Just bought a 6.2

[trevmountain]

So I just bought an 82 k20 long bed diesel. Bought the truck primarily as a parts truck but I'm kinda liking it and my plans have changed and I think I want to keep it and daily drive it. The problem lies in the 400 tranny with stock tires. The original owner did gear it to 3.42's to help with cruising but it's still in dire need of overdrive. My plan is to lift it a bit and throw some 35's on it. Wondering if this will calm the engine down enough to negate needing to swap in 700r4.

Tires on it now are stock. I think they measure like 29 inches tall. What is my 60 mph rpm cruise as is and what will the 35 inch tires drop it to?

Thanks

 

[trevmountain]

Ya and what is my target 60 mph cruise rpm with this diesel anyway? I would think something in the 1800 to 2000range correct?

I feel like now I'm more like 2500. The engine doesn't like it over about 45 mph with the 400 tranny. Really wants to shift but there's no where to go.

The majority of the cruise speed I'll be doing is 60mph tops so i'm thinking the 35's will help it some but will it be a noticeable difference is the question.

 

[diesel4me]

My '82 K2500 has a 6.2 and I dont know for sure what ratios it has in the diffs,but I am guessing its either 3.73's or 3.42's,whatever an SF can be had with for "tall" gears,because I could blast up to 35 mph in low before it starts to reach the govenor limits,with 245/75-16's on it......................................................................................................Not long ago I scored a set of 265/75-16 Goodyear Wranglers and those are about 32" in diameter,and I noticed a pretty big difference in acceleration and rpms at cruising speeds of 50 mph or so,it lowered the rpms quite a bit compared to the other tires that were just under 30" in diameter--in fact its a slug on take offs now!....I would put the 35's on first and see how it feels first,before thinking about swapping a weaker 700R4 into it....one guy I know with a CUCV he bought at auction put 235/85-16's on it (about 33" tall) and he feels its no longer winding out too high on freeways going 65 mph with it now...he was about to swap a overdive tranny in it ,but wasn't enthused about the 700R4,having a rather "bad" reputation for not holding up like a TH400 will...

 

[Duntz00]

With 35's on it, which will measure to be 33's-34's, will give ya a 60 mph cruise rpm at 2143rpm which would be pretty good in my opinion.

 

[K5dreamer]

how small are the tires that are currently on it??????

to get 2500rpms, you need a 27in or 28in tire (2462 - 2554rpm)

just by swapping to 31in, or 33in tires you could get 2224rpm or 2089rpm respectively.

I rode 33in tires on my M1009 without any mods to the suspension. and had 3.08 gears, and got 22-23mpg cruising at 55-60mph at a little less than 1800rpm.

a 4 in lift with 35s would get you to 1970 rpm,

 

[Duntz00]

how small are the tires that are currently on it??????

to get 2500rpms, you need a 27in or 28in tire (2462 - 2554rpm)

just by swapping to 31in, or 33in tires you could get 2224rpm or 2089rpm respectively.

I rode 33in tires on my M1009 without any mods to the suspension. and had 3.08 gears, and got 22-23mpg cruising at 55-60mph at a little less than 1800rpm.

a 4 in lift with 35s would get you to 1970 rpm,

Something ya got to remember is that most tires now days dont measure true to their tire size so thats why I put 34 in the calculator and got 2143rpm's as the rpm with 35's.

 

[trevmountain]

Just for fun let's say I do 35's and swap in a 700r4. Is the tranny going to want to jump in and out of overdrive? Again 3.42 gears. Tires that are on it now are like a 29 inch when measured.

Based on what im hearing the 35's will get me pretty close and will calm the motor down enough for most of the driving I will be doing.

 

[blazinzuk]

Hey man how goes it?

I have a Jimmy with a 6.2 35s and a 700. Also has 4.56 gears, its not bad for a 65 mph cruise speed, not sure of the rpms but I get decent mileage and its not bad power wise

 

[trevmountain]

good eric thanks,

and you? Ya it sounds like with your setup the 700 works great. For me with my long legged gears and if I went with 35's the 700 might not do me much good. Probably would need to hold steady at 65-70 just to keep it in overdrive. My gut tells me the the 35's with the 400 tranny and my gear setup I'll be pretty good for low speed daily driving. It's not like we even have freeway's here in Jackson anyway.

Throw me a pick of your new rig. I'm thinking a 4 inch lift to fit the 35's, that is enough correct? I'd like to see yours with the 6 inch that I believe you have???

Aside from the this how about some tips on general performance with this engine. It runs great when I can get it started but getting her to fire is a bear. The original owner put in a manual button for the glow plugs so you can just sit there holding it on. Aside from keeping the glow plugs replaced is there anything else I can do to make this old engine perform or I should say start better.


Obviously plug it at night.
Keep the glow plugs in good working order.

What about oil. Original owner used delo 15-40 and I would just assume stick with that but would a lighter oil be of any good in colder weather.

Its got a brand new injection pump and fuel pump. Gall what else is there on these things, that's about it right? Very simple. I'm used to gas where you've got all these variables with ignition, fuel delivery ect. Don't know squat about diesels, actually don't have clue on how they even work to be honest. I just know it's different.

Thanks

 

[blazinzuk]

Hard starting is typically a glow plug issue. You might want to replace the glow plugs before it starts getting too cold ( which is going to be soon )

New batteries and cables helped mine a ton.

My glow plug controller still works but with the new batteries and cables mine will start when its below zero without being plugged in.

So if yours is hard starting now I would say glow plugs would be your first step

Here is a pic of the Jimmy.

My 35s rub bad when off road with a 6" so if your going to take it off road I would trim a bit with a 4" but I like the 4" much better than the 6" for looks overall. I like the low lift big tire look

 

[diesel4me]

My 6.2 in the '82 starts pretty good down to about 20 degrees without having to be plugged in,and it only has 7 out of 8 glow plugs working the past 9 years--one refuses to come out after unscrewing it so rather than make life miserable I just decided not to fool with it and get in over my head..it has a manual push button to activate them,I use AC 60G glow plugs and dont leave then on more than 15 seconds at most to help them live longer --the colder it is the more glow time it'll need to start...................................................................................................My '85 Suburban's 6.2 starts hard even in warm weather,I know some flow plugs are probably dead in it as I only put a few new ones on the drivers side ,I bet no one ever changed the ones behind the A/C evap box,and I'm not looking forward to doing it either!............................................................................................................I may also replace the wiring harness to all 8 glow plugs,the original wires on these diesels get all gangrene after 30 years and the glow plugs dont get full amps to them--I am sure many glow plug "problems" are due to aged wires and corrosion at the splices GM made in the glow plug harness ,not so much the glow plugs themselves.........I'm not a big fan of the male spade connectors at the glow plugs ,they rust up and I've had more than one rot right off,when the plugs weren't even 3 years old...

 

[trevmountain]

Thanks for the tips.

Probably gonna change out all the plugs and see how she does.

Took a funny picture as I was stripping her down and doing my new 4 inch lift. Put one of my 37's from my K30 on just to see how it looked and fit. Course this was before I lifted the back of the truck but I like the look and eric I know you'll love it.

 

[K5dreamer]

Another thing to try, although you did say its got a new IP and injectors, is check out the top of the diesel forum on here, There's a sticky on doing a "Diesel Purge", something I learned from the guys on a TDI forum (Europeans have been dealing with diesels alot more than us here in the states) and did a "how to" on it. I also run a diesel fuel additive, for me its Power Service additive, I get it at advanced auto parts or napa or similar location. Use the grey bottle in summer, and the white bottle in winter. The diesel fuel here in the states is notoriously crappy, the additive really helps.

My M1009 had low mileage when I got it (50k) but it was 20 some odd years old, with lots of idling. The diesel purge absolutely made a difference.

With the glow plugs, note that the replacement plugs you get may not fit the military harness, The civi "male" spades are larger than the female connector on the harness. I tried making pigtail connectors to adapt the harness to the plugs, but what wound up working easier for me was just grinding down the male spades until they fit.

After replacing the spades, doing the diesel purge, and running the additive, I never had starting issues, ever. and i don't have a block heater, although the winters here are "mild" only getting down to the 20's and maybe the teens every once in a while.

 

[trevmountain]

Awesome just read the diesel purge write up and I will be doing this for sure. Can you explain how doing this plumbing deal is more beneficial than running your tank to near empty and just pouring in a few bottles of the diesel clean and idle it in the same way. You are the expert and honestly I have no idea so just throwing that out there. I assume you must need it in straight form, no mix with any diesel at all. Is this correct?

 

[diesel4me]

Many deisel fleet mechanics around here will dump a bottle of diesel injector cleaner into a new fuel filter instead of diesel fuel when replacing fuel filters,some use ATF instead,they claim it works well as a cleaner...................I've read about stuff called "Diesel-Treat" in a VW diesel parts place that you run the engine on with jerry rigged hoses to clean and purge the injectors in years past,they say it really makes a big difference..I've never used it myself...Stanadyne makes it I think..............................................................................................................I've never replaced the filter on my '82 6.2 and I've had it 9 years,and think its way overdue,a few times this week its felt like its plugging up on me...I may try the method I just related here when and if I ever get 20 bucks to DO it...those Wix 33123 filters used to be cheap,now they are 15 bucks at least...

 

[K5dreamer]

Awesome just read the diesel purge write up and I will be doing this for sure. Can you explain how doing this plumbing deal is more beneficial than running your tank to near empty and just pouring in a few bottles of the diesel clean and idle it in the same way. You are the expert and honestly I have no idea so just throwing that out there. I assume you must need it in straight form, no mix with any diesel at all. Is this correct?

The idea is to avoid diluting it down at all, the diesel fuel is the enemy here because as stated here in the states, its dirty crapy fuel. Rigging up the plumbing the way shown in the video, recirculates the unburned cleaner back through the system till its gone. As to what cleaner to use, It was made pretty clear that the one you want is the one shown in the "how to", Lubro Moly Diesel Purge. there are lots of other brands and knock offs, but this is the one that has been found to be the best.

The added benefit is that if you just run the tank low, and add that stuff, you stand a very solid chance of running the fuel lines dry, without burning all the cleaner, and then you have to go through the process of adding fuel to the tank, and repriming the system and getting all the air out of the system. HUGE PITA. If that happens we can run you through that wonderful process too. have a battery charger handy.