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Discussion Starter · #1 ·
I discovered a coolant leak on my 2018 Mazda 6 GT 2.5T. It seems to have originated at the plastic "canister" where the radiator cap is attached to. Luckily, there was still coolant left in the reservoir and there are no signs that the engine overheated. However, there are coolant stains all over the bottom of the engine below the side where radiator cap is (which strangely is located to the right of the valve cover rather than over the radiator). My question is if the type of leak that this appears to be has been found to be common for the 2.5 turbo. I know there is a TSB currently out on this engine regarding a coolant leak, but that TSB has to do with leaks associated with the cylinder head and exhaust manifold (cracks in the head near where the manifold is attached), and this leak doesn't appear to be related as the leak is very visible as to where it started or appears to have started. I will take it to the dealer, but just wanted to know if fellow owners (they are more trustworthy than the dealer) also believe (or know from their own experience) that it originated at this "canister" and if anyone knows if this is a common issue for this engine, or, as far-fetched as it may seem, if this is at all related to the leak covered by the TSB. Also, what is this "canister" (for lack of a better term) and what purpose does it serve? The leak appears to have here. See photos below (the last 3 images are shown with the
engine cover off. Any thoughts or help would be much appreciated. Thanks:

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Discussion Starter · #5 ·
That looks like a cracked coolant fill/reservoir/whatever-that-is-called. It ought to be reasonably cheap, I'd expect, which is the good news.
Also, is this a DIY job? This might be a dumb question, but can I replace this without having to bleed the system or clamp off fluid-filled hoses or anything? I wasn't sure, since it's connected to the hose to the radiator.
 

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Remove the underskirt and drain the radiator into a clean container. That should permit replacing that part with minimal mess, and you still have the coolant (assuming its not time to change it anyway.)
 

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What's crazy is the 3 of us are ( you, myself, and Tchrane), are all having the same issue at the same time. My car is just over 3.5 years old and is also a 2018 GT. It seems like just a crappy part that is prone to leaking.

I asked my local dealer and the service manager says it's not covered under powertrain so I am taking it to my local mechanic to replace the part. I ordered the part from the dealership though.

Funny thing is I just got an oil change 2 weeks ago and the issue wasn't there. I only noticed it because I had to boost my car a few days ago after leaving my accessory power on too long. It's a good thing my battery died and I noticed it as the reservoir was bone dry and could have over heated on the highway or something leaving me with a nice tow bill as well.
 

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Discussion Starter · #8 ·
What's crazy is the 3 of us are ( you, myself, and Tchrane), are all having the same issue at the same time. My car is just over 3.5 years old and is also a 2018 GT. It seems like just a crappy part that is prone to leaking.

I asked my local dealer and the service manager says it's not covered under powertrain so I am taking it to my local mechanic to replace the part. I ordered the part from the dealership though.

Funny thing is I just got an oil change 2 weeks ago and the issue wasn't there. I only noticed it because I had to boost my car a few days ago after leaving my accessory power on too long. It's a good thing my battery died and I noticed it as the reservoir was bone dry and could have over heated on the highway or something leaving me with a nice tow bill as well.
Yeah i only noticed it because I saw a few drops on my garage floor. Then another family member took the car out. Good thing mine didn't overheat either. It was really low in the reservoir though. The part was $55 at another online Mazda parts website, but a whopping $85 at the dealer. How much did your shop charge if you don't mind me asking? The reason is, I might want someone else to deal with cleaning the coolant residue from the engine bay, and I need to go into the dealer to have that fuel pump recall done.
 

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Discussion Starter · #9 ·
Remove the underskirt and drain the radiator into a clean container. That should permit replacing that part with minimal mess, and you still have the coolant (assuming its not time to change it anyway.)
Thanks for the tip. I'll have to decide how lazy I am. lol.
 

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Yeah i only noticed it because I saw a few drops on my garage floor. Then another family member took the car out. Good thing mine didn't overheat either. It was really low in the reservoir though. The part was $55 at another online Mazda parts website, but a whopping $85 at the dealer. How much did your shop charge if you don't mind me asking? The reason is, I might want someone else to deal with cleaning the coolant residue from the engine bay, and I need to go into the dealer to have that fuel pump recall done.
I haven't got a price from my mechanic yet but I'm going to in a few days and I'll let you know. My best buddy works in parts at my local dealership so he's going to at least get me a discount on the part. I gotta get my recall for the fuel pump done too but I'm not going to have the dealership replace the filler neck as they charge way too much for labor.
 

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I discovered a coolant leak on my 2018 Mazda 6 GT 2.5T. It seems to have originated at the plastic "canister" where the radiator cap is attached to. Luckily, there was still coolant left in the reservoir and there are no signs that the engine overheated. However, there are coolant stains all over the bottom of the engine below the side where radiator cap is (which strangely is located to the right of the valve cover rather than over the radiator). My question is if the type of leak that this appears to be has been found to be common for the 2.5 turbo. I know there is a TSB currently out on this engine regarding a coolant leak, but that TSB has to do with leaks associated with the cylinder head and exhaust manifold (cracks in the head near where the manifold is attached), and this leak doesn't appear to be related as the leak is very visible as to where it started or appears to have started. I will take it to the dealer, but just wanted to know if fellow owners (they are more trustworthy than the dealer) also believe (or know from their own experience) that it originated at this "canister" and if anyone knows if this is a common issue for this engine, or, as far-fetched as it may seem, if this is at all related to the leak covered by the TSB. Also, what is this "canister" (for lack of a better term) and what purpose does it serve? The leak appears to have here. See photos below (the last 3 images are shown with the
engine cover off. Any thoughts or help would be much appreciated. Thanks:

View attachment 246665 View attachment 246666 View attachment 246667 View attachment 246668 View attachment 246669 View attachment 246670
I had the exact same leak and it was covered under warranty by the dealer.
 

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I just had this issue coincidentally discovered a few weeks ago in July during my annual TX registration renewal check. Fortunately the service dept said the repair is covered under warranty so it was no cost to me, but it's clear the timing of this coolant leak is not coincidental! I'm in San Antonio TX, serviced at North Park Mazda in early July 2022.
 
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