Air pocket in IC? If coolant in the reservoir is at ambient temp, the heat exchanger is doing it's job and coolant flow is not too fast. However, even with the higher capacity pump, the additional plumbing may have actually slowed down flow thru the IC. As long as the HE is pulling the coolant temp back down to ambient, you can't overflow the IC. Faster flow = higher temp differential = more heat transfer.

 

That's what the dude from Magnuson said, possible air pocket. I'm going to try and reverse the flow through the IC (as soon as it stops raining here) to see if that solves it because, like I said, coolant in tank is very, very cool. If that doesn't solve it, maybe my IAT sensor went bad?

 

Also, looks like I won't make the track this weekend unless I can get this figured out REAL quick...Just did a pressure test on the new 4L80 yesterday while driving because the 1 - 2 shift felt extremely soft under boost but under part throttle (less than half throttle) shifts firm. Anything say over half throttle, the 1-2 shift firmness ONLY decreases...the more throttle the less firm it feels but other gears 2-3 and 3-4 shift firm at wot! The pressure test while driving revealed 200psi under part throttle and only 180psi @ wot for the 1-2. Chuck from FLT is still scratching his head saying it tested "perfect" on his dyno. This is a pre 1997 4l80e btw, BUT his other 4L80 I sent back to him did the exact same thing until the 1-2 clutches finally cooked. I didn't want to say anything about his first trans cooking in under 4k miles and 7-8 months of very limited driving because Chuck stood behind the trans and built me this new one for only the cost of the new Coan 6 pinion low planets, upgraded billet shaft and shipping back & fourth of course, but now I don't know what else to do but reach out to you guys here to see if anyone else has had this same experience and found a solution.

Chuck said he couldn't find anything wrong with the cooked 80e I sent back to him, I just hope the valve body from the old one wasn't re-used in this new one thinking it was ok when there was a possible failure he didn't know about...that's the only thing I can think of, but I'm FAR from an authority on transmissions.

Any help with this is GREATLY appreciated.

 

Shift pressure settings in tune, force motor table in tune. Not saying it has to be in the tune, just thinking of things that play a major role but are not the trans.

 

This.

I have a feeling this isnt the trans at fault.

 

I agree with you 100%. Not with 1 but 2 different 4L80E's that worked perfectly on the dyno, mysteriously don't once installed in his truck? The last time I went through this with another customer, the trans ended up being under filled?

 

Both transmission were filled to your specifications - to the top of the marked fill line on the dipstick and were filled by two certified GM master techs.

 

Post up some screenshots of trans shift pressure tables so we can compare against our own.

 

I would if I knew how

 

Mystery solved - at my own expense of course! Chuck from FLT suggested the pre '97 80e but failed to tell me the dipstick was a different part number. Just came in today from Chevy - a special order.



Note the witness mark I made on the "97 and later 80e dipstick after pulling the pan last weekend and marking the correct fluid level.