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 > Coast on the uphills accelerate on the downhills

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BenK

SF BayArea

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Posted: 01/07/20 09:23pm Link  |  Quote  |  Print  |  Notify Moderator

PPS...while changing fan clutch, change out both the serpentine belt & idler


-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?...

time2roll

Southern California

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

opnspaces wrote:

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
I would keep it close to the 4400 when working hard. 3000 would seem low. Sometimes you just have to downshift and go a little slower to keep the rpm where you want it. You should see a small drop maybe 100 to 300 rpm as the TC locks. I believe the TC will unlock between automatic shifts for a smoother transition. Really have to pay attention during these moments to know what is happening. Not always easy.


2001 F150 SuperCrew
2006 Keystone Springdale 249FWBHLS
675w Solar pictures back up

Grit dog

Black Diamond, WA

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Posted: 01/08/20 08:38am Link  |  Quote  |  Print  |  Notify Moderator

openspaces, sounds like you've checked most of the boxes for normal operating parameters.
I "think" I disagree with benk on the fan clutch being an issue. I'm not certain that you'd maintain proper engine coolant temp if it was failing. And I believe your truck just has an old school thermal clutch, which would sense heat from the radiator, not the small low mount trans cooler. Although replacements are pretty economical.
A larger cooler and or deep pan will certainly help considerably, but I think you also believe that you were not working the vehicle to the point that it should have been overheating the trans.

I think it's worth doing some research on converter lockup. The 4L80 has an electric converter lockup, which could also be faulty, but it appears to be working in 4th gear, correct?
More importantly, I'm pretty certain that with factory programming lockup can only occur in 3rd and 4th gear and 3rd gear it's only at higher rpms. There are several aftermarket lockup switches or programmers that allow for earlier lockup in 3rd and lockup in 2nd as well.
Possible that you were just below the lockup speed/rpms in 3rd and that is the only real "issue."
I'd research and do some test drives first to find what speed/rpm lockup occurs in both gears and compare to the rpms you were running when it got hot before throwing parts at it.
Just spitballing possible causes/solutions. Hope you figure it out easily.


"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.

discovery4us

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Posted: 01/08/20 09:04am Link  |  Quote  |  Print  |  Notify Moderator

[quote=opnspaces]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.
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Our trucks are 3/4 ton. I don't know if we were unlucky or if others have encountered this but our non HD 2 wheel drives came with the 4L60. Still great trucks we just encounter heat issues around 100K miles.

BenK

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Posted: 01/08/20 12:31pm Link  |  Quote  |  Print  |  Notify Moderator

I'm older than grit...so most likely experienced more fan clutches than the kid.... [emoticon]

Fan clutch failures generally start to couple less and less
water pump shaft RPM's...till they almost free wheel

Since a failing unit still couples, there is enough air being pulled to take care of low demand...but...as the demand for more air goes up...it can not a accommodate...therefore the coolant can not reject enough BTU's and the engine heats up

Lowest cost component or system first, else tossing money away....till you get to that lower cost thing...

time2roll

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Posted: 01/08/20 12:47pm Link  |  Quote  |  Print  |  Notify Moderator

BenK wrote:

I'm older than grit...so most likely experienced more fan clutches than the kid.... [emoticon]

Fan clutch failures generally start to couple less and less
water pump shaft RPM's...till they almost free wheel

Since a failing unit still couples, there is enough air being pulled to take care of low demand...but...as the demand for more air goes up...it can not a accommodate...therefore the coolant can not reject enough BTU's and the engine heats up

Lowest cost component or system first, else tossing money away....till you get to that lower cost thing...
I agree this could well be the issue. Engine temperature can stay at 190 but the transmission fluid cooler in the radiator is on the cool side of the radiator. So the water exiting the radiator might be cool enough for the engine but not cool enough to absorb enough from the transmission. Partially restricted radiator could do same.

BenK

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Posted: 01/09/20 02:07pm Link  |  Quote  |  Print  |  Notify Moderator

To the PM asking why I didn't talk about a radiator going bad, as it also has these symptoms...

Yes, but the OP somewhere in earlier posts on this thread said it had a radiator leak and had it fixed

So, assumed it was done correctly (assumptions are dangerous, but the OP said had it fixed). Also assumed either new radiator or the old radiator fixed (re-tanked, rod'ed out, etc...another assumption). That means it is or should not be the radiator

Hope they didn't just toss in a bottle of stop leak, one of the worst things you can do involving Deathcool (Dexcool...pink, or red coolant...AKA OAT's, Organic Acid Technology). It will react to form acidic globs that then stick to cooler surfaces (like inside the radiator, which will block flow and acidic means eat/rot the radiator from the inside

Curious why folks are harping on this small block's RPM while towing. The 4L80E is an 'automatic' and just leave it to it's computer to manage it. The manual does say to tow in 3rd, not OD. IF the OP is towing in OD, then the tranny will hunt and over work the gear sets

Gears get hot while working at or near it's design limits. The why differential gears get hot and there isn't a TC in there. Any gearbox will get hot and hotter as you approach design limits. Ditto in an automatic and toss in the hydraulic coupling losses of a TC...an automatic will get hotter than a manual, everything else the same

Of course, Grit and the others who think the 4L80E is failing could also be right, but the OP hasn't provided any info that would point to that. My guess is the fan clutch and is the lowest cost component fix at the moment based on the OP's info posted

PatJ

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Posted: 01/09/20 08:09pm Link  |  Quote  |  Print  |  Notify Moderator

I have owned and still own a few GMT400 and GMT800 trucks both 1/2 and 3/4. Your trans should not be getting as hot as it is with the weights you are talking about and 4.10. These are my guesses as to your issue, numbered from most to least likely in my opinion:

1. Your driving style kept RPM lower than designed and therefore your converter was unlocked and you were out of torque curve. Up hills with that load and 4.10 at low highway speeds you should be locked up in at the top of 3rd. The LS will rev more than your previous Vortec did, and transmission programming has changed to reflect that. The tow/haul mode does more than just trans shift points so be sure to use it.

2. At some point the radiator was replaced with a cheap aftermarket which notoriously have a very short straight piece of restrictive copper tubing in the tank as the "trans cooler" versus the large heat exchanger section that was in the tank of the OEM radiator. If this is the case then you are basically asking the external trans cooler to do all the work and it is fairly small. There are photo comparisons online of cut-open Autozone-class replacement radiators vs. OEM class and the biggest difference is usually the ATF cooler loop inside one end. Chevy designed for significant trans cooling to happen in the radiator (more than 50%.)

3. The trans is tired or has internal issues and needs rebuilt/replaced. Luckily this is a common transmission fairly inexpensive to rebuild/replace and the GMT800 trucks are worth it, especially the 3/4T.

Just my opinion/guess


Patrick

Grit dog

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Posted: 01/10/20 10:05am Link  |  Quote  |  Print  |  Notify Moderator

BenK wrote:

I'm older than grit...so most likely experienced more fan clutches than the kid.... [emoticon]

Fan clutch failures generally start to couple less and less
water pump shaft RPM's...till they almost free wheel

Since a failing unit still couples, there is enough air being pulled to take care of low demand...but...as the demand for more air goes up...it can not a accommodate...therefore the coolant can not reject enough BTU's and the engine heats up

Lowest cost component or system first, else tossing money away....till you get to that lower cost thing...

Lol, you're spot on there Ben! But I did grow up in the era of 3 kinds of radiator fans. Thermal clutch, flex fan, or invisible fan (removed).
I understand what you're saying and IMO, it's cheap peace of mind, as is replacing the other common wear parts on an older rig.

The "repaired" radiator leak may also be suspect, I agree.
This could very well be a combination of several "minor" issues stacking on each other under the right conditions.

Interesting note on the 4L60, 2001 vintage, was doing some unofficial testing last night with nothing better to do driving home late at night.
If I floored it at highway speeds and got kickdown to 2nd gear then an automatic upshift to 3rd with the trans manually shifted down to "3", I never felt or saw a lockup reduction in rpms in 3rd gear, but upon shifting to 4th, it would lockup a couple seconds after the shift, dropping another 2-300rpms.
This makes me question if that era of trans 4L60 or 80 does lock the converter in 3rd gear at all.

BenK

SF BayArea

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Posted: 01/10/20 11:11am Link  |  Quote  |  Print  |  Notify Moderator

Maybe Grit isn't as young as thought[emoticon]...as me too, flex fans were the coolest invention of that time. Almost put a SS flex in on my 1973 K5 Blazer, but never got around to it. It's still in the garage somewhere...

As for lock up. My 1996 4L80E locks up in 3rd and also around 200-300 RPM drop when it does lock

Difference is that mine is direct linkage to the throttle and yours fly by wire. So there is more of a lag flying by wire and checking requires eyeballs to stay on the tack a bit longer than mine

Also, fly by wire has the ECU 'think' a bit longer before it does whatever you told it to do...especially dealing with power mode...nailing the throttle to the floor will have it think a bit...check the sensors to make sure it is okay. Mine is NOW, unless it is already in a lower power mode

My 4L80E, manually in 1st will shift up a gear by itself once it approaches red line.

Marty dislikes the 400/4L80E, as they failed on him. Think his diff ratio the culprit, as 1st is not low enough (2.48) helped by the TC coupling losses & torque multiplication

Mine is 4.1's and going to 5.38's or whatever can find that has a front diff gear set to go with the rear gear set

Back to the OP, think he has the 4L85E. IIRC GM had the gears nitrided (hardened) and heavier duty clutches. Maybe some other goodies, but don't remember what else

Ask the OP if he has the work order, etc sheets listing what they did to 'fix' the radiator leak. Patrick is spot on for some 'El Cheapo' shops who will put in that kind of radiator. Fine for light driving, but anything demanding higher BTU rejection will over heat

OP, look into your radiator cap opening (assume you can, somewhere all the OEM's went away from that and had a pressurized over flow bottle). There should be an ATF radiator inside the cold tank of your main radiator. Small block had a 5 fin and big block had a 7 fin radiator. I'll find time to dig into my image file system (Photobucket screwed my posting system/files and have to go back to the HDD in the safe).

If you have that tube Patrick talked about, have it changed. Heard about them, but never eyeballed one

Agree with Grit...most likely you, the OP, has a few issues stacked up on top of each other due to several things 'fixed'. Again, suggest going to the least costly and IMHO, that is the fan clutch. Get the severe duty and change the serpentine belt & idler while at it

Good luck and please post updates as it goes

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