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The Skyactiv Resuscitation Project

761 Views 13 Replies 9 Participants Last post by  hioctaneda
Word of warning, this is going to be a fairly long post. I had debated going through all this, but figured there might be some here that would be interested. Still not at the end of the journey either, more to come.

So, after 9 years of loving the hell out of my 2014 Mazda6 Touring with a manual, I went for a drive this last February and got an overheat warning on the way home. Got it home fine and started some investigation. Didn't take long to figure out that I had a real problem on my hands


Obviously the oil ain't supposed to be in the radiator. Pulling the dipstick, I had a real nice looking milkshake going on. Not want to face the inevitable yet I called a local shop that I always take our cars to and talked through the options. Obviously the prime culprit was probably a head gasket, but I did recall reading about some early year Skyactiv engines that had cracked cylinder heads. My options were thus:
  • Pull the cylinder head and see what we're dealing with. If a head gasket, replace it and see where we are.
    • If not a head gasket, I'd have to make the decision to continue with a rebuilt engine or call it a day and be out whatever the cost was to get that far.
  • Forego the cylinder head and start looking for a new/used engine. This would be the more expensive option and possibly unnecessary, but it avoids the extra expense of the head gasket if it turns out the engine is shot.
After talking it through with the guys at the shop they started shopping around for a replacement engine for the car. With the amount of coolant that I was finding in the engine and vice versa I had a suspicion that I was dealing with more than just a head gasket. Third option was to obviously scrap the car, but at 9 years old and only 130k miles on it I wasn't ready to give up on her yet.

Fast forward a week and I got a call back from Jeff at the auto shop. Turns out Skyactiv engines don't grow on trees and he had been unable to locate a rebuilt one. He did talk to Mazda directly and was able to source a brand new one, but installed we were looking at over $10k. I love this car, but wasn't ready to commit to that. A used engine was another option, but while those can be in great shape you don't necessarily know what you're getting. I did some checking and was able to locate a few in the Midwest where I'm located. Again, they weren't coming out of the woodwork and for a mid/high mileage used engine it was looking like between $2-3k. Then I'd have to get it installed.

It was at this point I started accepting that this might be the end. I had thought I'd get another 4-5 years at least before I had to start thinking about my next ride, but here I was looking at needing something now. In the meantime, old red got put out under a shroud. Wasn't ready to scrap it yet.


After looking around a bit I was appalled at the limited options out there for a suitable replacement. I wanted something bit enough carry myself and various family members in comfort along with a few bags if needed. Plus, some of my trips tend to get long, which is why the 6 was the perfect size 9 years ago. Couldn't get into the Accord, none of the Hyundais or Kias appealed to me, and the geniuses at Ford and GM have decided no ones need cars so screw them. Decided to stick with Mazda.

After a few trips to dealers, I realized right away that the CX-5 and CX-50 were out. We made it about 1/2 mile into the test drive of a CX-5 and got a "ugh, this is terrible. Go back" from the missus. I had to agree. After my 6 anything in the suv class just felt heavy and dull. The Mazda3 drove better but headroom was lacking and the rear seats were cramped.

After more searching I decided what better way to honor Mazda's former motto of "zoom zoom" than to go find what's probably the last true driver's mazda out there. I located a 2021 Carbon Edition and we went home with it after some short negotiations.



I figured that was it, but three weeks in I was still fantasizing about my 2014. The new one was great, but it just didn't "click" like the one one did. It's a great car but the manual was still calling to me. I decided to make one last call.

My wife's uncle taught auto repair for over 30 years and I figured if anyone would have some ideas it would be him. I called him up, and after some foreplay I asked what he thought about doing a gasket repair and if needed an engine swap. He said his garage would be cleared out come May and I was free to bring the invalid over and see what we could do.

May arrived, and after swapping in a fresh load of coolant and oil I made the 10 mile trip to his place. Made it without overheating and when Saturday arrived we opened her up.


First order of business was to see if the engine was worth saving. I've done plenty of car work in my days but nothing to this extent, which is why I had engaged an outside consultant. In his words, "We'll pop the oil pan, pull the lower rod caps, and see if the bearings are washed out or still within spec". Now, I'm a mechanical engineer and have worked in engine design so I know what he's talking about. The thought of doing it on a modern automobile engine that's installed in a vehicle is another thing entirely. "Go to O'Reilly and ask for plastigage, one red and one green. Don't bend it, open it, or get it too warm". This was a new one to me, so off I went.

Turns out Plastigage is very thin plastic rod that you put in the bearing races then reinstall. When I asked at O'Reilly I got a blank stare from the younger guy and a "Holy hell, what are you working on?!" from the old gent in the back. I think I made his day. It took both of them working together about 14 minutes to dig it up in the back.

Once you pull the cap back off, you see how much the plastigage has squished and then compare it to ascale to see what the clearance is. Pretty ingenious. With the big oil pickup underneath the only rod we could see was cylinder 4, so we pulled that cap, popped the plastigage in, and retorqued it. Took it back off and took a look. Lucky me, the clearance was right in the middle of the factory spec. From that, we made the great assumption that the other bearings are probably okay too. So the engine might be salvageable, on to step two



I don't have a ton of pictures of the disassembly process, suffice it to say it's not something I'd want to do for fun more than a few times. Not much room in there and there are a ton of parts to be aware of, things to keep track of, and small parts that are easy to break if you don't know what you're doing. The timing chain cover sure wasn't fun and the exhaust header in back took some creative socket extensions to get all the bolts off. After about 7 hours though, the head came off.




Fuel rail and injectors

Don't mix up the cam bolts and lifters!

Pretty sure that green stuff shouldn't be there

Once the head came off we quickly looked at the gasket to see if we could find the smoking gun. Nada, couldn't see anything obvious.


However, it turns out we didn't have to look very far to find the issue. The dreaded cracked head. From what I've been able to dig up it seems like this is the spot where they tend to fail, between the coolant passage and area where the timing chain cover sits. This explains why I was losing coolant into the oil so quickly.



At this point we broke for beers and discussed options. The good news is it wasn't the block, but it never crossed my mind that something like this could be fixed. Imagine my surprised when my wife's uncle throws out "I'll call Bob the Cylinder Head Guy on Monday and see what he thinks". mean see if he can get a new one and install it? "No, he might be able to repair that". So apparently Bob's been around the block a few times. With a tentative plan of action, we broke for the day.

Monday comes and goes and I get a text from the Uncle. "So Bob took a look and his theory is that your thermostat failed, causing the engine to overheat. Once that happened the difference in expansion rates between the metal plug and the thin portion of the casting there caused it to crack. He'll pull the valves and that plug, weld the crack and plug hole shut, grind it, tank it, clean the valves and touch up the seats, then reinstall everything." According to Bob he's never seen a steel plug that size in a section that thin. With no other options on the table I tell them to go ahead.

As of this weekend, this is where we stand. The welding is done and the head is waiting for cleanup grinding and machining. According to Bob I got lucky, there's an oil passage in there and he was able to grind out the crack (which went a lot deeper than we though) and reweld it without affecting that passage. While Bob was working his magic I went over and we did all the necessary cleanup on the parts that came out to prep them for going back in, including washing and relubing everything and cleaning all the seal faces. We're waiting on additional parts as we speak and hope to start putting her back together next weekend.

To be continued!!




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@Ofted42 , that's an excellent post, and very instructive! Thank you for posting, particularly in such great detail, along with great photos to study.

Your uncle's comments re the big dia plug in such a thin section-size does give a person pause; just what were they thinking...?

If the theory re thermostat failure is indeed the reason for the failure it's particularly instructive as regards frequent coolant changes and changeouts of t-stats...

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OP, in retrospect, particularly re the pita factor with the timing chest cover, would it be prudent next time to pull the engine and transaxle for better access?
The fellow who welded-up the screw-plug hole obviously has experience in welding-up heads... but aluminum has such high heat conductivity that my concern would be cracks formed in the molten weld pool or in the heat affected zone due to too-quick cooling due to this high conductivity. Mebe just me being a "Nervous-Nellie"...
@Ofted42 , what's your sense, re the timing chest cover... whether you can [with adequate (?) space between the timing chest cover and the frame rail of the engine bay] - put the cover in place without smearing the just-applied RTV/sealant while the cover is being lined-up with its bolt holes and pushed "home"? Points of typical leakage are the head-to-block-to-timing cover joint, i.e. either side of engine (2 such locations)... Same situation with block to oil pan to frt cover.

Also, couple questions/observations re the photos...
i) interesting how multi-plate silent-chain (Morse Hy-Vo?) is used to turn the balance shaft assembly... and it's so HD, versus the single-row relatively light-duty conventional chain is used to run the cams + fuel pump;
ii) gnarly lobe on exh cam to turn that high pressure fuel pump!; and
iii) what is driven off the end of one of the balance shafts (under cyl 4) if anything? Is it the oil pump? It appears to have a drive-lug.



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Good job but I would NEVER attempt this without pulling the entire engine. And then once that is done I'd rather drop in a low mileage used one. I just checked online and within 50 miles of me are dozens of Mazda 2.5 skyactiv engines. 50,000 miles for $1,800. The labor to pull the engine is not that much different than what you are doing.
The OP indicated that he was having a prb finding a replacement engine and he was also concerned re the condition of a used engine...

Having said the above, there is the issue of whether any of the other bearings on his original engine were damaged... so it is a bit of an educated gamble to re-use this engine. Maybe they later-on pulled the balance shaft assembly off and checked all of the mains and big-end bearings... Also, with an overheat, line-bore of camshaft direct-in-aluminum bores would have to be checked by the head person; warpage could have occurred.

Re pulling the head, engine still in place, that's not an uncommon thing to do (particularly if a person doesn't have a lift... which they did have). But it is nice to be able to work unencumbered on the engine while it's out of the car; you could pre-emptively change water pump more easily that way... and possibly also timing chain, guides, tensioner, mebe sprockets(?) too?
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