[Autoengineer_]

I have to keep my TH350 overfilled according to the dipstick, which is the original as far as I know, in order to keep the trans pump from squealing under high rpms. I actually had it run "low" this week. I could hear the squeal if I reved up the car in park. CHecked fluid and its within operating range. Added a quart of fluid and the squeal goes away.

A couple questions.

Is this typical in a TH350 that had a performance rebuild? That it would suck up more fluid than normal? OR is it just likely my dipstick is off? I did add a trans cooler which would of course require more fluid.

My problem too is that I'm still not sure there's enough fluid in there. Assuming reving the engine was emptying the pan, how much extra fluid should be in the pan even under WOT? 1 quart? 2 quarts? Anyone have a feel for that?

I suppose one option is an extra deep pan. Thx.

 

[77 cruiser]

Fluid level to top of pan, maybe you filter isn't on right.

 

[goatless]

There's this, from HotRod.com:

1. Your Dipstick Is Wrong
Most people don't realize that transmission dipsticks are notoriously inaccurate. When you take into account the length and width of most transmission pans compared to their shallow depth, it is fairly obvious that a dipstick reading that is even a quarter of an inch off can mean you are running your transmission significantly low on fluid. In a performance scenario where fluid demand can be extreme, this can cause significant damage quite quickly.

It is a good idea never to simply assume your transmission fluid dipstick is correct right out of the box. To check it yourself, put the dipstick in place, drop the pan, and make sure that the full mark is even with the bottom edge of the transmission case (where the pan bolts up). If your full mark is low, simply make a new mark on the dipstick. A simple way to do this is to use a file to make a small notch in the side of the dipstick.

With the dipstick checked and properly marked, you can now be confident that you have adequate fluid for even the most demanding driving conditions.

From: What Causes Automatic Transmission Failure? 7 Ways to Destroy a Transmission