Automatic transmission fluid level question

[OregonNed]

Today I decided to check my transmission fluid level because I feel like it might be a bit overfilled. When I park after a drive with the front of the truck facing uphill, it seems to drain a small puddle of fluid from a vent or maybe a weep hole in the driveshaft yoke. When I check the level cold, the fluid is way above the crosshatch mark range. I assumed the level cold should be at the lower end of the check area. I siphoned out several ounces of fluid, about 24 I believe then warmed up the engine to hot and ran the shifter though all the gears slowly then back to park. When hot and running in park, no fluid touches the dipstick. I took about a five mile drive and checked again. Still not touching. This is parking level in my garage. I started adding back fluid and maybe put half back while running until the fluid was at the top end of the crosshatch range. After shutting it off and checking about 45 minutes later the level is back up high again on the stick. Am I thinking correctly that the level is now correct with it running hot, and the cold level will show higher once all the fluid drains down? I thought it might be the opposite. Thanks in advance for any ideas.

[OregonNed]

I should have added that when I siphoned the cold fluid I made sure it was still in the crosshatch range when the truck was level.

[Bigdav160]

When you start your engine, the transmission oil pump fills the converter. When you shut your engine off the converter oil drains back in the pan.

Your transmission should be checked with the engine running. Yes, the fluid expands quite a bit with heat. It will always show higher on the stick not running

[OregonNed]

Thank you for the help! Ned

[too much stuff]

Usually checked when at operating temp, running and in park or sometimes in neutral. May say on the dipstick also.

[FirstOwner69]

If you check it cold, the engine should be running.The procedure is the same as when you check it hot. You will probably see the level at or near the bottom of the crosshatch area on the dipstick. I believe "hot" is generally defined as after driving about 20 miles.

[54blackhornet]

what is proper way to change fluid in a Turbo 350 ? My pan does have a drain plug but I know you can’t get all out just by draining? Anyone ever pump it out through cooler lines ?....

[OregonNed]

I’ll check it tonight running and still
Cold and see where it hits the mark and if it’s different than hot at the top of the mark

[HO455]

Check it idling, when hot, on a level surface. No other way is correct. The two marks on the dipstick are the maximum and minimum levels. When the engine isn't running the oil drains out of the convertor and valve body and gives you an overfull indication. Being on a incline or angle will give you a bad reading. Even a large crown on the road can throw the reading off. This would be for a turbo 350's & 400's. Be sure to run it in all the gears prior to checking the level to ensure all the passages are full and your level indicated will be accurate.

[cleszkie]

You will never get all of the fluid out of the tranny by draining the pan. Some fluid always stays in the converter, pump, oil cooler, and oil cooler lines. that is just a fact of life. The drain plug in your tranny pan is just to prevent the mess that can happen when you pull the pan without being able to drain the fluid first. Do not stop at just draining the fluid. You should always remove the pan and replace the tranny filter as well.

[FirstOwner69]

Originally Posted by HO455

Check it idling, when hot, on a level surface. No other way is correct. The two marks on the dipstick are the maximum and minimum levels. When the engine isn't running the oil drains out of the convertor and valve body and gives you an overfull indication. Being on a incline or angle will give you a bad reading. Even a large crown on the road can throw the reading off. This would be for a turbo 350's & 400's. Be sure to run it in all the gears prior to checking the level to ensure all the passages are full and your level indicated will be accurate.

Agree 100%.The cold check I described in post #6 should only be used for an approximation prior to driving for the hot check. Thanks for catching that HO455.

[FirstOwner69]

Originally Posted by 54blackhornet

what is proper way to change fluid in a Turbo 350 ? My pan does have a drain plug but I know you can’t get all out just by draining? Anyone ever pump it out through cooler lines ?....

Do as cleszkie describes above. Now days a dealer may try to sell you a flush with a change. I wouldn't advise it. Allison specifically recommends that their transmissions in Duramax equipped trucks NOT be flushed.