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Discussion Starter #1
Help, I installed a set of new "stock" gauges from Heartbeat City Camaro, in the center console of my 69 Camaro. It was the plug in unit with all 4 gauges, Temp, Battery, Fuel, and Oil. The temp gauge doesn't quite "peg" itself all the way on hot, but it moves into the orange, while idling, but then backs off as I drive it. It states the engine is overheating, but like I said, then backs off when being cooled as I drive. I know the engine is not overheating, never had this problem with the old gauges. Anyone got a solution to get this gauge to read correct?
 

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It probably is reading correctly. Your old gauges where the ones I would suspect.

You didn't mention if this was a BBC or not, but unless you have a stone stock 307 it is probably doing as the gauge says. It is cooling off because the fan is not moving enough air at idle yet while driving it is cooling down due to the increased air flow through the radiator (and increased speed of the water flow as well). That is why I think the current sending unit is doing a better job of reporting on the correct water temp. That is normal behavior with a big block and a stock radiator, and five blade fan with a fan shroud.

Most BBC need a four core radiator if brass and copper, not the stock three core. The four core BBC radiator was used with an A/C application. A BBC radiator is two inches longer than a SBC radiator, with the A/C adding another row of cores to cool off the beast. Modern engines with more aggressive cams and better heads make more power today than they did when these things were first built. Heat is a function of horsepower. One third of the heat of combustion is shed out the radiator, so the more you burn the hotter it gets. So if you have increased the power of your engine above that of the stock rated power of a BBC then you also need the stock BBC cooling system to compensate.

Today everyone has a 500 horse motor with claims of a thousand being the attention getters. Back when this car was new 500 horsepower would have made the cover of every car mag in the country and had you leading Pro Stock in the national rankings.

I prefer an aluminum radiator, not because aluminum is a better conductor of heat (and electricity) than cooper (it isn't) but because the metal itself is stronger and the tubes are welded not soldered to the tank. That strength allows a higher pressure in the system (assumes you also have replaced your copper/brass heater core with one made of aluminum) to cool the engine better. Higher pressure prevents steam bubbles from forming which insulates the blocks water jackets from shedding heat. A seven blade fan driven by a thermostatic fan clutch mounted in a stock factory fan shroud and you can idle all day with your high horse motor. Aluminum also offers a larger tube which results in fewer tubes to reduce air flow and more surface area to expose the coolant to air flow.

Your problem isn't with your gauge but with your cooling system. The gauge is working in my opinion.

Larger Dave
 

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Yeah sounds like the issue is the cooling system. As you move additional air is crossing the radiator and block dropping temp. Stop at a light and the situation changes. The new gauge is more sensitive than your old one is more likely than it is defective.

As Dave says above the radiator, water pump would be the usual suspects, but it could be the fan, fan belt and or clutch fan is so equipped, or a cracked or missing radiator fan shroud.
 

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A quick mental gauge calibration is with a cold engine and a 180 deg thermostat,
start cold engine and feel the upper radiator hose.
When stat opens, hose gets hot. Check gauge indication.
Gauge needle should be around the 10 o'clock mark as noon mark is 210 degs.

But, as suggested, broken or missing shroud, plugged radiator, loose belt, or, maybe a bad connection. Did previous gauge show differently?
 

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Discussion Starter #6
Gentlemen, I am sorry, I forgot to add that this is a 350 small block chevy engine. I do apologize if this changes your thinking. The old gauge was reading around 180 degrees. Now its just the classic stock gauge that originally was in the car. I have never had a problem with overheating in the car. Any more advice would be greatly appreciated. Again, I apologize for not stating it was a small block 350.
 

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The temp gauge doesn't quite "peg" itself all the way on hot, but it moves into the orange, while idling, but then backs off as I drive it. It states the engine is overheating, but like I said, then backs off when being cooled as I drive.
More details please. Are you letting the car idle for a long time before driving? Have you been driving and then come to a stop light where the gauge climbs then when you take off it comes back down? Where does the gauge sit when steady driving? 1/4 mark? 1/2 mark? 3/4 mark?
 

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The set of gauges you purchased from Heartbeat City are electric. The temperature gauge has a single green wire going to the sending unit in the driver's side head. If you have an aluminum intake manifold you can move the sending unit to it. You get a better reading from being in the intake manifold, the head gives a hotter reading. To accurately check the system you need an infrared thermometer like this one. http://www.harborfreight.com/infrared-thermometer-93984.html. The water pump, thermostat, or low fluid level in the radiator can be causes of what you describe. To eliminate the thermostat, drop it in a pot of water and heat to a boil. Watch it carefully to see when it starts to open because you will have to take the temperature of the water at the same time. I have purchased thermostats that I could watch it open and close by my water temp gauge in my truck. I would take it back, explain what the problem was and get a new one. (Lifetime warranty) Another way to check that gauge is by removing the gauge from the car and remove the sending unit too. Bring the gauge and sending unit into the house to test. You will need a piece of wire (2') at the most. Hook it and a ground wire to the gauge. Set the gauge on the counter where it is easily seen and drop the sending unit into a pot of water. Check the water temp as you heat the water (the infrared thermometer would would be nice to have) at different times and compare to what the gauge is reading.
 

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Discussion Starter #10
Ok, here is what I have tried so far. I bought a Infrared heat gun at Harbor Freight, and started the car, and let it run for a good half an hour, and the gauge in the car never went above the hash mark just past the "high noon" hash mark. The readings on the gun never got above 150 degrees on the thermostat housing or about 160 degrees on the block itself. The upper radiator hose was hot, so I know the thermostat was open. It read overheating when i was driving it at normal speeds, then would get into the warning area at a stop light, then back down after I started driving again. Not sure why today, after idling for over 30 mins, that it never even came close to the readings I got the last time I drove it. Any suggestions?? I would believe I have the wrong sensor for the gauge, installed. Any more help would be appreciated. Thanks, Chris.
 

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Lots of things could be causing the spikes, sitting at idle put little load on the engine, so driving heats her up deeper - quicker then the system is able to loose heat through the radiator.

A few tests. In traffic does the temp still raise if you have the heat on full blast? If not then your water pump and or fan are not working fast enough, or your radiator is clogged.

Is this an automatic? Transmission fluid may also be tasking the radiator if it is unable to rid the heat quickly.
 

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Did you reinstall the old 86 ohm resistor from the back of the original gauge across the terminals on the back of the new gauge? Without that resistor the gauge will read way higher than the actual temperature seen by the sender.
 
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