I was removing the coolant from my engine today for an unrelated job and made a horrific discovery, there is metal shavings in the coolant. What could this be? Need help
Not an MX-5 but I once asked about metal flakes in a radiator and was told that some radiators have an internal coating and it could be pieces of that, so hopefully it will turn out to be nothing to worry about, but someone with more knowledge will no doubt reply 
I do hope that is what it is because I have very recently installed a new radiator.
It could be swarf that has not been washed out when the radiator was made. Are there any threaded holes in the radiator? If so then these may have been tapped out after construction and not cleaned properly.
I wouldn’t know if there are any treaded holes, it is a genuine Mazda replacement from Japan.
Swarf from cylinder head machining is well known issue on Mk1 1.6. They can block the thermostat bypass, causing the engine to run a bit hotter, and the fan to wear out prematurely.
Metal from the radiator is usually just aluminium dust, hence run a hose through a new radiator before fitting.
I wouldn’t have thought that aluminium swarf would be good for the water pump either.
Gah! Why didn’t I think to rinse my new radiator out.
Rookie mistake.
Hope yours is nothing to worry about Xander-T