have a lil problem. drained the oil out of the tranny on my 91 pickup and lo n behold the filler plug is rounded off.no problem says I ill just pull the shifter n fill er that a way.so I did but n heres the stickler how much oil do I use.put 1.5 gal in it.do I need more or is that too much?

 

1.5 gallons? holy crap that's way too much my 89 runner manual says capacity is 3.2 quarts!!! you really need to get that fill plug off. I'm assuming you have a manual transmission.

 

yep hell if a lil is good a bunch is better

 

^^ if that is your train of thought why did you ask?

Weld a nut to the drain plug and replace it...

It is all gonna blow out the breather

 

Too much oil in a gearbox will cause the gears to "churn" in the oil more than necessary and create heat which can be excessive and beyond the capabilities of the respective oil cooling system to handle (i.e. oil coolers, air flow cooling over the case, etc) and result in thermal runaway of the oil. In extreme cases the internals can reach temperatures that will cause distortion/melting. It can also cause to much aeration in the oil which could be more than what the stock breather system can handle, which will reduce lubrication capabilities (foamy oil doesn't lubricate well).

Theres a fine line between effective cooling/lubrication and thermal runaway when oil system capacities are determined by the engineers.

You really should drain and refill.