Temp Sensors

[Matt DeYoung]

I am rebuilding a couple of Merc model 250's. I decided since all the cast iron is now new, I would add closed cooling. The carb is a Holley 600 vac sec and requires an electric choke. This needs 1 temp sensor. The other temp sensor is the one that goes to the gage on the "dash". The thermostat housing that came with the closed cooling kit came with only 1 hole for a temp sensor. When I replaced the intake manifold it provided (2), 1/2" npt ports on the front of the engine. Maybe this is a good place ? <br />I have 3 questions :<br /> 1. Do the sensors need to be on the engine block side of the thermostat or the housing side.<br /> 2. It there a certian type of sensor I need for each application<br /> 3. Where can I get them ?

 

[Don S]

Re: Temp Sensors

Electric chokes do not require temp sensors. They do require an electric choke coil that mounts on the carb. I sure hope that Holley is a marine carb. NO Automotive carbs on boats ya know.

 

[Matt DeYoung]

Re: Temp Sensors

They are automotive carbs. Is this terrible or just bad? They are returnable. There must be a fire hazard risk here ?

 

[Don S]

Re: Temp Sensors

Very Bad. A flooding condition in the carb, say a stuck float (common problem) would put the gas outside the carb and onto the ground with an automotive carb this would be in the closed engine compartment on a boat. You now have a serious explosion/fire hazard. <br />Get a Marine carb, they are designed to prevent explosions.<br />If you did have an accident, explosion, or fire, your insurance may not pay when they found things like automotive carbs, fuel pumps, starter, alterenataors and many other non marine parts on your boat. Could also be legal problems if the lawers get involved.

 

[Matt DeYoung]

Re: Temp Sensors

Gotcha.<br />I'll get marine carbs.<br />But the temp sensors question still has me confused. How does the carb know when to stop Choking if there is no water temp sensor ?

 

[Don S]

Re: Temp Sensors

It doesn't work on a temp sensor. There is system voltage (12V) applied to the choke coil when the ignition is turned on. As long as power is applied to the choke coil, it heats up and opens the choke and remains open.<br />I'm not trying to be mean, but I suggest you get a service manual and start doing some research on how marine engine systems work and work together before you start changing and modifying things you know nothing about.

 

[Don S]

Re: Temp Sensors

Here are a couple of sites that may help you with some questions on "Marine" items.<br /> West Advisors <br /><br /> Mercstuff

 

[waterone1@aol.com]

Re: Temp Sensors

Pirate, what don said about the marine parts is extremely important. The electric choke thing had me baffled years ago when I first encountered one. I sat there with a volt meter on the choke terminal expecting to see the voltage change as the engine warmed up.....obviously it didn't. It just requires Pos. 12V that is on anytime the key is on. Internally there is a large heat coil (looks like a spring) as the heat coil heats up from the 12volts, it moves the choke lever. Keep in mind that the assembly rotates to allow you to adjust how "closed" the choke is. You can get a manual and set it properly the first time, or spend a whole weekend doing the trial and error method to get it "close".

 

[Jimmie.jazz]

Re: Temp Sensors

Originally posted by Pirate of the Cumberland:<br /> <br />I have 3 questions :<br /> 1. Do the sensors need to be on the engine block side of the thermostat or the housing side.<br /> 2. It there a certian type of sensor I need for each application<br /> 3. Where can I get them ?

1. The sensor needs to be on the engine side of the thermostat. You want to see the coolant temperature of the engine, not the cooling system.<br />2. Your carb question has already been answered, but you'll need the temperature sender specific to the gauge you are using. The simplest way to do that is to use the temperature sensors from your old Merc 250 blocks, or buy new ones for the Merc 250. That way your gauges will register and be calibrated correctly.<br />3. You can pull the old ones off your old blocks, or buy one from your local Merc dealer.<br /><br />I just replaced mine witha new one, and the peace of mind is well worth the price, hehehe.