If you don't want a main dealer, then there's a garage opposite the church in Blanchardstown village. Their number is 018203386. I used them for a few years when I lived in the area and found them reliable and reasonable.
Theres a gut in Mulhuddart just beside the graveyard there called Advanced something or other. He's open Saturdays which is a big bonus for a mechanic as its so hard to get anyone to have a look at a car at the weekend.
Dunno the number but im sure if you call up there im sure he'll book you in. Quite reasonable too.
If you go across that little bridge there from clonsilla, go straight up and just before you head right into damastown Ind Est., there is a red and yellow sign pointing to his premises.
There's a guy who works down near the Hospital called Aidan English, who has a good reputation. Think his details have been posted here before, if you search you may find his phone number.
No connection to him myself, my father and brother use him regularly for their car services.
I used a guy few times in Rosemount business park, Alan Gilmore 01 8665997, he came to me recommended and I was happy with work and cost. Used a different guy nearer my house last time and was totally ripped off, so it's back to Alan for me - even if he is 25 miles from me.
No connection only satisfied customer.
Discount Tyres and Auto in Rosemount Business Park are great. Last service I had they did for €60 less than the next cheapest quote. The guys are really helpful up there and have sorted problems for this damsel in distress on more than one occasion. www.tyres4less.ie
No connection at all, just a very satisfied customer.