It is a vacuum line.
This memeber has a similar issue.

1.5D What for is this vacuum line on the valve cover? | 2004 to 2020 Mazda 3 Forum and Mazdaspeed 3 Forums

 

Thank you 👍. So I presume I can just leave it. It's still working. But would have preferred it if the garage actually fixed the problem in the 1st place. Thanks again 😊

 

This is part of the crank case ventilation system and should not be blocked. Doing so can lead to excess crank case pressure which will cause oil leaks. Tell the garage to fix the problem, not mask it which will cause other issues…

 

 

Thank you very much. The cars warranty was last year so the warranty will be out now. I won't make the mistake of going to those cowboys again. How much S.UKbiker would I expect to pay to get this sorted. TIA.

 

Sorry, I can’t answer that, partly as it’s not known what the problem is. Personally I’d try a Mazda specialist, even if it means travelling. Have a look at YouTube: Mr nice guy - he has built his business around these cars.

 

Thanks again I will take it Mazda. I will need to write a review on the garage that sold it to me 🤬

 

Thanks again. I asked a mechanic at work and he thinks there is a type of gauze in the ventilation system which might be dirty and clogged up. There is a Mazda dealership 10 miles away from me. I will take the t there 👍

 

Other turbocharged diesel engines have what is effectively a one way valve in the crank case ventilation system, (which works on a vacuum from the intake side of the engine) as there’s actually a pressure (not a vacuum) in the inlet system most of the time. PCV valve? Hope your Mazda dealer / mechanic proves to be a good one and sorts it out for you.

 

It's going to be costly. They are getting back to me tomorrow. This is the bill so far

 

Told them to put it back together. All together it was going to cost over £5000 and even after that they told me it might not be fixed properly. To get the top picture done cost me£780. It is now on the way to being sold for half the price I paid 8 months ago.