How to test the temperature switch

[thegipper]

My 1970 60hp johnson has a warning light on the control box if the engine gets too hot. I am in the process of adding a tell tale (thanks for the help with that guys) but I want to make sure that the warning light works too. I have located the switch (item# 74) on the power head group and it looks like it is mounted underneath the cylinder head cover.

Can I just apply some heat to the side of the cover near the switch to see if the light come on? At what temp should the light come on? I am thinking of applying small amounts of heat with a torch until the light comes on unless that is a terrible idea. If it is a terrible idea, how else would I test it without taking the cylinder cover off?



Thanks

 

[F_R]

The switch is supposed to close at 211 +/- 6 degrees F, and reopen at 175 +/- 7 degrees. The approved way of testing it is submerge it in hot oil. Whether or not it will close using your method, I have no idea. Never tried that. To test everything but the actual switch, ground the wire leading to it. Warning light or horn should light up or sound off, whichever is the case.

 

[Bosunsmate]

Yes as above but to test light you will probably need to have the key switched to on.
Go easy with the torch as they are aluminium but i cant see why not to give that a go, test the light circuit first obviously

 

[thegipper]

I looked at the switch again and I only see one wire coming out of it? Here is a picture of the replacement part which clearly has two wire coming out of it. What am I missing?? The only wire that is coming out of it is the tan wire. Was this part changed at some point? Would the ground wire be on the inside of the cylinder cover? What exactly do I ground to test the light, the tan wire?

 

[Bosunsmate]

You ground the tan wire to test it with the key on. There is a rubber sleeve, slide that apart on the wire and you then ground the meal connector that connected to the wiring haness that you see when its apart.
Ive no idea about why this new unit has two wires, i will be interested to hear why. It looks like it might take power on the black wire if necessary to complete a circuit via the tan wire to sound a horn etc as an alternative to just using the tan wire gound system. So it might be dual purpose

 

[GA_Boater]

The switch works by making a ground path to the tan wire. It's possible the original one wire switch relied on the body of the switch making contact with the block for the ground and it was not as reliable as it should be.

The black wire lug is attached to a more solid ground source, under a head bolt.

 

[thegipper]

Cool thanks. I'll ground out the tan wire tonight and test the light. I'm assuming the key has to be in the ignition in the on position too.

 

[GA_Boater]

Cool thanks. I'll ground out the tan wire tonight and test the light. I'm assuming the key has to be in the ignition in the on position too.

Most likely, so try it both ways.

 

[thegipper]

I looked at the schematic a little closer and it looks like the original part only had one wire so maybe you are correct, the body on the original sensor grounds to the cover. The updated part has an external feed for its ground. If I test it and it doesn't work, how hard is it to remove the cover? Is there anything special to it other than removing the bolts and pulling the cover off? I'm assuming I would need to put a new gasket on it.

 

[Bosunsmate]

Yes GA is correct. They can be very hard to remove, id try heating it up to test it before i attempted a removal. Gasket replacement for the water cover is cheap

 

[thegipper]

Is heating up the side of the block with a torch the only way to do it with it still on there? Or is there some other method?

And if I do end up removing the cover, I simply remove the bolts and pull the cover off? When I go to install it again, just put a new gasket on it?

 

[Bosunsmate]

Well since its a heat switch i cant think of any other way, unless you drop the LU and run the motor until it gets hot. You would want an IR temp gun there to check it didnt get too hot.
Yes remove bolts and then afterwards reinstall tightening in a pattern from inner to outer

 

[thegipper]

Well I got some great news. Part of the wire insulation on the brown wire was torn so I was able to ground the wire out and the light did turn on. I still wanted to know if the actual temp switch works so I started to apply heat with the torch. I did it in small amounts and gradually got it hotter and hotter. I did use my IR gun until it was about 220 (figured 220 on the outside would mean the inside would be about 30 degrees less). I turn the key on and sure enough, the light was on. I left the key on until the light turned off, which only took about 2 minutes.

Thanks for the help everyone!

PS. I fixed the torn wire insulation

 

[racerone]

Now you have to convince yourself to look at the tell tale and the light on the control box instead of the 2 legged scenery around you.---------------They replaced the light in the control boxes with a buzzer after the mistake was realized.

 

[Silvertip]

Temperature senders and switches cannot (or should not) be tested using external heat sources unless the actual temperature probe is a contact type meaning it is in physical contact with the metal block or heat surface. If it is not, it must be contact with the water in the cooling jacket or you get no switch/sender action as it would be seeing air temperature. Using an external heat source "localizes" the heat which can warp things. Feel free to proceed but I would not pursue that course on any engine.

 

[thegipper]

I was very careful about applying the heat but I get your point.

How hard would it be to add a buzzer? Tell tale, light and a buzzer would be best!

 

[juno pierrat]

should be easy to add buzzer , everythings 12 volts, wire to brown lead under console by alarm light