Have a look at ASK HJ on this site.

Google Mazda Diesel failures, Mazda Diesel reliability,.......................

You will get people with fully serviced cars - under 5 years old and reasonable mileages - write-off engine failures. The older they get the failure rate increases as you would expect with any car

I do agree that you may be lucky but that is up to you.

If it is the car of choice and you can stretch the budget to a brand new car, 3 year warranty and then sell is probably the best route.

I found a summary in YouTube comments:

"This is a known fault with the mazda 2.0 and 2.3 diesel engine. The injector seals are not great and let gasses pass by which causes carbon build up in the engine which finds its way into the sump, which then blocks the oil pickup. When the oil pick up is quite blocked it stops oil getting to the furthest piston which is why piston 4 tends to fail first. It is recommended on every oil change to check the oil pickup to make sure it is clean. Of course most people will never check this as other engines do not suffer with this problem. It does look like the oil pickup was heavily blocked. If you check the material build up it will likely be carbon deposits. This is just what I have learnt from having a Mazda 5 2.0 diesel and alot of time reading other peoples posts on the web."

- @AimeeSmart84, YouTube.

...but no reasons or stats or even stories about why. I think Mazda offer two diesel engines in the CX-5, paired with a manual or auto transmission. The car is high on my shortlist, so I need to find out why they have this heresay around them.

I'm considering diesel because most of my driving is long distance and I find petrol engines feel weak and need a lot of gear shifting. I'm not yet convinced the mild-hybrid skyactiv petrol engine will be enough for the car.

Indeed have a look at other discussion threads and the reviews section (Good & Bad part in particular) for the car and other Mazdas that use the same engine.

The problem mainly comes from how such cars are used, because they (IMHO) appear to be far more sensitive to predominantly low distance driving from cold, plus the driver switching the engine off during a DPF active regen, which seems to cause oil dilution and its serious knock-on effects, plus the usual DPF clogging.

Whilst keeping an eye on the oil level and make-up, changing it more often and never switching the engine off during an active regen will certainly make a big difference, this would have to be done throughout the car's working life in order to stand a reasonable chance in avoid the engine problems it can suffer from.

For the second hand buyer, that requires the near impossible task of knowing every previous owner well enough to guarantee either the car was either driven as intended (predominantly longer trips and no active regens stopped) or the above significant mitigations if driven otherwise.

For the from new owner, the onus is on them to drive / look after it in a sympathetic way.

If you feel that the petrol version of the CX-5 isn't suitable, given the 2L skyactiv-G (especially in TC auto form) is more suited to the smaller / lighter / more aerodynamic Mazda3 for faster driving (a shame they haven't paired the CX-5 to the more powerful 2.5L SA-G or the newer design, better mpg 2L SA-X engines), then perhaps something from another make might be in order, paired to a diesel engine that is more reliable (e.g. the 1.6 from Honda) or a petrol engine that is powerful enough and still efficient, such as the TSIs from VAG.

I'd watch out for dual clutch transmissions though, at least when buying second hand, for similar 'usage' related reliability reasons.

Also bear in mind if you are buying second hand (you didn't indicate age / budget), and especially a diesel, that it would need to be EU6 compliant (from new) to be able to drive into an increasing number of major UK cities in the coming years (either at all or without significant daily charges), not just London.

That means approximately engines coming into production around 2015 (check for compliance), whereas a petrol car currently only needs to be EU4 compliant, a standard from 10 years or so earlier.

That gives far more options, especially at the moment where second hand car prices are on average about a third higher than before the 2021 price rises casued by shortages of new cars being built due to the pandemic lockdowns.

The answer to your (implied) question is: how lucky do you feel?

There must be many (perhaps even most) Mazda diesel owners who have no problems. As has been said elsewhere in this thread, buying new and treating the engine optimally is your best bet, avoiding the scenarios that seem to bring out the worst in these engines.

The CX-5 is much better to drive with the torque of a diesel and the car handles so well it is almost crying out for that extra push. That said, the petrol version will shift pretty well if thrashed, but that hardly leads to a relaxing driving experience.

When I bought my CX-5 (second-hand) I studiously avoided the diesels. My driving style these days is pretty much just floating along, maximising fuel consumption, so I am fine with the petrol version. It has proved a lovely car to own and drive, needing only four tyres and rear discs replaced in the seven years I've had it. It has been entirely fault-free in that time. It is now nine years old, still on its original battery, exhaust etc.

Edited by FP on 11/08/2023 at 14:59