Controlling Tranny Temp

1638 Views 9 Replies 4 Participants Last post by etk300ex, Aug 16, 2011

speediq99

Discussion Starter · Jul 17, 2011

I am sure that most of you around here know this already, however, I have found that running the truck in 4th gear when towing and keeping the RPMs around 2500 makes a huge difference in the tranny temp.

I live in Arizona and on a recent trip to San Diego, I noticed this huge change. In Az, you can drive at 75 while towing, not that anyone would. That means that you can legally go at 70 mph in 4th, which gives you about 2400-2500 rpms if you are towing over 6K lbs or so. In my case, my tranny runs at around 160 degrees in very hot weather.

Now, as soon as I cross the AZ/CA border, I need to drop to 55 mph by CA law. That causes the RPMs to drop to 2100 while towing in 4th in flat. That makes the tranny run much hotter in the same weather. In my case, my tranny shoots to 185 in flats.

So, drive a little faster, keep your rpms at 2400-2500 and your tranny will run a lot cooler. In my case, I lose 1 mpg when driving [email protected] vs [email protected] My truck goes from 10.5 to 9.5 while towing 8500 lbs.

Mike

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speediq99

Discussion Starter · #3 · Jul 18, 2011

I am not sure that the PML by itself did the trick for me.
I had to add an external tranny cooler to see a difference.

The problem w/ the PML pan is that once it gets hot, it stays hot and it is probably harder to cool off.
More fluid is not necessarily better.

Mike

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speediq99

Discussion Starter · #4 · Jul 18, 2011

To elaborate a bit more on the PML pan and in my experience, the pan keeps the tranny running cooler under normal driving.
When towing and pushing 3rd and 2nd gear, the tranny fluid will heat up. Under these conditions, a lot of hot fluid may not be necessarily easier to cool and a tranny cooler seems to make a big difference.

Day-to-day driving with light towing, either a PML pan or tranny cooler is all you need. If I had to do it over again, I would do a tranny cooler first and the pan second if needed.

Mike

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speediq99

Discussion Starter · #9 · Aug 9, 2011

It sounds like the PML/cooler combo worked for you.

You may want to get a tranny temp gauge rather than use the one from the truck. in my experience, these gauges stay in the 1/2 way mark or below for a long time (long temp range). Once you reach a certain temp, the difference between a visual half way mark and near the H mark is 3-5 degrees.

If you manage to stay in 3rd gear, all is usually well. It is when you have to do 2nd gear that things begin to fall apart. My truck does not like to stay in second for very long, water and tranny temps quickly jump up.

Mike

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