Overheat sensor

[Arkman]

I have a 67 Mercury 200. Last year I had a water pump failure and took out one of the pistons. Even after I made sure it was serviced properly it still failed. I guess thats life huh.

Anyways, I'm wondering if there is any way to add some kind of sensor to it so that if it gets too hot it will just kill the motor or something to that affect. I know newer motors have gauges and stuff, but mine doesn't have that. The only indication on if the water pump is working is if I have a stream...I can't always look back when I'm driving. I make it a habit to look as I go, but as I found out. It happens so fast.

 

[flimsyjim]

Re: Overheat sensor

What I'm hearing is:
1. How can I tell if I'm pumping water?
2. How can I tell if the engine is overheating?
3. Is there a way to automatically kill the motor if the engine is overheating?

My advice:
1. Install a water pressure gauge. This will save you from having to look back at the stream.
2. Install a temperature gauge. This will give you an idea of the temperature range that the motor runs and more importantly you'll be able to see when you're approaching dangerous territory.
3. Not sure if your setup has the overheat buzzer, but if so, you could figure out a way to wire it similar to the mercury switch so when the buzzer sounds the engine would cut out.

I would install the gauges, skip #3, and leave the judgement in the operators hands.

 

[Arkman]

Re: Overheat sensor

I'm not sure I can do all of those things. My motor is old enough that it is really basic...I think. I don't know that there is anyway to wire any of that stuff in. I guess thats what I'm asking. Can you do that stuff on an older motor?

 

[flimsyjim]

Re: Overheat sensor

The beauty of the two gauges is that they are complete, universal kits that can be mounted to anything and include everything you need (except for maybe a fitting or adapter that can be found at the hardware store for <$10).

A temp gauge will include the gauge and sensor. The sensor bolts up against the engine block and has 1 wire that runs to the gauge. There are a few ways that it can be mounted (described in the instructions for the gauge), but it is a universal kit so it will work. The gauge has 3 connections: the sensor wire, power, and ground. The gauge is just a volt meter that measures the voltage of the sensor. The sensor is a thermistor that changes resistence (thus the voltage) as the temperature changes.

For the water pressure gauge, you get the gauge, a long length of plastic tube, and a bunch of fittings. Once again, there are a few ways to install it and the instructions describe the process. This gauge measures pressure and requires no electrical connections to operate- just a hollow tube that runs from the engine to the gauge. On my '79 outboard (150HP), there is a plug with a square 1/2" drive (looks like an automotive differential fill plug) on the top, rear of the engine that provides a passageway into the cooling system. For my application, I removed the plug, replaced it with one that had a nipple with which to connect the tube. Run the tube up to the gauge and that's it. There are other ways to connect the tube if your motor doesn't have the plug (like putting a T-fitting in one of the cooling lines). Your water pump pushes water through the engine and tries to force it through the tube, but because the gauge is sealed, water doesn't flow through the tube it just compresses the air in the tube. The reading on the gauge is that air pressure.

 

[Arkman]

Re: Overheat sensor

OK, thanks. I'll have to start looking for one of those kits. I wasn't sure if I was out of luck because of the age of the motor. Nice to know I have options.

Thanks again!

 

[flimsyjim]

Re: Overheat sensor

I liken the overheat buzzer to an 'idot light' on a car. You don't know there's a problem until there's a big problem. With the gauges you can tell if something is even a little off and be able to monitor the situation more closely or take action instead of being surprised by a catastrophe.
When it comes to boating, where you can't just park it and walk to a gas station, that's really good piece of mind.

 

[Chris1956]

Re: Overheat sensor

A water temp gauge will not help you. That motor will run dead cold all the time until it overheats. The water pressure gauge is the way to go. If you have a threaded plug on the waterjacket over the cylinder head, use it for the pressure gauge fitting. If not, remove the elbow that supplies the telltale and insert a brass tee in it's place. Now the elbow goes on one side of the tee and the pressure gauge fitting on the other side. Water pressure is only a few PSI, so get a 0-30PSI gauge or less if you can find one.

 

[flimsyjim]

Re: Overheat sensor

A water temp gauge will not help you. That motor will run dead cold all the time until it overheats.

You can interface the temp sensor with the head/block and not use the water passage. I installed mine where the overheat buzzer sensor was.

For the water pressure, I agree the 30 is the way to go. I think mine runs ~10-15 PSI.