I will start with a little back history. I have a 92 miata as my DD. It has 319k on it. I picked it up at 303k. When I got it I did timing belt, water pump, head gasket, and replaced the radiator and all the coolant hoses.
It has been driving fine for the past 1.5 years fine. When I got home from the Mitty yesterday after driving 5 hours/300miles my over flow tank was gurgling so I popped the hood. I pulled out the over flow tube and this is what I saw.
WTF causes that. My whole overflow tank is covered in it. The car has not over heated at all. It just looks disgusting. I am planning on continuing driving the car since it has not seemed to affect cooling at all.
So my options as I see them are.
1. Ignore and just keep driving until I actually start over heating.
2. Replace overflow tank with a clean one.
3. Replace overflow and radiator.
4. Pull motor and swap in 1.8 and new overflow and radiator.
The future plans for the car have always been to drop in one sort of 1.8, although I was not planning on that until end of summer or fall. Other then that I want to hit 500k on the car.