1999 175 EFI Overheat Warning Horn

[2000Ranger]

Took my wife and the dog out yesterday in the boat when I noticed the psi was around 5 when the boat was on plane (motor was "pissing" like normal) and before I could react I got a warning horn (the horn was a continuos beep) so I came off plane and shut it down. I took out the owners manual and it said that the long horn was an engine overheat warning so I let it cool off and limped it back to the trailer. I'm going to change the water pump and Impeller, I'm also going to have a mechanic do a full service/maintenance check. My question is what else should I check or change before I bring it to a mechanic? My parents friend is really good working on motors so I can get him to help me, just wondering what else I should look at? The serial number is OG945053. Thanks

[Rip Bass]

May as well check or replace the t-stats and poppit valve while you're in it,especially if it hasn't been done lately.complete water pump kit for sure.

[EuropeanAM]

+1.... ALWAYS, ALWAYS start at the SOURCE: The Water PUMP.

Part# 96148A8

Then, and only then is it appropriate to move out to other components or potential causes.

For information specific to your engine series, see:

Mercury - 2.0/ 2.4/ 2.5 Liter High Performance
For discussions related to 2.0/ 2.4/ 2.5L motors (Carb, EFI, Optimax or Racing).