Just recently noticed that modern engines rarely 'ping' when cooling down after the engine's turned off, I remember as a kid my father's celica (and many other cars from the late 70s, early 80s) pinging very loudly when cooling down for at least a few minuets.
Just curious if the lack of pinging now-a-days is from better engineering ('less NHV'), cooler running engines, or something else?...
Used to be a lot of pinging and cracking noises came from the exhaust system contracting as it cooled. Many catalysts were made with the substrate in direct contact with the case, this caused a lot of that. Later the substrates were wrapped in stainless steel mesh and then put into the case, helping a lot but they still clicked and snapped some due to the welded multi piece construction. The latest ones have the ends of the converter cases 'spun' to shape them, thus eliminating welds and their associated metal stresses. You'll also see 'bellows' in many 'built up' OE manifolds which helped lessen stress cracking and the noises.
My 97 van sounds like popcorn as it is cooling down. It comes from the exhaust as it is cooling back down. If you stop in a rest area off the interstate it will tick and ping while idling.
ah, great info Jensenman!
In reply to Jensenman:
no catalysts on my early cars (50's & 60's)... would it have still been the exhaust system ?
When I first bought it, Miata used to ping from the exhaust system while cooling down. After a while, it just stopped doing it. My hypothesis is that the previous owner's maintenance or driving style contributed, and my "spirited" driving and religious maintenance cured.
Exhaust systems in general were bad about clicking and popping all along. The catalytic converters just made it worse.
When I park the 914 people ask if it burns coal. Air cooleds have a particular ping and smell.
You'll need to log in to post.
