Engine Coolant Reservoir Level Low, maybe leaking? 2018 CX-9

[copofop]

I have a 2018 CX-9 AWD with almost 31k miles. Just recently found out about the cracked cylinder head problem on this forum. Out of curiosity, I checked the engine coolant reservoir level on mine while the engine was cold and found that it's right at the low L mark. I opened the radiator cap and saw the green coolant in there which is good, so at least the radiator is full. The car has never overheated on me, but I'm concerned now that I might be at the early stages of this cracked cylinder head problem.

I bought the car new in December 2017, so I've had it for almost 5 and half years. Is it typical for the engine coolant reservoir needing to be topped off all the way to the full line in that much time or could I have a slow leak developing? I do my own oil changes and maintenance, but can't say I really looked closely at the engine coolant level all these years since I know it doesn't need servicing for like 120,000 miles. I should've kept a closer eye on it. I do know that I don't have any external signs of a leak because I removed the large cover under the engine to get eyes on the transfer case as I'm planning on changing that oil soon. I didn't see any fluid stains on the inside of the large cover, nor do I have fluid stains on my garage floor where the car is normally parked.

 

[Zoom49]

. Is it typical for the engine coolant reservoir needing to be topped off all the way to the full line in that much time or could I have a slow leak developing?\

On our 2017 we had for over 6 years, I had to add
coolant twice about 1/2 reservoir each time. With all the underhood heat, I felt it was just evaporation. Never had any coolant smell under the hood.

 

[Bronco Boy]

I checked the engine coolant reservoir level on mine while the engine was cold and found that it's right at the low L mark.

Next, check it when warm. Should be at the high mark.

 

[Liminator13]

I have a 2018 that I'm pretty sure suffered from a slow leak but I spent observing for about a year and a half. The levels were rock steady for months and then I started to see it go down very slowly from full to low in about 6 months. Topped it off and it took another 6 months for it to get back to low. Car never overheated and I never saw any coolant on the ground. Took it to the dealership and they confirmed the cylinder head issue and is fixed now.

I was told in another thread to try:

Pull your under cover off and look for dried green coolant crust. Look at the exhaust manifold (between engine and firewall)

If you can't do that (which I could not) then you need to look at the levels when its hot and cold and see if it changes. As Bronco Boy says, with a hot engine it could be at the full level.

 

[copofop]

I have a 2018 that I'm pretty sure suffered from a slow leak but I spent observing for about a year and a half. The levels were rock steady for months and then I started to see it go down very slowly from full to low in about 6 months. Topped it off and it took another 6 months for it to get back to low. Car never overheated and I never saw any coolant on the ground. Took it to the dealership and they confirmed the cylinder head issue and is fixed now.

I was told in another thread to try:


If you can't do that (which I could not) then you need to look at the levels when its hot and cold and see if it changes. As Bronco Boy says, with a hot engine it could be at the full level.

How many miles did your 2018 have when you noticed the problem and the dealership confirmed it? Did Mazda perform the fix free of charge or did they pin it on you? Head replacement or full engine?

I'm going to check the level today after driving the car and the engine is hot and see where it's at. In the owner's manual it does specifically say if it's at/near/below the low level marker when the engine is cold then you need to top it off, so I'm going to the dealership today to buy a gallon of FL22 coolant to top it off. After I top it off when the engine is cold, I'm going to mark where it's at on the reservoir and keep track of it. The wife is planning to visit family 3 hours away this weekend so will be interesting to see where the level is at when she gets back. Thanks for the input, guys.

 

[copofop]

Wife came back from running errands. Checked the dashboard engine temperature gauge and the marker was on the leftish side of the 200F line so the engine was at normal operating temperature. Turned it off and checked the coolant reservoir and the level was about 1 inch above the low level marker.

Heading to the dealership to buy the coolant.

 

[joenintiesc]

How many miles did your 2018 have when you noticed the problem and the dealership confirmed it? Did Mazda perform the fix free of charge or did they pin it on you? Head replacement or full engine?

I'm going to check the level today after driving the car and the engine is hot and see where it's at. In the owner's manual it does specifically say if it's at/near/below the low level marker when the engine is cold then you need to top it off, so I'm going to the dealership today to buy a gallon of FL22 coolant to top it off. After I top it off when the engine is cold, I'm going to mark where it's at on the reservoir and keep track of it. The wife is planning to visit family 3 hours away this weekend so will be interesting to see where the level is at when she gets back. Thanks for the input, guys.

This is exactly what I did on the 2019 i just bought a few weeks ago with 26k miles. I saw the coolant level below the full level line - but then I checked the manual and when cold it's supposed to be in between Full and Low. I marked the actual level with a sharpie, and I'll check it once a month or so.

 

[Liminator13]

How many miles did your 2018 have when you noticed the problem and the dealership confirmed it? Did Mazda perform the fix free of charge or did they pin it on you? Head replacement or full engine?

I noticed the coolant level changing around 55k miles. Went to my independent mechanic first to look at it but they didn't see any issues. Coolant level kept dropping slowly and finally went to dealer at 66k miles and they confirmed it. I have a CPO mazda so they fixed everything for free with a head and gasket replacement.

 

[PTguy]

Don't overfill it cold. If the system was fully hot, such as heavy driving on a summer day, then I'd want to see it at the Full mark. You're OK above the Low mark when cold, but do keep an eye on it occasionally, and check the level when it is at the same temperature. Note that the temperature of the coolant in the radiator is not often the temperature of the coolant at the sensor in the cylinder head. The thermostat modulates to send just enough to be cooled in the radiator to keep the cylinder heat temperature near-constant.

 

[copofop]

Okay so after my wife's road trip and a week's worth of local errands and 761 miles later, with the engine cold this morning the coolant level is now a good 3/4 of an inch below the full level marker where I had last topped it off to on April 13th also with the engine cold.

This is a pretty significant drop in level for such a short period of time and miles right or am I wrong? I made sure to be precise with the conditions and levels. When I topped off the coolant reservoir on April 13th to exactly the F full marker line the engine was fully cold and when I checked it this morning the engine was fully cold again not having been turned on since yesterday.

Before taking it into the dealership, do you guys have any recommendations on next steps to try and confirm the coolant leak into the engine? Engine oil analysis? I've heard about some kind of tester you can attach to the coolant reservoir that has a fluid in it that changes color if engine exhaust works it's way into the coolant reservoir and tester? Any links or recommendations on the tester or an oil analysis company? I believe if coolant in the engine is confirmed then Mazda recommends a full engine replacement (is this right?) so I want to make sure I have all my ducks in a row so I don't get the run around from the dealership/Mazda. Thanks everyone!

 

[ctbale]

If it was my car? I wouldn't touch a thing except pulling the stick and checking the oil for color and level.

I wound not add any coolant. Dont pull the radiator cap, just do a visual of the plastic overflow jug

I would take a picture of the 3/4" below full and keep driving it. Or use a tape to get a consitant reading so you can trend the level.

Check it stone cold frequently, parked in the exact same spot before first start.

If you do your own oil changes I think Blackstone is a popular oil analysis lab. I used them 15 years ago but then I was like, this is a waste of time. So what if I have a particular metal that's high. What am I going to do pull the engine because of a soap sample? Nope, I would just change the oil and drive it until it fails. Waste if time in my opinion. But doing a oil analysis in this situation is not a horrible idea because if you catch it right away its just a head replacement vs a long block.

Edit:. You're correct Mazda will absolutely recommend a full engine replacement if coolant is found in the oil but that's not saying they're going to pay for it. you're probably on your own on this one

 

[ctbale]

I have said this on other posts, I someone is gunna loose sleep over this, its not a crazy idea to go buy an updated head ($600) and updated gaskets, find a picky as hell mechanic (like me) and swap the head. You can reuse the valves if its in the lower mileage range if they get lapped in the new head.......CORRECTLY.

 

[copofop]

If it was my car? I wouldn't touch a thing except pulling the stick and checking the oil for color and level.

I wound not add any coolant. Dont pull the radiator cap, just do a visual of the plastic overflow jug

I would take a picture of the 3/4" below full and keep driving it. Or use a tape to get a consitant reading so you can trend the level.

Check it stone cold frequently, parked in the exact same spot before first start.

If you do your own oil changes I think Blackstone is a popular oil analysis lab. I used them 15 years ago but then I was like, this is a waste of time. So what if I have a particular metal that's high. What am I going to do pull the engine because of a soap sample? Nope, I would just change the oil and drive it until it fails. Waste if time in my opinion. But doing a oil analysis in this situation is not a horrible idea because if you catch it right away its just a head replacement vs a long block.

Edit:. You're correct Mazda will absolutely recommend a full engine replacement if coolant is found in the oil but that's not saying they're going to pay for it. you're probably on your own on this one

Thanks for the feedback. I will not be adding anymore coolant. I wish I would've known about this problem before I changed my oil at 30k miles a few weeks ago because I would've caught some of the oil during draining for analysis.

I'm definitely going to be keeping track of the level now and will mark the current cold engine level with a label from a label maker with the date printed on it and continue to do so. If I see the level continue to go down dramatically in next few weeks to month, I'll just do an early oil change, catch a sample and send it off for analysis. Question for you guys, say an analysis comes back confirming coolant in the oil and I present that to the dealership/Mazda. What do you think their response will be? What is their method for confirming coolant in the oil or do they not even bother being thorough to check for that and just slap on a new head and send you on your way?

 

[sm1ke]

The first time you bring the issue to them, they will check the level, fill (if necessary), and then ask you to monitor the level. Then, if the level continues to drop, they will do a basic visual inspection of the engine to look for coolant leaks, and they may pressure test the system. If they still can't find anything, they may do another investigation that involves removing some bits in the engine bay to get a better look at the problem area. If they don't find anything there, they will just ask you to monitor and check the dipstick occasionally.

This is what they would do if your car was still under warranty. Their process may be different with a car that isn't under warranty.

 

[Duke Yugo]

2016 CX-9 with 91,000 miles.
I noticed the coolant level in the tank was consistently low, even after adding more. After a week of repeatedly topping off the coolant every other day, I removed the engine undercover and discovered a messy green residue all over the place. I contacted MazdaUSA and confirmed that my 2016 CX-9 is still covered under the CPO Limited Powertrain Warranty until 7/28/23 or 100,000 miles, which is just about another two months in my case. Initially, I suspected a leaking water pump or gasket when I brought it to my local dealer. However, they informed me that it's actually a crack in the cylinder head. Fortunately, this issue will be covered by my CPO warranty, but I'll have to wait for a week to get the replacement part. In the meantime, I'm using the dealer's courtesy vehicle for free since the loaner car is not covered by Mazda. I'm uncertain about how long I should remain optimistic. I had plans to continue driving my CX-9 for a long time, but now I'm not sure what to expect.