2015 CX-5 2.5L SkyActiv coolant in oil

After another 2200 miles, the coolant-indicating numbers are the same, but the oil interval was 1000 miles longer. To me, it indicates that this engine can finish its service life with 2,000-mile oil changes. Blackstone report attached.
Other thoughts:
1) The heater core is now producing heat at about 80% of its original capability. I'm planning to replace the heater core and flush the coolant once more to make it safer/more comfortable for Winter driving.
2) If you have this 2.5 SkyActive engine, I would urge you to send your used oil for sampling at every oil change. Catching it (relatively) early saved major damage to my engine.
3) For those whose UOA already indicates high Iron shedding, I would advise a FilterMag be attached to the oil filter. This will only catch Ferrous metal but will capture tiny amounts that can pass through the oil filter. Ferrous metals cause the most damage inside the engine. (A regular magnet won't work; only rare-Earth magnets retain their strength as temperature rises).
4) One thing I wish i had thought of before using the Head Sealer is re-torqueing the cylinder head bolts. I recently saw a Subi engine that failed due to this. I realize they are completely different engines but I believe this one was modified for higher-compression. At 13:1 (US engines) and 90,000 miles, I believe it is worth considering.
Has anyone checked the torque on head bolts for the 2.5 non-turbo SkyActive?
Do any of you Gurus know the torque spec and tightening sequence?

Once I find this information, I'm planning to start well-below the spec, increase incrementally, and determine which ones ones are loose (if any), and by how much. Of course, I'll share my findings immediately.
 

Attachments

  • BlackstoneMazdaMay22anonymous.jpg
    BlackstoneMazdaMay22anonymous.jpg
    181 KB · Views: 122
Head bolts are torque-to-angle using 4 passes, which means that the final torque value is not known and cannot be checked using a torque wrench. However, given that you found zero leak down, IMO the probability of finding a loose head bolt is basically zero as well, so I suggest just calling them good.

But if you feel compelled to check them, then use 40 ft-lbs, which is just 6 over the initial (non-angle) torque, and should not be anywhere close to approaching the actual final torque. As previously stated, doing this will not confirm that the final torque is correct, but it will tell you that none of them are significantly loose or 'backing out' (which again was almost certainly already confirmed by your leak down test results). Sequence is basically inside-out, but won't matter with this low torque setting, which won't do any actual torquing.

You don't want to ever 'experiment' by trying higher torque settings on head bolts, because if any of them are turned beyond the final torque, that might cause a much larger problem than you currently have now.
 
What I hear you saying is.......
Zero Leak Down = Leave Them Alone!
Thanks, edmaz - I'll take that advice!
 
From reading your posts, it sounds as if a miniscule leak that is not visible to the naked eye is considered "Severe" by UOA analysis standards.
And that by the time one can see signs of antifreeze in the oil or vice versa that it is probably too late to save.

Never had this happen on any of my previous vehicles but with the potential for these Mazda engines to have this problem,

Sounds like all the more reason to get the oil analysis done on a periodic basis even if it's every other oil change.

Thanks for posting your experience and observations.
 
If you're not going to do anything to correct the coolant leak (and I don't say you should or you shouldn't), then you should probably stop wasting money on the UOAs. If it's purely a hobby, fine, but if it's about detecting trouble or being able to make proactive corrections (which you're choosing to not do), that's basically never cost-effective on personal automobiles.
 
...or maybe the first lab report report was simply a glitch. I've used Bars leak before, I can't see it fixing a high compression engine.
 
The UOAs are not a waste or a hobby (or a "glitch"). They have saved me about $5k (new engine) by detecting a problem and fixing it in the most cost-effective manner. This is not a one-time decision. Every time I receive results, I reconsider the factors and decide what to do going forward. As evidenced by my July '22 post, the Bars Leak was effective enough to correct the coolant leak, or at least slow it enough to allow this engine to achieve a normal service life.
 
your experiences seem pretty similar to mine so far. I'm wondering if it would be worth it to bypass the heater core (probably don't need it much here in summer lol) just temporarily, while using the Bar's product. Might save the heater core from getting stopped up and reducing efficiency.

Out of curiosity, how were you able to estimate the 50% efficiency reduction after using the stop-leak, and the increase to 80% after the chemical flush? Did you check vent temperature output with a thermometer before and after using the stop-leak, and before/after the chemical flush?
 
Bypassing the heater core is a brilliant idea - I wish I would have asked the shop to bypass mine.
The heater effectiveness estimates were purely my best guess. I remember that the ambient temperature was quite different after the flush, so I didn't measure the output temps. I wish I had noted both because Temp Rise would have been accurate information.
In my engine, the results of zero leakdown and negative Block Test tell me the leak is not related to the head or head gasket. I don't pretend to know where the leak is but suspect the base of a water jacket. This goes along with the observation that oil (under pressure) is not getting into the coolant. Even a tiny amount of oil would produce some visible sheen in the reservoir. There has never been any.
It has been suggested that the leak is a tiny crack that seals when the engine is at operating temperature. If that is the case, number of starts (heat cycles) would be more important than number of miles driven between oil changes.
I hope this info helps as you decide how to proceed.
 
I'm still trying to decide what to do. Everything I've learned and heard over nearly 25 years of working on my own vehicles, tells me to never use any sort of "stop leak" product, but in this case it might be warranted. I think I would bypass the heater core, and also go ahead and replace the entire radiator after flushing it all back out. In the grand scheme of things, a new OEM radiator is pretty cheap compared to the time and money to replace a head gasket.

And if I did go through the trouble to pull the head off, besides the cost of all the various seals and o-rings (probably timing chain and guides too since I'm in there) I would need to get in addition to the head gasket, there's no guarantee that the miniscule crack in question isn't in the actual cylinder head or block itself.

*edit* also looked up FilterMag, seems like a good idea but HOLY CRAP $130+ for a couple of sets of magnets that stick onto the filter housing! That seems insane.
 
Last edited:
How about just let it ride, change oil more often and monitor to see if the condition worsens?
 
Yeah possibly. I’m just wondering if I should switch to a different oil or different viscosity other than the OEM Mazda Moly 0w20 oil I’ve been using the past 6 years.
 
Yeah possibly. I’m just wondering if I should switch to a different oil or different viscosity other than the OEM Mazda Moly 0w20 oil I’ve been using the past 6 years.
IMO, you should try DaveIndy’s way by using Bar's Leaks Cylinder Head Fix and bypass the heater cord first. This’s the cheapest and easiest way trying to stop the very minor coolant leak on your 2.5L NA. Another reason is for such a minor leak you may not be able to find anything after you took everything apart. And reuse the cylinder head with new head gasket and seals may still not be able to stop the minor leak you currently have. Bar's Leaks Cylinder Head Fix should reach and seal the leak area wherever it is by itself, and it may have more chances to fix your problem.

I just don’t think using a different oil would help your engine situation.
 
Well for one thing a regular commercially available synthetic oil like Mobil1 would be considerably cheaper than OEM, and easier to get.

Also we just did our vacation trip and I saw ZERO evidence of coolant loss. I’ll change the oil again soon and get it analyzed to see what it shows.
 
Well for one thing a regular commercially available synthetic oil like Mobil1 would be considerably cheaper than OEM, and easier to get.

Also we just did our vacation trip and I saw ZERO evidence of coolant loss. I’ll change the oil again soon and get it analyzed to see what it shows.
I’m using the Mazda Moly 0W-20 oil as well since new. The price from my dealer isn’t too high ~$7 per quart but that was a couple of years ago when I bought 2 boxes. Considering the OEM parts price from Mazda has been skyrocketed in recent years, not sure the current price for it now. I plan to switch to a GF-6 / SP oil such as Castrol Edge 5W-30 after I use up my moly oil stock.

I saw your posts in another thread, and it’s great you can’t see any sign of coolant leak during the long road trip. I guess right now you can only keep monitoring the oil and send in for analysis. I believe chances are slim that BlackStone made a mistake on your UOA. You may still have very minor coolant leak that you can’t see any obvious symptoms. It could get worse as the time goes by. Your next UOA should give you more confirmation on your problem.
 
Like you, I never imagined using any kind of "fix in a bottle" product in a modern engine. I decided to (not saying you should) after discussing the coolant-in-oil situation with a good friend who has been building race engines for 25 years. He said that they sometimes have customers who choose this option when faced with a rebuild (current average $40k) or when parts are no longer available for a classic engine (Offy, Cosworth, etc). They have had surprisingly good results. Of course, there are no heater cores and the radiator issue is easily solved by precise temperature control on a dyno.

I agree with HyFlyer's suggestion that managing the leak with oil changes is an option to be considered. I wasn't able to see your UOA report so I don't know how serious the concentration of coolant is in your oil.

My latest report is attached, a total of 7,000 miles since using Bar's Leaks. It seems that Potassium in the teens (ppm) is out of the danger zone for bearing wear. Not sure about Sodium as I'm not there yet. As Blackstone guessed, the fluctuation in K and Na is because I used Mazda coolant to top -up after the flush but the shop obviously used another brand (It is important to fix this since mixing different brands can result in an undesirable pH - ie: rust inside the engine).

Your experience level is evident in your posts, so I know you'll keep the oil change intervals very short, at least until you have a fix in place. I hope my posts/data help you through this situation.
 

Attachments

  • BlackstoneCX52023Anon.jpg
    BlackstoneCX52023Anon.jpg
    182.6 KB · Views: 48
Unfortunately my last report showed higher potassium than yours ever got (in the 400's), but sodium never got as high as yours. My iron levels have been running higher than yours since I started getting reports in 2019, but that's likely from excessive idling time from my wife sitting in the school pickup line for an hour every school day. I hate that she let the car idle for so long so often.
 
I have a different vehicle that has high Iron for a similar reason (remote start and warm-up in the driveway during cold mornings). I've seen identical results at the end of each of the last 2 Winters - 31ppm iron. The universal average for that engine is 18ppm.
If your numbers are significantly higher than that, it is likely the coolant in your oil is causing premature bearing wear not school-line idling.
Hope this gives you some reference going forward.
 
I have a different vehicle that has high Iron for a similar reason (remote start and warm-up in the driveway during cold mornings). I've seen identical results at the end of each of the last 2 Winters - 31ppm iron. The universal average for that engine is 18ppm.
If your numbers are significantly higher than that, it is likely the coolant in your oil is causing premature bearing wear not school-line idling.
Hope this gives you some reference going forward.
I was getting 14 to 20 ppm on iron for as long as I've been getting the oil tested. 25 this last time which they said was likely due to the coolant not lubricating bearings as well as oil does.
 
Back