496HO manifold over heating
 

Port manifold on Starboard engine over heating to 190 degree , computer reducing power to 4%.

Sea water pressure only 3psi

Starboard manifold staying cool at 125 degrees, engine staying cool too.


Have tried:

inspected impeller (only 10 hours since new)
new sensor
new valve
back flushed
switched pcm with other engine
hooked mechanical pressure gauge, same result, sea water pump only has 3psi (other engine is 12psi).


I don't understand how it only has 3psi but the engine and starboard manifold is running cool.

Thoughts?

Thanks

3psi at idle is normal for the water pressure.
Does it go up with RPM?

You may have a worn SWP housing.

What rpm is your 3 psi water pressure reading ? At idle or above, water pressure reading increase with rpms if everything is correctly working.

Mercruiser at dead idle recommends a bare min of 1 psi for water pressure readings. It is posted in their service manual. When I carried new boats that had smartcraft gauges the normal readings from new boats were 2.2 to 3.5 psi of water pressure at dead IDLE from every single boat especially for the 496.

Your problem might be the sensor in the manifold itself.- its called EMCT - Exhaust Manifold Coolant Temperature sensor.

You have a fault code in your scan - what is it also look into fault history and report that.

Bump up the RPMs when you first start engine, just went through this. Had a sea pump that was a little slow to prime. Or like BUP says change the sensors, if they are the old style (plastic) they go bad all the time. So I would change them anyway.

Replaced EMCT. Manifold is much hotter to the touch then the other.

Sea water pressure is less then 2psi @ idle, only increases to 3psi at 3,800rpm, then the engine power is reduced to 4%

You have a water flow problem. You should pull around 15 psi at that RPM or so. Your Guardian is kicking in due to low water pressure.

I am no where near an expert on the 496s, but from what I learned fixing my problem if you have wear on the plates on the pump, its bad. Hardin marine time.

inner transom input hose connection and or connector check that out also. If the hose that comes of that (input hose) is to long it can kink so make sure there is no kinks in it or any hoses. Also you might want to hook up some clear hoses to replace the cooling hoses to see if you have air entering into your water flow plus its an easy why to check flow volume. It can pinpoint the area that you have an issue as you test certain areas thru out.. Mercruiser calls it the clear hose method for testing cooling problems.

Like above said housing wear hurts the flow bad from the Gen VII pump and last year Mercruiser came out with SB about the impellers were off spec with the tolerances. If you bought your impeller this year you are fine. Which brand impeller did you use ? OEM or aftermarket ?

I'm guessing your sea pump housing is scored and needs the rebuild kit with the stainless plate.

Already has the stainless steal plates. Can I just keep replacing the plates?