Author Topic: Trans fluid change...overfilled?  (Read 443 times)

Offline krigermoose

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  • 1986 GMC C1500 5.7L
Trans fluid change...overfilled?
« on: July 07, 2020, 03:25:07 PM »
Hey all, Ive got an '86 GMC C1500 with a TH350C under it. Yesterday I did it's first transmission fluid change, and it was also my first, so I had to do some research and I followed some steps from other forums' old topics. After draining the fluid, replacing the filter, and bolting up the pan, I added 6 quarts of fluid. I let it run for a while and get a good heat cycle and to get the fluid flowing, but the dipstick indicates that it's pretty overfilled, a good 3-4 inches past the "full" indicator.

So did I overfill it? I guess the answer is pretty obvious, but I thought the trans + converter held 10 quarts, which is why I added 6 at first, expecting to add more.

There is no fluid coming out of the top of the fill tube either.

One thing I noticed, if this makes a difference: The new filter was a bit smaller and is square shaped compared to the stock filter, which was  larger and had a more wavy shape.

Thanks.

Online Poppy 87

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Re: Trans fluid change...overfilled?
« Reply #1 on: July 07, 2020, 03:35:52 PM »
Hey all, Ive got an '86 GMC C1500 with a TH350C under it. Yesterday I did it's first transmission fluid change, and it was also my first, so I had to do some research and I followed some steps from other forums' old topics. After draining the fluid, replacing the filter, and bolting up the pan, I added 6 quarts of fluid. I let it run for a while and get a good heat cycle and to get the fluid flowing, but the dipstick indicates that it's pretty overfilled, a good 3-4 inches past the "full" indicator.

So did I overfill it? I guess the answer is pretty obvious, but I thought the trans + converter held 10 quarts, which is why I added 6 at first, expecting to add more.

There is no fluid coming out of the top of the fill tube either.

One thing I noticed, if this makes a difference: The new filter was a bit smaller and is square shaped compared to the stock filter, which was  larger and had a more wavy shape.

Thanks.
It's over filled. Start with 4 quarts, start engine, run through gears, check level. Add fluid as required.

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Offline JohnnyPopper

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Re: Trans fluid change...overfilled?
« Reply #2 on: July 07, 2020, 03:39:34 PM »
Your torque converter doesn't fully drain when you drop the pan. That's why you're overfilled.

Filters come in different form factors, as long as the bolt and intake port match you're good.

You will need to lower the level to the correct point on a hot dipstick, or when it gets real hot it  can blow out of your filler tube and create a fire hazard.

I use a oil extractor, (looks like a grease gun with a plunger and rubber hose on the end) to pull the oil out through the filler tube.

Buy some clear rubber tubing, like 1/2 inch, or what ever will fit into the pipe.

In fact, I changed the filter when I bought it, and every 25K miles, I use the extractor to change the fluid. I refill, let it run through the torque converter, rinse and repeat.

Nice clean fluid keeps your transmission happy and makes for a long life.
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline krigermoose

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  • 1986 GMC C1500 5.7L
Re: Trans fluid change...overfilled?
« Reply #3 on: July 07, 2020, 04:52:43 PM »
Okay, thanks, both of you, for clearing that up. I'll pull some fluid out.