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Old 05-02-2007, 01:27 PM   #1
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Transmission Temp too high?

Hello all,

We have a 1990 Suburban,1/2 ton 4wd. The other day we hooked up the camper to move it. Pulled it around the block and then backed back in the driveway. Now to get into our driveway it is a job, takes a few minutes of manuvering and it is up hill. Anyway when I finally got back in the driveway the trans temp was up near 250. Was wondering if this is normal after all the manuvering around? Normally when not pulling the camper and going down the road the temp runs 160-180. Unless we are sitting in traffic for long periods of time, then it reaches close to 210. It has a transmission cooler,extra capacity pan,etc. Just curious if these are normal temps, or do I need to start looking for a problem?

Thanks,
John
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Old 05-02-2007, 01:58 PM   #2
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yeah, that'll happen in "R"...its got no leverage, so the tranny will have to work really hard to push it uphill backwards.

I have the same problem...(steep driveway...need to back in/up). the solution is to put the truck into 4-wheel LOW. putting the transfer case into "L" will give you the torque you need. It'll go up the hill as easily as if it were flat.
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Old 05-02-2007, 03:24 PM   #3
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Thanks

Thanks for the good information!! Glad to hear that it is not a major problem. Had me worried!!

John
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Old 05-02-2007, 03:39 PM   #4
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Reverse is noted to be a heat generator. The clutches never lock up and you have no airflow over the radiator/cooler. Plus shifting from fwd to reverse generates a lot of heat (the equivalent of the tranny "hunting" on a big hill).

I'm curious where you're measuring the temperature. My gage measures at the sump. I added a deeper sump and synthetic fluid but haven't yet installed an additional transmission cooler. Normal driving I see a range of 120-140, going up a steep hill maybe 180. Towing I'd see ~150 with a peak of ~200 pulling long grades (2nd gear, 50mph). I'm sure the brand of gage makes a difference; maybe even from one gage to the next of the same model. I'm just curious how my numbers are in comparison to other peoples.

-Bernie
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Old 05-02-2007, 04:00 PM   #5
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If you want to see what you may are working against take a look at my web page noted below. The Suburban air flow design is about as poor as it could get. It is not uncommon for the lower front left corner, between the AC coil and the radiator, to be full of leaves because of the way the AC coils set in front of the radiator with respect to the sheet matal in that area. Also the design of the newer radiators use a fin construction that creates a venturi, as apposed to the old straight through designs, and this venturi traps bugs in the fins at a point where you can't see them when looking straight down. You will also see this inistrated on my site.

As for pulling a hill at very low speeds, forward or reverse, I would use 4 wheel LOW if you are not making very sharp turns on a hard surface. This will reduce the load on the convertor, the source of heat.

Another thing I have done to keep the trans temperature down is remove the trans cooling lines from the radiator altogeather and installing a fan driven cooler with a thermostat set at 160 degrees. This combination holds my trans temperature at about 150 degrees at road speeds, the temperature flowing back off the engine. Cooler in winter. Yes hills will cause the temperature to go up to 180 and yes a very steep low speed driveway or campground will cause it to spike higher.
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Old 05-03-2007, 05:07 AM   #6
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Tammy & John, once the temp has gone that high you MUST change the trany fluid!

Don't get it flushed, just changed.
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Old 05-03-2007, 09:55 AM   #7
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We also have to get our 20' Safari up a hill, but to make the job easier, we PUSH it up. I made a hitch that bolts to the front tow hook locations on our 2004 Jeep. Have not checked trans temp, but have absolutely no problem pushing it in low gear (and having more accurate steerage for tight spaces, too). Roger S
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Old 05-03-2007, 10:41 AM   #8
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250F will shorten the fluid life but it's not going to kill it immediately. There are charts of how the life of the fluid changes with temp. 250F can't be good for plastic seals in the tranny but I think critical is 280F. Of course if it's 250F leaving the cooler then it's almost assuredly over 280F leaving the transmission.

" As a rule of thumb, every 20 degree increase in operating temperature above 175 degrees F. cuts the life of the fluid in half!"

If you haven't already done so a switch to synthetic fluid is well worth it. The cost of the ATF is a small fraction of the price of service and it's extended life makes it worth it. One thing that sold me is how much better it is at low temperature performance. With added coolers, deep pans and such the fluid never even gets up to temp on short drives. We drive up in the mountains during the winter I noticed a big difference in how well the transmission worked on start up when the outside temperatures were well below freezing.

You will want to get the transmission flushed if you switch to synthetic. If it's been more than 30,000 miles with a lot of trailer towing I think it's worth paying the extra for flushing the fluid anyway. -Bernie
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Old 05-03-2007, 11:20 AM   #9
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Where's your sensor?

This has something to do with your readings.Mine is located just before the fluid enters the radiator, the fluid is hottest here I suspect. PO located it here, I pretty much run 160 temp on the flats and it creeps up on the pull uphill.Every so often it will go 220 for a brief time but that's also when the pedal is to the metal and I'm watching the needle on the fuel gauge drop. Always runs hotter in stop and go traffic(my trailer hates the city anyway).My Tranny guy gave me the same advise that Bernie just shared! BTW 93burb 454 pullin 8000lb excella. Just get a baseline going then when something out of the ordinary happens check it out. Also keep the sending unit contacts clean!! I ran a separate ground from the sender to the frame.
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Old 05-03-2007, 12:31 PM   #10
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Definitely the location of the sensor will effect the readings you see on the gage; at least you hope it will . Mines in the sump right now just because that was the easiest place to locate it. Since I'm planning to add an additional cooler I'll probably move it. Toying with the idea of having two sensors wired through a switch so I can actually see the temperature drop.

Anyway, I think the idea of having it on the outlet side makes more the most sense. It will certainly show the most immediate changes. I'm wondering how other people mount the sensor. With mine mounted in the pan it just screws into the hole provided for draining the sump. I think the external coolers are set up only to accept a rubber hose and clamp (i.e. not threaded). I'd prefer to minimize the number of hose clamps in the system so I'm thinking a fitting is going to have to be screwed into the output port on the tranny that has a barbed end inline for a hose attachment and a threaded Tee connection for the sending unit. I've also heard there may be additional locations that can be found on the tranny (4L60E ?)


I've also noted that the manufacturers of the external coolers universally recommend not bypassing the stock head exchanger on the radiator. One argument for this is improved start-up and cold weather performance. However, the cooler manufacturers reasoning is that it's the most efficient set-up for heat removal. This makes sense. The heat transfer to another liquid is going to be much better than to air. My experience is that the tranny temp spikes much quicker than the radiator so it's hard to imagine that in a situation where cooling is critical (pulling a steep grade, backing into an awkward space, etc.) the antifreeze is going to be hotter than the ATF. If it is then you're probably not going anywhere anyway as even at the ideal mixture the boil over point is 276F .

-Bernie
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Old 05-03-2007, 01:18 PM   #11
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I taped a sender unit to the output line close to the tranny, as described here, a few years ago:
http://www.airforums.com/forums/f159...ages-7588.html

It's worked perfectly for 7 years, so far.
Nick
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Old 05-03-2007, 01:42 PM   #12
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Nick,
Interesting thread. What is "self-amalgamating tape". Is that British for duct tape .

I suppose a heatsink compound and tape would work fine on a metal line and I shouldn't have to otherwise disturb the stock line from the tranny to the radiator. I remember reading somewhere (not sure if it was on this forum) that there was a tapped hole already on the tranny that could be used. It would seem to make sense as the same unit I would guess is used in vehicles that come from the factory with the tranny temp gage. Then again it may already be occupied as it's suggested the sensor is there on all vehicles as part of the engine management system. "Information available, but not to you!"

-Bernie
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Old 05-03-2007, 04:52 PM   #13
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So, a quick Google search turned up this on using a pressure test port on the 4L60E to mount the gage. Since the van is due to go in for some other service tomorrow I'll ask my mechanic to relocate the sending unit. It will be interesting to get a baseline temperature reading with it there as opposed to the sump before the aftermarket cooler is installed.

-Bernie
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Old 05-03-2007, 05:06 PM   #14
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Quote:
Originally Posted by bhayden
Nick,
Interesting thread. What is "self-amalgamating tape".
-Bernie
Bernie, here's a link that describes it:
DIY - Self Amalgamating Tape 19mm×10m

It's useful on boats, cars, trucks and any similar hostile environment. After a few hours the turns of tape fuse together to make a solid material. I know it's available in the USA, but I seem to recall it's known by a different name.
Nick.
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