Checking the transmission oil level

redbugdave · February 17, 2006

Something I have always wondered...maybe a transmission expert can explain it. Why can't I check the transmission oil level after the truck has been sitting for a day and not started? Like the engine oil. Seems that the oil would settle overnight in the transmission and would be easier to read.

That is...first check it the regular way and see if it is full, (checked when the engine is hot and running in park), then why can't I make a mark on the dipstick at the level it settles to...after sitting overnight or for a day. Seems more convenient, then you could check it at the same time as the engine oil, before starting up.

Supurban · February 18, 2006

I think it has to do with the large volume of fluid the torque converter holds. When it is not pumping, the fluid level would be way different than while rotating at idle.

Would be nice though.

dougmac · February 18, 2006

Engine oil pretty much drains completely back to the sump in a short period of time. So checking the oil level in the sump after it has been shut off for a minute or two, gives an accurate reading

A transmission holds fluid in the converter and other areas that slowly drain back to the sump. It can drain back over a period hours or even days. The amount of oil that drains back and how fast it drains back can vary a huge amount depending on a number of factors like temperature, manufacturing tolerances, transmission wear, etc.

With the engine running, fluid is pumped throughout the transmission and the amount of fluid in the sump is much more consistent running than off. Even with it running, temperature has an affect on the level due to the expansion of the oil. That is why you will see cold and hot settings on the stick or they recommend only checking the level with the transmission warm.

Doug

redbugdave · February 19, 2006

Thanks Ron and Doug,

I have always wondered about that. I did not realize the tolerances and such did not allow the oil to drain back down as in an engine. I've learned a great deal from you guys. (Did the diode headlight mod the other day. Boy, what a difference!)