Piston Slap: Wither Synthetic Oils?

Sajeev Mehta
by Sajeev Mehta
piston slap wither synthetic oils

TTAC Commentator Halftruth writes:


I am in the market for a new mid size truck. I have been looking at Tacomas both new and used and came across a used one at a decent price. Thing is, the owner states that “purchased new and immediately changed all fluids to synthetic from the oil to the rear diff”.

I am not crazy about this as I have heard of nightmares from folks going to redline, purple stuff etc etc for a better (shift, mpg whatever). Why dont folks leave well enough alone? What is your take on this???

Sajeev answers:

Considering many vehicles run synthetic (motor) oil from the factory and even more run semi-synthetic stuff, I’m pretty much indifferent. Making the switch in the first few years of ownership isn’t gonna hurt anything, provided you use the right weight/type and there isn’t a huge warning from the manufacturer about deviations from the factory stuff. (Subaru, Ferrari, BMW have all done this in the past, IIRC.) Hell I switched to synthetic (engine) oil in my Mark VIII when I bought it at the ripe old age of 117,000 miles! Aside from one common gasket fail point, I had no problems.

So why not switch to a full synthetic for most vehicles? You gotta love your ride for the next 10-20 years, that’s why not. That said, I switched my Ford Ranger over to Mobil 1 after 6,000 miles…so I guess I’m in it for the long run, too.

Perhaps synthetic rear axle fluid is also better, but I’ve switched before and never noticed a difference. But, on an older vehicle, if you’re going in there for something else…might as well make the switch.

Transmissions? That’s where the shit gets real. The sheer number of fluid requirements for gearboxes (mostly automatics) is more than a little horrifying. You gotta be REAL careful here. Any aftermarket synthetic oil you choose had better be compatible with the factory fluid. So do your homework: like a Q&A session with an answer right from the horse’s mouth.

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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3 of 25 comments
  • Nrd515 Nrd515 on May 09, 2013

    I've used Mobil 1 for over 30 years, changing it twice a year. The only one of my engines that I was able to look at was my '93 Grand Cherokee's 4.0, and it was amazingly clean with 70K on it. The valve cover gasket cracked or split and had to be replaced when it started trickling oil out the back end of the cover. I saw a friend's 2001 GMC 5.3's innards when he put a cam in it, and it was amazingly clean with over 150K on it. The cross hatch marks were still on all the bores, and everything looked to be in spec, so a new timing chain, valve springs, and water pump were put on and off it went. I don't think the cam change was worth it, but he's happy with how it runs.

  • 300zx_guy 300zx_guy on May 09, 2013

    on a slightly different subject, what a about oil changes for a car that doesn't rack up the miles very quickly, say 4-5k mi/yr. Do you change every six months? every year? Does conventional vs synthetic make a big difference in this case?

    • Corntrollio Corntrollio on May 09, 2013

      Definitely every year at minimum. 6 months wouldn't be terrible. The issue is that if you're not getting up to operating temperature regularly, you'll end up with more moisture in the oil and things like that, so you may still need to get the oil changed. If you want to go for the year, synthetic is probably better, but the operating temperature issue is more important. I've had daily drivers where I drove approximately this much, but I regularly got up to operating temperature, so I didn't worry about it too much. If you really wanted to find out, you could get an oil analysis done.

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