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 > Coast on the uphills accelerate on the downhills

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discovery4us

California

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Posted: 01/07/20 02:36pm Link  |  Quote  |  Print  |  Notify Moderator

Our work trucks have towed all their life and all have the 6.0 with the 4L60 4 speed automatics with factory cooler and tow package. All at 100K miles starting having transmission heat problems. Had the transmissions rebuilt and problem went away. At 200K same heat issue and same fix. At 300K same heat issues and same fix. At 400K I guess we know what to expect [emoticon][emoticon][emoticon]

BenK

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Posted: 01/07/20 03:33pm Link  |  Quote  |  Print  |  Notify Moderator

The Lowest cost and easiest things to look for before taking on larger/expensive items

Thermostat might be sticking, coolant might need to be flushed (Deathcool...pink/red and when it needs to be changed...it goes south fast), fan clutch (and if so, there are three levels...OEM, HD and Severe Duty...get the SD) and as noted by others, check the radiators for debris (all three, main ENG coolant, AC and AFT.

Also, the ATF might be in need of a flush, but if it has been neglected...the fresh fluid might loosen up some varnish to ruin the tranny. So take our time checking into that area

{edit}...do NOT open the radiator cap to check coolant fluid level. Use the over flow bottle. It is translucent and check the level there. Air (O2) and Deathcool do NOT mix well


-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...

Grit dog

Black Diamond, WA

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Posted: 01/07/20 06:10pm Link  |  Quote  |  Print  |  Notify Moderator

smarty wrote:

would any of this "data" indicate the vehicle is exceeding its towing capacity?

The OP is certainly not exceeding the towing rating based on the trailer weight he gave. Not even close.
But as mentioned by others as well, a 19 year old vehicle with a presumably unknown history and those miles may have reduced or limited current ability without some repairs, or upgrades to reduce the stress on old components.


"Yes Sir, Oct 10 1888, Those poor school children froze to death in their tracks. They did not even find them until Spring. Especially hard hit were the ones who had to trek uphill to school both ways, with no shoes." -Bert A.

deltabravo

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Posted: 01/07/20 06:42pm Link  |  Quote  |  Print  |  Notify Moderator

In my truck, I replaced the OEM trans cooler for an HD aftermarket cooler which was total bolt on and fit the stock location.

I don't know if anyone makes an HD style OEM replacement cooler for gas GM trucks/ Suburbans


2009 Silverado 3500HD Dually, D/A, CCLB 4x4 (bought new 8/30/09)
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time2roll

Southern California

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Posted: 01/07/20 08:13pm Link  |  Quote  |  Print  |  Notify Moderator

what RPM are you running during the climb and overheat?
I would aim for about 200 to 1000 rpm over peak torque rpm rating. Pull the lever and hold the gear. Adjust your speed to get the RPM in the zone and just set the cruise.

AFAIK you should get lockup in all gears except 1st when using this method.


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opnspaces

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Posted: 01/07/20 08:26pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks for all the responses. I pulled the shields back and there is in fact a small factory transmission cooler in front of the AC and radiator. I didn't see any external obstructions, but I gave all the coolers a good blast of water to make sure they are clean.

The radiator was leaking when I looked at the truck on the lot so they had to replace it. So at least I know the radiator and dexcool are new. But I'm wondering now if the external cooler might be partially plugged internally. Tomorrow I'm going to warm it all up and then run my hand across the cooling fins and see if the cooler is even getting warm.

I'm thinking about what BenK said about the fan clutch. But the radiator doesn't run hot. It stayed at 195 the entire trip so would a fan clutch still help?

As far as the fluid flush, well that ship has sailed as I had the fluid changed when I bought it last month. The old fluid didn't look too bad so crossing my fingers that the was minimal or no varnish buildup.

As far as the work truck transmissions failing around 100k. Yes I've heard that about the 4L60 and talked to the local transmission shop when I bought my original Suburban. Their recommendation was to avoid the 1/2 tons with 4L60's and go with a 3/4 ton since they come with the 4L80 which is supposed to be much more stout. It was one of the reasons, but not the only reason that pushed me into a 3/4 ton.

It could be as Grit Dog says and it might just be more worn out than I thought. All I can say is I hope not on that front as I need it to last a couple of years before I think about buying something different.


2001 Suburban 4x4. 6.0L, 4.10 3/4 ton
2005 Jayco Jay Flight 27BH
1986 Coleman Columbia Popup.

opnspaces

San Diego Ca

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Posted: 01/07/20 08:40pm Link  |  Quote  |  Print  |  Notify Moderator

time2roll wrote:

what RPM are you running during the climb and overheat?
I would aim for about 200 to 1000 rpm over peak torque rpm rating. Pull the lever and hold the gear. Adjust your speed to get the RPM in the zone and just set the cruise.

AFAIK you should get lockup in all gears except 1st when using this method.


3 - 4.5K. I've never been shy to let my gas engines rev though I try to stay at least 1k shy of redline. Though on this gauge cluster there is no red and it goes up to 6,000. I'm assuming it would rev limit if I went too high, but personally won't push it much past 5,000.

I agree with you on finding that gear. It was what I was playing with on the drive home and it really helped keep the heat down. I'm hoping to go out again an a few weeks and I'm going to pay more attention to lockup and see what happens.

opnspaces

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Posted: 01/07/20 08:57pm Link  |  Quote  |  Print  |  Notify Moderator

In looking at some searches including one from RV.net it seems max torque is at 4,400 and max HP at 5,200. But I wonder if it's a double edged sword. On the one hand the engine is okay with the high revs. But on the other hand if the converter is not locked I imagine the temperature might spike pretty quickly.

rv.net post

Second site

BenK

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Posted: 01/07/20 09:00pm Link  |  Quote  |  Print  |  Notify Moderator

What you experienced is a classic fan clutch going bad symptom.

It will run just fine...until it needs more CFM

On that, the thermal system is designed to run at a preset temp range (thermostat, fan cutch, etc).

As you demand more cooling...AKA towing, hauling, going up an incline, speeding up, etc...the cooling system will increase until al of their component/sub-systems reach their max performance capacity...then the temp will raise until the temp reaches preset safety temp points

Then the ECU will drop off of power mode and start to go into ever lower limp modes...if you continued...you would have experienced it going into limp modes, until it would only allow crawling

OEM fan clutches couple water pump shaft RPMs around 40%-50%. HD and SD couples around 80%-90% or more water pump shaft RPM’s. The main diff between HD & SD is in the bearings, shaft clip, etc...to keep it from taking off like an airplane into the radiator

It is about time anyway. Fan clutches d wear out. F you go with a new one...suggest only getting a severe duty

ROAR will be significant, so beware and don’t get startled...a very good thing to have almost twice the CFM of an OEM fan clutch...

I like TRW fan clutches and hope they haven’t gone bean counter management of decreasing quality for a few more bucks profit...

Almost forgot...let the new fan clutch sit over 24 hours with the nose “UP”...has to do with settling the coupling fluid internal to the clutch

(Edit)....dash temp gauge drops like a rock once my fan clutch kicks in

* This post was edited 01/07/20 09:14pm by BenK *

Edd505

Elephant Butte, NM

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Posted: 01/07/20 09:19pm Link  |  Quote  |  Print  |  Notify Moderator

opnspaces wrote:

1

1) I most surely was overheating my old Suburban transmission driving the same roads in the past.

2) Accelerating on the downhills and going easy on the up hills is surprisingly effective at keeping the temperatures down.

3) I now need to change my transmission fluid, even though the current fluid is less than a month old.

4) And I need to start researching an aftermarket cooler.

Anyway I was surprised how altering my normal driving habits to going easy on the uphills really made a difference in the heat of the transmission.


Congratulations your now a trucker!


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2006 F350 SRW 6.0 crew longbed sold
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