temp gage/thermoswitch

[noah4009]

I have a 1971 55HP Chrysler model 557HC serial 3188. I want to put on a water temperature gage. On the top of the head to my engine is the thermoswitch. It looks to be about 1/4 inch or 3/8 inch hole that it is screwed in to. The gages that I saw all had a thermoswitch that was much larger in diameter. Can I buy and put a temp gage on and use my old thermoswitch? It also looks like its the original. Looks like it is actually a part of the head. Seems like it will be a pain to get out or possible break off. Are there any temp gages with the same diameter thermoswitch or is mine so old that it is no longer made in that diameter? Any advise on this mater would be greatly appreciated, also can you tell me who makes one that would fit in the same hole if I do need to put a new thermoswitch in.
thank you

 

[Silvertip]

Re: temp gage/thermoswitch

When iinstalling a temperature gauge you cannot use a standard switch type temp sender (thermoswitch as you call it). These are simple ON/OFF devices that trigger the overheat horn. A water temp sender for a gauge is a thermister (a variable resistor) that changes resistance based on water temperature. In other words it works exactly like a gas gauge or trim gauge. Temp senders are of two varieties as shown below. The copper brass unit screws into the water jacket and is in contact with the water hence it is a true water temp gauge. The silver type is a contact type. It bolts to the cylinder head and measure cylinder head temperature. The brass type can also be mounted that way with a special bracket. When you buy a temp gauge you cannot use one from a car or truck as these engines run much hotter than an outboard and the needle would never move. The best outboard temp gauge is calibrated at 60 degrees on the low end of the scale but those are getting hard to find. Most start at 100 degrees. Many temp gauges today are calibrated C - N - H which is about as useful as a hand full of warts. Here are the sender types. You must use one for an outboard.

 

[noah4009]

Re: temp gage/thermoswitch

When iinstalling a temperature gauge you cannot use a standard switch type temp sender (thermoswitch as you call it). These are simple ON/OFF devices that trigger the overheat horn. A water temp sender for a gauge is a thermister (a variable resistor) that changes resistance based on water temperature. In other words it works exactly like a gas gauge or trim gauge. Temp senders are of two varieties as shown below. The copper brass unit screws into the water jacket and is in contact with the water hence it is a true water temp gauge. The silver type is a contact type. It bolts to the cylinder head and measure cylinder head temperature. The brass type can also be mounted that way with a special bracket. When you buy a temp gauge you cannot use one from a car or truck as these engines run much hotter than an outboard and the needle would never move. The best outboard temp gauge is calibrated at 60 degrees on the low end of the scale but those are getting hard to find. Most start at 100 degrees. Many temp gauges today are calibrated C - N - H which is about as useful as a hand full of warts. Here are the sender types. You must use one for an outboard.

I understand. I need to remove my thermoswitch and put in a termister. I do understand the difference now. So can I find a thermister the same size as my thermoswitch hole in the head. Or do they just come in one size. I also would have to use the brass one. It seems to have the top where my wire would screw on to with the little nut. Can you recommend where or who would have this type with the same size hole as the one in my head (LOL) So as to not have to drill another hole in my head.
thanks

 

[Silvertip]

Re: temp gage/thermoswitch

The wire is not an issue. You use either a ring terminal on the screw-in sender or a spade terminal if you use the contact type sender. Both types of senders are available from whoever the gauge manufacturer is (Faria or Teleflex).