So I just bought a Mac X....

[Drifter]

I'm not entirely sure what or where the temperature sensor is?

The thing in the manual does not exist on my engine; there's a blanking plate there. Evidently the sensor is somewhere else, maybe that white switch thing?

The other day in the tub, after changing the thermostat, I ran the engine at 5000 rpm for some time, and no alarm sounded. However that was basically just a very fast idle in neutral, with no load on the prop at all.

The white switch is actually right in front of me. Has what looks like a probe, and somewhat corroded, so does indeed look like it was inside the water jacket, with a white plastic exterior plug socket (female), which has 2 pins.

I could probably pull the plastic connector (male) off, though I didn't try before in case I broke it, as there may be some technique for removing it that I don't know about.

If I were to pull it off I guess I could place a wire from one of the pin sockets to the side of the block, to see what happens when it earths..? There's 2 of them, so would have to try 1 at a time - or just try connecting them together and closing the circuit? I guess that's what the switch does, when hot enough?

I'll post the pics again:

[Drifter]

OK, re-reading earlier posts...

""There should be two sensors on the port side of the engine. The top one is the temperature switch and should have a single yellow wire. The bottom one is the oil pressure switch and has two wires. I don't remember the colors for that one."

Mmm, well it is indeed the top sensor that has a single yellow wire, and looking at the manual page it says to dip it in hot oil or fluid (not water) - so yeah, I guess that thing IS the temperature sensor switch?

And Russ asked:

"Is that electrical tape on the yellow wire? If so, why? Could that wire be grounding and causing the alarm? Or is the tape just to prevent chaff?"

Mmm.

so the over-temp sensor is in the oil, not water?

OK...

No no, wait - that white thing is corroded and looks like it was in the water...?

OK, tomorrow I'll pop the rubber cover off the yellow-wired thingy, and try shorting it on the block with the ignition on, see if I get the buzzer.

I'll also carefully try unclipping the lower plastic connection, and see what happens if I unscrew that.

I am confused thought, because that top sensor with the yellow wire definitely had oil dribble from the hole, not water. So I really would have put money on that being the oil pressure, and the white plastic one with 2 wires being the temperature sensor, which is probing the water temperature?

[Drifter]

Another uppydate...

I'm now totally convinced the white plastic thing is the temperature sensor, because on the side of it there's a number, 40228. So I tried a search for that, searched for 'Honda 40228 temperature sensor' and found this:

https://www.lazada.com.my/products/madi ... 52328.html

That's for a Honda Civic - but it's virtually identical!

I'll post pics in case you can't access that link:






Heck, at 33 ringgit that's so cheap I'll order one and see if it fits... It's black plastic instead of white but other than that it looks the same.

[Tomfoolery]

That looks like a temperature sensor for a Honda car. Might be an analog sending unit, rather than a switch.

And I would not short either lead to ground, as you're likely to blow a fuse. Better pull out the multimeter at this point.

https://www.ebay.ca/itm/OE-37870-PNA-00 ... 0008.m2219

Edit: Damn! Missed it by this >< much.

[Drifter]

Hehehe!

I'm guessing any Honda temp unit is going to react the same, ie if it fits then it will be OK, as they will all be reacting to the same kind of temperature, right?

Thermostats may open at different temps, but "coolant too hot" is "coolant too hot" for any sensor. I'll order the one for the Honda Civic and give it a try.

On a lighter, more cheerful note, the crew get their own hats!

[Be Free]

The temperature switch completes the ground side of the alarm circuit. That's why I suggested he short it to ground.

If the Civic in question has an "idiot light" rather than a gauge it may use a similar switch.

I've never needed to remove my temperature switch so I don't know if it is sensing water jacket or oil temperature. Both are valid ways of measuring engine temperature. Oil temp is probably better since the sensor would be past the thermostat if it is in the water jacket. It might even make casting the engine easier since the oil pressure switch is just below it.

Anyone know if it is measuring oil or water temp?

[Tomfoolery]

The temperature switch completes the ground side of the alarm circuit. That's why I suggested he short it to ground.

If the Civic in question has an "idiot light" rather than a gauge it may use a similar switch.

That's true, but his switch or sending unit has two wires instead of one, so one of them may be an actual 12V hot line, and that's why the multimeter reference.

[Drifter]

So nobody is going to compliment the oh-so-tasteful crew hats?

Wait till you see my nifty Captain's hat, and the one for the First Officer

Having ordered that temp sensor on a whim, I now remember that a car cooling system is pressurized, meaning temperatures can exceed the boiling point of water and still transfer heat. The Honda system has no actual pressure, just pumping water through it, so presumably that would trigger an alarm at a noticeably lower temperature?

[Tomfoolery]

What's this gauge? It looks like there's a "C" at the bottom. Is that an analog temperature gauge?

[Russ]

Cool hats!

[Jimmyt]

So nobody is going to compliment the oh-so-tasteful crew hats?

Wait till you see my nifty Captain's hat, and the one for the First Officer

Having ordered that temp sensor on a whim, I now remember that a car cooling system is pressurized, meaning temperatures can exceed the boiling point of water and still transfer heat. The Honda system has no actual pressure, just pumping water through it, so presumably that would trigger an alarm at a noticeably lower temperature?

Crew hats are cool!

You are giving us a bit of a nervous breakdown with your temperature sending unit/high limit switch approach. Tom and Be Free are trying to get you to ID the type of device you have before you go slapping the automotive piece into your motor.

A temperature sending unit will tell the motor controller what the actual temperature of the cooling jacket is. A limit switch will close a set of contacts when the "limit temperature" is reached. You shouldn't plug a car sensor in without having a really good idea that it's the right device.

If you have a temperature sensor, the limit temperature is programmed in your engine controller. Whereas, the temperature switch just closes (or opens) at a certain temperature. Pressurized or not isn't really the issue.

And, since you weren't the one that did the deeds to this rig, it would be good to make sure exactly what device triggers the high temp alarm, and what type animal it is. If you have an analog gauge, there may be two temperature probes in the engine...

Once you have determined, as fact, that you have a temperature switch that grounds when it closes, you can consider shorting the wire to ground. However, indiscriminately shorting engine sensor wires to ground can be a really bad idea.

The only thing worse than an engine that won't run over 3,500rpm is an engine that won't run.

[Be Free]

I found my service manual but it does not cover all of the older models. It does mention that the "early" models used a 2 wire temperature sensor. Newer models used a one wire. His engine is older that the "early" models my manual covers so it is likely a 2 wire version.

I withdraw my suggestion that he ground the wire. That would only work on a switch with one wire going to it.

My diagram shows the G/Bl wire as thermo sensor ground and the R wire as thermo sensor. Both wires run back the engine control module so I don't think metering them will reveal much. It is probably returning a variable voltage to the ECM.

[Jimmyt]

I found my service manual but it does not cover all of the older models. It does mention that the "early" models used a 2 wire temperature sensor. Newer models used a one wire. His engine is older that the "early" models my manual covers so it is likely a 2 wire version.

I withdraw my suggestion that he ground the wire. That would only work on a switch with one wire going to it.

My diagram shows the G/Bl wire as thermo sensor ground and the R wire as thermo sensor. Both wires run back the engine control module so I don't think metering them will reveal much. It is probably returning a variable voltage to the ECM.

Good info!

I was thinking of checking the sensors with the meter - new vs old. Also, he could check the voltage at the old sensor terminals with everything hooked up to get some insight on what he's dealing with.

I would like to think that the devices are the same, because they look alike and both are for a Honda product. BUT, I wouldn't bet my ECU on it without making sure first.

[NiceAft]

I like the crew hats.

I've been thinking about that for years; I just have not come up with anything tasteful for "Nice Aft", I'm looking for a design to go with the name.

Looking forward to see what you do for the captain and first officer.

[Inquisitor]

I like the crew hats.

I've been thinking about that for years; I just have not come up with anything tasteful for "Nice Aft", I'm looking for a design to go with the name.

Looking forward to see what you do for the captain and first officer.

Is https://niceaft.com/ yours? Either way, surely you have plenty of choices...
Me, I'd be looking into WWII aircraft nose art. There ought to be plenty of nice afts there.