DIY Dialog

Synthetic vs. conventional oil?

  • Hi! I have a 2002 Toyota Highlander and am coming up on 80k miles. I am debating switching from conventional to synthetic motor oil, but was not sure if it would be the best thing for my vehicle. I am also concerned about “oil sludge” common to this model. Any advice would be greatly appreciated.

  • My understanding is that synthetic can indeed help to clean out the oil sludge, but my understanding is also that doing so can cause oil leaks as the sludge that clogged up those leaks gets whisked away.

    That said, I've never experienced this so it could be an oil man's myth. FWIW I have a '91 Toyota MR2 that was always run using conventional oil and I've never bothered to switch it to synthetic. It probably has close to 200,000 miles on the clock now (odo broke 10 years ago and I just now bothered to fix it). I do run synthetic from new on all my other cars, though. 

    I'd recommend spending some time poking around on here to learn more than you ever wanted to about oil:

  • Good question I am sure can provide ample discussion.

    In my experience, synthetic works well if you use it from day one. There are several high-mileage conventional oils which have a specific formulation for high mileage cars and may serve your needs better than switching to synthetic. Switching from one oil variety to another may cause engine seals to let go, especially as mileage increases.

    If the engine is consuming oil or the oil is "sluding" up, I would be suspect of internal engine breathing issues, or a lot of stop-and-go driving.

    If this is a common sludge problem in a specific engine (which I have heard about some Toyotas), there may be a TSB issued or common knowledge throughout the internet.

    Good luck!

  • FWIW, I have used both types and find syn to be better for hard driving such as city and long haul, it keep it's viscosity and lasts longer for less time changing oil ( 5000 mi between changes to 3000 for conv). But it is really a personal choice, My sonoma and C70 Volvo only get Syn.

  • Synthetic!!!! No question. More expensive but your engine will last significantly longer!!!

  • My experience has been to use synth in a new/clean engine. The synthetic will "clean out" an old engine quickly, but the old sludge wants to cling together in clumps and will restrict the oil flow in smaller oil ports. Start a new/clean engine out with synthetic, but be careful if changing an older engine over. Make sure it is clean.