thermo quail

Maclab58

Maclab58

Well-known member
I just bought a quail radiator cap with a thermometer in it and i am assuming since it came with no instructions that if i stay keep the red indicator within the viewing oval im ok?
 
Most owners i have talked to say thiers run just below the circle.Mine runs about a Quarter inch below.I just dont trust those thermo s for true temps.J.M.H.O. RAY
 
If you look at the bottom of them you will see they don't reach the water level and hence only measure air temp in system.
 
I am interested in my water temp in system. If that is what you want maybe you need to put a wick on the bottom of the unit. I prefer an inside meter that gives me a true water temp. That's what runs through system not air.
 
Ray A from PA said:
I am interested in my water temp in system. If that is what you want maybe you need to put a wick on the bottom of the unit. I prefer an inside meter that gives me a true water temp. That's what runs through system not air.
Click to expand...

I agree that a gauge type thermometer is more accurate than a motometer type thermometer. I am interested in detecting a system failure causing overheating. If the actual temperature were to go up or down 5 degrees I wouldn't take action even if I knew about it. I agree that the temperature will be different at different locations. As for the motometer reading I don't believe the air temp in the radiator could be significantly different than the water temp. What could cool or heat the air at that location to a different temperature than the water it is in contact with?
 
Jerry Parr WI said:
. . . As for the motometer reading I don't believe the air temp in the radiator could be significantly different than the water temp. What could cool or heat the air at that location to a different temperature than the water it is in contact with?
Click to expand...

Despite the water and air in the top tank being at the same temperature, the MotoMeter will read lower and react much slower if only in contact with air. This happens because of two factors: 1) the much lower thermal transfer rate of water contact vs. air, and 2) the top half of the thermometer is outside, dissipating heat. If the bulb cannot source heat much faster than the top of the thermometer is losing it, the reading will be lower. Glass lab thermometers usually have an immersion mark that needs to be observed for the most accurate reading.

The thermal transfer rate of water to a solid is anywhere from 50 to 100 times that of air to a solid. If your engine goes from 160 to 200 in three minutes, a Motometer touching water will follow the rise and give warning, one in the air will not.
MotometerMisbehavin-1.jpg
 
From the pen of Harrison Hurlbert Boyce of Jericho, New York
as written in one of his many patents for a genuine Motometer . . .

“As will be readily seen from the drawings, my device consists of usual casing
having an integral hollow stem adapted to project thru a radiator cap into the
space above the water in the radiator.”

Regards
Art
 
Motor Meters are not very accurate, however, I have one on my driving A and only because if it suddenly rises way above the normal reading I know to shut down the engine and investigate before I ruin a good engine.

Ron
 
MikeK said:
Despite the water and air in the top tank being at the same temperature, the MotoMeter will read lower and react much slower if only in contact with air. This happens because of two factors: 1) the much lower thermal transfer rate of water contact vs. air, and 2) the top half of the thermometer is outside, dissipating heat. If the bulb cannot source heat much faster than the top of the thermometer is losing it, the reading will be lower. Glass lab thermometers usually have an immersion mark that needs to be observed for the most accurate reading.

The thermal transfer rate of water to a solid is anywhere from 50 to 100 times that of air to a solid. If your engine goes from 160 to 200 in three minutes, a Motometer touching water will follow the rise and give warning, one in the air will not.
Click to expand...

You are correct in theory but there are other factors that I think tend to minimize pure theory. The upper portion of the thermometer is not in free air but is contained in a closed heated housing. Still some heat disipation but I suspect it is at most fractions of a degree. The major factor I believe is the air in the radiator is saturated with heated moisture. When you open the radiator cap the bulb is dripping with moisture. Perhape not quite as fast as immersed but I anticipate the lag in rise time will be seconds rather than minutes.
 
The Motometer is not a thermometer, but just a guide to tell you what range of heat in which you are operating.
I think that about all you need to know is at what point, it is getting ready to boil.
MIKE :)
 
Jerry Parr WI said:
You are correct in theory but there are other factors that I think tend to minimize pure theory. The upper portion of the thermometer is not in free air but is contained in a closed heated housing. Still some heat disipation but I suspect it is at most fractions of a degree. The major factor I believe is the air in the radiator is saturated with heated moisture. When you open the radiator cap the bulb is dripping with moisture. Perhape not quite as fast as immersed but I anticipate the lag in rise time will be seconds rather than minutes.
Click to expand...

Jerry,
You can anticipate all you want, but the motometer lag will be minutes, not seconds if it does not touch the water and the reading will be lower. Set up a pan & lid like I posted above and try it yourself. I've done it many times. You might also want to try it at a lower water temperature like 160 and you will see a significant difference in reading between being above the water and touching the water.
 
You must log in or register to reply here.
Back
Top