Topic: Accuracy of temperature gauges?


Tim I    -- 04-11-2011 @ 10:09 AM
  Speaking of running hot, my '38 coupe doesn't seem to. Now that I'm driving it (albeit just a bit,until I get new tires)the red liquid in the gauge seems to go up to 160 degrees and stay there. Are those old gauges generally reliable? The radiator does seem to puke a bit of coolant out the overflow when I drive it, but I'm thinking it may be that it's a little overfull.

Are these cooling systems pressuized?

Tim


supereal    -- 04-11-2011 @ 10:20 AM
  Tim: Dash gauges of most cars, particularly old ones, are seldom very accurate. They are sort of like weather vanes. They give indication of flow and direction, but not velocity. Many install auxilliary mechanical gauges for temperature and oil pressure, just to be sure. You will note that most modern vehicles have eliminated numbers on the gauges, while others depend on warning lights. If the relative inaccuracy of old car instruments bothers anyone, they are probably in the wrong hobby. Get used to what the gauges say, and compare it with what you see, while you drive and enjoy your car.


Tim I    -- 04-11-2011 @ 10:58 AM
  Given that the gauges aren't particularly accurate, can I assume that I don't have an overheating problem as long as the radiator isn't boiling, and the engine seems to be running well? (I plan to run a 50/50 mixture of antifreeze.)

Thanks.

Tim


supereal    -- 04-11-2011 @ 12:49 PM
  Always check the coolant temp with a thermometer in the neck of the radiator. Don't rely on an infrared gun, as they are widely influenced by the surface being checked. They are useful in spotting flow problems in radiators by scanning the surface from top to bottom. Any anomalies will quickly show up. Any serious overheating will produce overflow from the radiator tube. Some loss is normal after refilling the system as the expansion of the coolant takes place, but should quickly subside.


ford38v8    -- 04-11-2011 @ 10:40 PM
  Tim and Bob, I have only one thing to add regarding the accuracy of Tims temperature gage... Tim, your gage is as accurate as the thermometer you put under your tongue when you suspect a fever. It is factory calibrated, each and every one, with an etched line at the level the fluid attains when the bulb is at 212ºF. You will see that your dash gage has the number 212, and close inspection will reveal that the etch on the tube is, or should be, lined up at that mark.

If an original sending unit is not accurate, it has been tampered with. To verify accuracy, remove the unit and place the bulb in a pot of water on the stove. As the water boils, it should show at the mark. An etch mark that no longer indicates 212º means the unit has been damaged. The bulb may be dented, the line crushed or kinked, or a leak has occurred.

Gage units that have been removed from service and stored incorrectly may entrain air bubbles in the line. If there are air bubbles visible in the glass tube, there are a couple of ways to remedy, basically similar to shaking down the aforementioned under-tongue-themometer.

Boil and cool repeatedly while hanging the unit vertically to allow gravity to work in your favor. A vibrator may be used to induce the bubbles to rise and escape. The process can also be speeded up by attaching to a pole (for stability) and swinging it around in a wide arc to increase the G force. Patience will produce positive results, these are the tried and true methods, but you may find a better way.

Alan


TomO    -- 04-12-2011 @ 8:32 AM
  Tim,

Coolant coming out of your overflow can be normal if it was overfilled or could be due to foaming of the anti-freeze. Skip's pressure valve will help control both conditions.

You can purchase a candy thermometer at your local hardware store to check the temperature of your coolant and the accuracy of your gauge, without having to remove the gauge from the car.

I agree with Alan that the dash gauges in Ford cars are usually very accurate unless they have been messed with.

Tom


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