i think they are pretty reliable for an old car, since its simple design i believe when something goes wrong you can easily find the problem, i have a 4age 16v in mine never had a mechanical failure at all nothing has gone wrong for a long time. My friend had a 4ac which was overheating all the time manage to drive for ages with that engine before he chucked in a 4age, i believe the 4A block is built tough.