After having a common-rail diesel car with low mileage who broke 4th injector, and one year after the 1st injector, I tend to be suspicious about the system.

It features a deposit where fuel is at thousands PSI of pressure, which has the injectors immediately after in the pipeline, so it makes me think it wears too much the injectors and puts them under very heavy stress!

I've read:

All seem to accompany my direction of thought.

So my question is: Is the common-rail system unreliable by design?

2 Answers 2


Earlier diesels had separate high pressure pipes to each injector and injectors still failed. The conditions injectors have to work in and what has to be achieved (in terms of spray pattern and spray duration) require them to need servicing / replacement eventually.

Some components will fail early - you don’t mention mileage but some cars can need injectors at 70k miles while others are still fine at 240k miles. I base this on my car and the other forum contributors and their experience...

The general opinion seems to be that cheap fuel will kill injectors earlier, while quality fuel helps the lifetime. Using a fuel additive to help improve the lubricating properties is a common practice : about 1ml of a low ash two-stroke oil per litre of fuel is a common measure.

And, no common rail is not unreliable by nature - we now expect longer servicing intervals as the norm and greater reliability.


I once read an article in a car magazine about the facilities to repair common rail injectors. The facility needs to be especially clean, almost like a semiconductor cleanroom. What I found useful was that there is such a facility in my country, Finland, that has only 5 million population.

I've never heard anything about facilities to repair gasoline injectors. Presumably because they don't exist.

Based on this, there seems to be demand for repair facilities. The reason is two-fold: firstly, the injectors are so expensive that repairing them is more cost-effective than replacing them, and secondly, there is a continuous supply of failed injectors from diesel-powered cars.

I wouldn't buy a common rail injected car. The failure of injectors is only one reason. I would be concerned also about exhaust gas recirculation, turbocharger, dual-mass flywheel, diesel particulate filter, selective catalytic reduction, etc. None of this is a problem in a naturally aspirated gasoline engine.

The fragility of diesels is evident by what happens if you accidentally put gasoline there. If you somehow manage to put diesel in a gasoline powered car, the damages are much smaller, despite the fact that diesel has lower octane number than gasoline.

  • Can’t make cars idiot-proof : putting the wrong fuel in is hardly the manufacturer’s fault - and they do try with different nozzle sizes and filling holes...
    – Solar Mike
    Apr 28, 2018 at 7:34

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