1998 Merc EFI 225 hp overheating. HELP!

[csmith1951]

Just bought a 98 mercury 225 hp efi and it is overheating pretty quick. I took the lower unit off of it this weekend and the water was all intact and the impeller is pretty much brand new.

Once I get the boat on plane and run it around 50 mph at 4000 rpms, the temp gauge stays around 200-220 degrees. My low oil/ high heat light will come on and flash 3-4 times then turns off. If I continue to run my motor will lose power and stall.

Has anyone every had this problem, any answers or suggestions?
Is this a common problem in this model merc?

Thnaks

 

[Faztbullet]

What type of hull is it on??? Has it had the t-stat update? Post pic's please...

 

[jerryjerry05]

How old is the impeller?
"pretty much brand new" ??
​If you go to all the trouble to check it?? you should replace it.
Pull the thermostats and see if they are clogged.
​On the stbd. side is a pressure relief.
Pull that and see if it's clogged.

​

 

[csmith1951]

It is a fiberglass astro 21 foot 1996 bass boat.

The impeller is less than 3 months old but has only been in the water 7 times since them, 5 of which are me. I just bought this boat 3 weeks ago. I have no had time to tear apart the motor yet. This weekend I am going to replace the t stat, the impeller I know is fine because I took it out of the lower unit when I first bought it to check it.

The boat isn't peeing like it should be. There just isn't much water pressure and I don't have a pressure gauge. With rpms the temp raises and pressure raises (as it should), then once I idle the motor for a few seconds the water temp decreases fast.

Is there anyway for me to check for blockages through out my entire cooling system?


My current ideas for fixing the issue
t stat
new fuel lines
emptying both gas tanks and oil, to replace with all new and add c foam

Thanks for replying! Please feel free to add any input or advice!