Northstar Engines and System Technical Discussion Discussion, Question about the transmission fluid in Cadillac Engine Technical Discussion; When I leave the car sit overnight the trany fluid dipstick doesn't touch any fluid, but when the car is ...
When I leave the car sit overnight the trany fluid dipstick doesn't touch any fluid, but when the car is running and engine warm the fluid is almost at the top of the opening. If I suck out the tranny fluid my engine revvs up and the fluid level bounces up and down. The dipstick has a "COLD" and "HOT" range, so isn't COLD should be where the car has been sitting overnight and HOT means engine on and warm? If so how's mine dry while COLD and full in HOT??? The car manual says to check it when the engine is running and warm.
Automobile(s): White Diamond '03 DHS (with DTS floor shift)
Re: Question about the transmission fluid
The trans is supposed be a dry sump, which I thiink means that the fluid is held in the side cover, not the pan. That would lead me to believe that there must be a check valve. I know when I changed the trans fluid on my '97 I got almost all of the fluid from the pan and very little from the "hidden drain plug".
The transmission fluid is NEVER checked with the engine off.
COLD on the stick means engine idling in park with the trans cold....i.e....it hasn't been driven.
HOT on the dipstick means engine idling in park with the trans fully warmed up...i.e....driven 5 miles or more to make sure it is completely warm.
The 4T80E transmission is a dry sumped transmission meaning that the oil is pumped from the lower pan by a scavenge oil pump that desposits it in the side cover while the engine/transmission is running. The main oil pump for transmission line pressure (as well as the actual transmission oil filter) is in the side cover. The dip stick in the trans oil fill cap measures the fluid level in the side cover so as to accurately depict what the transmission oil level is when the unit is operating...i.e...engine idling in park.
When you park the car overnight the oil in the side cover partially drains down to the bottom pan. This means that the side cover oil level will always show "low" when the engine is cold in the morning and has not been started. The oil has drained from the side cover as well as some of the oil that drains from the transmission operating components was still in the bottom pan and not scavenged to the side cover. Checking the oil level of the trans without starting the engine is pointless and misleading. It means absolutely NOTHING unless the engine is running. Don't waste your time checking it cold or when the engine is not running nor should you try to draw any conclusions at all about the trans oil level when the engine is not running.
Just warm up the engine and trans thoroughly by driving it, park on a level surface with the engine idling in park and then check the trans fluid level. It isn't something that needs checking frequently. Unless you notice a leak on the ground the trans oil level is completely stabile and will stay that way for 100K miles or more.