1999 Merc optimax alarm

[zimnucks]

Ive got a 225 optimax and when i run at WOT the overheat alarm comes on , on ocassion if you go into neutral then it will stop or I have to restart the engine . This only happens after about 1-2 miles .I changed the impeller , thermostats , checked the poppet valve and changed the water pressure sender today but have not run it yet . If I keep it at lower RPM then I dont have this problem , any ideas ?

 

[racerone]

Blown head gaskets can cause overheat as well.

 

[zimnucks]

I agree but the engine is not overheating just the alarm coming on and if I keep running the engine then the Gaurdian kicks in .

 

[guyjg]

...but the engine is not overheating...

How do you know? Do you have a temp. gauge? If not get a laser thermal temp. gauge and take powerhead temps. A water inlet blockage will reduce water flow.

 

[Docksidemarineservices]

Also, do you have a flush adapter screwed to the back of the engine? If yes, get rid of it and put the plug back.

Have you ever overheated this engine?

 

[nixes mate]

If you are certain its not overheating, (the laser/IR prob as recomended works great) then check the alarm sender.

Nixes mate

 

[zimnucks]

I cant say for sure that it never overheated before , there are no signs of overheating . I will remove the hose adapter and run it tmr . Thanks for the post

 

[Docksidemarineservices]

I cant say for sure that it never overheated before , there are no signs of overheating . I will remove the hose adapter and run it tmr . Thanks for the post

While you are running it tomorrow with the hose adapter removed do like "Guyjg" Suggested and bring along a IR temp gun and a friend to pilot the boat. If the alarm sounds, check the temp on the engine while running. Check both heads and the engine block on both sides.


Problem on this engine with an over heat is.....There are plastic temp sensors screwed into each head. They melt when you over heat.

 

[zimnucks]

I did check the sensor on the compressor but not on the heads . I will check the temp tmr , thanks

 

[Docksidemarineservices]

I did check the sensor on the compressor but not on the heads . I will check the temp tmr , thanks

Sent you a PM with a link.

 

[zimnucks]

thanks for all the help it was the water pressure sensor at the end