I recently purchased an '85 Fiero SE that has a SC Series II 3800 and 4T65E-HD swapped into it from a '99 Grand Prix GTP. I do not know and do not have anyway to contact the person who actually did this conversion. The transmission is behaving in a way that I believe indicates it's low on fluid. However, it had an aftermarket transmission fluid tube on it to clear the exhaust, but no dip stick. A new dip stick was $137 so a snagged a stock tube and dip stick off of a '97 GTP instead. It required SLIGHT bending to get around the headers but now fits nicely, and the amount of bend I put it in shouldn't affect it's accuracy (I think). When I measured the fluid level (after getting everything warm of course) it read pretty low. As far as what was done to the transmission by the previous owner, all I know is that he dropped the pan and refilled it with about 7.4 quarts (according to what he found online about the 4T65). The transmission has a ZZP pan on it, however, I found nothing on ZZP's website indicating that their pan increased fluid capacity. I've read that the 4T65 needs about 10 quarts after an overhaul, and 7.4 quarts for a fluid change. I'm wondering if the transmission was overhauled at some point and was only refilled with 7 or so quarts. Also, I see no reason as to why the '97 tube and dip stick I got would be reading incorrectly since the '97 was the start of the 7th gen Grand Prix's with the Series II. I'm leaning towards simply adding more fluid according to the level indicated by the "new" dip stick. Does anyone have any suggestions for how I should proceed? I'm new to all of this and I'm not an experienced mechanic by any means.

Any help would be appreciated! Thanks in advance.

[This message has been edited by Crazy_ones24 (edited 05-02-2023).]

Aftermarket Pan likely just adds "Cooling" fins.
● In cool to freezing weather, might cause problems w/ oil too cold.
● Often they install "trick" pans ignoring/removing the OE Magnet. Unlike many aftermarket Magnets for engines, OE Magnet for auto trans are Part of Oil Filtering and need to be there.
● This pan has a magnet attach to the drain plug but isn't same as very large OE Magnet.

Trans oil cap for this is FWD cars. Fiero long cooling lines need some more oil.

If stick and tube match then a little bending shouldn't affect reading.

I would add some oil but not trust the stick yet. So only say 1 cup to 1 Pint max at a time and drive to see if problem stops. If not add a bit more.

Stick saying Add is often above level when have low oil problems. IOW In many cases, Add mark say Add 1 Pint but start to have problems ~ 1 Quart low driving on level roads.

Then to "test" the stick, add more in small amounts so can watch out for foaming oil.
Foamed oil can act the same as Low Oil.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

@theogre

So I put about a pint in tonight. It brought the level on the dip stick up to about the A on ADD. Problem didn't really seem any better. To be clear, my transmission shifts fine if I'm accelerating normally. I only have issues when I'm gunning it. I was doing some more research and I found a wiring instruction sheet for this swap. It mentions an optional toggle switch for a performance shift switch. I've never heard of this in a vehicle, but, there is a toggle switch in the center console that the previous owner didn't know the purpose of. I decided to turn it on and test it, it shifted perfectly. At least it felt like and sounded like it to me. If nothing else it was miles better than the results I was getting prior to turning that switch on. I'm not sure if you've seen that before, but could that have really been all it was?

[This message has been edited by Crazy_ones24 (edited 05-03-2023).]

Low fluid can do that...
When you floor the gas, turn, drive up/down/both for a hill then fluid moves and pickup sucks air.

If changing a switch setting fix you problem, often something else is wrong and the "Fix" is only temporary.
IOW the switch in "performance mode" may make PCM to put more hydro pressure on an Iffy Clutch or Band that will fail totally and w/o more warning trying to merge on a highway etc.

Sorry it's taken me awhile to... respond to your response... but as of now I still have no transmission issues when gunning it with that switch engaged. I've been keeping an eye on the transmission fluid level and it's still reading low. I've added a pint since last time but the level didn't seem to move. I'm a little dumbstruck as to why the dip stick seems so inconsistent. That being said, the transmission doesn't feel like it has low fluid when I'm driving it, it seems to operate fine. Again though, I'm not very experienced.

If the stick and tube are from the same tranny, you can believe the stick reading, as it is measuring the distance
from the pan/trans case interface to the fluid surface in the pan, to assure proper level relative to the filter.

That was my thinking. However, according to the previous owner, it was refilled with the appropriate amount of fluid. I actually trust the guy as he is a knowledgeable mechanic. In addition, like I said, I've added about 2 pints and the level hasn't seemed to changed. I run the car up and down the road for a bit to warm the engine up and then check it while it's idling. I am kind of lost as to why the level seems so inconsistent despite the transmission seeming fine.

If the tube and dipstick are a matching set, they will read properly, whether the pan holds 7 quarts or 200 gallons.

The critical measurement is distance from bottom of tranny case, not how much the pan holds....

I have a series I 3800 S/C in an 88 GT. I had a transmission fluid leak and when it was low on fluid it felt like a high stall speed torque converter. It would rev up a bit before the torque converter would grab.

The Pontiac Bonneville that this drive train came out of had a "sport shifting" switch. That is now permanently on via PCM configuration in the Fiero.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

That's why I'm inclined to believe the reading on the dip stick. There should be no reason it wouldn't read correctly. However, I also haven't found any leaks as of yet. You're right that the critical measurement is the distance between the stick and the bottom of the pan. But, from what I understand, that ZZP pan holds the same amount of fluid as the stock pan. So if 7 quarts were added to it, it should be at the correct level. I'm tempted to empty the pan and refill it myself to have a clean slate.