Overtemperature Protection

[jsw123]

I am being told that a standard coolant temperature switch or sender is not adequate for a slow speed engine. Was told I should use a engine block temp. switch instead. Is this correct?

[somian]

I don't see why it needs to be on the block. My setup, which I have yet to run, has the temperature sensor on the water outlet pipe from the cylinder head. They may not get quite as warm as the head, but I reckon they will get warm enough; providing there is a good supply of water, or course. Which is why I intend to have a low coolant sensor as well.

[mike90045]

If you loose coolant, (which would never happen in a 'roid)  the coolant based sensors notice nothing.    I'd spend my time on the head as a sensor

[ronmar]

Thermal snap switch bonded to the side of the head.  System full of coolant, the side of the head reads a particular normal op temp.  Loose all the coolant, and the temp on the side of the head will exceed the normal coolant operating temp and still trip a sensor/snap switch.

[jsw123]

What high temperature should the snap switch open/close at?

[somian]

Measuring the temperature at the side of the head is not going to be very effective if the head is not full of water, because the inside of the head will be rather hotter than the outside. This is why intend to measure water temperature and detect low coolant level. If it overheats (about 90C) the alarm will sound, if the coolant level drops a little the alarm will sound, either way there is time to do something before damage occurs.

[billswan]

What high temperature should the snap switch open/close at?

Depends on what part of the head you speak of, my 10/1 under load when checked with a infrared hear gun varies quiet a bit. 2 inches back from the ex port can be over 250 Fahrenheit but near the water outlet port it is much cooler. Going from memory, so not sure of exact numbers. But have thought of using a snap switch as backup for a coolant loss situation. And there is the same question how to fasten, where to fasten and what temp would give the best results?

 Now here is what would Be nice but not KISS.

A sensor close to the ex port so a quick response would take place if coolant flow were some how stopped.
A resetable snap switch so if it opens and causes a shutdown you can readily see the cause hours later. ( considering no coolant loss)
And an adjustable switch so it can be set up or down if you happen to guess wrong when you acquire it.
Not asking for much am I

Billswan

[dubbleUJay]

I would think that monitoring the exhaust temperature would be my first entry point for protection.

There was this guy that used plumbers solder to melt at +/- 400degC (cannot find the website now) and operate/break a switch, but I think that a more elegant way would be a snap switch for that temperature, adjustable if available.

dubbleUJay

[adhall]

So, what about this, then:

http://www.grainger.com/Grainger/items/4E120

Item                                 Snap Disc Control
Type                          Limit, Automatic Reset
Switch Action                          Open on Rise
Switch Type                                       SPST
Temp. Range (F)                        210 to 250
Element Type                                     Flush
Height (In.)                                       1 1/2
Width (In.)                                        1 3/4
Depth (In.)                                              1
Circuit #1 Switch Closes @ (F)                210
Circuit #1 Switch Opens @ (F)                250
Differential (F)                                        40
Inductive Amps @ 120V                           10
Inductive Amps @ 240V                           14
Pilot Duty Contacts (VA)                         125
Resistive Amps @ 120V                            25
Resistive Rating 240V                              25
Voltage Range                            120 to 240

And all this for a mere $22.63 USD.

It doesn't offer the manual reset function, but you could easily implement that with a relay.

Best regards,
Andy Hall

[billswan]

adhall

Yes that is the type of snap switch I was thinking of. It is the first I have seen that is adjustable,cool. I do own one that has a button on it in exactly the same spot that the adjusting knob is on the one you found in Grainger. When it trips it stays tripped until the button is pressed to rest it, after cooling that is.
To bad it trips at 180degrees F. to cool for the side of the head on my 10/1.

Billswan

[dubbleUJay]

I found the website article I was referring to previously: (Being on the Utterpower site, you guys might have seen it)

http://utterpower.com/autoshutdown.htm

It a crude but efficient way and the principle behind it makes sense to me if one reads the whole article.
Specially this part: ( I hope I wont be slapped for quoting from the mentioned site ;-)

"Construction Principles

Engines seize due to high cylinder temperatures.  The cylinder is encased in a water jacket.  When Thermo-siphon cooling systems are in operation, water temperature cannot be above boiling point.  So it was decided to use exhaust gas temperature as the trigger.

Experimentation was done on a ‘China’ diesel engine.  The 195 has one cylinder and a bore of 95mm.  It is a water cooled 12hp diesel engine.  Exhaust manifold temperature under a constant heavy load hovers around 550 degrees F.  Seizing temperature of the engine is above 1,000 degrees F.  If the engine could be shut down when the exhaust manifold temperature reaches around 600-650 degrees F. then there should be no engine damage."

I wonder if a lower than 300degC snapswitch mounted on a heatsink of aliminum on the exhaust can be setup to trip at a higher related temperature of the actual gasses? In other words, the exhaust gasses would be say 315degC and after conducting through the pipe and heat-sink, be around 200degC, 'cus I don't see a switch that will trip a very high temperatures.

dubbleUJay

[billswan]

dubbleUJay

I think it could work but it may cost you a lot of trial and error to get it just right.

Please give it a try and report back on how you make out. That is the way to prove your theory, test modify repeat

Billswan

[vtmetro]

After doing a few lookups I see that lead melts at 620 F (327 C).

What if I stretch a spring and attach to a small drilled hole in the rack so it wants to shut it off.

Then make a small hole in the exhaust pipe near the head and insert a lead plug. Easy to cast the plug from lead tire weights and a plaster of Paris mold. Make it look like an eye bolt -- threaded bottom and a loop top. Tap the pipe and thread the lead plug to fit the tapped hole.

Then string a loose cable (say braided 1/8" dia.) between the lead eye bolt plug and another hole in the rack.

Pull on the center of the cable to open the rack. Place it over a hook to hold it open.

If the plug melts it releases the rack. It should melt before the EG temp reaches 1000F

Note: this could be all done in a more elegant mechanical fashion than I've described here, but I wrote it this way just to make the basic principle simple and clear.

For instance instead of hooking the cable over a stationary hook, you could use a lawn mower style cable as a rack opener. It would be attached to the shutoff cable in the middle instead of a stationary hook. The lawnmower throttle lever could then be used to open the rack by pulling on the cable.

(ps. safety note : plaster of Paris must be completely dry for molding lead -- either dry it for at least a week, or bake it in an oven. Otherwise lead can splatter from steam buildup in a moist mold. Please read up on lead casting before trying it.)

(pps. Lead solder melts at a lower temperature because it is alloyed with tin. Probably too low -- it might melt at ordinary operating temps.)

[Tijean]

I think the fusible link idea is excellent. There are alloys available ranging down to below 200 F so the same idea could be used on the coolant. With a bit of creativity I bet you could have the eye pull out without even losing the molten metal.

[vtmetro]

Thanks!

Also true about other metals like the low temp fusibles, if you want a cooling water based shutoff.

But then earlier in the thread people were talking about how water temp wasn't a reliable or fast acting overheat indicator in case of coolant loss, and were wondering if EGT could be used for this. They spec'd 1000F as the high before damage and asked for a 600 F shutoff temp. Then went on to say commercial snap switches weren't available at the necessary higher temps for EGT overtemp shutoff.

That's why I started looking up metal melting points in that temperature range. Zinc was too high, and solder and tin too low. Lead turned out to be just right for what was asked at 620F. Easy to find as scrap, too, and easy to cast and thread with a simple die from the hardware store. I've cast lead melting it in a tin can outdoors over a camp stove, and pouring into a plaster mold. Of course safety precautions are imperative -- outdoors only, because of fumes, goggles, gloves and a dry mold. But it's pretty easy.

To make the mold it might even be possible to use an existing eyebolt as a plug. If you're careful the threads might even stay and you could clean up with a matching nut rather than a die. You'd just need a matching tap for the exhaust pipe hole.