3.73 vs 4.10 - Suburban

cyoung

Well-Known Member
Joined
Apr 7, 2005
Location
Gibsonville, NC
Looking (still) at 3/4 ton, 4x4, Vortec burbs. Many I've seen have the 4.10's but wondering in the real world would 3.73's really hurt you towing? I know they should improve mpg when not towing. Max weight I would ever tow would be about 7k lbs. Probably a 454 engine.
Thanks!
 
Sent pm sorry it took so long to reply I was using my son's computer.
 
My 97 454 w/4;10 gets at best 13.9. The 99 350 gets 15 onthe highway. The 01 w/6.0 gets 14 +. I sold the 93 5.7 that could get 16 going to florida( all downhill) but it couldn't tow alot.
 
I think with the earlier engine, I'd stick with the 4.10's.. Get you near torque peak at 65mph...

If it's constantly downshifting because it can't pull a molehill in O/D, you'll regret getting those 3.73's.
 
Sorta on subject. I have 3.73s in my 99 Tahoe with the 5.7 and I got between 10 and 11 towing 7k from Greensboro to Harlan a few weeks ago.
 
Here's a real world for you:

'99 Sub - Vortec 5.7L/4L80E/3.73

Towing right at 7000# in OD (70mph) at 85*F ambient there was no indication(s) anything was struggling pulling the hills on US52 between Rural Hall & Mt.Airy.
Since both oil & tranny cooling circuits enter the radiator tanks, I figured if the tranny was getting too warm (was NOT "hunting", just dropped out of OD on the uphill), it would have manifested in higher coolant temps. While I'm still running the stoopid console gauge, it rose maybe 10-20 above normal (empty), but dropped each time the thermostat opened...

3f693358.jpg


15b5aaf0.jpg
 
Dave - That's a big assumption. But if the TC stayed locked, the trans won't get very warm at all. It's when you drop down under 50 that things start to heat up...
 
Rich said:
That's a big assumption.
Click to expand...

The CTDs coolant temp dang sure jumped 40*-50* once the tranny got hot (attempting to pull OD *downhill* :rolleyes:) and it had 2 HUGE air/oil coolers the Sub doesn't have...

Rich said:
But if the TC stayed locked, the trans won't get very warm at all. It's when you drop down under 50 that things start to heat up...
Click to expand...

School me! :confused:
Outside of a scan tool, is there a way to determine when the TC is locked/unlocked? What I saw/heard at the base of each hill when the cruise lagged a bit:
- RPMs took 1 single increase all at once (not what I've seen on past vehicles where the TC unlocked = increase in rpms & then out of OD = another increase in rpms) that I assumed was 3rd, except for the time it hit 2nd (foot assisting cruise) :D
- After cresting the hills, I felt it shift/rpms dropped (OD?), and shortly after saw another slight drop (few hundred, which I assumed was the TC locking back up)

I also did about 20 miles thru the country in 35-55mph with the shifter in OD, but don't think it actually hit OD (based on RPM), so I'm guessing you mean 50mph pulling a hill?
 
CTD - Why would the transmission get hot on a downhill? unless that gauge was finally reacting to the heat the trans was shedding climbing that hill. (Your CTD had a non-locking TC right?)

RPM rise - You might have seen the TC unlocking and the downshift to third all at once?

I don't know about the trans logic in the older stuff, but mine will lock in the TC in 3rd or OD above 55, and stay locked until 50 with the OEM programming. most of the heat in a trans comes from an unlocked converter. The trans temp will never break 190° on the hottest day if I am able to keep the TC locked. But once it unlocks and you're putting power to it (hill, heavy load, stop & go, etc.), it'll heat up.

Easiest way to tell if the TC is locked or not is give it a little gas.. if the RPM's flare a little, it's unlocked. ;)

My comment about it being a big assumption is just that without a trans temp gauge (which no one should be towing without), you're assuming that's why the temp is going up. could be the motor. Could be stuck thermostat. Could be a small child stuck to the grille, blocking airflow.
 
Back
Top