Max safe highway RPM for a 6.2L

I looking at buying a used 86 5/4ton 4X4 chevy pickup. It has 4.56 gears, a 3spd automatic trans, 31 inch tall tires and the 6.2L diesel and @43K miles on it. I understand that the safe operating range for the 6.2 is between 1800-2800rpm. But what is the maximum safe rpm to be used for an extended period of time, like highway driving. The truck is located in PA which is about 4 1/2 hours from my house. With the 4.56's the truck has a max speed of @50-55 mph at roughly 2450-2750 rpm. Would driving at those speeds and that rpm be bad for the engine? Is the 2400-2500 @ 50mph ok? Before I lock myself into this truck I want to make sure I can even make it home to my house without doing 40mph all the way. I would like to use the truck to make similar trips to go camping, snowmobiling, 4 wheeling etc... and every place I go is at least 3-5 hours away. Will the engine handle 2400-2800 rpm for extended periods of time like 4-6hours of highway driving and not fail. Is that type of driving going to severly shorten the engines life span? I want the truck for it's ruggedness because it adds some piece of mind while bouncing around in the woods over 200 miles from home. Any help would be greatly appreciated.

I have recently asked member of this forum that same question and the anwser was it will run up aginst the govonor all day long. And My truck is a old body style 88 c3500 crew cab fully restored, 6.2 th400 and 235/85/16. I just took a trip from va to tn 785 miles round trip pulling a fully loaded car trailer, 4 adults, luggage. It ran happly at 70 mph the whole way there and back. This was the trucks first trip out sense pulling out of the paint booth. It has a jasper 6.2 with 9000 miles so i knew the motor would be fine. It got 14.5 miles per gallon. Not too bad the noise will get to you a little. Im looking into a 700r4 ad a turbo lacks a little power going up hill but it made it only casulity was one clutch fan on the way home, lucky we were 2 miles from autozone. I went with a friend and he has a 2002 chevy 2500hd with a 6.0 and we did pretty well keeping up. Need a turbo. Your new truck will due just fine.

Do you know what gear ratio your truck has? Trying to do 70mph with the 4.56's would really be sreaming the crap out of the 6.2L. I was always under the impression that the govenor was there to do just that. Protect the engine from failure due to over reving. But still, the impression I keep getting from everyone Italk to is that running the motor that high is still not good for it. I'm just very new to the whole diesel scene and don't want to make an expensive mistake of blowing up a motor due to reving the heck out of it just to get somewhere a few minutes earlier. If I can use the truck at 55 or 60mph for now without doing any damage I'd be very happy. I can always swap rears or change gears or even do a 4spd auto swap later on. But I need to be able to drive it theway it is without having to worry about it taking a dive on me.

Welcome to the Forums!

If you can fit a sheet of tissue between the skinny pedal and the firewall, it's got some left. They will run against the governor all day, every day, if it's healthy. Bad for your ears and fuel stops, but no problem otherwise.

the truck will do 60mph all day long with 4.56 gears in the differentials.

I had the same combination and drove like that for two years before lifting my truck and putting big tires on it.

Hi there,
I have a 85 M1008 which I have used for 11 years as a Work truck in my job as a Self employed Caterpillar mechanic, the truck will cope with 60mph without any problems. It will cope with higher speeds (75mph) but I tend not to push it as it is not the quietest of trucks with the 4.56 diff gearing. I would recommend getting the fuel filter, engine oil and filter changed before the long journey home and maybe check ALL oil levels including axles and transfer box, don't forget the power steering level too.

Over the years of using this "Old Truck" as an everyday (and I mean everyday) work truck and it's been round the clock a couple of times, I have a lot of respect for it as it's been a good hard working reliable truck. By the way it's still on the same engine that was in it when I bought it 11 years ago and has been one of the most reliable trucks I've ever owned despite working hard.

Good luck

Jim

I have owned 3 of these beast & they are tough they will run 85 mph wide open & 70 as long as you can stand it. If you can find an intake silencer off a civilian model it helps with the noise .I also put an electric fan on one & it was quieter
OM

If you're gonna run some highway, just put some bigger tires on it... Sure, I under stand if your truck is show quality, you're not gonna want to trim the fenders, but on a stock width rim, 35/12.50's will fit with no lift and minor fender trimming, you'll feel like you got over drive (kinda! LOL) and you'll gain ground clearance. I ran my CUCV 1028 like that for a few months when I first got it, then went to 6" lift and 39.5 boggers! Without a turbo, it was barable with the 35's on it, since then I've put on a turbo, went to 4.10 gears, have the 35's back on it, and it will run 75 MPH if I want it to, and if the tires were ballanced better, I could hold that speed for as long as I want. (bent rims ruin my day) I'll soon be putting the 4.56 gears/lockers back into my truck, as time permits, it will be returning to "play-toy" status.

In a nut shell, from my experiance, I would recomend:
Trim front fenders, get a good set of 35" radial mud/all terrain tires
Turbo the motor, get a few gauges, keep the filters and oil changed, that truck will last for years.
Be sure to keep some chains in the truck, you'll be the one moving in the worst weather, people will want you to pull them out of the ditch!

Greg

well, it's nice to hear from people that have actually had these trucks, and this engine that to expect to do 55 or 60 is not out of the question. No the truck is not a show truck, but I would like to keep it as original as possible so 35's probably not. Fender triming, deffinately not.For now anyway. When the tires wear out, 32's or 33's for sure. I hear you on the guages, I'm a firm believer in them. Even the cheapest set of parts store gauges is better than an idiot light. Plus I have a 88/87 body style blazer with a blown rear that I may grab some stuff off of before I scrap it. Mainly the instument cluster and some dash parts. If all goes well I'll be looking at the truck tommorow and possibly bringing it home so we'll see.

Tires....

Have a look at 255/85/16. They are 33" tall, and not too wide. Speedo calibration is as simple as changing the speedo gear at the rear of the transfer case. You should not have to do any fender modification to fit them.

Invest in an exhaust temperature guage first and foremost!! The coolant temp may stay in check but the second you start to climb some of those hills pulling a trailer, the exhaust temps can climb rapidly and warp the heads.

And I worry about my 6.2 in the motor home at 60-65
I havent checked the gears but she's wound pretty tight

Chicken Little I guess

without adding a turbo or turning up the fuel you dont need a EGT guage, also the m1008 is governed @70mph wide open as they come from the military, I speak from experience.

for more info on your truck, please visit us at www.steelsoldiers.com
its a military vehicle site, and we can answer any questions that you have about the military systems on your truck.

cool, I just registered there the other day haven't had a chance to cruise through yet.

i go by the same screenname over there, and am the moderator of the cucv forum.