Locating safety thermo switches on the head

[Jens]

Thumper now has a proper over/under voltage sensor on the generator. If the belt should pop off it will shut down. I have also placed an order for some 110 degree C thermo snap switches. These will act as secondary heat shutdowns and will be located on the heads.
Has anybody looked at the best location for a switch of that nature on a listeroid head ?
I could just clamp them to the side of the head but am curious if there is an advantage to one location vs the next. I am thinking that the location should provide quick shutdown .... say that the coolant dumps for unknown reasons. This would disable the regular coolant based high temperature shutdown and the engine would be completely at the mercy of the snap switches. I would want a direct and short path for the heat to go from the combustion chamber to the sensor. Of course the head is riddled with passages so this mystery spot may not be that easy to find. Heck, maybe it really doesn't matter all that much since the head absorbs some of the heat. I don't know. I thought I would ask and see what the more knowledgeable people had to say.

[mbryner]

Why do you need to disable the coolant based switches?   Can't you use both?   Does one kind break the circuit and the other complete the circuit?   If it's just like the Murphy coolant temp switch, just put it in parallel, correct?

My guess on your other question, stay away from the air intake and exhaust areas which will give erroneous reads.   If I were doing that (which sounds like a good idea), my first inclination is to put it on one of the flywheel-sides.

[Ronmar]

If you were placing it to deal with the total loss of coolant, I would say somewhere adjacent an exhaust port.  Someplace that is held below the switch trip point by the prescence of coolant, and that would probably quickly exceed that temp if coolant suddenly went away... 

Another thought would be a float switch in the primary coolant loop expansion tank.  A sudden loss of coolant in the system should quickly drain the expansion tank.  This would cause a shutdown before the engine ever got the chance to overheat from lack of coolant...

[bschwartz]

If you were placing it to deal with the total loss of coolant, I would say somewhere adjacent an exhaust port.  Someplace that is held below the switch trip point by the prescence of coolant, and that would probably quickly exceed that temp if coolant suddenly went away... 

Another thought would be a float switch in the primary coolant loop expansion tank.  A sudden loss of coolant in the system should quickly drain the expansion tank.  This would cause a shutdown before the engine ever got the chance to overheat from lack of coolant...

When I had an overheat several months ago, all of my coolant boiled over INTO my overflow tank!!

I suspect that event was bad enough to carbonize some engine oil into the underside of my piston which has recently released said carbon chunks back into my oil......  I'm in the middle of a rebuild now 

[bschwartz]

Jens,
I didn't have an overheat situation..... I had an OVERHEAT event!!!!
All coolant boiled out, no safety, and was only alerted to the problem when the expanding parts caused enough friction to slow the engine enough to cause a NOTICED flickering in my lights.

The oil on top of the cylinder head (rocker drippings) were SMOKING, and the cheapo HF infrared thermometer indicated that my upper radiator hose (5" from the cylinder head) was 360 degrees F.

I think it was that event that may  have caused the carbon problem.

After letting everything cool off for 3 hours, I refilled the coolant and started it back up.

The head gasket amazingly held through this all, and it has run for the last few months.

I suspect as I get it apart, I'll find poor connecting rod bearings, and worn cylinder, and cruddy rings etc.
I was just too lazy to do the tear down before figuring that It would all have to be done anyway, and I might as well get some more time out of the wrecked surfaces as long as they would hold up.

Oh well..... all just part of the fun 

[mbryner]

Not to divert the thread, but Brett, what caused the overheat event?

[AdeV]

Loss of coolant should be detectable by the coolant sensor, depending somewhat on where it is... but, then, I don't know how you're controlling your system - micro-processor, or a simple "analogue computer" (switches)?

As I have temp sensors on both inlet & outlet ports, I should be able to detect a coolant leak by the lower sensor starting to read higher than the top sensor. Of course, none of this applies until the engine's been running for a couple of minutes, and the coolant has started to do its work; so level sensors will also be required to prevent startup from a no-coolant situation.

I haven't even begun to consider oil levels yet...

[bschwartz]

Marcus, I suspect it was the family not paying attention to how many appliances were turned on at the same time.  Simple overload.  I remember watching TV and later found out that the dishwasher was running while the washing machine was on.... and the clothes dryer was running at the same time no one remembered to turn the heater off on the hot tub...........

Or something like that.

I also think my radiator is just barely large enough for a full load, but when presented with an overload, It couldn't keep up.  Along with the rebuild will be a larger radiator.

[mike90045]

You could use an IR thermometer to locate a "sweet" spot, while the engine is hot and under load.  Glue sensor on there and hope it does it thing.

[potter]

I have had good results with my snap switch located at the top of the cylinder (flywheel side) by the water outlet. It has saved me already when  I had a hose crack from vibration.

    Potter                     

[Crofter]

I'm also for the spot near the exhaust port, but I dont think that snap discs give nearly quick enough response.. I have seen lots of cracked heads from coolant loss and boiling can cause chugging and gurgling that can intermittenly splash cool overheated surfaces. Temperature differential is worse than high temperatures for cracking heads. By the time you have active boiling in a closed head like a CS you are in troubled waters. A hopper cooled cylinder designed to continually boil off is a different animal.

Wherever you place the snap discs it is important to get tight, flat (even spring loaded) contact with metal of the head I use one on my lower rad hose to kick in the radiator fan and found that a thick wad of fiberglass insulation on the outside of the whole switch makes it come on about 10 degrees sooner.

[Ronmar]

When I had an overheat several months ago, all of my coolant boiled over INTO my overflow tank!!

Oh, you have a siphon type overflow, I didn't think of that...  With that type, ANY leak in the system will keep coolant from being drawn from the resovoir/overflow back into the system.  Just like in a car, when the radiator is empty, and the catch can is still full, you have a pinhole leak somewhere preventing the system from pulling a vacume when the system cools to draw fluid back into the system to make up for any losses.  So the radiator level just keeps getting lower and lower and the catch can never makes up the losses...  In a thermosiphon system using an auto radiator, it dosn't take much coolant loss to break the siphon, then you are in pure evap/tank cooling mode... 

I setup my expansion tank with a bottom feed, located ABOVE the vent port on my system.  This way the tank can reliably maintain the system completely full under ALL situations.  I can watch the level go up as it warms, and back down as it cools.  Since this is the actual system level up in the tank, this will show me a leak quickly at a glance.  It is usually the first thing I see when I walk into the generator room...  The best place is above the radiator, gravity fed.  The ONLY reason to put it below the top of the radiator is because the engine compartment on an auto won't allow that...  A float switch here could give me an alarm with as little as a cup of coolant lost from the system... 

In an overheat, the expansion tank would bubble up in a boilover as the steam passed up thru it, but as the system gulped between boilovers, the coolant level would get sucked down into the system pretty quickly...

[bschwartz]

Ron, while I put in the larger radiator, I may redo the expansion tank.....
Do you have pictures of yours? (aside from your cute avatar)

[Crofter]

Wherever you place the snap discs it is important to get tight, flat (even spring loaded) contact with metal of the head

I will be using heat transfer paste as used in transistors

Fan cy! yep, that is a good added touch, still it is shutting the barn door after the cows are gone, but better than letting things continue till meltdown. The damage from over heating is not always instantaneous and often you get away with it many occasions before it accumulates stress till it self relieves in a crack.

Yah, preaching, I know, but I grew up in an auto wrecking yard and used to seeing lots of cracked blocks and heads. If you were boiling an engine you were doing something bad.

[potter]

Don't laugh its worked for the past year and a half.