Audible Alarm

I started my 1988 175 up today for the first time since last season when it was winterized. There were no running issues last season. The motor ran fine for two minutes then the audible alarm came on. How can I find out whats causeing the alarm? I only have a voltage guage. So in not sure if it's oil injection or temperature causeing problem. When I was running it with garden hose hooked up the water was squirting like a water pistol from the upper part of the outboard like normal operation. The oil tank under the cowling is full. and the volt meter was reading 13 volts. Any help would greatly be appreciated. Thanks Carl

is the alarm one long horn, or is it on-off-on-off?
does it sound as soon as you turn on the key, or does have to run for awhile?
when it goes off disconnect the temp sensor and see if it goes off.(don't forget to rehook the sensor)

Hey Thanks for the reply. The alarm is a steady one. I shut the motor down after 10 seconds of hearing alarn to prevent damage.The alarm came on after 2 minutes of the motor running hooked up to the water flushing muffs. I will chek it Saturday regarding the Temp. Sensor and will report back.