Transmission fluid check procedure temps
 

Hi all,

So I was going to check the fluid level in my transmission since I realized I had not done it in a long time. To make sure I did it correctly I decided to consult the owners manual.

This is what I found:
"To get the right reading, the fluid should be at normal operating temperature, which is 180'F to 200'F (82'C to 93'C).

Get the vehicle warmed up by driving about 15 miles (24 km) when outside temperatures are above 50'F (10'C). If it’s colder than 50'F (10'C), drive the vehicle in THIRD (3) until the engine temperature gauge moves and then remains steady for 10 minutes. Then follow the hot check procedures."

Now this has to be a typo.

I can see how you'd want the engine coolant temperature to be from 180'F to 200'F, which is the normal operating temperature of the engine and thus a good reference, but those temps are at the low range of what I have seen can be damaging to a transmission. Furthermore, few us have a way of measuring the transmission fluid temperature itself. I happen to be able to measure the transmission fluid temperature because I have an OBD Gauge (an Ultra Gauge) that I installed just for that purpose.

So I then consulted with the the service manual to see what it said.
"Start the engine and operate the vehicle for 15 minutes or until the transmission fluid reaches an operating temperature of 82-93'C (180-200'F)."

Ever since I installed my transmission cooler (Hayden 699 with a thermal bypass) nominal transmission fluid temperature is about 140'F to 150'F. The last time I got my transmission fluid temperature up to 190'F to 200'F I was pulling my 2,200 lb boat and trailer at 60 mph, up a grade that gained 1,700 ft in 6 miles while using the AC on a 105'F day!

So, thoughts? Is getting the engine coolant temperature to about 190'F sufficient?

I think the point is enough driving to get you to your normal warm operating conditions for measurement. IOW myou want the level correct where your truck lives. Given that you use enhanced cooling there is another level of trans heating under the worst case conditions so if you really want to dial it in, fill to just below the full line after a 15 min garden variety ride or stop after a summer trailer hill climb and spot check. I have never checked the cold level vs the hot level back to back to get a sense of the rise in level on the dipstick but I suppose that you could try that experiment to see for yourself. Start, run through the gears, park, measure.

I appreciate a diligent technical analysis as much as the next guy/gal but I have never been very good about trans fluid level. I have owned over 50 vehicles spanning 55 years and the only tranny I ever ate was on my first junker car (in 1975) which had parts falling off and holes in the body. I have multiple vehicles now with over 200K miles. Point is that I don't think that this is hyper critical, especially since you monitor trans temp.

George

Thanks George.

Great thoughts as always. I think you are spot on with checking the level with respect to the type if driving I do.

BTW, my post was an example of my overly nerdy and technical side coming out. LOL

As an engineer I have fought the tendency to over analyze most of my life. As I have gotten older I am more selective for when I nerd out. In some cases windage and technical intuition gets you close enough. Its dark and lonely in these geeky rabbit holes. lol.

George