Piston Slap: Sucking At Fluid Changes?

Sajeev Mehta
by Sajeev Mehta
piston slap sucking at fluid changes

Longtime TTAC Commentator ajla writes:

Hi Sajeev,

I do a more through job at the time of purchase, but every year after I do a drain/refill on the radiator and replace some transmission fluid by using my fluid extractor to vacuum up as much ATF as possible through the dipstick tube.

I know that I’m not getting all the fluids exchanged this way, but my question is how much of a positive impact is this regiment actually having on my cars? Am I just wasting my time? I haven’t suffered a mechanical failure since I started doing this, but I don’t know if that proves much.

Keep in mind that the vehicles I tend to own are 20 to 30 years old.

Sajeev answers:

In theory, fluid changes via modest exchanging of old for new is a great idea. I’ve done this countless times to my brother’s C5/C6 Corvette hydraulic clutch reservoirs, especially after his ZR1 ( that some might remember) lost the clutch on an especially hot afternoon of autocrossing…and I’m far from Jack Baruth around the rubber cones!

But the need for annual coolant/ATF servicing is unlikely: both coolant ( even the old green stuff) and ATF lasts far longer than a year, at least double for coolant and more like quadruple for ATF. Assuming modest annual mileage, vehicle age is somewhat irrelevant, unless it’s an old truck regularly towing an overloaded trailer.

For you and your cadre of classics? Do fluid changes like ATF/Coolant every 2-5 years, more often for engine oil (duh) and less for other wear items (brake fluid).

[Image: Shutterstock user Nor Gal]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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2 of 43 comments
  • AFX AFX on Aug 27, 2014

    Suctioning out the fluids ?. I know they do that in the Hood with a siphon hose for the gasoline, but I didn't know people did it for other fluids too !. Another quick and easy method for gasoline removal is an ice pick into the bottom of the gas tank, and a garbage can lid to catch the gas under the leak. As an example of modern progress in vehicular safety, since the automakers switched over to plastic gas tanks less kids in the Hood have to worry about getting themselves blown up now.

  • AFX AFX on Aug 28, 2014

    As far as transmission fluid goes, my non-expert opinion is that you're better off changing it too early than too late, like engine oil. New fluid and a filter is cheaper than a new transmission. Are you people actually changing the fluid yourselves ?. If not you should try it sometimes. You let it go too long and it's no longer that nice cherry cough syrup red color anymore, it turns into a brown mess that looks more like partially used engine oil. That metallic particulate crap floating around in the internals of the transmission that eventually settles to the bottom of the pan doesn't help your transmission's life either. With every car that I've owned with an auto transmission they've always shifted better right after a transmission fluid change, and the new fluid makes the car feel like it's gained another 5-10hp too. With old transmission fluid it really does feel like the car has a slushbox, and you're losing efficiency, with new fluid it shifts harder and pulls harder when accelerating. Maybe it's additives breaking down in the old fluid, but my guess is that it's more like the viscosity breaking down and lowering the efficiency of the transmission.

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