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Discussion Starter · #1 ·
When the weather is hot and I am in stop and go traffic the transmission seems not to want to shift as soon as it normally would. I have several questions about this, the answers to which may help me to understand what's going on and what I might do about it. First of all is the stock transmission cooler integrated into the engine cooling radiator? When the engine gets hot does this heat up the transmission more than the transmission might otherwise get hot form it's own operation? Is there a good reason to warm the transmission fluid up from engine heat in normal or cold weather? Do add on transmission coolers normally run the fluid just through the add on cooler? Or do they run the fluid through both the stock cooler and the add on cooler? Is it worth the trouble of adding a add on cooler? Or should I just stay on the highway and out of stop and go traffic when the weather is up in the high 90s?
 

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The best way to set up an auxiliary cooler runs through the radiator cooler second (keep in mind the radiator cooler is also a fluid warmer in very cool weather).

That said, you should not notice a difference in shifting unless something else is wrong.
Have you tried changing your fluid and filter?
Note: don’t have it flushed… just change it.
 

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Discussion Starter · #3 ·
The best way to set up an auxiliary cooler runs through the radiator cooler second (keep in mind the radiator cooler is also a fluid warmer in very cool weather).

That said, you should not notice a difference in shifting unless something else is wrong.
Have you tried changing your fluid and filter?
Note: don’t have it flushed… just change it.
Yes changed the fluid but not the filter. Did not drop the pan. Pumped old fluid out. No doubt leaving crud in bottom of pan if there is any.
 

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2000 Lifted 4x4 Astro 92 V8-350 Shorty
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When experiencing "transmission issues".... always drop pan for inspection, and change filter.
It's a no-brainier, inexpensive, and not too difficult.

It could just be a case of "sticking valves".. in which case I've had excellent results with a product called "Trans Tune" made by Seafoam company. It's available at Walmart and most autoparts stores. Ideally you put it in first, run it though system for a short time, then pull pan and filter. My experience is that results were almost immediate.

Seals also get hard and don't perform as expected. The servo (on side of transmission) is responsible for shifts. A nice replacement and upgrade is the "Corvette Servo", which improves pressure and shifts (available on Ebay). You can buy kit (for about $20) or the complete assembly for a little more. It will definitely pep up your shifts, and maybe cure your issue too. I have this servo in both my vans.

If pan is clean, then you're probably in luck.

Good luck

PS: External trans coolers are mostly for towing applications, but any trans can benefit from them with longer life. Both my vans have them. They are cheap and easy to install. Note: this will not solve your shifting issue.
 

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Discussion Starter · #5 ·
Thanks for the information. Since you told me about the Servo I looked at some youtube videos of people changing them. First part of the process is to remove a heat shield that is between the catalytic converter and the servo on the transmission. I wonder if the people who changed the transmission failed to put the heat shield back in, or put it in incorrectly. That would definitely make any overheating happen sooner. Will higher temperature at the Servo make the fluid or the springs inside it operate differently than normal? Unfortunately I am about 3000 miles away from that van now and cannot look at it. I can check out my other van to see how it looks, but that one isn't giving me any trouble.
 

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2000 Lifted 4x4 Astro 92 V8-350 Shorty
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I do not believe removal of the heat shield would cause the transmission to fail or shift incorrectly immediately.. but that it might reduce the longevity of the trans (or that specific part) over a long period of time. This is my best guess. The shield is not hard to remove or install, so it seems unlikely it would have been left off and not put back on. Catalytics DO generate a lot of heat however, so who knows.

My 92 has no heat shield on side of trans (nor did it ever have one as far as I know) and it works perfectly
 

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Discussion Starter · #7 ·
I do not believe removal of the heat shield would cause the transmission to fail or shift incorrectly immediately.. but that it might reduce the longevity of the trans (or that specific part) over a long period of time. This is my best guess. The shield is not hard to remove or install, so it seems unlikely it would have been left off and not put back on. Catalytics DO generate a lot of heat however, so who knows.

My 92 has no heat shield on side of trans (nor did it ever have one as far as I know) and it works perfectly
Next time I have access to that van I will look and see whether there is a heat shield in place. The problem is definitely temperature related because it only happens in really hot weather and only when in stop and go traffic. On the open road, even in hot weather no problem. In cool weather even in stop and go traffic no problem.
 

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1998 LS AWD Forest Green metallic
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This is way off in left field, ( and related to heat related failures) but years ago I had a customer with a Datsun 240 ( or maybe 260) Z. Her problem was that if the trip was more than about 30 minutes, her factory voltmeter would suddenly begin to drop, then after a while 'wierd' things' ( her worlds) would happen,. She mentioned wipers running slow, or heater fan slowing down, etc.

She had been to several other shops who were not particularly good at electrical issues, and they all pronounced the alternator and battery in good condition. This was a classic case of the system voltage dropping, and even evidenced by the decent factory voltmeter. I headed out on the highway armed with a voltmeter and a clamp-om ammeter. About 15 minutes later, the ammeter went negative, and the voltage began dropping.

Returning to the shop, we found the alternator was in fact bad; but it was only bad, apparently after the aluminum housing heated up. Opening up the alternator, we found the brushed were very short. They are easy to rep[lace, and we did that. Problem solved.
We suspect the the alternator brushes were right at the point where if the housing heated up and expanded slightly, there was no tension on the alternator brushes, so the field was not getting energized. As soon as it cooled own, the alternator worked properly...for a short while. If the customer had driven that way for another week, or three, the alternator may have been completely non-functional.
Strange things can happen in the automotive electrical world.
I am not saying this particularly related to your transmission issue, but it just illustrates weird things that could cause a temperature related failure.
Rod J
Issaquah, WA
 
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