Mixing Conventional And Synthetic Atf

[jbeall]

Hi All,

 

I'm thinking of moving to synthetic for my 2003 Yukon XL, with about 57k on it.

 

I don't have the parts and I don't think I'll be able to do the "manual flush" like this, and I'm wondering if it would be a problem to just put in Amsoil ATF, or some other synthetic ATF. Drop the pan, drain the fluid, change the filter, then refill with Amsoil. I understand this is going to leave about 50% of the old fluid in the vehicle, so I'll now have 50% convention and 50% synthetic.

 

I'll likely drop the pan and drain again in short order, perhaps 6 months or 10,000 miles, whichever comes first, and then again 6 months later or 10,000 more miles. I figure that way I'll get most of the conventional ATF out and have it replaced with synthetic.

 

I've searched and read a ton on transmission fluid changes, and it seems that the general consensus on mixing synthetic and conventional ATF is that it's ok, it's just that you won't get the full benefit of synthetic ATF as long as you've got it mixed with conventional. After three changes, I should be to 87.5% synthetic, if dropping the pan will drain out 50% of the fluid.

 

I thought I'd ask here, one last time, to see if the conclusion I've drawn (mixing is ok) from my own reading is in error. Let me know your thoughts. Thanks!

 

-Josh

[2COR517]

Just change to all synthetic at once. After you drop the pan, put in about 8 quarts of the new synthetic. Remove a cooler line, and start it up. The old fluid will pump out. Put a few feet of hose on the line and put in a drain pan or bucket. After you've pumped out 4 or 5 quarts, about a minute and a half, shut it off. Put in another 4 quarts and start it up. Pump out some more till it changes color. Put everything back together and top off.

[jbeall]

Just change to all synthetic at once. After you drop the pan, put in about 8 quarts of the new synthetic. Remove a cooler line, and start it up. The old fluid will pump out. Put a few feet of hose on the line and put in a drain pan or bucket. After you've pumped out 4 or 5 quarts, about a minute and a half, shut it off. Put in another 4 quarts and start it up. Pump out some more till it changes color. Put everything back together and top off.

 

I know that sounds really easy to you, but I keep having visions of ATF spilling all over the place, not being able to get the cooler line reattached correctly, etc. I'm just thinking that it would be a lot easier to do the drop the pan and drain bit and then do another change in the near future. Is it going to do any *harm* to not change all the fluid?

 

I might try the pumping it out thing, I haven't completely decided against it--it just sounds much easier to drop the pan and drain and refill. If I had somebody to actually be there and walk me through the process, it would be a lot different, but I'd be totally flying blind--I don't have any buddies that are interested in helping me out with this. And I couldn't even tell you where the cooler line that I need to detach is.

[dlstewart01]

You can mix them. API requires that all fluids whether engine oil or trans fluid mix with each other.

 

Have a good one

[2COR517]

Sorry, I didn't see the link you posted the first time. There's nothing wrong with mixing the two, you just won't get the full benefit of straight synthetic. It's not quite as scary as it sounds, but I'll be honest that if you don't know what the trans cooler lines look like, or where they are, you are probably not up to the job. I would suggest you find a shop that will do this for you. Don't let them talk you into a flush, tell them you want it done this way only.

 

Ideally, go to a shop, ask them how they do it. If they describe this procedure, use them. The money you will spend dropping the pan three or four times will offset the cost to have a shop do it.

[jbeall]

Sorry, I didn't see the link you posted the first time. There's nothing wrong with mixing the two, you just won't get the full benefit of straight synthetic. It's not quite as scary as it sounds, but I'll be honest that if you don't know what the trans cooler lines look like, or where they are, you are probably not up to the job. I would suggest you find a shop that will do this for you. Don't let them talk you into a flush, tell them you want it done this way only.

 

Ideally, go to a shop, ask them how they do it. If they describe this procedure, use them. The money you will spend dropping the pan three or four times will offset the cost to have a shop do it.

 

Here's a question--when you pour fluid in the fill hole for the transmission, where does it go? Straight to the pan?

 

The reason I'm asking is, what happens if you're just pouring fluid in the fill hole with the pan off--is it just going to go straight down into your drainpan under the vehicle? That's what I'm assuming, but I thought I would doublecheck--this "flushing" type of procedure would not work by just leaving the pan off and filling the transmission fluid while the engine is running (and pumping the transmission fluid out of the torque converter). I'm guessing this would just burn out your transmission as it dumps the old fluid out without refilling it with new?

 

-Josh

[2COR517]

Whoa.....

 

What ever you do, don't run the engine with the tranny pan off. I think you would be wise to get a shop to do this. Hopefully you can find one that will let you watch.

 

To answer your question, yes, the dipstick/fill tube dumps into the pan.

[Spurshot]

 

Dexron VI ATF IS SYNTHETIC at least a blend anyway.

 

[REV353]

Just spend the money and have it done right the first time

[jbeall]

Let's talk about the location of the cooler lines. The more I can know about my truck, the better.

 

 

 

So here's where I think they are (light yellow lines highlighting what I think are the cooler lines):

 

 

 

 

 

 

Am I correct? And the one I would want to disconnect is the bottom one?

The top one seems like it would be easier to get too :-/

 

Also, people have talked about a clip that you remove to take them

off--mine appear to have nuts holding them in place.

 

Unless I am mistaken about these, and they aren't the lines I'd disconnect, or at least that's not where I disconnect them?

[jbeall]

Ok, how's this for a closeup?

 

This is the top line (which, if I understand correctly, is the return line from the radiator).

 

[txab]

You can pull back on the plastic ring to reveal the clip that holds the line. The fitting will then look like this:

 

 

With a clip like this:

 

 

The plastic ring is to make sure the clip doesn't pop off