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MX5 NC Oil Burn


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#1 dave_3296

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Posted 10 August 2017 - 06:18 PM

Hi Guys,

 

Been a owner of a MX5 for about 2 years, loving it but seem to have developed one of many issues. I am curious if anyone has had any luck freeing piston rings. I have had my 80,000 km MX5 NC Burning Oil due to a faulty PCV Valve. The PCV valve must have been faulty for a while because it has polished the bore of the rear most cylinder and as a result we believe the oil ring seal maybe stuck. This is resulting in catastrophic oil burn. 1l is burned about every 500km to 700km. A compression test and leak down test has been performed and all the results are within spec (sadly I do not have the official results I am going off a mechanic I have dealt with for years and trust). This is why we believe the oil ring maybe stuck.

 

Has anyone ever had any luck with freeing a oil ring e.g with ATF fluid or using an Australian equivalent to sea foam.

 

I am quite reluctant to perform any of the above steps but at the same time I'm sadly not in the financial position to do a rebuild or swap an engine. The car drives wonderful especially after all the carbon build up was removed from intake valves and throttle body was cleaned but I am worried driving it while it burns this much oil will destroy my 02 sensors and cat. 

 

Any input would be appreciated. 



#2 JBT

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Posted 11 August 2017 - 09:30 AM

How do you know that the rear most cylinder bore is polished? Borescope? Are you sure that valve seals are all OK?

 

I don't know of any fix for glazed cylinders other than mechanical deglazing with a bead hone or similar. Head would have to come off etc. = $$$  :sad: 


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#3 dave_3296

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Posted 15 August 2017 - 12:52 PM

How do you know that the rear most cylinder bore is polished? Borescope? Are you sure that valve seals are all OK?

 

I don't know of any fix for glazed cylinders other than mechanical deglazing with a bead hone or similar. Head would have to come off etc. = $$$  :sad:

 

The mechanic placed a borescope down all the spark plug holes and noticed 2 and 3 had very minor glazing while 4 had significant glazing ( i have not seen this with my own eyes). He felt the best thing to do was to do an engine flush through the oil ( this has been performed). Then for me to drive the car and monitor oil usage to see if it gets any better. 

 

There is a concern that its a stuck oil seal ring but i guess if its glazed then its not so much about it being stuck but rather it sealing correctly i assume?

 

The strange thing is for a car that burns 1l of oil every 700km it blows very little smoke. No smoke on startup cold or warm and only occasional light smoke (so faint you can barley see it on camera) when i rev engine. The smoke occurs as the engine is coming down from revs e.g let off accelerator and the needle goes back to 800rpm. 

 

anyway sounds like theirs no cheap fix for this one.



#4 dave_3296

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Posted 15 August 2017 - 01:06 PM

 Are you sure that valve seals are all OK?

 

 

I am not 100% certain. but a leak down test was done by mechanic and it all passed. Also no smoke occurs on startup.. i believe smoke on cold start is a classic case of valve stem seal failure.

 

If there is any thing else you can recommend for me to check please let me know.


Edited by dave_3296, 15 August 2017 - 02:14 PM.


#5 JBT

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Posted 15 August 2017 - 03:22 PM

It seems to be a case of glazed cylinders rather than a stuck oil ring. Very rare in a modern car engine. I really don't know of any fix other than honing the cylinders and replacing the rings. A replacement low km used engine might be no more expensive. Try Automotive Plus. The guys there might be able to help.


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#6 dave_3296

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Posted 16 August 2017 - 09:57 PM

Thanks mate yea I have been dealing with them over the past year. Excellent guy. Currently waiting for a quote. Considering my engine was stuffed any way I decided to Goa head with this old wife stale using atf down the spark plug hole and will report back on my success. Needless to say I'm not expecting any changes haha.

For a car that has a well known history of being one mighty tough car I must be honest I have never had such an unreliable car in my life ( previous vehicles being mostly euro). Maybe the mzr motors arnt quite like the bp motors they replaced. ..... or I just have a lemon lol

#7 JBT

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Posted 17 August 2017 - 07:34 AM

..or I just have a lemon.

 

Quite possible. Bought ours new and it has been tracked, khana crossed, hill climbed and driven all over the country without using a drop of oil in that 125,000km. Only issues have been a serpentine belt tensioner and idler. The rest has just been normal service - which I have done myself since end of warranty.

 

Maybe yours was babied at low revs on short runs (cold running) as well as having the PCV issue. Mind you, I've never heard of a PCV going on an NC either.  :blink: 


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