Mpg/tire size

[91W350]

The civilian 6.2 was governed at 3600. It was designed in the early 80's as a light duty diesel to replace the sorry Oldsmobile 350 gasoline engine that GM had previously converted to diesel. The engine was not designed to be a powerhouse, they were looking for a fuel mileage altenative to gasoline. To that end they were pretty successful and it is not hard to find 1/2 ton Suburbans and Blazers that with the overdrive transmission ran over 300,000 miles. Some of the guys that were running the 6.2 back nin the day in 2wd Suburbans and 2wd pickups would get mid to upper 20s for fuel economy. That is cheap running down the highway fuel mileage.

The guys that ordered them in their one ton trucks were not nearly as happy with them. The lower gear ratios made them run at a much higher rpm. Those guys fought oil leaks, rods through the sides of the block, tired engines, broken or cracked blocks in the main bearing web area and most of those trucks got new engines or were converted to gasoline before they hit 100,000 miles.

I have read that the military version is governed at 4000 or 4400 and these engines will do that for a short period, but if you want yours to survive, I would recommend running it at a reasonable rpm range of less than 2600. We are not talking about a Cummin 4BT or 6BT here. These engines were great as a light duty engine at a low rpm, happily churning away running 65 to 75 mph pulling a high geared Suburban or pickup with some guy's bass boat tied on. They were not so happy turning 3,000 rpm running 70 mph in a low geared 1 ton truck pulling a construction trailer.

A lot of the local racers bought one ton dually pickups with the 6.2 to pull their race trailers. They liked the fuel mileage, they were disappointed on the power, and they scattered them before they made 100,000 miles. The common fix was normally a large cubic inch small block Chevy that could stand the rpm. In rural Kansas you can still find civilian pickups parked with bad 6.2 diesels in them.

You can run your 6.2 diesel on the governor all day long if you want to, it is your truck and you pay the bills. I am just trying to keep some new guy from thinking this is the answer to his search for a solid off road truck that can easy run 80 mph with a taller set of tires. These engines will not live running on the governor like a lot of other diesels will. Glen

 

[91W350]

I will share with you guys where I learned about the 6.2 diesel engines. I used to rebuild a lot of Toyota Land Cruisers. They would commonly have burned exhaust valves. I would buy the Cruiser, put stainless steel seats in the heads and then run a race quality Chevrolet exhaust valve. The guys would take these 6 cylinder 4.10 geared trucks out on the highway and drive them 70 mph. We never had any trouble with them with the speed limit was 55, but as soon as it went up, the Land Cruisers started dying. What does that have to do with a 6.2? I wanted to swap one in.

I had a friend that was rebuilding 6.2 diesels all the time. His shop lot always had two or three 6.2 trucks on it. So I stopped by to talk to Mark and he told me he was not rebuilding the engines. He would tell the customer that he was going to rebuild the engines, but he was hooked up with a Chevy dealer and was buying new crate engines for 2599, then selling his "rebuilds" for 3600 installed with a 12 month, 12,000 mile warranty. He had a whole pile of 6.2 diesels behind his shop. He was doing pretty good with his "overhaul" business. He was doing good until he tried to lean out the truck door and listen to a driveline squeak while running down the road and ran off in the ditch. He busted himself up pretty badly and does not work anymore.

He was previously working for a wholsale engine rebuilder and they did a lot of 6.2 diesel engines, in fact that was Mark's job. He said the farmer/rancher that bought his 6.2 diesel and used it to feed cattle, run errands, and do general farm/ranch work was a happy customer. That truck never got over 30 miles from home and lived on ruby red farm fuel out of the tractor fuel barrel. He would beat his truck to death before he ever had an engine problem. He would fill up once or twice a month and use his truck everyday, smiling as he escaped the 50 cent road tax.

The neighboring farmer/rancher would not be so happy because he used his to pull a large livestock trailer. Running down the highway every weekend from fairground to fairground and home for his kid's livestock shows, he hammered his 6.2 to death.

Mark also compared the couple that runs from craft show to craft show pulling a light trailer full of nick-nacks with their Suburban that grandpa makes to the couple that bought a one ton truck to pull their camper all over the US. Mark said the Suburban will never need his services. They will churn down the highway running around 2000 rpm and never have an ssue with their 6.2. The couple running down the road with their tonner pulling a camper will need an engine in 100,000 miles.

I decided not to put a 6.2 in a Cruiser, I still think it would make a great vehicle. I know a 327 or 350 works great! Anyway, it was the application and more specifically the rpm range of the application that killed them.

Mark said he originally set out to rebuild the engines, but when they came in from high rpm applications, they frequently had main bearing/crankshaft isssues from the pounding they took cracking the main bearing webbing in the bottom of the block. The bearing would get pounded loose and spin. He said by the time he got a replacement crankshaft and block, it was much cheaper to just replace them.

So with my newfound knowledge, I went and talked to the mechanic at our city shop. He had just retired from the Chevrolet dealer and was working to age 65 for the city. He confirmed what Mark had told me. He said the guys that ran them in low rpm applications very seldom came in. The guys that ran them in high rpm applications could not keep them together. He also cited the broken head castingss on the earlier 6.2 engines and said GM pretty well had that stopped by 1984. He said they warranty replaced a lot of 6.2 engines with broken main bearing webbing.

GM later improved the block's structure when they came out with the 6.5 engines. However their reputation in the dieel pickup market was pretty well soured by then and Ford scored a huge hit with their International built Powerstroke. Later in 1989 Chrysler/Dodge made the diesel pickup market what it is today with their introduction of the Cummins six cylinder in a pickup. You could not work that engine hard enough to hurt it. Governed between 2450 and 2650, you could run a Cummins on the governor all day long, 24 hours a day, for weeks on end and never hurt it. With clean fuel and air, they would outlive any truck Dodge built around them..... provided the killer dowel pin did not fall out... Guys were buying Cummins powered Dodges and pulling huge loads with them. You would frequently get passed by some hotshot pulling a loaded trailer behind a Dodge running 80 mph in the plains of Kansas.

Remember guys, this was an engine designed to replace an engine that Chevrolet sold in a pickup that was not to be used to pull a trailer. Imagine looking at a brand new 1980 Chevy 1/2 ton pickup with a diesel engine and having the salesman tell you that you cannot pull a trailer with this truck.

 

[DeuceNewb]

well according to that gear calculator that somebody posted, 2700rpm is just about 55. It that a safe rpm to cruise at for 2-3 hours or still a bit high?

 

[91W350]

I try to stay under 50 but I get impatient and run 55 occasionally. We ran it 65 for 450 miles. And when we got there it was dripping oil. We were between snow storms and had an appointment to pick up the M1009. I ran off without my paperwork and had to. Make a trip back home for it. That error cost us a hundred miles and I was trying to make up some lost time. We drove it about a thousand miles that day.

I am probably conservative on rpm. I like to stay under 2400 if I can. It is not that they will not or cannot run against the governor. I know from personal experience it does shorten the engine life. Glen

 

[SPECIALTYLC]

I try to stay under 50 but I get impatient and run 55 occasionally. We ran it 65 for 450 miles. And when we got there it was dripping oil. We were between snow storms and had an appointment to pick up the M1009. I ran off without my paperwork and had to. Make a trip back home for it. That error cost us a hundred miles and I was trying to make up some lost time. We drove it about a thousand miles that day.

I am probably conservative on rpm. I like to stay under 2400 if I can. It is not that they will not or cannot run against the governor. I know from personal experience it does shorten the engine life. Glen

Thank God you and your type (driving 45mph on the hiway) are few and far between in my area.

 

[91W350]

I stay off of the Interstate, drive the regular blacktops and old highways. The speed limit for most of those is 55. Some are 60 or 65, if traffic starts gathering behind me, I will pull off or run 55. Since buying my M1009, the M1008 does not make many trips. You would be surprised at what you see running below 55.

A M1008 or their twin chassis trucks are just not suited for extended highway use as they left the military. Right truck, wrong application. Glen

 

[spink7124]

'84 1008, 4.56 gears, 39.5" tires, gets right around high 13's around town.

 

[CUCV85]

tires/rims

Doghead,
Did you get your 37's and lift on? Curious to hear how it came out...

Mark,
Eric (DOGHEAD) will get back to you on his build.
Did you ever get a second M101a2 series trailer so you'll have a set?
your brother​

 

[doghead]

Mark, ​

Eric (DOGHEAD) will get back to you on his build.
Did you ever get a second M101a2 series trailer so you'll have a set? ​

your brother​

My parts will be arriving this week. Should finally start this project! I ordered a 4" lift from Skyjacker(only company I found, that actually has a kit with the correct front axle hardware included).

I will post up as it goes.

 

[Bob H]

thanks for the reply, I will ask again at the tire shop and try to find out why thier giving incorrect info.

......................................................................

235/85R16 and 265/75R16 are both 32in diameter
Minor variances between manufacturers

 

[Croatan_Kid]

Same height, different widths. Just like a 285/75-16 and 305/70-16 are the same height. The 305 is almost 12" wide and the 285 is somewhere around 11. The first number is the width in millimeters, second number is a percentage of the first number (aspect ratio) and gives you the sidewall height in millimeters also.

 

[Alredneck]

A Old wise man once told me, " If it is to big then milage will suck, If its to small then mileage will suck" He was a man of few words!

 

[T_F_E]

M1009 turbo 33x12.5 bfg all terrains about 19.75 on winter fuel.