I think I've tried a little of everything over the years, but for me I've gotten the most noticeable improvement
from adding a quart of ATF shortly before performing an oil change.
The last engine I added ATF to was my previously-enjoyed DD. Overall I think the original owner's preventive maintenance
was better than average, but if I had to guess as the years piled on the service intervals started to stretch out a bit?
The symptoms I was trying to cure was overall sluggish behavior with (of course) no check engine light. Plug
colors were good, no issues with coolant consumption, and oil consumption was within normal limits.
The 19 year old motor simply wasn't performing to expectations. Steady state was OK, but transient behavior
was not what I would expect from a K24a engine. (2.4L {146ci}, 160hp & 162 ft/lbs of torque, into a 5-speed manual AWD.)
I tried all the normal deep tuneup tricks, including setting the lash on the solid roller follower DOHC valvetrain. NOTE:
With the valve cover off, there wasn't any build up of sludge, but there was a lot of varnish to see. (!)
Since the iVTEC has a hydraulic cam phaser on the intake camshaft, my theory was that this phasing was sluggish
as compared to what the designers intended? And I had also noted that the VTEC function was noticeable when it
occurred, which is actually another sign of sluggish operation? So, after the normal tune up / valve lash / Techron
steps, I decided to add a quart of ATF, followed by a weekend road trip to visit my sis. This was a ~500 mile round
trip, and I immediately changed the oil & filter upon my return.
By changing only 1 variable at a time (on purpose) I was able to correlate which change made what difference.
Thanks to the complicated hydraulic nature of the intake cam phasing and also VTEC operation (<4 min. technical training video)
the ATF made a noticeable (complete) improvement to the overall driveability of the vehicle.
I know this is a big claim, especially in a public forum, but I did all this a year ago, and the fix has remained in place.
Not only is the engine as responsive to transient inputs as one would expect, but the VTEC transition is faster/smoother,
and the oil consumption has actually improved.
Again, if I attributed all this on my L29 motor that would be sheer nonsense. (No cam phasing or other engine oil-based
performance enhancement modes.) On the other hand, IF you think you have any varnish build up inside your engine
and you think that it might be affecting the tiny spring-loaded check ball/check valve inside your hydraulic lifters, then ATF
seems to be able to clear up the varnish. And this was taught to me by my mechanical mentors half a century ago...
specifically to quiet sticky hydraulic lifters. (!)
Food for close-tolerance thought. Disclaimer: ATF will clear up varnish where none can be tolerated. Essentially a worn-in engine
with good clearances with a varnish condition affecting close-tolerance parts. By the same token, ATF is not recommended on a
worn out engine with excessive clearances where the varnish build up is actually helping to maintain the fragile status quo. (!)
There -is- a difference, and if anyone reading this can't explain that difference, then please err of the side of caution and *do not*
add ATF to your engine oil.
It really is to be used as a specific fix, not a generic miracle fluid. It's an old dog trick, handed down by the elders. YMMV.
FWIW --
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