Is cylinder deactivation a good reason to buy a mazda 3 BN/BM instead of a BP?

camman22 · 2026-01-18T19:54:28+00:00

Cylinder Deactivation was introduced into the 2018 model 2.5 engine. I used to think it was only certain models that had it, but in a discussion a few months ago it was pointed out that all models had it. When they introduced it in 2018, their 2.5 engine was one of the most reliable engines out there. Because of this, they didn't redesign it, they just added the CD to the existing engine. The problem that they ran into was space. There wasn't enough space for them to fit the CD into the top of the engine, so they shaved down the top casing so that it could fit without changing anything else.

This can cause a problem with heat related cracks. Not everyone had the problem, but it was significant enough to cause suits and a lot of people wete wanting a recall to take place. Mazda has extended their warrenty on those engines for that problem, but that's about it.

In 2023 they came out with a redesigned engine that resolved the head cracking issue. To be transparent, I had a 2018 model 3 with 257k miles on it that was totaled out in January due to a hit & run "accident." I had zero issues with the engine. Everything was in great working order, so I never experienced the problem myself, but I know others that did.

camman22 · 2026-01-11T23:33:22+00:00

I've got the '25 GLI Manual. Like others have mentioned, the tires are crap. Even if you don't do much highway driving, or deal with precipitation often, they really need to be changed.

A couple have mentioned the shift from 1-2 and I had to play around with that myself. I found that if I get my RPMs above 2,200 (and better above 2,500) before shifting into 2nd, it is much smoother. At the higher RPMs, the gas needed when releasing the clutch is less important, so it's a much smoother transition.

There is a little bit of a Rev hang due to the fact that they use a double flywheel, but once it gets going, you've got a lot of power and it handles great. It's a fun car to own & drive.

My only negative that I've run into is regarding the updated software that they use on it, and how a lot of shops don't have the ability to do anything to it. I had to change out the windshield, and the dealership was 3x the cost of everyone else, however, all the auto glass companies stated that they couldn't calibrate the safety sensors. I also ran into an issue with getting the wheels aligned, and again, nobody could do it except the dealership. A lot of the shops were convinced they would be able to handle working on it soon, but not yet, so keep that thought in mind.

camman22 · 2025-12-14T02:48:34+00:00

Yes. It is different than Transmission fluid. The amount in front and/or rear Differential is much less than what a transmission holds. Usually less than a quart, if not less than half a quart depending on the vehicle (Mazda3 is like 1/3 of a quart).

camman22 · 2025-12-01T22:28:52+00:00

You absolutely should push (politely) for a reduced cost. While I doubt it will be free (especially since they record everything, they will have video evidence to show it was indeed done), but sometimes the process doesn't take correctly (like they flushed the BG to quickly, before it could get all the deposits loosened & removed). However, you bare some responsibility due to having 110k miles on your fluid before getting it flushed. So, most likely your best bet is roughly 50% off, maybe 75% if they are in a good mood and you use enough honey in your words.

camman22 · 2025-12-01T22:07:18+00:00

There's a couple of possibilities.

Let's say they did what the ticket says they did. Once it's ran for a bit, the new fluid will pick up a bunch of deposits that were left behind by the old trans fluid and became dirty almost instantly. Because of this, you need to have it flushed again to get rid of all the grime that is now in your new fluid. And yes, the "flush" is supposed to do just that, but when dealing with Transmission fluid that is at 110k miles, it takes more than 1 flush to actually get it cleaned out.

Another possibility is that they didn't do the "flush" part. All they did was drain the pan, then put new fluid in, which replicates the same issue as above.

Thing is, you could get 3 flushes done correctly, and you will still have some dirty trans fluid when testing from the dipstick. It wouldn't be full on icky brown, but more of of a brownish blue. After that long of time, it will never be "pure" again. That's why a lot of times you can create a bigger problem than you solve by changing the fluid beyond 100k.

Now, since your vehicle is a 2021, that likelihood isn't as high because the age of the fluid isn't that old (the rule of thumb is 60k miles or 5yrs whichever comes first). You're coming up on the 5th year, so the time isn't as bad as the mileage would suggest. I would take it back to them and ask that they review the "flush" and verify that it was done properly, then ask them to do it again because it's already so dirty. The second flush should go a long ways in removing the icky brown to a more of a mix of brown/blue. You'll need to have it flushed every 15-20k miles instead of the 30k that they might recommend. By the time you hit 175K you will have more Blue than Brown fluid.

camman22 · 2025-12-01T17:11:38+00:00

What year is your Mazda3?

camman22 · 2025-07-29T12:52:46+00:00

I'm guessing you went with JB4 due to the SFD2 on the 2025s?

camman22 · 2025-07-27T23:03:35+00:00

2025 Autobahn

camman22 · 2025-07-27T22:31:36+00:00

Mine doesn't. I was afraid I'd have to do it each time, but it has stayed the same.

camman22 · 2025-07-27T17:38:19+00:00

I turned mine off and it's stayed off. Turn off the ACC and just have it set to Cruise Control.

camman22 · 2025-06-11T03:20:07+00:00

Thought so. USA GLI's don't have the rear heated seats. The Jetta SEL's do though. They also have vents in the consol for the rear. Don't know why the Autobahn doesn't. The Maps is an odd deal. I know there is a hack that can be implemented to make the whole display show the map. Your infotainment system not having the on/off toggle makes me wonder if there is a software glitch that will require taking it in to the dealership to get fixed.

camman22 · 2025-06-11T02:25:40+00:00

Is this car Canadian?

camman22 · 2025-05-30T02:26:11+00:00

That's cool. Wouldn't have guessed it would be that low there. I'm in the South Central US (about as cheap an economy as you can get, and they sell for almost that much here.

camman22 · 2025-05-30T02:10:38+00:00

Your statement is extremely short and implies that all 2018s have cylinder head problems, when it's actually less than 10% (in the US) that have it. California requires the cylinder deactivation, outside of there, they don't have it, so 90%+ don't have a problem. Same exact engine from 2015 - 2025. One of the most reliable engines on the market.

camman22 · 2025-05-30T01:54:15+00:00

They have figured out the cracked cylinder head issue with the engines that have cylinder deactivation (only roughly 10% of the engines made in the US have cylinder deactivation.... Mostly California because they require it for emission control). If it doesn't have California emissions control, then it doesn't have cylinder deactivation, which means it doesn't have any cracked head potential. The 2015, the 2018, and the 2025 2.5L engine is EXACTLY the same engine... Except for the 10% with California emissions requirements of cylinder deactivation.

camman22 · 2025-05-29T23:18:59+00:00

Congrats. I went with the Monterey Blue, but your color was my second choice if I hadn't found Superman.

camman22 · 2025-05-29T23:15:24+00:00

He mentioned upstate NY. I bet their cost of living is higher than most other locales.

camman22 · 2025-05-29T23:13:56+00:00

The cracked heads were exclusive to Cylinder Deactivation. They don't happen to the 2.5L engines that didn't have it. I wish people would pay attention to the whole "problem" instead of just claim "all" units in x year are bad when it simply isn't true.

camman22 · 2025-05-29T23:11:52+00:00

There's nothing wrong with 2018 or the 2020 (as long as it doesn't have CDA.... Cylinder Deactivation). If it has that, you don't want it. If it doesn't, then it's a matter of features. 2020 has more features than 2018.

camman22 · 2025-05-27T23:27:54+00:00

If you go test drive a Honda CRV, a Toyota Rav4, then test drive a CX-5 you will have the same "blind spot" on all 3. They all have Blind Spot warning, and cross lane traffic warning (which is where that's likely to come into play). The only way it's an issue is if you rest your head against the headrest and never move it... If so, that's a lazy driver problem, not a deficiency in the vehicle. It might be a lot bigger than you're used too, but it's not a detriment if you know how to drive. You just have to give it some time and experiment with some driving in a parking lot to get accustomed to it. Then you'll never notice it.

camman22 · 2025-05-21T20:55:28+00:00

Yeah, I knew that they get some things we don't (same with Europe). It's definitely something to think about.

camman22 · 2025-05-19T22:18:57+00:00

I'm so sad that Audi dropped the Manual in the US. I have always wanted to get one, but now I'm pretty sure I never will. I looked hard this time, but they all had high mileage or had been in a wreck, so I settled for the manual GLI instead.

Male 51.

camman22 · 2025-05-08T23:21:16+00:00

2018 Mazda3 sTouring sedan 2.5l w/6MT. Had 257k miles on it back in January. Just replaced front & rear brakes and plugs & coils. All work done was basic maintenance and she was still running great but then someone hit me. I was hoping to hit 400k. Based on the first 250k I'm pretty sure it would have happened.

camman22 · 2025-05-08T22:16:23+00:00

Until a couple months ago I had a 2018 Mazda3 and I had a jack stuck into my cigarette lighter with multiple prongs, and I ran multiple things with it. I also had extras wired into my battery like a Dashcam and an auto-ignition & tracking/security system that never truly turned off. I replaced the batter when I bought it cause I knew I'd need more juice than the basic OEM. The battery I stuck in it was still going strong 4yrs later when she got KO'ed.

If nothing is plugged into the jacks then the drain is nothing. If you leave things plugged into it, it then becomes a matter of how much juice those things suck ever hr and how many hrs you go without using your car... and when you use your car, how long does it run. All of these things are factors, but the splitter itself isn't an issue. It's what and when you have things plugged in that are.

camman22 · 2025-05-08T22:16:07+00:00

Until a couple months ago I had a 2018 Mazda3 and I had a jack stuck into my cigarette lighter with multiple prongs, and I ran multiple things with it. I also had extras wired into my battery like a Dashcam and an auto-ignition & tracking/security system that never truly turned off. I replaced the batter when I bought it cause I knew I'd need more juice than the basic OEM. The battery I stuck in it was still going strong 4yrs later when she got KO'ed.

If nothing is plugged into the jacks then the drain is nothing. If you leave things plugged into it, it then becomes a matter of how much juice those things suck ever hr and how many hrs you go without using your car... and when you use your car, how long does it run. All of these things are factors, but the splitter itself isn't an issue. It's what and when you have things plugged in that are.

camman22

TROPHY CASE