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Old 10-10-2005, 10:26 AM
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How to check a temp. gauge.

I have a 355 Chevy with the Holley aluminum heads. The temp gauge is in the drivers side head. How do you check to see if its reading right? The gauge will go from 140 to 250! back to 200,up to 210, its just all over the place. It does this slowly while driving. Dosent make any difference if the A/C is on or off, weather can be cold, hot, rainy, etc. I have Dolphin gauges in the car.
Ive tried changing the thermostat from 160 to 180 to 195 Doesent seem to affect it. The compression ranges from 150 to 160.
Before I start checking timing, carb, etc. I want to make sure the gauge is right.
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Old 10-10-2005, 10:37 AM
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Sounds like you have air in the system............

If its a mechanical guage, boil some water on the stove, stick in the probe that goes in the head....it should read 212 on the guage.
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Old 10-10-2005, 12:27 PM
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Sound to me like there is air in the system.
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Old 10-10-2005, 12:40 PM
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Sounds like steam (air) in the system, bleed it best you can, keep checking the overflow and make sure there is water in there to pull into the rad when it cools. It should cure itself with a lot of hot & cold cycles, keep the overflow FULL.
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Old 10-10-2005, 05:33 PM
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Air...

Doc here,

Yup...You got air...

A Sender can't read air, as the flow goes past and a bubble lodges at the sender, the sender goes up ... when the bubble moves on , and the water quenches the sender, it returns to normal..(175 to 230 excursions)

Best way to Clear it, (assuming the system is otherwise operating good) is start it and warm, Be sure the recovery Kit is full to the cold line, and wait until it Belches..It will expel all the air and draw back coolant from the recovery tank to replace the air. That usually does it..Your Cap MUST be proper pressure and operating! If not replace it.

If you don't have a recovery tank, you need to get one, because without it, when it belches, it draws back more air..Temporary you COULD use a bucket full of coolant , but it won't solve the problem.

If you have problems, try jacking the front of the car up and belch it..and worst case scenario..you can drill and tap the Goose-neck for a standard brake bleeder to bleed off air...

To test the instrument and sender, Boil a pot of water, While doing that (before you evacuate the air) remove the sender, and wire..

Bring your pot of water to the sender (car) and score a kitchen thermometer (known accurate) and place Carefully the sender in the pot..up to the threads..(if electrical, you need to jumper a ground)

Watch the meter for "Excursions" should not have any, shake lightly the wire, then verify the temps are +/- 10 degrees of the Test thermometer, and watch as the temp falls, It should remain close to that temp first read (+5 error, or -10, whatever difference you read) all the way down to like 90...If so you should be good..

Doc

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