MM1 Overheating
 

I bought an MBX7 Eco 2nd hand and it came with a Mamba Monster 1 ESC. First race it worked perfectly. On a test day the fan stopped working and it went into thermal shutdown. Now even with the fan working it intermittently goes into shutdown. Today I ran it and the fan was on and it went into shutdown. Tried it again and it ran through a pack.
What is happening? It's really starting to frustrate me.