Overheat black max 200

[Karl_Childers]

Greetings,

I have a 1988 Black max 200hp that is overheating. I have a good stream out of the tell tale, but the heads are really hot to the touch. I have no idea if the overheat sensors are working, but I am guessing not, and I don't really know where to start troubleshooting them. Anyway, I pulled the heads and exhaust cover, (and by the way I didn't snap a single bolt) and the heads were really really clean. So was the exhaust chamber other than a little leftover oil. The pistons and cylinders weren't all that carboned up at all. A little, but not much.
Someone before me has removed the t-stats, so all the above information is without thermostats. So what gives?? How hot should the heads get? I heard somewhere that Mercury has some sort of screwey grommet on the water tube at the base of the powerhead that gets messed up and restricts flow. Is this true on my 200hp? Any and all advise/comments will be appreciated.
thank you for reading my long post!!

Rob

 

[red cobia 17']

Re: Overheat black max 200

Have you tryed putting new thermostats in yet? My 96 225 Merc. runs about 140-150 degree's.I would think yours would be in that same ball park.Do you have a temp. gauge on your boat?If so how hot is it showing?Is your overheating alarm going off?

 

[gss036]

Re: Overheat black max 200

A water pressure guage is your best defense and tool to monitor the engine. Check the poppet valve to see if there is one and does it work.
There should thermostats in the engine, they normally open at 143 degrees, that is hotter than you standerd hot water tank in your house, those are normally set for 120 degrees or less.

 

[Rocky_Road]

Re: Overheat black max 200

Have you ever wondered why car owners don't run their engines without the thermostats? Seems like they would run that much cooler...right?

Wrong! Without the thermostat in place, the coolant circulates through the block too quickly to absorb enough of the harmful heat that is generated. The thermostat, once opened, slows the coolant flow to a level that allows the coolant to remove heat from the block, and then exit....

I have to assume that this would be no different for a marine engine block.

Otherwise...why would the manufacturer even bother designing in a thermostat, at all?

 

[red cobia 17']

Re: Overheat black max 200

I think there is a difference between auto and marine.A auto cooling system is circulating thru a radiator and being cooled by air flow going thru it, this keeps the temp at a consistant temp.a marine engine(outboard) does not have a rediator the water is always cold coming in to the engine.Thermostats allow the engine to warm up.If you put your hand on your engine when it's at operating temp. it will most likely burn you,or at least feel very hot.

 

[CharlieB]

Re: Overheat black max 200

The very FIRST thing you need to do is to check your temp alarm system.

Engine OFF, key ON, ground the temp sensor wire, the alarm should sound, repeat test on other side.

You can test the sensors themselves with an Ohms Meter and a pan of water on your stove. Check Ohms cold, then check again after heating in the water. If you are worried about getting the sensors wet then place it in a zip lock bag, leave the wires hanging out to use as a handle and so you can test the Ohms while the sensor is immersed in the hot water.

After confirming that your alarm system works THEN it is safe to begin testing the motor.