# Need to flush old auto oil out or not



## fiesta62 (Jan 12, 2011)

hi. i went to buy some auto oil for my 67 gto , i was going to use the valvoline maxlife dex/merc synthetic oil, Valvoline - Automotive Products 
but was told by the sales guy i need to completly flush out the auto before i fill as it might have mineral oil in it now and i should not mix synthetic with mineral, well i dont know what oil is in box now, so i am unsure should i buy synthetic or mineral, he says draining the auto does not drain all oil , there is still some litres in the torque converter, so how do you guys go about this, do i run litres of oil thru to flush it , he said drain old oil then fill with new run it then drain and throw away oil, then fill it again with new oil, or even remove auto to drain properly this seems way to difficult just to change oil, any thoughts on this ?


----------



## fasterfiero (Sep 6, 2011)

I posted in your other thread.........

I'm not putting down counter help, but......... just say-in......

Valvoline.com > FAQs > System Fluids Car FAQs > Automatic Transmission Fluid


----------



## geeteeohguy (Feb 2, 2008)

Here we go again......Fiesta, my advice: drop the pan, replace the filter, and add the 3-5 quarts it takes to fill it back up. The TH400 in my '67 took 14 quarts of fluid after I rebuilt it last March, including converter. If you are bent on changing all the fluid (unnecessary unless the trans blew up and there is debris in the cooler, lines, pan, etc), then the trick is to disconnect one of the cooler lines to the radiator, and run the engine in spurts adding trans fluid to the trans as it is pumped out from the line into a bucket. You need to time this in spurts, as you can very, very easily ruin your trans this way if you are not an expert auto technician. What I do is fill it up, start it up, watch the atf pump for a few seconds, and shut it off and repeat. I use clear plastic hose and a clean bucket. When the fluid is no longer darkish, you're done. You will use about 30-40 quarts of ATF at $8 per quart, so you can do the math. I have done these complete flushes as part of a fleet protocol, not by my own edict. They are, in my opinion, a waste of time and resources. But, you wanted to know....


----------



## fiesta62 (Jan 12, 2011)

geeteeohguy said:


> Here we go again......Fiesta, my advice: drop the pan, replace the filter, and add the 3-5 quarts it takes to fill it back up. The TH400 in my '67 took 14 quarts of fluid after I rebuilt it last March, including converter. If you are bent on changing all the fluid (unnecessary unless the trans blew up and there is debris in the cooler, lines, pan, etc), then the trick is to disconnect one of the cooler lines to the radiator, and run the engine in spurts adding trans fluid to the trans as it is pumped out from the line into a bucket. You need to time this in spurts, as you can very, very easily ruin your trans this way if you are not an expert auto technician. What I do is fill it up, start it up, watch the atf pump for a few seconds, and shut it off and repeat. I use clear plastic hose and a clean bucket. When the fluid is no longer darkish, you're done. You will use about 30-40 quarts of ATF at $8 per quart, so you can do the math. I have done these complete flushes as part of a fleet protocol, not by my own edict. They are, in my opinion, a waste of time and resources. But, you wanted to know....


hi, well that explains it but buggered if i am going to try that, i will do just as you say replace the 5 quarts and only drop the pan, it dont really change much oil though does it as there is still about 9 quarts of old oil in there going buy your math, but i get to change filter too so i will do it, ok thanks


----------



## fiesta62 (Jan 12, 2011)

fasterfiero said:


> I posted in your other thread.........
> 
> I'm not putting down counter help, but......... just say-in......
> 
> Valvoline.com > FAQs > System Fluids Car FAQs > Automatic Transmission Fluid


hi , ok so the syn and mineral oil are ok to mix so no worries then, thanks for the info


----------



## pontiac (Mar 6, 2011)

Mechanics have machine to flush out old trans fluid including the convertor. Best to let them do it. Old method, per shop manual, drill hole in convertor, drain out and plug hole with solid rivet. was done all the time before machine was invented.


----------



## 66tempestGT (Nov 28, 2009)

are you having a problem now? 

i just read #1 and #5 on the link page. seems pretty clear about mixing. what advantage does the synthetic really offer?


----------



## geeteeohguy (Feb 2, 2008)

Synthetic oils offer no "real" advantage if all is working as it should (nothing gets too hot). Synthetic oil has better "cling" and doesn't coke up until it gets to over 400 degrees...so in a unit that is severely overheated, like an engine without any coolant, you may be able to make it 5 or 10 more miles before the engine locks up and you die. That's why I run it in my Toyota 4x4. An engineer once explained that syn. oil was like a room filled with golf balls. All the molecular strands are the same. Mineral based oil is like a room full of bb's, marbles, golf balls, baseballs, bowling balls: they still "roll" , just not as smoothly. That's why synthetic oil "leaks" easier out of a marginal seal..it "flows" better due to it's polymer chains being the same, uniform size. Is synthetic oil useful in our old cars?? Sure. Is it needed? No. I'm running mineral based in all components in both my GTO's. Diesel rigs go hundred of thousands of miles between overhauls on mineral based oils. The MAIN THING is to not overheat the unit and burn the fluid, and not to contaminate the fluid (burst cooler in the radiator). Any reason to run synthetic? If you want to, go for it!!


----------



## Rukee (Feb 8, 2007)

After you get the pan and filter off start the engine for just a few seconds and that will pump some of the fluid out of the TC. I would not drill a hole in it as getting it to seal up again might be a bitch, plus you run the risk of the rivet coming out down the road or having the rivet interface with the internals of the TC.


----------



## stracener (Jul 27, 2010)

Just remember when your doing this to beware of your surroundings. Starting the car, draining the tranny.. if you don't watch out it can get away from you. Check out what happen to my brother and his 77 Buick Skylark with a mechanic trying to do this same thing as he was having some problems with his tranny  ...attached below.

EDIT: I removed your attachment. It said, "the file is damaged and could not be repaired".... It's a bad file....


----------



## geeteeohguy (Feb 2, 2008)

Again, no need to flush. Drop the pan, replace the filter and gasket, and top it off. Good to go. It's called a "Transmission Service" in the automotive industry. It is effective, easy to do, and economical. NO NEED TO FLUSH if the fluid is clean and free of debris. Fluid flushing is the new automotive ripoff angle. Cars now are so good and so reliable, that the dealers are losing money on maintainence that is no longer needed. The whole oil flush, coolant flush, trans flush thing is a gigantic rip-off engineered to clean the pockets of the uninformed.


----------

