Temp light and wiring Q - '63 40hp

[baytonemus]

I was able to acquire a wiring harness and junction box (with no regulator) from a salvage yard for my 40352D - Big Twin Electric. The service manual wiring diagram shows a tan wire running from the temp warning light back to the temp switch on the motor. There is no tan or any other color wire for this in the wiring harness and I'm not sure what to make of that.

Also, the temp switch wire on the motor has no connector, so I assume it was cut off at some point. Were these switches prone to failure? Removing it for testing would appear to require that I replace the head cover gasket in the process.

Lastly, It seems to me that either replacing that warning light with a horn or buzzer, or at least adding one to the circuit, might really be a good idea. I'm wondering if anyone has done this successfully with a simple motorcycle horn, for instance.

Thanks.

 

[F_R]

Re: Temp light and wiring Q - '63 40hp

I don't know what wiring harness you got, but if it were the correct one it would have the tan wire. I suppose you can run a separate wire if you can keep it from becoming damaged.

There is no way to test the sensor, other than overheating it. That requires removing it---don't intentionally overheat the motor.

About failure: I have seen dozens of burnt-up motors where the owner swears the light/horn never went off. In case of sudden water pump failure, it will fry the pistons and sieze before the temp switch ever gets hot enough to turn on. But still, it is better than nothing.

Motorcycle horn?? That's an interesting thought. It should work if it doesn't carry too much amperage for the rating of the sender switch contacts. It probably would.

You can also install a temperature guage instead. You can monitor that at any time. They probably are for sale here at iboats.

 

[baytonemus]

Re: Temp light and wiring Q - '63 40hp

I don't know what wiring harness you got, but if it were the correct one it would have the tan wire. I suppose you can run a separate wire if you can keep it from becoming damaged.

Yeah, I'm not sure what to think about that. The ends of the wires for the voltage regulator are still sealed off inside the box, so it seems like it must have been for a BT Electric rather than a Lark.

About failure: I have seen dozens of burnt-up motors where the owner swears the light/horn never went off. In case of sudden water pump failure, it will fry the pistons and sieze before the temp switch ever gets hot enough to turn on.

Why is that? That should be exactly what the sensor was designed to prevent. Isn't it properly rated?

Motorcycle horn?? That's an interesting thought. It should work if it doesn't carry too much amperage for the rating of the sender switch contacts. It probably would.

You can also install a temperature guage instead. You can monitor that at any time. They probably are for sale here at iboats.

Yes, I would want to be careful about selecting something with the proper amperage. I'm not sure how I would determine the rating for the switch contacts, though.

Thanks, F_R!

 

[F_R]

Re: Temp light and wiring Q - '63 40hp

About failure: Just what I said. If the impeller suddenly comes apart at high speed, the pistons will melt before the whole powerhead gets hot enough to turn the sensor on. We had a LOT of V-4 motors do that. The impeller hubs in those would spin and the impeller stand still. It takes a certain amount of time to heat up that big hunk of metal. It can cook the pistons in a matter of well less than a minute because they are right there in contact with the fire. That is why in all reality, a hot light is worthless, because you won't be looking at it anyway. A horn isn't much better because it doesn't turn on quick enough.
Your best defense against overheating is a known-to-be-good water pump. Then stop worrying.

 

[baytonemus]

Re: Temp light and wiring Q - '63 40hp

So the hot light/horn would only protect you against something like a partially plugged water tube?

I just rebuilt my water pump so I'm sure that it's solid right now. What is the best way to evaluate that it is continuing to operate properly?

 

[lindy46]

Re: Temp light and wiring Q - '63 40hp

The old motors are designed well and if properly maintained, you shouldn't have a problem. Just change out the impeller every 2-3 years. I've been running old Johnnyrudes of all sizes for over 50 years and I've never had one overheat on me. When I start the motor, I usually check to make sure she's peeing ok, and then I forget about it.

 

[baytonemus]

Re: Temp light and wiring Q - '63 40hp

And with my motor that would just be through the exhaust relief port after the thermostat opens? It's a little hard to tell from the manual and I've never owned one of these motors before.

 

[lindy46]

Re: Temp light and wiring Q - '63 40hp

You should get a healthy spray/dribble out the exhaust relief port. With my '57 it's more like a gusher - she puts out a lot of water. It's not a stream like on newer motors with a telltale.

 

[baytonemus]

Re: Temp light and wiring Q - '63 40hp

You should get a healthy spray/dribble out the exhaust relief port. With my '57 it's more like a gusher - she puts out a lot of water. It's not a stream like on newer motors with a telltale.

That makes sense. With all of the references to "peeing" and "pee holes" on this forum, I thought I'd mistakenly drifted over to the FlowMax site. We had a 40 horse Johnson of a similar vintage when I was kid, and I knew it didn't "pee." At least, if I was peeing like that, I'd make an appointment with a urologist.

Thanks, Lindy!

 

[F_R]

Re: Temp light and wiring Q - '63 40hp

If you want to monitor it on a day by day schedule, install a temperature gauge.

 

[baytonemus]

Re: Temp light and wiring Q - '63 40hp

If you want to monitor it on a day by day schedule, install a temperature gauge.

How would you mount the temperature probe on this motor?

 

[F_R]

Re: Temp light and wiring Q - '63 40hp

Get the kind with a sender that goes under a head bolt. I see lots for sale here at iboats, unfortunatly none of the listings tell what kind of sender it comes with. Looks like a call to a customer service rep is in order.

 

[baytonemus]

Re: Temp light and wiring Q - '63 40hp

Great! I'll check into that. Thanks.