Mazda Repair: mazda 3, engine, knocking sound at idle, hydraulic valve lifters, mazda oil filter

Question
QUESTION: My wife have a Mazda 3, 2004 with 60,000km.\r\nwhen running idle, sometime I have a wear sound coming out of the engine (like knocking). as soon as I increase engine speed, the sound goes away. I may think it is from an hydraulic lifter but how I can be sure ? how many of them ? can I take the valve cover off and run the engine to check it out ? do I need to replace all them ?  can I visually see which one is wrong ?  quick stop at the Mazda dealer, they  told her the engine need to be replace.......!. I would not bet on their honesty. thanks a lot for your help. Denis

ANSWER: Not my area of expertise however, hydraulic valve lifters on overhead cam Mazdas can capture air bubbles which cause the lifter(s) to collapse.  The problem is remedied once the oil pressure forces the air bubble(s) out and the hydraulic state is restored.  To avoid this issue change the oil every 3k/3month (conventional oil) or switch to a full synthetic (we use Valvoline) changed every 5k/5months.  Depending upon your climate use 5w-20 (colder regions) or 5w30 (average) or 5w40 (hotter regions).  Also use a Mazda oil filter or a K&N filter.  These filters are designed to prevent back flow when the engine is shut off.  Back flow causes the oil galleys to drain back through the pump when the engine is off.  Once restarted the oil pushes air in front of the oil back into the galleys and thus into the lifters which can form bubbles until purged.  Hence your problem.  

Liken it to drinking out of a straw, some air always comes first.

Unless you overheated the motor or ran low or used something other than oil or ran out of oil or left the same oil in for way too long, I would seriously doubt the need for a new motor at 60km (under 40,000 miles)

service@miatashop.com

---------- FOLLOW-UP ----------

QUESTION: well, after asking her more questions...the engine actually has 90,000KM (not 60,000) and she said her last oil change was ....13months ago. I check the level and it is still over the minimum level . what is my best option now. change oil and try synthetic one to see if sound goes away ?  if sound still there, can it be limited to lifter ?  thanks

Answer
The mileage is still not extreme, maybe once you get to 160k.  That's a long time on one oil change though not the longest I've seen, that type of neglect will lead to the engines early demise if she keeps that up.  

For now I suggest getting a Mazda oil filter and changing the oil without delay, use a conventional 5w30.  Run it for 2k/2month then change it again, replace the filter again also and consider that a oil flush of sorts.  This measure should help to remove burned oil residue and varnish build up.

The following oil service you can either elect to trade up to synthetic or use conventional again you'll have to be the judge based on the appearance of the oil coming out.  If heavy in color use conventional again this time extend its use to a normal 3k/3month service.  Synthetics are more expensive but, you get more use so it pays off, especially on highway cars.  No sense in using the expensive oil as a flush.

service@miatashop.com