4.3 l tks 2008 overheating alarm

[Larry Baloun]

Serial # 1a312851
It seems like I have tried everything possible to resolve my problem and no change.
Under about 3000 rpm - it runs at about 170 degrees - no alarm. Over 3000 it goes up to about 180 degrees and the alarm comes on intermittently. I know it is the hot alarm because if I detach the wire on the thermostat housing the alarm stops.

I have: 1) changed the heat sensor
2) changed the impeller (which was in good shape)
3) changed the thermostat ...all with Mercruiser parts.

Two question: 1) should it alarm at just 180 degrees - if not, how do I get it to stop
2) If 180 degrees is too hot ...how do I get it to run cooler ...it has always been in fresh water.

 

[Bt Doctur]

Had a gen II drive do the same thing. It was leaking under the bottom gasket sucking in exaust gas when on plane.

 

[Fun Times]

You'll want to try to verify if the temp is truly getting up to 180+ degrees using an infrared temperature gun pointed all around the thermostat housing while comparing the readings to the temp gauge.

While 180 sounds about roughly 15 degrees to low to sound the horn, none the less the gauge is getting past the comfort part and so is the warning sensor system which the 2 sensors are separated from each other.

I'd first suspect you probably have a water flow blockage of debris somewhere inline of the inlet water flow system though other aspects of water flow circulation and water flow out blockage of the engine could cause heat issues too.

When you did the Alpha drive impeller, did you only drop the lower gear case housing or did you pull off the whole drive unit off of the boat?

Did you replace any of the components under the stainless steel wear plate of the impeller?
http://www.mercruiserparts.com/bam/s...30862/2686/140

Also have you done any work to the thermostat housing and base gasket recently?