Opinions NEeded: Low Temp Thermostat

[Stryder106]

Are you monitoring the transmission temp? When I installed a scanguage2 on my Blazer I was surprised to see it was running 220F in normal city traffic without a load. If I had tried to tow with it without addressing the problem no doubt I would have smoked the trans.

Not yet. A trans temp gauge is on the planned to do list. But, interesting info posted in the thread about running the trans-fluid through the radiator and it not affecting the trans temp. That is counter-intuitive as metal will transfer the heat to whatever is inside of it (logically) yet the info posted suggests otherwise. My trans guy said the first thing he does is get the transfluid out of flowing through the radiator due to the high heat in the engine coolant. I inquired about running the transfluid through the radiator, then through the transclooer and back to the trans. My thinking was additional cooling and capacity. This was also mentioned in the thread. My trans guy's response was "No, because the high heat of the engine coolant will increase the temp of the transfluid - and you don't want that".

As mentioned, there has been a lot of really interesting stuff posted in this thread that I previously did not know about the heat management process in my vehicle. really interesting and useful stuff.

 

[Korben]

FWIW I might as well add something here on the subject that I've started doing recently. ATF management is kinda a pain, few have drain plugs, level is very important, maintenance is important etc. So many of us end up having to drop the pan, or drain it all or something to change the fluid or even just to lower the level if somehow too much was put in. Recently on one of the vehicles I maintain I simply added a drain valve into the line to the cooler. I put a "T" in the line, put a valve on it and a length of hose. Now it's really easy to as a part of my regular maintenance to for example swap out a quart of ATF with each oil change. I just start the car, use the hose and valve to drain a quart into a jar(that then goes in my diesel), and add a quart of new ATF. It's working out great so far, thinking I'll do it on all my rigs with automatic transmissions.

 

[rayra]

Stryder, ask your mechanic if radiator temp is so detrimental why has GM been piping their trans cooler lines thru their radiator tanks for over 30yrs? (that I personally have experience with)

And another anecdotal bit of info, for whatever it is worth, in all my online time on car / truck forums, almost all the folks reporting trans cooling trouble started by removing the plumbing thru the radiator. Not saying it's causative, but it's an interesting correlation IMAO.

I've towed a lot of varied loads from light to moderate to an enclosed 14' tandem axle UHaul stuffed full of household goods out of the Sierras, up to Fresno and back down to L.A. via the steep side of the grapevine. Our Tahoe hauled it like it wasn't even there. The only thing I did was set the heater to max heat on that last killer grade and kept it around 60mph. At no time did I floor it or keep it at high RPMs. Didn't have any power or heating problems. I didn't try and force it to maintain a higher speed.

The only thing I can figure is that it comes down to individual transmission pumps / seals or driving habits. As a class, as a vehicle type, they just don't seem to have chronic trouble, so I don't think dropping the radiator from the trans loop is a good first move. Or that leaving it in is a primary fault.

But it's hard to say. The last guy that spoke of grief while towing with a Sub and running THREE coolers and not thru the radiator turned out to be hauling heavy loads well beyond what the max GVWR was for his vehicle.


I think the actual reason the trans is put thru the cooler is so when the trans does overheat it drives your vehicle cooling temps up and gets you to lay off the throttle or pull over and cool down, BEFORE you kill the trans.

Figure out something to change things up, to keep your drivetrain in the power band. Somethign that precludes having to take a high speed run at the base of a grade, and mashing the pedal thru the floor trying to maintain the speed despite physics. That **** just don't work. Or just accept being the guy that has to keep far to the right with his hazards on, on a steep grade.

 

[Stryder106]

Rayra - good stuff. The 02 Avalanche is a 6000# truck with a 327CI engine that only makes 285 hp and equivalent torque. That's a serious detune on GMs part for that engine - as the more recent engines (same CI) but with 350-385HP and torque indicate. Combine the detune with the heavy vehicle and you have what amounts to a dog - it's OK, it's MY dog so I can call it that.

I have blown 3 transmissions in this truck. Always the same symptom, always the same issue, always the same type of driving.

Transmission 1: Completely stock Avalanche - ZERO mods. Cruising 70mph, flat freeway, 10 5 gal cans of fuel in bed of truck (I was a VP dealer) ~500#. Cruise control set and just tooling along - rpm's start flaring, as soon as I noticed what was going on and took the cruise off - too late - bang. Lost 3rd-4th gears. Limped it home in 2nd.

Transmission 2: (less than a year later) Completely stock Avalanche (except for rebuilt trans). Same scenario, but completely unloaded coming DOWN Grapevine near Magic Mountain. Same thing, 70 mph, cruising, rpm flared to the moon, before I could react - bang. Lost 3rd-4th. Drove it home to Riverside in 2nd gear.

Transmission 3: Modded the truck and added the trans-cooler. Noticed the flare ups would happen after 45 mins or so of steady driving - got wise to the RPM flare. Would watch and wait for it - as soon as it would start to creep up, I'd let off the throttle, coast for a second or two and get back in it and it would be fine for a while. Sometimes this would happen once, sometimes more than once - but I managed it with my head and foot. Then we were on our most recent trip to Lake Mead (loaded and pulling the popup - not much actual weight) noticed it flaring more frequently. Did one wheeling trail and it did just fine, but then on the road back to camp it really started acting up. Decided to not chance any additional wheeling and just get it home. On the way home, same occasional flare up, but around the base of Cajon Pass, it REALLY started acting up.

That's when I decided I was done with this transmission - I didn't want ANYTHING from it. And now I have transmission #4 - and so far everything is really solid - albeit this one has beefed up internals.

Transmission shop owner (along with my research - this is a pretty common issue with the 4L60E) told me the issue is common and is caused by GM using an aluminum drum and a steel shaft - they heat at different rates. The fluid thins as it gets hot and the 3rd gear fluid starts seeping into the 4th gear clutch pack. When it goes - that's why it takes out those two gears.

Since I'm a drag racer - I decided to check into late model Chevy racers (I race a Mopar) who use the 4L60E - and guess what I find? The same issue, but for $6500 you can get yourself a bulletproof 4L60E that corrects that exact issue (along with making it a full race trans). But, my point is - that's a common enough issue that a very well known race trans shop who specializes in GM race trans - thinks it's important enough to call out and specifically identify their solution to this problem. That means it's a real problem in the trans design.

The transmission shop owner who did my first trans, never diagnosed the cause - he just fixed what was broken. The second shop owner who did my second trans - fixed what was broken and was trying to determine a cause and used Corvette servo and thicker band and had me bump up the line pressure on the 3-4 gears in my tuner trying to prevent what he THOUGHT could be happening. He actually thought it might be a glitch in my computer.

Now -the owner of the shop I'm currently dealing with is the first guy who said "I know what this is - I'm really familiar with it and here's what's happening and why". When he took my old trans out, he showed me what was going on by putting an air hose on the shaft (with it cold) and it was leaking into the next gear pack.

After enough research and finding this issue all over the place, and it seems to be unique to this trans - I'm pretty certain GM has a design flaw that they will never acknowledge. I am extremely familiar with the corporate side of the big US auto-manufacturers and they will not willingly admit a fault (Ford has still never acknowledged the issue with the Pinto - but I digress).

So - my hope is that with the new trans, with upgraded parts, built by a guy who seems to: 1) Know about the issue; 2) Understand how to address and prevent the issue from occurring - that my transmission troubles are behind me. The new trans has not yet had to climb a grade nor has it towed anything - so I'll keep an eye on my temps.

I also took some advice offered earlier in the thread and added a bottle of Water Wetter (or the Lucas version of it) into my coolant tank.

Many thanks.

 

[justcuz]

Good info on the transmission. I have heard that most trans shops automatically upgrade some of GM's design deficiencies when rebuilding a trans. My last 4L60E was rebuilt and upgraded to 4L65E specs by a guy who specializes in Allison automatics.

It's been a month, how has the transmission performed?

Maybe your transmission rebuilder should be shared with the board members, sounds like he knows his stuff.

 

[rayra]

All news to me. The only problems I'd seen with these transmissions have been those abused or grossly overloaded. I haven't read of any trouble just driving them around. And as mentioned earlier, a lot of personal direct experience and miles without such trouble. I have to think it's more due to individual habits. Sure, could be a 'design flaw', but it doesn't seem to manifest for a huge majority of its users. So is that really a 'design flaw'? Better to say that the 4L60E can't sustain heavy loads with high heat. Period.

Was your Avalanche routinely used for hauling a drag car / trailer? what was to towed load / GVWR? It's a fair bet you were exceeding the max recommended by a good margin. Is that a 'design flaw'?

Were it me, I'd likely have gone to the 4L80E after the second failure. Or got heavily into the sensors, programming / diagnostics. Transmissions are an expensive thing to just keep replacing.

Boats, open trailers with motorcycles, 'off road' pop-up camper, the above pictured UHaul and others like it. All three vehicles, all well above 100k miles, all in SoCal / desert southwest, all temps, all altitudes / grades. eta - we live at the foot of the Grapevine, every time we go anywhere north we go over that vehicle killer. All three with 4L60-E transmissions. Never any trans trouble or even severe heating. What am I doing different from the OP? Only thing I can think of is staying further way from the GVWR and load limitations. And not continuing to drive it hard when temps increase. Those are the only things I can guess at that I'm doing differently. IF a 4L60-E is gonna crap out just from ANY towing, it would have happened to our vehicles at least once, a long time ago.

 

[justcuz]

rayra,
When I did the online search, I found several postings about the rpm flare that occurred after rebuilds.
It may have more to do with assembly than design, but GM has consistently upgraded that trans over the years.
Transmissions do come improperly assembled from the factory also.

There is a problem with the Ford/GM transaxle that is used in the Explorer and Traverse that had clutch discs installed with the bevel facing the wrong way that caused a lot of warranty problems for both manufacturers.

 

[rayra]

Could very well be the case, especially with raised heat and fluid viscosity changes. Guess I'll find out when I finally get one rebuilt. Expecting to put another 100k on each of them, at least.
I'll go look for info on 'rpm flare', learn what the precursor conditions or clues are, so I can try to avoid such a thing. Sounds like a death spiral. And I still wonder if protracted or repeated hard use even after seeing elevated temps is what dooms these transmissions. like any transmission.

As to the repeated updates, that's been sorta true of GM transmisisons thoughout the entire modern era. One evolves into the next. Had a THM400 in my old Formula 400 Firebird, put a shift kit in that, drive it hard for a while without trouble. The THM350 in my '85 is on its 4th life, but that's 350k+ mi and I drive it way too fast for a 3-speed, so its failures were my fault (and that crappy lockup converter / pump design). Always swore I'd swap in a 4-spd 700R4, never did. Skipped that trans altogether, now that I think about it. Been driving the 4L60Es fast and far and sometimes hard, for a lot of years and miles. Been quite happy with them, consider(ed) them a vast improvement over the old THMs. Guess that's why I'm being so resistant to the idea that there's a flaw hiding in their design.

 

[Martinjmpr]

$6500 to repair a 4L60E? Wouldn't it have been cheaper to just go with the 4L80E swap?
.
FWIW I've been doing a lot of towing with my 2004 Suburban, most recently (yesterday) over Berthoud Pass at 11,300'. Trailer is a T@B travel trailer, weight is only about 2,000lbs. The engine temp gauge stayed pretty much in the center, I never even noticed an increase in engine temp. Transmission got up to 210 at one point but manually shifting to 2nd kept it from getting any higher.
.
By way of reference, on my V6 4runner the trans temp would routinely hit 220 - 230 when ascending a steep grade pulling a trailer and that was even with me manually shifting (highest trans temp I ever saw on the 4runner was 269, coming up out of Death Valley pulling a 1,000lb teardrop trailer.)
.

 

[ExplorerTom]

The engine temp gauge stayed pretty much in the center, I never even noticed an increase in engine temp. Transmission got up to 210 at one point but manually shifting to 2nd kept it from getting any higher.

Do you have a ScanGauge? I have a ScanGauge in my Explorer and an UltraGauge in my Expedition. I might like the UltraGauge a little more (can display 8 gauges at once- although I can only figure out how to do 6). It's interesting to see the temp readout vs the needle on the instrument cluster. The needle will be "in the middle" when the coolant is still warming up around 150 degrees. And yet the gauge is still in the middle when the coolant is over 200 degrees. There is a serious deadband filter as part of the factory cluster.