Max Vehicle Operating Speeds

Glider

Active member
216
155
43
Location
South Pittsburg, TN
I was reading the placard for M998 6.2/3 speed. It says in High range max speed in 2nd gear is 45mph. How can that be anywhere near accurate? When driving I'm afraid to hold second past 33ish. Am I missing something?
 

TOBASH

Father, Surgeon, Cantankerous Grouch
Steel Soldiers Supporter
2,261
1,025
113
Location
Brooklyn, NY
My unit did 55. Juan Prados unit does 70. Not sure why. Maybe differential gearing?
 

LouWon

Active member
391
36
28
Location
Michigan
Mine will do 70 at about 3400 in third gear( GPS speed from iphone app), never really maxed out on second gear....
I will look at my placard tonight.
 

Coug

Well-known member
Steel Soldiers Supporter
1,810
1,676
113
Location
Olympia/WA
Max possible speed and max sustained speed are two different things.

When most of us talk about max speed, it's the max sustained speed you can do. That's why 55 is considered max top speed for the 6.2/3 speed. You can go faster than that, but you risk destroying the motor if everything isn't 100% (and with the GM blocks the odds of having everything 100% aren't the best.

I'm pretty sure you could probably hit 45 in second gear, but not sure how long you can hold it there without blowing the engine.

Without a tach installed you don't actually know what your RPMs are, and therefore don't know how close you are to maxing them out.
 
49
24
8
Location
Aguanga, CA
Max possible speed and max sustained speed are two different things.

When most of us talk about max speed, it's the max sustained speed you can do. That's why 55 is considered max top speed for the 6.2/3 speed. You can go faster than that, but you risk destroying the motor if everything isn't 100% (and with the GM blocks the odds of having everything 100% aren't the best.

I'm pretty sure you could probably hit 45 in second gear, but not sure how long you can hold it there without blowing the engine.

Without a tach installed you don't actually know what your RPMs are, and therefore don't know how close you are to maxing them out.
For clarification what is the max RPM for these engines? I've been keeping mine under 3000 because I wasn't sure what the redline was.
 

86humv

Well-known member
Steel Soldiers Supporter
1,537
248
83
Location
Texas
3 Speed trucks shift so fast when you think your in 2nd...your in 3rd.
 

86humv

Well-known member
Steel Soldiers Supporter
1,537
248
83
Location
Texas
I was reading the placard for M998 6.2/3 speed. It says in High range max speed in 2nd gear is 45mph. How can that be anywhere near accurate? When driving I'm afraid to hold second past 33ish. Am I missing something?
No way to hold it in 2nd if shifter is in drive....unless trans is AFU, or you manually shift it.
 

LouWon

Active member
391
36
28
Location
Michigan
For clarification what is the max RPM for these engines? I've been keeping mine under 3000 because I wasn't sure what the redline was.
6.2L GM Diesel Specs
Manufacturer:Detroit Diesel ( a division of General Motors at time of inception)
Max Engine Speed:3,600 rpm (4,000 w/ no load)
Peak Horsepower:• 130 HP @ 3,600 rpm (introductory) • 160 HP @ 3,600 rpm (peak)
Peak Torque:• 240 lb-ft. @ 2,000 rpm (introductory) • 275 lb-ft. @ 2,000 rpm (peak)
 

Glider

Active member
216
155
43
Location
South Pittsburg, TN
I know why I was confused by the placard. After playing closer attention to the motor it will reach the speeds listed. I was mistaking fan noise for engine revs. My cooling fan is always on. The previous owner by passed the Cadillac valve and connected the two hoses from pump together. Now im doing my homework on the cooling system. I verified with compressed air the fan clutch is working. Going to start testing the rest of components this weekend. I'm also looking forward to a hotter heater mine will not go over 160 unless really being put under a load. Highest I've seen is 175. I thought it was a really good cooling system but after reading the engine needs to run much warmer.
 

Action

Well-known member
3,499
1,338
113
Location
East Tennessee
I know why I was confused by the placard. After playing closer attention to the motor it will reach the speeds listed. I was mistaking fan noise for engine revs. My cooling fan is always on. The previous owner by passed the Cadillac valve and connected the two hoses from pump together. Now im doing my homework on the cooling system. I verified with compressed air the fan clutch is working. Going to start testing the rest of components this weekend. I'm also looking forward to a hotter heater mine will not go over 160 unless really being put under a load. Highest I've seen is 175. I thought it was a really good cooling system but after reading the engine needs to run much warmer.
This still doesn't explain why you drive with it in 2nd gear.
 

Glider

Active member
216
155
43
Location
South Pittsburg, TN
This still doesn't explain why you drive with it in 2nd gear.
I don't drive the truck in second gear. I live in a mountain area. I will often manually downshift to second when climbing hills. The trans doesn't want to downshift unless I have it to the floor and it is still slow to shift.
 
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks