M1008 on the Highway

[chubbynova]

I have been looking at M1008 with 6.2l diesel, turbo 400, np208 and 4.56 gears.I would put 34x10 swamper ltbs on it. I would like to be able to daily drive it. My question is can this combination work on a highway driven vehicle,say 65-70mph?
My blazer has 350 motor, 350 trans, np203 and 4.56 gears and 35 inch tires. I have no speedometer in it but I beleive I am at about 2400-2500rpm at 55mph. Does this sound right?
2400-2500rpm seem high for a diesel motor. Is it to high to cruise at for say and hour long drive? Does anyone daily drive M1008 or drive them on the highway?
Thanks

 

[imiceman44]

I have been looking at M1008 with 6.2l diesel, turbo 400, np208 and 4.56 gears.I would put 34x10 swamper ltbs on it. I would like to be able to daily drive it. My question is can this combination work on a highway driven vehicle,say 65-70mph?
My blazer has 350 motor, 350 trans, np203 and 4.56 gears and 35 inch tires. I have no speedometer in it but I beleive I am at about 2400-2500rpm at 55mph. Does this sound right?
2400-2500rpm seem high for a diesel motor. Is it to high to cruise at for say and hour long drive? Does anyone daily drive M1008 or drive them on the highway?
Thanks

If you are turning 2500RPm at 70, drive at 65 and you get better mileage.
That wouldn't be too bad for a daily driver, could be better with some 36 or 37" tires though, where are the original tires that come on it, they should get you good mileage.

 

[tRustyK5]

You'll be running at 2950 rpm at 65 mph even with 34's. 36's get that down to 2750 rpm. 37's get that down to 2690 rpm...

It's not particularly hard on a 6.2 to spin those R's, but it is hard to listen to and doesn't make for the best fuel economy. My K5 has 4.56's and 39.5's. With a SM 465 4 speed it was spinning at 2575 rpm at 65 mph. I drove at that rpm for 22 hours down to Moab, and another 22 hours home. I managed 16.3 mpg average over 2300 miles of freeway.

Rene

 

[chubbynova]

Not too worried about fuel mileage. Just dont know if 2950rpm is bad for the motor to cruise at, dont want to blow it up.
trustyk5 do u have a 6.2 in your blazer. you said it would be hard to listen to, would stacks make it any quieter?

 

[tRustyK5]

In my K5 Jimmy. no carpet, no sound deadener on firewall or floor, 39.5" TSL's. The exhaust is 2.5" single with a 50 series flowmaster...which you can't hear at all. It was so loud you couldn't have a conversation with someone without nearly shouting.

I stuck a NV4500/203/205 behind the 6.2 so now it cruises at a sane 1900 rpm.

2900 rpm is what the military ran them at. top usual speed on the freeway for them was 55 mph, on 31's. The 6.2 is designed to run right up to it's governed limit of 3600 rpm for hours and hours on end. For an aging 6.2 the only problem you might have is the rear main seal may start to weep. By the time I got back from Moab my formerly dry and leak free 6.2 had a nice rear main seal drip.

As for noise, look into dynamat, brownbread, or a generic polymastic from McMaster-Carr and do the floor, firewall, inside of doors and anything else it'll stick to. (or get an iPod and crank it up while you're driving)

I also have a C10 with a 6.2 (it's very quiet, but is also dead stock)

The K5...

Rene

 

[kennyw]

Another problem I've found running those RPM's for a length of time is cracked blocks or cranks tend to be terminal... I resealed the 6.2L I put into my '79 K10 a while back and didn't see any signs of a cracked block (don't know how close I looked at it at the time though). I replaced the crank damper shortly after that as well because the original wasn't perfect (but not as bad as others I've seen. I ran at 70mph w/ 33" tires and 4.10 gears about 9 months later and the crank snapped and the block cracked between the journal and #7 rod. My guess is the crank had developed stress risers long before I got the motor, but after 9 months of steady used it let go.

If I had been running lower RPM's at the time it went out I might have got lucky and not damaged the block at the same time, but I can't really be sure either.

 

[AJMBLAZER]

You need bigger tires to tame the 4.56's and no OD. Mine had 34-35" tall 36x12.5-16.5 HMMWV tires on it when I got it and even with those it was a revving high at 65-70. Might be able to do it but I never wanted to make it do that for any length of time. As tRUSTy said be prepared for LOUD. I put dual Cherry Bombs on mine and yeah...can't really hear them at all over the engine noise in the cab. Even after a nice CD player and speakers I can't hear some music because it's NOT LOUD ENOUGH even on a "low setting" of 34 or so...with the engine off 20 is loud.

I'm about to put 37" tall 38's on it and hopefully that will make it a bit more trip friendly.

Around town? Sure. Gets up and goes just fine. Freeway work? Nope, not unless it's for short blasts or you put an OD tranny in.


tRUSTy...yeah, mine leaks from the rear main. How bad is this?
In fact, mine seems to leak on both ends as I have two spots under the pan and then one under the t-case's rear output.

 

[tRustyK5]

Rear main is just messy. More of a big deal with a manual tranny as it fouls the clutch and pressure plate causing clutch chatter. Not spendy to fix, just time consuming...step one, drop tranny and T-case.

Finally not covered in oil...

Here you can see the oil caked crossover pipe...

Rene

 

[AJMBLAZER]

So is this a common problem due to crappy factory seals or something?

I just find it odd that BOTH main seals are leaking on mine. The level never goes down much but the spots on the floor are always there and always about the same size.
At least the transmission crossmember will never rot out...

 

[tRustyK5]

I think, like mine, it's a combination of age and usage. My 6.2 had sat for a while, and had been used in a K20 with 4.10's, 4 speed and 38's for quite a while before that (In town). I got it, and those poor 18 year old seals were subjected to those R's for that long it's not such a surprise they started to leak.

Rene

 

[AJMBLAZER]

Yeah...50k in 21 years I bet mine are just a bit dried up from not being used much or subjected to more than weekly driving and daily warm ups.

Something else to add to the list. Guess I'm not so worried about it anymore unless the oil levels just plummet suddenly or the spots get bigger.