I'm hearing and feeling a tapping/grinding noise when accelerating (at a stoplight, sometimes uphill). Sometimes it's there, sometimes not. I bought the car two months ago (Mazda 626 LX 1998, 125K Miles), and found (after a check engine light) that the engine oil was very low. Adding oil only temporarily decreased the noise. The noise tends to be less when more people are in the car (!?), and is also (almost) absent after driving 10-15 min, stopping for 5-10 min, and then restarting... Should I try a 'Complete engine system cleaner' before consulting a mechanic?
Thanks!

It sounds like your HLA's (hydraulic lash adjusters). HLA's can be somewhat noisy on a car that has had insufficient oil changes over it's life time.

What type of gas to you run? You must use 92+ octane gas, and I'd suggest Sunoco....it's the cleanest gas on the market.

Moving to sythetic oil is of great benefit to this 2.5 motor. It's a very high performance engine, however many folks simply think of it as a motor on a family car.

If interested, email me at christopher.dewar@sympatico.ca and I'll send a good website just on this motor...which should help answer alot of questions you may have.

Good luck....

I use >92 octane gas since a few weeks now, but I didn't notice any improvement....

I've also read somewhere that the 1998 version of the 626 doesn't have the HLAs anymore.... (but I'll have to check when exactly my car was built).

...after adding an octane booster. Have to admit that temperature was near freezing this morning. Anyone an idea?

Try having your timing checked, perhaps it's good old fashioned spark knock.