This engine definitely should have an overheat alarm in addition to a light on the System Check gauge. The fact that you got no warning means that you either have defective temperature switches in both heads, you have a bad warning horn, or you have a wiring problem.
1) When you turn the key to the on position, do you hear a beep?
2) When you turn the key to the on position, do the System Check lights (2" gauge or tach) come on then turn off sequentially?
To test your overheat warning, disconnect your starboard temperature switch from the wiring harness and turn the key to the ON position. Next, connect a piece of wire to the harness side and the other end of the wire to a good ground. Under normal conditions the temp switch is an open circuit, but when overheat is sensed it shorts to ground. This jumper wire replicates the short to ground so you should hear a constant horn and System check gauge should have a light on the Hot/Water Temp. If you have a light on the System Check gauge but no horn sound, you likely have a bad warning horn. If you have neither a light or horn, then it's probably a wiring problem.
