oceanbreeze

96 EX with auto transmission.

I was looking at the smog check test results for the past several years and noticed something changed a few years back. (background: here in CA they do two tests, one at 15 MPH and one at 25 MPH.)

For the 15 MPH test, the engine RPM shows at approx 700 early on, but in the last few years it shows around 2000 RPM consistently. This seems to clearly indicate that the transmission is staying longer in low (first?) gear than before. I also noticed that when driving the car on flat road.

For the 25 MPH test it looks like they are more consistent but with wider variation, mostly around 2050 RPM with a couple 2480-ish and one at 2700 RPM.

I am going to change the trans fluid. Is there anything else I should do, or need to be aware of when I change the fluid? Is there a transmission fluid filter I need to change also? For some cars I hear things get worse after you change the fluid. What is the recommended auto trans fluid?


Many thanks.

ezone

Your type of test is done on a dyno, on rollers. The car is "driven" on the rollers until the machine says "this is 15 MPH" or whatever number it needs to see. It does not care what gear the car is in, what RPM, what the cars' speedometer says, or anything else. Once the machine sees the desired speed, the test sampling begins. The RPM must remain consistent for the duration of that portion of the test, so if the trans shifts during the test then the test is aborted. One way around this might be to keep the shifter in a lower gear so the trans does not make its shift.

Some variables might include: engine running condition, trans condition, tire inflation, wheel and tire sizes. Tire diameter changes can alter true road speed, and you can't ever see that on a speedometer. The dyno reads true road speed.

You can probably tell what gear the trans was in by driving at 15 or 25 and moving the shifter to different gears and watching the tach.



Hondas DW-1 fluid is recommended by Honda. Others here may chime in with Valvoline Max-Life or some such.
You can't change the trans filter.
Do not let any shop use chemicals to flush the trans.
Drain and fill only. A Honda approved "flush" is multiple drain and fills until about a case of fluid is used. Search here for the actual procedure, I have posted it a dozen times.