"Flushing" trans w/ motor oil

[heathenbrewing]

Ok…bear with me here:

Im ready to do a drain and fill on my manual trans (first change, ~11k miles)…will be using wither Redline or Royal Purple GL4. Im thinking that after a majority of my 75w90 drains out of my hot/warm trans, I would like to dump a quart (or two) of dino 5w30 motor oil through the fill hole to "rinse out" the trans of as much old fluid as I can before refilling with a synthetic fluid. My thinking is that the lower viscosity of the motor oil will flow easier and "pull" more "gunk" out with it. Then I would let the motor oil drain out for 25-35 minutes before refilling with syn 75w90. I only have 2 quarts of dino motor oil left as I made the switch to syn, so I figured this would be a decent way to get rid of it. Questions/comments:

1 - Is there any compatibility issues between the motor oil and any trans mechanisms?
2 - Will the motor oil react in a negative way with the new 75w90 (FYI - Im not concerned with the possibility of altering the weight in the tiniest of ways

)
3 - Am I just being too cautious with getting rid of the possible left over "gunk" in the trans?
4 - Should I allow a longer drain to insure as much motor oil is removed as possible?

I figure as infrequently as I change the fluid (every 2yrs/24k miles…not 5yrs/60K as recommended) I want to do as thorough as a job as possible.

Thanks
Na Zdrowie!
Keith

 

[heathenbrewing]

"wither" should be "either"

 

[KBFXDLI]

If you are worried about leftover debris in your trans get some cheap ST dino 75w90 and run it 2000 miles and drain it. Then go with the syn. A trans or diff should create most of it's debris in the first 2000 miles and then very little after that.(unless you have a mechanical defect). You might also consider a magnetic drain plug if you don't already have one. I wouldnt bother flushing with motor oil.

 

[heathenbrewing]

"I wouldnt bother flushing with motor oil. "

Could it hurt anything? Like I said, if I don’t do something with this oil, it will most likely just sit on a shelf since I no longer use dino in the crankcase.

 

[wileyE]

Had a 90 ford truck that used a mazda built tranny, spec was 10w30, severe use 80/90. Guess they didn't care too much if a little got mixed? I'm in the "why bother" camp for rinsing, just drain it hot.

 

[KBFXDLI]

I always "rinse" my engines or gearboxes when new to eliminate break-in debris. (especially diffs)but use the same weight oil so mixing is never an issue. If you pour the motor oil through the trans it won't suspend the left over debris like running some cheap 75w90 dino through for a short interval. I doubt you have any build up in the bottom of the trans that the motor oil will rinse anyway.

 

[ConfederateTyrant]

Get the cheap Super Tech 80w-90 to fill up, then drive around for about 30 miles, then drain it and fill it with your Redline/Royal Purple.

 

[Auto-Union]

I'm into rinsing, but not with motor oil unless its' to provide some cleaning. GC would be an interesting MTF.

 

[tom slick]

the viscosity is not that different between the motor oil you want to use for rinse and the gear oil you are going to install. I don't think you will hurt anything through chemistry though.

 

[BMWR1150GS]

I would rinse with ATF....fill and drive a few miles light load, drain and fill with spec fluid.

 

[heathenbrewing]

Thanks for all the input.

I think I will go ahead and flush w/ the motor oil and refill with Redline MT90.