I just bought a new motometer and when installing it I got to thinking about how it works.
It obviously doesn't measure water temperature as the sensing bulb is far above the water level in the tank.
So does it measure air temperature, or steam temperature or what? I guess the temperature of the water could be transfered to the air in the tank and the motometer would measure air temp, but I'm guessing.
So whats the mechanism involved here ??
Thanks in advance
Bud, it should measure water temperature - usually has a sensor that pokes down and into the water. maybe a photo please?
There is no mechanism, just the fluid in the tube. It measures the air space above the water, so it would be the steam heating it.
A moto meter reads the temperature of the water VAPOR in the radiator. I don't believe there's a way for the water to touch the bottom of the meter.
Yes, just measures the air/vapor temperature above the normal water surface. Probably the good thing is that the hotter it get the better/more accurate it works because steam blowing out the over flow tube would be right near the motometer temperature probe.
Was the unit you bought a new reproduction? I recently bought one but sent it back because the threaded part of the cap was too short and too small in diameter to securely screw into the radiator opening. It would only catch on one thread before it bottomed out. I ended up finding a vintage motometer/dog bone that fit well.
Here is a face to face comparison of the vintage and reproduction cap.
The repo ones have been made poorly for several years, you would think they would be right by now.
I had to spin the thread off in the lathe and cut the threaded part off an old T radiator cap and silver solder it on, that fixed it!
I thought about doing that too. I also thought about just turning a relief in the area above the threads so it would thread into the radiator opening further. However the outside diameter of the threaded part was just too small small to fit correctly, no matter haw far in threaded in.
I wrapped a piece of wire around the tip of mine and extended it down into the radiator about 2 1/2" with a cicrle at the bottom of it to allow it read a little more accurate. Seems to help.
The repro one on my Model A doesn't read anything normally. If you ever see even an 1/8" of red, you are too hot. I asked about it on the Model A forum or maybe the AACA forum many years ago when I first got it. I was told to take it off, put it back in the box and forget about it, because they were notoriously inaccurate. Kinda gun shy now. I hear people on here saying theirs reads OK, but I'm afraid to spend the money again. I still use the one on the A. It looks nice on there and I guess it does tell me a little something. They look too fancy for an unrestored black era T to me, so I doubt either of our T's will ever have one.
I am reluctant to use a motormeter now. I just run 50-50 antifreeze and water and drive the car.
Years ago, I took off the motormeters and waterpumps and let the car do what it was designed to do.
I had to repair the top tank on my '24 after the weight of the motormeter and dogbone fatigued the metal. The radiator neck along with the motormeter cap were close to falling off.
I have the Thermoquail on my '31 A and like Hal Davis says, it doesn't read anything. I now believe ignorance is bliss when it comes to knowing my radiator temperature.
Thanks for the great responses.
Right now I'm going with the theory that it measures air/water vapor/steam temperature. Which one is contributing the most to the measurement probably depends on temperature.
I find Gene's idea of wrapping a piece of copper wire arround the sensing bulb and extending it down to the water in the tank, intrigueing. Might give it a try...the price is right.
Has anyone ever measured the actual temperature of the water/radiator using a infrared thermometer? Of course it will vary depending on conditions. I guessing that under (normal) conditions it would be within a few degrees of the boiling point. The thermosiphon should work better just below boiling...no?
I'm sure others use 'em, for me a temp meter is fun on the Ford. Mine is a dash mount, unknown brand or year, but does have nifty old time needle and numbers.
Reading at start up, when warm and running at road speed the meter reads around 180.
Mounted the input sensor on the upper water outlet, that catches the hottest coolant as being pushed up into the radiator.
The fun I have noticed is at road speed the meter needle will read right at 180 or so.
Then if you ramp up speed for a while, or pull a long hill, the temp gage will begin to climb slowly, then when it gets near 200, a change begins and the needle goes back down, .....the needle then maintains 180.
It will do this from time to time as the 'thermosyphon' system burps the hotter water from the cyl head.
Ford Sales manual
My vintage meter has a extension on it that kinda swivels around and gets down into the coolant. Seems to read fairly accurate and the patina just matches the roadster. Jim
I have seen an adaptation using wire screen wrapped into a tube with cotton cloth inside clamped around the thermometer base to "wick" the heated water up to the meter.
Other ideas I saw in Spokane.
The bottom of the moto meter is not supposed to touch the water. It measures the temperature in the top of the radiator.
In a tight, closed, small-space environment at the top of the radiator, there is only a small difference in temperature between the water, vapor and air, so the difference to the motometer is minimal. However, in a boiling engine, if the water level drops too low, the motometer reading will begin to drop as the air in the nearly empty top tank will begin to cool while the engine is still getting hotter. Well seasoned motometer users know this and consider that the last warning to shut down before real damage is done. Personally, I don't let them get that far.
All that is why the simple and beautiful motometer was replaced by a sensor in the block. It gives a more direct reading of the true engine temperature.
Drive carefully, and enjoy the season! W2
I don't think you want to try a piece of copper wire. I used a piece of stainless steel welding wire. It maintains a good grip around the thermocouple with its spring tension. Not sure the soft copper would do that as it heats up.
Mostly it doesn't touch down into the water so I guess we're measuring vapor temps there.
I carry a infrared sensor which is fun to check temps in different parts of the radiator and others such as brake drums, hubs and dif's.
"However, in a boiling engine, if the water level drops too low, the motometer reading will begin to drop as the air in the nearly empty top tank will begin to cool..."
The top tank will not be "nearly empty", it will be full of steam and the motometer will read it well.
Actually, it really doesn't matter what the water temp is until it begins to steam. The motometer is probably most accurate when steaming as the steam will be in contact with the temp probe.
I don't use a motometer. If it ain't steaming I don't care what the temp is. If it is steaming, I'll know it anyway.
I'll agree with both of Jerry's last posts.
The origional Moto Meters are a steam gauge and are calibrated to operate that way.
I don't know anything about the new reproduction Moto Meters, so I can't comment on them. I don't know what they use in the thermometer on the repops but the originals were Glycerin and alcohol.
The reason for the stem not being submerged in coolant was intentional. I would think any modifications to imitate a submerged condition would alter the reading intended, at least in the lower reading and might insulate it, slowing reaction time of the meter. Boyce's theory was that the air in the radiator tank above the coolant could be as much as 30 to 50 degrees cooler than the coolant itself. If boiling occurs this changes very quickly as the steam from an overheat condition sends the red column into the danger zone very quickly. The meter is calibrated to show a low reading for operating temp and to show a spike in the sight glass when boiling. Operating temperature is very close to boiling so on a submerged thermometer your gauge would register very high all the time with very little movement as it moved in to the boiling range.
If you would like a better explanation of this, click on the link for the patent information below. Scroll down to page 5 about line 10. Boyce explains his reasons in detail much better than I can.
http://www.google.com/patents?id=lU9eAAAAEBAJ&pg=PA1&dq=1090776&as_drrb_ap=q&as_ minm_ap=0&as_miny_ap=&as_maxm_ap=0&as_maxy_ap=&as_drrb_is=q&as_minm_is=0&as_miny _is=&as_maxm_is=0&as_maxy_is=&source=gbs_selected_pages&cad=1#v=onepage&q&f=fals e
If your not a purest and have converted to 12 volt you can buy at any parts store the complete unit and just drill and tap your top outlet bracket. The gage can be mounted under the dash or you can drill and plase in dash. They work
well. They may make one for 6 volt also I didn't check.
I've compared a number of Motometers by suspending them above a pot of water and then both gradually and quickly heating the water, taking temperature measurements with both a meat and infrared thermometer. It is interesting to see the variations between them - the ones I like are the ones that have a fairly wide range of movement in the 10-20 degrees near boiling.
One thing that I don't think was mentioned above is that besides seeing if the motor is too hot, it is also good to see if it is not getting hot enough. Of course that is much more of a concern with a car with a water pump than it is with those that just have thermo-siphon.
John C. That's a very interesting side by side comparison test you've done. Just for curiosity sake, if they were tested one at a time all without caps, with all the stems completely in the pot, in the same location so that steam wouldn't escape at a different rate at a different opening, would it change the results? Again I'm not doubting your results, I'm just curious and asking your opinion.
Bob, Don't need a 12 volt system. Just get a mechanical temp gauge vs an electrical one. I put one on my T and later on changed to 12 volt system. Just had to change light bulb.
Unless steam is superheated, not likely in a Model T, the steam and water temperatures are the same. The gas above the water level in the radiator, a mixture of air and steam, should be approximately the same temperature as the water in the radiator.
I think that with a motometer in your car, you will learn its reading under normal operating conditions and recognize the reading when an abnormal condition occurs. The temperature accuracy of a motometer is of secondary importance,
The reason for the Electric is I find it easer to hide the wire and not need to be as careful locating the hole through the firewall and maybe crimping the tube. It also gives a wider range for placeing the gage in the dash.
I agree with Jerry. There are only two indications necessary in a T. >212 and <212
The T has a built in audible warning. It is called the overflow tube with steam escaping.
John B.- I don't know if testing it that way would make much of a difference - these are not precision devices... I was just curious to know how similar they were to each other and to get some idea of how the temperatures corresponded to the markings on the gauges. I've put them on cars as well and used the infrared temperature sensor on the head, outlet and upper tank, etc to compare and the results seemed pretty similar.
Thanks for the patent referance. Boyce explains it beautifully!