First, thanks for any information anyone may be able to provide. I've searched the forum for this issue, and know it's been discussed in the past, but really didn't find any answer's to help me.

I drive a 2007 Mazda5 with a manual transmission. At about 77,000 miles, out of the blue...no warning lights, nothing, a piston ring let loose and the engine blew. I've since replaced it with a used engine, 77,000 on the used engine as well.

Since having the engine installed, it is using an alarming amount of oil. It runs quiet and shows no outward signs of oil consumption. No smoke, no visible leaks, nothing that would usually come with burning oil. At this point, it uses about 3 quarts of oil every 250 miles or so. I've got to keep a constant check on it as you can imagine, and it's become both expensive an annoying.

I've had two different mechanics look at it on three separate occasions, and they both came back with the same answer. No oil leaks, nothing to show it is burning oil, nothing. They can't figure out why it's doing this. Sometimes there is the smell of oil when I turn on the AC, but it comes and goes, not always there.

Does anyone have any ideas or advice? I'm at a loss.

 

What is the oil weight specified for your vehicle?
ie: 5W20?
The catalytic is probably preventing visibilty of burning oil---it is also becoming clogged.

 

It is 5W 20.

 

How to tell if it is burning oil, pull a spark plug. These are high energy ignition, but it should still be evident. Have you checked the coolent? Also check the pvc valve.

 

I don't know what that is, but i've heard of a PCV valve.

Mazda's service technicians never change this valve, so change it!
You may want to try a different oil. I had no luck with Royal Purple.
I've had luck with Amsoil and Lucas Oil.

Did you read: https://www.mazdaforum.com/forum/gen...ls-0w__-32291/

That article might explain a bit, but not what you are experiencing.
After i got rid of royal purple and changed my pcv valve, i did notice a difference.

If it leaks, you would have spots on your driveway, otherwise it's burning.

Checking coolant is a good idea as per Kevinkpk, as if oil is getting in there then you may have cylinder head problems where oil is getting in coolant.

 

Thanks everyone for your help! I'll give these suggestions a try. I'm mechanically inclined, but in an Air Cooled VW sorta way. These new cars scare me! I'm hoping to pull a plug and check that out soon, and sell as the PCV Valve. Coolant is definitely no the issue, had that checked out.

 

Just an updated, had the PCV valve replaced. And car looked over by two more mechanics, no luck. Now in addition to using oil, it has begun drinking engine coolant.

 

If you can get a spark plug out, look at it. it will show if it's burning oil.

 

Yes, have checked that, not burning any oil.

 

Well you either have one heck of a sludge issue or a leak. I'd suggest degrease the whole engine, make sure it is clean. Drive for 50 miles or so, put it on a lift, and check for oil leaks (oily areas). You might not have a leak setting, but something isn't right.