratings of say, the carbed 305's to the 6.2L, as the one I had back in the day was certainly no rocket. The current motor makes the 305 look silly, but I was able to live with it.

I really don't want to take the plunge only to find out I don't get the MPG (really range, but that's how you figure it) I thought I would. Made that "mistake" with this motor, if I'm going for MPG, it better be good.

 

[ccarley]

Here in CA, one of the things I consider is smog. Not the actual stuff in the air, mind you, but that terrible time every 2 years I have to take my Suburban in, and a shop has their way with it. It's worse than going to the dentist, especially since they keep changing what they want to see out the tailpipe (the numbers tend to get lower all the time, I think it needs to be cleaner now than when it was new!).

The combined issues here of smogging every 2 years, and gasoline which is expensive & sucks in the summer (or compared to gasoline in other states anyway), the old 6.2 Diesel makes a lot of sense out here. Things are probably different where you live though.

Now, a buddy of mine at work picked up a 6.2 powered Suburban recently. It's sitting on 37's, has 4.10 gears, and I believe he has the TH400 trans. He's reporting, with what appears to be a stock 6.2, round about 20 mpg. He was surprised to see the mileage so similar to his Bonneville that he was driving. My Suburban, with a TBI 350, 700R4, 4.56 gears, on 35's, is definitely not getting 20 mpg. I'll know better mileage figures soon, but the gears have only been in for a couple of weeks, and my EGR was acting up. Still, I doubt I'll see anywhere near 20 mpg.

Since I don't own one personally, I haven't looked deeply enough into any modifications, however I'm sure a turbo would be beneficial overall (as has been mentioned).

Looking forward to seeing what you decide on doing!
Clay

 

[ryoken]

My Suburban, with a TBI 350, 700R4, 4.56 gears, on 35's, is definitely not getting 20 mpg. I'll know better mileage figures soon, but the gears have only been in for a couple of weeks, and my EGR was acting up. Still, I doubt I'll see anywhere near 20 mpg.

I'd be impressed if you get 15....




Dorian, bigger fuel tank...

 

[rjfguitar]

Seems like a lot of work to change over a running vehicle that you put, like 4K on a year. The difference between a 6.2 and a TBI 350 over the course of a year is roughly 100 gallons, or $300 in savings.

I would assume it would be a tough find, to find a good running 6.2/6.5 that doesn't need to be gone through before considering the trouble of dropping it in. What I would do before messing with an old Detroit, is a 4BT Cummins. Better power, better reliability, and better FUEL mileage than a 6.2/.5.

I wouldn't be surprised if you could save another 100 gallons of fuel per year with a 4BT over a 6.2, that would be $600 savings over your 350, now you're talking some decent savings. And again, I have a hard time believing a 4BT would cost much more than a 6.2 swap, as I'm assuming a 6.2 would have to be rebuilt first to be worth even messing with.

Oh and a 6.5 has an issue with the turbo hitting the A/C box. I also don't believe you will break 20mpg with a 6.2, maybe with a 6.5 but not much better. a 4BT Cummins should bring you up into the mid 20's.

 

[tRustyK5]

Dorian, I managed 25 mpg in my 83 pick-up...twice. Both on long freeway drives between Alberta and BC. That truck is geared ideally for fuel mileage. 700R-4, 3.42's and 28" tall tires puts the rpm's at 65 mph right at 1800 rpm. The truck will do 90 mph, and I have towed a 17' camper trailer with it (4000 lbs).

My old 81 Jimmy had the SM 465 behind the 6.2 with 4.56's and 39.5's. It was a lot snappier than my pick-up...but my best mpg was 16.5. Again a long freeway trip.

So, all that being said if you're looking for more range I'd carry more fuel. My pick-up had awesome range (1000 miles) but had dual 20 gallon tanks.

 

[black dawg]

4bt would be cool, but the cost to get one, around here anyway, has gotten stupid. Lots of good running 6.2 motors around to choose from.

My 6.2 burbs, would get right at 20mpg (but this was before the fuel change, I would expect 19 or less now). They were geared for 2k or less at 65. I have talked myself out of swapping a 6.2 back in year after year, based on the fact that my gas motors (tbi 350 and tbi 454) are soo cheap to keep going, and highway mpg alone hasnt been enough to get me to do it. The thing that keeps drawing me back is the mpg difference driving around in the hills 6.2 vs gasser is huge.

 

[blazinzuk]

I will say that off road my 6.2 owns any gas motor I have had as long as your crawling with it. It also is a great motor off road. My gearing is good but the control and power down low is in my mind very very good.

My mpg numbers are pretty solid. Gallons figured with filling the tank up till fuel is at the top of the filler neck. Milage is figured off a GPS speedo app I use on my phone or after the fact on Google maps or map quest.

Where I live now I can count on 16 to 17 on most of my trips. That is because I live at high altitude and there are lots of ups and downs.

When I lived in Idaho Falls I drove this truck to Boise several times. I could count on 17 to 18 occasionally doing better. My best on that particular trip was right at 20. Keeping 65 for the most part. If I head on up to 75 or 80 ( flat ground when the jimmy is in a good mood it will mmaintain 80) I expect around 14 to 15. That was on 35s 6" lift with 4.56 gears. I have always had a 700

 

[dremu]

Sounds like you're in the typical CK5 place of "If it ain't broke, fix it anyway." It's a dangerous place...

-- A

 

[dyeager535]

Hmm, not as much of a lock on range as I thought. As I thought final drive is important, and the only way I'd drive that down is an NV4500 (or 3500) swap, and that's a lot of money itself. I was hoping I was presently in that gearing range.

I've already got a spare 100 gallon tank I haul...but anymore I can't "contribute" to the camp with fuel (so everyone is hauling a bunch of their own 5 gallon cans and/or driving ~2 hours to get more), because they all run diesel, and the trailer has no room for another tank.

I can probably eke out a couple more MPG with tuning, which sounds like it will put the truck closer to 6.2L change with no physical changes needed.

Thanks for reining me back in CK5.

 

[campfire]

Hmm, not as much of a lock on range as I thought. As I thought final drive is important, and the only way I'd drive that down is an NV4500 (or 3500) swap, and that's a lot of money itself. I was hoping I was presently in that gearing range.

I've already got a spare 100 gallon tank I haul...but anymore I can't "contribute" to the camp with fuel (so everyone is hauling a bunch of their own 5 gallon cans and/or driving ~2 hours to get more), because they all run diesel, and the trailer has no room for another tank.

I can probably eke out a couple more MPG with tuning, which sounds like it will put the truck closer to 6.2L change with no physical changes needed.

Thanks for reining me back in CK5.

Here's my $0.02:

It sounds like the biggest advantage you stand to gain is being compatible with your buddies. You're the only one who can decide whether that's worth the swap. I'm pretty confident that you could also get better mileage/range if that's what you're looking for. But with 130 gallons of capacity, you already have enough fuel range to drive from Washington to Chicago. Both goals are achievable, but it seems like a lot of work compared to simply bringing along a barrel of diesel to help your buddies out.

As for my 6.2 experience, I run a 1983 K10, NA 6.2/700R4/3.08 axles/28" tires. Cruising RPM ranges from 1300-1650RPM on the highway (peaking at 2500RPM if I downshift @ 70MPH). Over ~16,000 miles of driving I have come to expect 19-20MPG in town, 22MPG @ 65MPH, and 23-24MPG @ 55MPH (carrying 2 passengers & 300# cargo). I have seen as high as 26MPG, and I'm hoping to get a 1000-mile run out of my dual 20-gallon tanks on my next long trip. I have achieved about 875, but I didn't run it dry and now I'm haunted by wondering how far it would have gone.

My Suburban has a similar setup, with 3.73 axles, 31" tires, and its TC doesn't lock up at this point. I only have a couple thousand miles on it so far, but it hasn't beat 20MPG yet (still hoping ). It tows very nicely, and I have twice tipped the scales above 11,000# while trailering, but for normal driving around it's just not nearly as pleasant as the highway-geared K10.

Don't expect to get the mileage/range extension unless your truck is geared properly. 6.2 engines don't magically fix mileage. Your truck is closer in setup to my Suburban than to my K10, if you're cruising at 2200RPM. So I would expect the mileage to match.

YMMV, of course.

I live in the Upper Midwest (<1000' altitude), so I can't speak about high-altitude performance, but I have driven up 7% & 8% grades with my K10. I can't pass anyone, but haven't had any problem getting up the grades. I do hafta downshift if it gets above about 3-4%.


I'd stick with bringing an extra barrel of diesel fuel. So much easier than swapping the engine out.

 

[evolve991]

Before I swapped my 6.2 out for a 350 my truck got excellent mileage. But with the higher price of diesel and my lack of attention to mileage I didn't notice it until it was too late. I wish I hadn't jumped the gun and swapped to gas now. That 6.2 nonTurbo with 235 16s and 3.42s had more takeoff and high end than any 350 I've had with my 3.73s and 31s. It may have taken more cash at the pump but I hit the pumps alot less and never lacked for power.

 

[Big Ray]

4bt would be cool, but the cost to get one, around here anyway, has gotten stupid. Lots of good running 6.2 motors around to choose from.

My 6.2 burbs, would get right at 20mpg (but this was before the fuel change, I would expect 19 or less now). They were geared for 2k or less at 65. I have talked myself out of swapping a 6.2 back in year after year, based on the fact that my gas motors (tbi 350 and tbi 454) are soo cheap to keep going, and highway mpg alone hasnt been enough to get me to do it. The thing that keeps drawing me back is the mpg difference driving around in the hills 6.2 vs gasser is huge.

check this guy out...click...thinking about a 4bt myself. Don't have a need for a beastly tow rig, just better performance over my 6.2. (n/a)

My 6.2 is in a 2wd 'Burb 2500 with a TH400 trans. It gets about 17 mpg on the hiway. But over 60 mph it's a screaming be-otch that will make your ears bleed...

 

[blazinzuk]

One thing I know for sure the only swaps I have considered in my jimmy are to a newer 6.5 turbo, 4bt or 6bt, duramax or a newer 5.3 or 6.0 ls motor .

I would never swap an old school small block

Since I can barely afford to keep my junk running it's getting a turbo and I will run it till it dies

 

[rjfguitar]

One thing I know for sure the only swaps I have considered in my jimmy are to a newer 6.5 turbo, 4bt or 6bt, duramax or a newer 5.3 or 6.0 ls motor .

Exactly my mentality these days. I will never mess with a small/big block again, and a 6.2/6.5 is out of the question. I'm going Cummins for any kind of diesel swap. There is no comparison between the old GM/Detroit engines in comparison to a 4 or 6BT. A Duramax swap peaks my interest too, I considered it for my K5 before settling on a 6L LQ4 swap, but the Duramax swap looks complicated still with having to retain the factory gauge cluster.

 

[dyeager535]

The 4/6BT's all require a lift of some sort though, correct?

I know a few have swapped those into these rigs, I can't recall who though. I would expect a 3.9L should get significantly better MPG than the 6.2/6.5?