Rad boil over

[dcroswell]

Hi
I have a Zetor 7045. Today while cutting my field the rad boiled over. The engine temperature gauge was at 90 degrees so it wasn't showing it running hot. Any suggestions on what to check?

 

[dave_peters]

1st radiator cap
2nd thermostat
Also, suspect the temp guage sender.
Are the rad fins clear?
When did you last flush out the radiator ?