High(er) temperature engine alarm

[Peregrine1983]

Hi all,

We have an a Westerbeke 58 from the late 1990's. The motor runs great.

The only issue I have is the high coolant temp buzzer installed by a mechanic when she was for sale. It is a simple buzzer type attached a wire to the temp sensor in the thermostat housing.

The problem is it is set for (I believe) 180F, but the engine coolant consistently runs at about 190 (according to the cockpit gauge), so when the motor warms up, the buzzer goes off. I had to disable this buzzer so as to not lose my mind, but of course, now I have no way of knowing if my engine is overheating.

The engine temperature at the thermostat read from the engine exterior with an infrared thermometer is always 179F. Always. Coolant temp on the gauge is always 190. I've changed impellers, installed all new coolant hoses, the motor just runs at 190 and I've come to accept that.

I know next to nothing about engine temperature sensors, so my question is - is there such a thing as a 195 or 200 degree temperature sensor? Or some other alarm that will go off at 195 and tell me if the motor is actually overheating?

Thanks in advance and please forgive my ignorance on this subject.

[AndyEss]

The engine coolant temperature is set by the thermostat which is installed inthe thermostat housing. If you open the housing, you will find the thermostat, and its opening temperature is usually stamped on it somewhere.
Temperature sensors are of various types, some give an analog signal, proportional to temperature, which is fed to a readout gauge or meter. Some temperature sensors are just on/off switches, set off by temperature. Some can be combinations of the two.
It sounds like you have a simple on/off type temperature sensor - it opens (or closes) once its setpoint temperature is reached.
Figure out what thread your sensor is, and then google for engine temperature sensors. It sounds like you can use a on/off over temp sensor set at 195 or 200 deg F.
Make sure you match the on/off state also. You can use an ohm-meter to figure that out.

[GordMay]

The sender for your cockpit gauge is a variable resistor type, and can't be used for a buzzer (or idiot light).
A buzzer requires an additional temperature switch,

Water Temperature: Normally Open, Close on Rise (190 deg or 200 deg).
Oil Pressure: Normally Closed, Close on Fa l (normally at 5-10 PSI)

[wingless]

Here is a 200°F coolant temperature switch.

[Peregrine1983]

Thanks all very much for your responses. So, in theory, just installing the 200F properly sized switch wingless recommended will just trigger the alarm at 200?

Edit: Photo below of the switch currently on my engine. It appears to have one electrical contact instead of two.

[wingless]

A switch w/ one contact must use the body as the second contact.

If a two contact switch is swapped-in as a replacement, then the second contact must be provided with a wire that connects to ground.

[Peregrine1983]

Originally Posted by wingless

A switch w/ one contact must use the body as the second contact.

If a two contact switch is swapped-in as a replacement, then the second contact must be provided with a wire that connects to ground.

Got it. Thank you!

[Pizzazz]

You may want to consult your engine manual to confirm if it is designed to run at 180F or 190F. May the thermostat is not original. Basically, engines run more efficiently at higher temperatures but it is not recommended to exceed their design temperature.

Another option to consider, if you are willing to leave the overpriced marine world, is an industrial temp sensor ($15 from Amazon, typically 4-20mA, all sorts of threads are available) and a process gauge ($20-60 from Amazon). Once you have that you have digital pressure readout and two alarms that you can set to any temperature. It is a robust industrial solution but not marine.

[Singularity]

FWIW and old-fashioned way of checking temp sensors is to pull the sensor from the block and place it into a pan with hot water (or oil, depending on the sensor temp) into which you've placed a candy or cooking thermometer for reference.

Of course this relies on the accuracy of the cooking thermometer and requires care so as to not get burned, but it may be a little more accurate than an external IR gun temp.

[Dsanduril]

The factory thermostat (24690) is 180F, so the switch sender should be higher than that. The factory switch (30125) is unknown (to me) temp but has 1/8 NPT and uses an 1/8 to 1/4 bushing in most installations. A 200F switch seems appropriate. Both parts seem to be available, might want to see if the mechanic put in something else and switch back to factory.

[AndyEss]

Originally Posted by Singularity

FWIW and old-fashioned way of checking temp sensors is to pull the sensor from the block and place it into a pan with hot water (or oil, depending on the sensor temp) into which you've placed a candy or cooking thermometer for reference.

Of course this relies on the accuracy of the cooking thermometer and requires care so as to not get burned, but it may be a little more accurate than an external IR gun temp.

I remember doing that with my first car - in the 1970's.
Muchos gracias for the memory nudge Singularity.

[AndyEss]

Unfortunately, it does date me as being old-fashioned.
Oh well, just like a fine wine, I am only getting better.
����

[GordMay]

Originally Posted by wingless

A switch w/ one contact must use the body as the second contact.

If a two contact switch is swapped-in as a replacement, then the second contact must be provided with a wire that connects to ground.

Just to clarify:

He has, both, a gauge and a buzzer, so he's not swapping the switch instead of the sender, he's adding the switch (for the buzzer), and leaving the sender for the gauge.
wingless' switch, linked in post #4, is the right one.

[Brewgyver]

That thermostat housing has only one threaded opening, so you may need to install a close nipple and tee to have both the temp gauge and overheat buzzer while keeping things as simple as possible. I did that on my Atomic 4 to add a low oil pressure buzzer.

[BruceS]

The one for the gauge is separate and more likely in the side of the block.
If you liik closely you can see something further down on the right side? Not sure if that's it or not?
Even the Perkins has two independent sensors.
One is 'outlet' water temperature & the other is block temperature.