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Open Roads Forum  >  Towing

 > UPDATED Coast on the uphills accelerate on the downhills

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BurbMan

Islip, Long Island

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Posted: 01/19/21 06:14am Link  |  Quote  |  Print  |  Notify Moderator

Glad you got it fixed! I had the same truck with the 8.1 (but same trans, 4L80E) and it would run at 175* but never got hotter than 200* no matter the hill or outside temp. Our TT was close to 9000 lbs loaded.

The transmission actually has 2 coolers, the cooling line goes from the trans into the right side of the radiator, then out of the radiator and into an external cooler mounted in front of the a/c condenser, then back to the trans. The cooling was very effective and never had the need for an aftermarket cooler.

Not sure about the 6.0L, but the other side of the rad on the 8.1 had an engine oil cooler. That was a fun job replacing that, dealing with oil, trans fluid and coolant in the same bucket [emoticon]

Anyway, now that you have replaced the rad, I would drop the pan and change the filter in the trans at the next fluid change. These came from the factory with Dex III fluid, the new GM fluid is Dex VI, which is full synthetic and backwards compatible with Dex III. Of course there are different opinions about using Dex VI in an older vehicle, but I found the full synthetic ran cooler than the Dex III.


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opnspaces

San Diego Ca

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Posted: 01/19/21 09:28am Link  |  Quote  |  Print  |  Notify Moderator

Yes I'm definitely familiar with the trans cooler on one side and oil cooler on the other. Like you say, catching all the different fluids is a bit of a challenge. My 6.0 also has the second cooler in front of the radiator.

I'm glad to hear that your transmission temp basically mirrors mine. I was a bit suspicious that after the radiator replace the temp would climb to 200 and basically just sit there no matter how hard I pushed it when towing. It almost seems like there is some kind of thermostat on the cooler line that is mostly closed during normal driving. But after reaching 200 it just opens wide and lets the fluid flow.


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1320Fastback

Vista, Ca

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Posted: 01/19/21 07:29pm Link  |  Quote  |  Print  |  Notify Moderator

Looks like you got it sorted out Opnspaces. I am San Diego local too and have gone though Alpine out to the desert many times. Not sure if I've taken our current setup on S2 yet. 9/10 I go up over Palomar Moutain as I am north county but if we are going to Glamis or Superstition/Plaster area I'll take I8 out.


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afidel

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Posted: 01/25/21 10:12pm Link  |  Quote  |  Print  |  Notify Moderator

drsteve wrote:

And to think I get nervous when the trans temp exceeds 200...


I was thinking the same, over 205 and I'm letting off even if it means slowing way down, don't want to boil the fluid! It's actually the only gauge that's ever made me alter the way I drive, engine RPM has never bothered me and none of my other gauges have ever been much out of the sweet spot.


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1320Fastback

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Posted: 01/25/21 11:35pm Link  |  Quote  |  Print  |  Notify Moderator

We Live and Die by EGT.

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