Hi - I have read all the various opinions online on keeping trans temps below 180/200 at all costs, but I am pretty sure the factory specs allow for a higher upper range for the 700R4. Hoping for Vorteciroc to chime in with actual GM engineering info?
I have a 1990 K5 Blazer with a 700R4 behind a stock 5.7 TBI, 4:88 gears with 35 inch tires. Running a B&M 29K Super Cooler with a 700 CFM fan and B&M temp gauge getting fed from the pan, and using Dextron VI synthetic. I tow a 4000# travel trailer with this truck, never in OD, and would like to know what GM's recommended temp range was for that year/model. I live in Colorado and pull some long uphills at times. While towing this trailer, my trans temps stay mostly below 220, but at times will climb up around 230/240 on long passes, at which time I usually pull over and let it cool down. Also, when driving 65 in OD on mostly flat highway without the trailer, my temps will stay around 220. Slowing down to 60 and shifting to D immediately bring the temps down to 180 or so. So, does the above sound normal and would running synthetic fluid and avoiding extended 230+ temps be within the "safe" design specs for a 1990 700R4?

Thanks so much!

 

You do NOT want to run that Transmission as hot as GM said was okay, Trust me!

180*F is were I personally like to keep ATF temps under (and above 160*F).

GM had no qualms with coolant temps in the 230*F-240*F range...
and ATF in the 210*F-220*F range.

 

Thanks for the reply! So does it sound like I have a problem with the trans running 220 in OD on the highway at 65 mph with no trailer? Could there be bands slipping in OD/4th? 4:88 gears with 35 inch tires seems like a good gear ratio, but I could regear to 5:13 if needed.

 

I would do your best to knock that down a good 40*F... and make certain that "Lock-Up" is occurring in OD.

 

Thanks very much for your help!

 

People in the business say the optimum temp for trans fluid is somewhere between 165 & 185. It doesn't work properly at all below 165, and starts to become acidic and otherwise less ideal above 185. Vorteciroc can no doubt fill in FAR MORE details than I can given his job history. 180 is pretty much what the trans builders mostly recommend as a target as well.

A properly working stock auto trans cooling system should make the trans run at just a few degrees above the cool side of the cooling system since that's where the stock trans fluid cooler is. That temp will vary depending on the ambient but should never be above 205 or 210. 220 or so is about as hot as a stock setup should ever go, unless abuse (towing, racing, rock crawling, etc.) or failure is involved. Might be as low as 160 or so fully warmed up on a sub-zero day on the highway.

An aftermarket cooler always seems to help. The better ones ("plate" type) with a built-in thermostat are the best. They should be mounted somewhere they can get good airflow but shouldn't block the radiator or AC condenser any more than necessary. More easily said than done in these cars. Such a cooler should be plumbed downstream of the factory one, or bypass the factory one altogether if your other is big enough and you dare.

 

Thanks much for the input! I'm a little mystified. As above, I have a B&M stacked plate cooler with a 750 CFM fan mounted in front of the cold side of the radiator. I have run the cooling lines with and without the radiator heat exchange before the B&M cooler with little change either way. 4th gear lockup is functioning perfectly and all shift points are on target (1 to 2 at 15mph, 2 to 3 at 25mph and 3 to 4 at 45mph). Fluid is synthetic and always seems pink and no burned odor.
On the highway with no trailer, if I slow down from 65 in 4th (trans temp typically stays right at 220) to 60 in 3rd/D, the trans temp cools right down to 180/190. When towing the 4000# travel trailer in 3rd/D, the trans temp stays around 180/190 except when pulling a long incline, which can get it up to 230, at which time I pull over to let it cool off. I'm out in Colorado, so I wonder if the altitude is a factor maybe?

 

Im curious why the temps would go up in overdrive when not pulling anything? If the converter is solidly locked it shouldn't heat up any more than in third gear, maybe converter isnt locking up or tcc clutch is slipping?

 

I thought I had heard that the cooling circuit is reduced in the 700R4 in 4th? I'm curious as well. No sign of slippage in 4th. No dropping in and out of TC lock unless adding power. If cruising in 4th on level highway, if I slightly push the brake pedal while keeping the gas on, the tranny definitely drops out of lock, then back to lock when letting the brake off. One other factor is ambient temps. It's in the upper 90's to 100 F when this is going on. Definitely runs a bit cooler at night - 190 to 200 in 4th at 65mph with ambient temps in the 70's.

 

I reason that I mentioned both the Engine Coolant temperatures, and the ATF temperatures...
is because they will affect one another.

It is no surprise that Sofakingdom was paying attention... I was hoping others would as well.
As Sofakingdom explained, the Engine Coolant temp can prevent the ATF temp from cooling down as far as desired.

I would improve the Engine Cooling temps or segregate the ATF Cooling System (however this is much more involved).

 

The THM700-R4 Cooler Circuits are perfectly fine in OD as long at the TC is locked.

Cooling issues will arise if driving in OD without locking the TC.
If using a non-locking TC... the TCC Valve-Train needs to be replaced with aftermarket parts to restore proper Cooler Circuit function without lock-up in OD.

 

Thanks again for your help. Like I said earlier, I have plumbed the trans cooling lines both through the radiator and bypassing it. No real difference. TC is definitely locking up and not slipping. Whatever. I'll just keep driving it till it has a problem. No issues so far after 5 years, but I want to make sure everything is set up as best possible.

 

A small standalone ATF Cooler is often not up to the task of cooling the Torque-Converter and Transmission on it's own.
This is why I stated that this would be the more involved route to take.

Standalone ATF Coolers will often need to be LARGE and have excellent air-flow (Via a great Fan or direct air-flow exposure).

 

With all due respect, I don't think you're really bothering to read what I'm posting very carefully. From my first post - "Running a B&M 29K Super Cooler with a 700 CFM fan and B&M temp gauge ". That is not a "small ATF cooler".

 

Thanks

I did read your post, however I do not use the GVW ratings that you referred to.

If my math is correct, (for a B&M stacked-plate Cooler) that should be about an 11" x 11" Cooler...
If so, that is an adequate size Cooler.

 

I thought your were not supposed to tow in OD....ever. ???

 

That is correct. I did not mention anywhere I was towing in OD. Only in 3rd/D.

 

You are right...I read these two back to back....towing in Colorado....cruising in 4th....and thought your were talking about both at the same time.

Thanks for clarifying.

 

Welcome! Lots of info all over the place.

 

One other thing to double check is to make sure you have your coolers plumbed properly, hot fluid out of transmission goes into stock radiator cooler and then into the b&m aftermarket cooler to cool it down even more before going back to transmission, I don't remember off hand but maybe someone can chime in and let us know for certain which line comes out of transmission and which line returns to transmission. It sounds like it could be plumbed backwards getting cooled down by the b&m cooler then heated back up to engine temps by the radiator cooler. check and double check after confirming with others on here the proper routing of lines as it is easy to get them mixed up when tracing them.

 

Thanks for the reply. Cooler line plumbing is verified. I can see the temp variation at all connection points with infrared thermometer. 700R4 out line is the bottom, input line from coolers on top. Cooler inputs are on lower fittings, and outputs on upper fittings on radiator and B&M cooler.

 

On a relatively cool day (60*F - 70*F); if you went on a 15 to 20 minute drive (casually driving, not hot-rodding around)...
How long does it take for the ATF temp to reach 180*F?
Does it take a long time, but then climb too high very quickly?

Do you use a Thermostat for the ATF Cooler (if so what are the Temp settings)?
Do you use a Thermostatic-Switch for the ATF Cooler Fan (if so what are the Temp settings)?

The Cooler is a good size, and sounds to be in direct air-flow through the Radiator Grill-Opening...
Fan function could be poor...
How many Amperes does the fan draw on start-up, and at speed?

 

"On a relatively cool day (60*F - 70*F); if you went on a 15 to 20 minute drive (casually driving, not hot-rodding around)...
How long does it take for the ATF temp to reach 180*F?"
If I stay off the highway, it never will. Stays between 160 and 170 or so. In traffic, no matter how hot it is, or how long sitting in heavy traffic, it barely gets above 160.
"Does it take a long time, but then climb too high very quickly?"
Never climbs quickly. It will only go above 180 if driving over 60 in OD and it climbs very gradually up to 220 and pretty much stays there. Then, if I drop to 60mph and downshift to 3rd, it immediately cools down to 170/180

"Do you use a Thermostat for the ATF Cooler (if so what are the Temp settings)?"
No
"Do you use a Thermostatic-Switch for the ATF Cooler Fan (if so what are the Temp settings)?"
Manual switch in the cab which I turn on at around 180. I watch the gauges like a hawk.
"The Cooler is a good size, and sounds to be in direct air-flow through the Radiator Grill-Opening...
Fan function could be poor..."
"How many Amperes does the fan draw on start-up, and at speed?"
That I'm not sure of, but it seems to be very strong. You can feel the air blowing back through the radiator into the engine compartment when it's on. I have done all the wiring in this truck myself. All the accessories have fuses and in some cases, relays. Everything is isolated and labeled and the battery, body ground, and frame ground are brand new 2 gauge cables. All the accessories are wired through distribution blocks and carefully kept within amp limitations (wire sizes, fuses and distro block connections).

Thanks!

 

I would then be looking at the Torque-Converter Lock-Up Clutch...

 

I have lockup in 3rd and 4th. If I touch the brake, RPMs go up, then down again when I let off. Originally with this post, I was hoping to get some insight from a GM factory perspective. I know these systems pretty well. What I don’t know is what the original factory specs, ranges and limitations were back in 1990 for the 700R4. My suspicion is that everything is working perfectly. The web is full of opinions and hearsay about old trucks. Was hoping for a bit of the original info from the design floor. 😊

Thanks!

 

what size radiator are you running? 90/91 suburban w/ 454 has the same rad as diesel it is a nice upgrade for towing. you will need new upper mounts, shroud and upper rad hose. you can also upgrade to the earlier "big block" rad, which isnt as wide as suburban rad. i'm a big believe in the primary cooling be done by the rad and the AUXILIARY cooler be ran down stream of that.

https://www.gmsquarebody.com/threads...adiator.15474/