2024 Mazda CX-90 Pricing and Specs

Mazda (and other car-makers) have been having lots of problems with the oil level rising in the engines of some of their diesel models. The problem is caused by the Diesel Particulate Filter attempting to regenerate itself. In an ideal world, these diesel vehicles would be driven for at least an bour or so at freeway speeds at least once a month. That would get the exhaust system hot enough for the DPF to regenerate on its own (burn the contaminants from the exhaust to ash and expel them, basically).

But in cars that don’t see this sort of use and are more commonly driven around the suburbs at moderate speeds, the exhaust never gets hot enough for this to occur. So, the solution has been to inject extra diesel into the engine to make the exhaust hotter and, therefore, get it all to a temperature where DPF regeneration can occur. The problem is that some of that diesel can get into the sump of the engine where it dilutes the engine oil. And that’s why you’re seeing the level rising on the dipstick over a period of weeks and months.

Diluted engine oil is bad news because it may not lubricate and protect the engine as well as non-polluted oil. The warning light you’re seeing is telling you that you might be at that point and that an engine oil change is probably a good idea, even if the service interval hasn’t been reached yet. Just draining some of the contents of the sump away is not the answer as the oil is already diluted by the diesel.

It’s a bit silly, isn’t it? There’s absolutely no reason for a speedo in an Australian delivered car to read to 260km/h, particularly in a car that would never manage to gain that much velocity without the help of a mine-shaft. There’s no ADR requirement for it, either, so it’s probably a hang-over from other markets where average freeway speeds are much higher than they are here. In Germany, for instance, where there are still unrestricted sections of autobahn, the 200-plus-km/h speedo makes more sense.

You’re probably right when you suggest this is all a one-size-fits-all approach by Mazda (and many other car-makers) who can save a few dollars by making only one speedo calibration and fitting it to cars for every market. More recently, a lot of cars have both a conventional and a digital speedometer fitted. Many owners have come to rely on the latter for clarity. My preference is for an analogue (needle) speedometer that has 100 or 110km/h at the 12-o’clock position on the dial.

This is a really common problem with this model (and the Ford Ranger with which it shared its mechanicals). Many buyers avoid this model for this very reason. Even though many fixes have been tried it seems that this car, shown a hill and a hot day, will often overheat.

Several theories exist including that the EGR valve is the problem, as it fails and allows coolant to escape (usually into the engine cylinders). But even when the EGR valve is working properly, this engine is prone to running too hot. Some other theories hold that the thermal management of the engine itself was just underdone and there’s no real fix for it. That’s borne out by the number of people who have tried different radiators, thermostats and cooling fans and still have a vehicle that overheats.

But you could try reverse flushing the radiator and making sure than every part of the cooling system is working efficiently and properly. That will maximise your chances of not having the engine overheat but, in this case, there are no promises.