New For Me 1985 Silverado 20 6.2 Diesel

[Craig Nedrow]

I am convinced that this truck has passed the reliability test. I drive it everywhere, handles and steers great with the new tires and alignment, it was out a bunch, back as well. It starts every time with the manual glow plug mod. It is cool, there for I to am cool by association, gotta developed that sneer for lesser rides, and she's purdy. Also I used to hate the 6.2, but I have had to learn about it and have a pretty good feel for it now. It seems to me with the 32' tires, 1:1 trans and 4:10 gears that between 55 and 65 is a good rpm. Actually 62 sounds best. 3600 is max rpm, so with 4.10 gears, 31.7 tall tires and a speed of 62, my rpm is 2811. When I get the over drive trans, (700r4, or 4l80e?) at 75 rpm's will be 2343. Going through parts of Idaho, Nevada speed limits are 85, so at that speed the rpm will be 2655. That is the same as the 3.075 rear end, interesting stuff. Oh yeah torque at 240@ 2000 rpm's, peak torque 275@2750, so in the ball park.

 

[mcarlo86]

I am convinced that this truck has passed the reliability test. I drive it everywhere, handles and steers great with the new tires and alignment, it was out a bunch, back as well. It starts every time with the manual glow plug mod. It is cool, there for I to am cool by association, gotta developed that sneer for lesser rides, and she's purdy. Also I used to hate the 6.2, but I have had to learn about it and have a pretty good feel for it now. It seems to me with the 32' tires, 1:1 trans and 4:10 gears that between 55 and 65 is a good rpm. Actually 62 sounds best. 3600 is max rpm, so with 4.10 gears, 31.7 tall tires and a speed of 62, my rpm is 2811. When I get the over drive trans, (700r4, or 4l80e?) at 75 rpm's will be 2343. Going through parts of Idaho, Nevada speed limits are 85, so at that speed the rpm will be 2655. That is the same as the 3.075 rear end, interesting stuff. Oh yeah torque at 240@ 2000 rpm's, peak torque 275@2750, so in the ball park.

I have a 1990 K2500 with a 6.2 and 4.10's. It originally came with a TH400 auto and you are correct, about 60 mph was its sweet spot. I swapped in a rebuilt 700R4 with all the updates and having overdrive really made it an awesome highway cruiser. I was in the same boat as you and thought the 6.2's were junk until I got this one. It's definitely not fast, but the torque is decent and the fuel economy is great. I love driving it for sure. I have the same size tires as you also, but mine shows 2500 rpms at 70 mph. I am using the alternator for a tach signal and I wonder if the pulley is the wrong size possibly so it is showing higher rpm than actual?

 

[Blue Ox]

I have a 1990 K2500 with a 6.2 and 4.10's. It originally came with a TH400 auto and you are correct, about 60 mph was its sweet spot. I swapped in a rebuilt 700R4 with all the updates and having overdrive really made it an awesome highway cruiser. I was in the same boat as you and thought the 6.2's were junk until I got this one. It's definitely not fast, but the torque is decent and the fuel economy is great. I love driving it for sure. I have the same size tires as you also, but mine shows 2500 rpms at 70 mph. I am using the alternator for a tach signal and I wonder if the pulley is the wrong size possibly so it is showing higher rpm than actual?

We put a Gear Vendors in ours. It was like a different truck.

The Suburban had a 700R4. It was okay, but I wasn't as pleased with it because of the different ratios from the 400.

 

[Craig Nedrow]

Went to the Dr, and when I came out, truck wouldn't start. Luckily a fellow farmer saw my dilemma, had cables and got it started, God bless him. Sooo bought two new red top odyssey batteries, and man what a difference. Yes still have to use the glow plugs, but parked for ten minutes at the store, and came out and started without using the glow plugs, first time ever. Hope they last awhile...

 

[Craig Nedrow]

I am considering swapping engines with the K20. The 6.2 D Diesel is just a gem, and if I put this into the K20, I would have, in my opinion, the ultimate practical truck for where I live. I would reseal the engine, remove all the diesel wiring from the harness, (I will probably remove the whole harness and transferer this complete to the K20. Since the K20 dash does not have any "water in fuel", and "Glow plug" provision, I will come up with sone way to incorporate that into my dash. With the 4l80e trans I had planned to swap into this truck bolted to the 6.2, (direct swap except it is about two inches longer,) a US shift fast four controller, I could cruse at 70+ and get 23 or maybe more mpg. So anyway I think that is the direction I am going with this. I will also post this on my K20 build.

 

[Craig Nedrow]

As some know, I am hooked on the salt, and want to run another rig down there, and this truck would be a great candidate. Huge engine bay, 14 semi Floater with 4:11, (will change the rear gears,) with a 4l80e trans should get me into the 130 mph club, and a good place to start. While I have never lowered a truck, thinking of installing a handling package front and rear, so it handles really good, and less air underneath. I will install a adjustable front dam, and do not know if I can do all those projects, so will start with the drive train and get that installed right and tight. Will for sure remove the front end and clean and paint something like what I did earlier with the bed and back frame, probably the cab to finish the underneath stuff. Not looking for perfection, but protection, salt is corrosive.

 

[Frankenchevy]

My wife wants a 6.2 4wd burb. Well, actually she wants a 4wd square body burb to drive daily, regardless of the engine. The 6.2 is the only option to not feel the pain at the pump when she drives 400 miles per week.

We keep looking. They aren’t super easy to find in decent condition.

 

[mcarlo86]

I have a 1990 K2500 with a 6.2 diesel. It originally had a TH400 with 4.11 gears. She was screaming to go 65 mph. I swapped a 700R4 in it and that was a dramatic improvement for highway driving. I think 3.73’s would be ideal instead of the 4.11’s. I’d like to find a Banks turbo for it someday…

Now I looked up and see that I had commented on this thread earlier…haha

 

[Ricko1966]

I am considering swapping engines with the K20. The 6.2 D Diesel is just a gem, and if I put this into the K20, I would have, in my opinion, the ultimate practical truck for where I live. I would reseal the engine, remove all the diesel wiring from the harness, (I will probably remove the whole harness and transferer this complete to the K20. Since the K20 dash does not have any "water in fuel", and "Glow plug" provision, I will come up with sone way to incorporate that into my dash. With the 4l80e trans I had planned to swap into this truck bolted to the 6.2, (direct swap except it is about two inches longer,) a US shift fast four controller, I could cruse at 70+ and get 23 or maybe more mpg. So anyway I think that is the direction I am going with this. I will also post this on my K20 build.

This is the same plan I have,I have a decent 1975 K10 but a 350 just isn't affordable for regular 150 mile trips. Bought a 91 parts truck with a 6.2 4l80E,drove it home drove it around a little to test it. Plenty of power to pull trailers and do truck stuff and incredible mpg.I think my K10 could become a daily or semi daily with the 6.2 swap and still pull anything I want.

 

[Frankenchevy]

I could cruse at 70+ and get 23 or maybe more mpg.

If this could be the case, we would be extremely happy. If we end up getting the burb we are looking at, we have plans to lower it back to stock height and put it on the mildest 3pms rated tires we can find. It’s a 3/4t, but I saw in an old brochure that it could have a 700r4 or th400. It probably has a th400, but I’d be really happy if it has the 700. The guy is out of town until Sunday, so I should know early next week.

 

[Craig Nedrow]

I've been driving this diesel for a year now, learned how it works, checked mileage once with the TH400 and 4:11 got 25mpg, I do not drive over 65. With the 4X4, 4:10 and 4l80e in the K20, I think this will last me and be really reliable for the duration. Yes I do maintain my rigs, and that helps a bunch, proof was when I tore the 454 down, how nice it was and clean inside. So anyway will wait for a bit of better weather so I can pressure wash and paint, as we got another four inches of snow last night.

 

[Frankenchevy]

I've been driving this diesel for a year now, learned how it works, checked mileage once with the TH400 and 4:11 got 25mpg, I do not drive over 65. With the 4X4, 4:10 and 4l80e in the K20, I think this will last me and be really reliable for the duration. Yes I do maintain my rigs, and that helps a bunch, proof was when I tore the 454 down, how nice it was and clean inside. So anyway will wait for a bit of better weather so I can pressure wash and paint, as we got another four inches of snow last night.

I’m the same most of the time. I average 62mph in the slow lane when on the freeway and most of my driving is rural two lanes. I have a very fast car if I want to drive that way, but in the Jeep and trucks I just cruise.

25 mpg with a 3-spd sounds really high. If that’s the case, I’m not sure how much you could improve on it with a 700r4.

 

[Grit dog]

I’m the same most of the time. I average 62mph in the slow lane when on the freeway and most of my driving is rural two lanes. I have a very fast car if I want to drive that way, but in the Jeep and trucks I just cruise.

25 mpg with a 3-spd sounds really high. If that’s the case, I’m not sure how much you could improve on it with a 700r4.

Agree. 25mpg avg is rose colored glasses even if in a half ton with OD and tall gearing.
I’d be very suspect of a result like that in a 3/4ton turbo 400/4.10 combo from what I recall and heard back in the day when more of them were on the road.
By the same token, while the 6.2 would be an absolute fuel sipper compared to a big block in a K20 for local driving, @Craig Nedrow, I think it would make a very poor road trip right compared to your newer C20 which I thought was your plan. Plans change of course. Not trying to debate or dissuade you, but it doesn’t quite register with me why you’d totally disassemble a cherry original truck that seemed to meet your goals….and then reassemble it again with something else or end up with a Parts for Sale add.
I’m certain you could find the 6.2 K20 project with a different 6.2 engine (they are not hard to find) easily through the sale of a solid, can her run and drive 454.
Whatever JMO.
It’s all squarebody so it’s all good.

 

[Ricko1966]

My 91 got better than 20 for sure I actually calculated it at 25 mpg but thought it was to good to be true,but even if I assume the odometer is not 100 percent accurate I still believe at least 22mpg G30 6.2 4l80e . A coworker a long time ago had an 80s1 ton dually 4x4 extended cab. manual transmission,Don swore it got 18 mpg loaded, unloaded,pulling a trailer nothing mattered.