[1967Tempest]

I have an electric fan,and the low speed operates off of a sending unit. It is to turn the fan on at 195*. I have the high on a toggle switch. I have yet to see consistantly the low speed turn on. Eventually it will but the temp on the gauge is over 210*

Is the gauge wrong??

I have a laser temp gun that, when the gauge says 180* the lase gun says 150-155 @ the waterneck. I am running a Performer intake. So the sending unit, t-stat and gauge are within 5 inches total of each other.

So what is right and what is wrong. Because if I am too cold, then I might not need to run the fan on high when I think that it is not turning on for the low speed.

Is there a better way? I.e. meet thermometer???

Thanks
Dave

[Old Goat 67]

I'm thinking like you are, you need a good benchmark.

What gauge, what sending unit? Is laser gun correct?

Can you compare with another laser gun?

Maybe check it with a pot of water that is just starting to boil? May not be totally accurate, but close enough?

Charles

[1967Tempest]

Originally Posted by Old Goat 67

I'm thinking like you are, you need a good benchmark.

What gauge, what sending unit? Is laser gun correct?

Can you compare with another laser gun?

Maybe check it with a pot of water that is just starting to boil? May not be totally accurate, but close enough?

Charles

Good idea. I could boil water to see if the gun is close. Might get a good baseline. Gauge is http://www.summitracing.com/parts/ATM-2433/

Question:
Is the metal t-stat housing the same temp as the water going through it after a good 40 mile run? If it is, then the gun needs to be benchmarked as above.

Dave

[1967Tempest]

Did a quick test. 1 meat thermometer, one pyrex general thermometer and the laser gun. Water temp off of stove was 180*

Meat: 180*
Pyrex: 188* Middle of 180 and 190 which is small
Laser: 179*

I have to say that the laser gun is accurate to 1*.

So, is the metal (aluminum) of the t-stat housing the same temp as the coolant. if so looks like my gauge is off.....

[Old Goat 67]

"is the metal (aluminum) of the t-stat housing the same temp as the coolant"

It sure wouldn't be 30° off.

What thermostat are you running?

[1967Tempest]

160* high flow

[Geeto 67]

I think the problem is where all these different sensors are located. Presumably you have the autometer sensor in the manifold where the idiot light used to be which is different from the waterneck. Also cooling systems operate under pressure so if you are taking a reading of the water at the water neck, then you are taking a reading of colder than what is in the rest of the engine due to the cooling system evaporating and not being under pressure.

if you are pointing the lazer at the manifold then the Gun isn't taking a reading of the water temp, it is taking a reading of the cast iron (or alloy which I think the performer is) manifold. It is entirely possible for the metal to be a different temp from the water as the water is moving through it and an incomplete heat transfer is taking place.

Remember, your engine is not a steady temp, it is in constant flux regulated by the thermostat housing.

[lust4speed]

Electric or manual gauge? I remember Auto Meter cautioning not to use thread sealant tape on the electric sending units because it would screw up the sender unit ground and produce erroneous readings. Just a thought.

[mike nixon]

You really should be taking the fan control reading off of the cyl head.

[77birdman]

My electric autometer has been off almost 10 degrees since I got it. Ordered a second sending unit, same problem. I did the laser test, however my gauge sending unit is in the intake and the fan control sensor is in the head, I think the head gets hotter than the intake.


So now I just carry a calcualtor and subtract 10 degrees from what the gauge is showing

[77birdman]

Originally Posted by mike nixon

You really should be taking the fan control reading off of the cyl head.

Why is that?

[1967Tempest]

Originally Posted by lust4speed

Electric or manual gauge? I remember Auto Meter cautioning not to use thread sealant tape on the electric sending units because it would screw up the sender unit ground and produce erroneous readings. Just a thought.

Manual.

[Pontirag]

using a sealant will change the conductivity and possibly increase resistance. That will show up as a false reading (high). I dont know who makes a sealant that conducts electricity but there is a neversieze product that is copper colored rather than silver. It is designed to conduct electricity. Never had a problem with its sealing.

Also other electrical connections can cause false readings if the wrong lubricant is used to lubricate the contact surfaces. Make sure the block itself is properly grounded. You might get away with the factory grounding under the best of circumstances but..depending on wheather the sender is in the intake or the head you want to make sure that component is also grounded. Dont assume the intak bolts or head bolts are enough. The factory never assumed that. also do the math on the electrical load and see if your alternator can handle it. Quick check, but not conclusive, is to warm up the car and turn on all the electrical accessories one by one and watch your guage does it change as you add accessories?

While your reading the guage and adding accessory loads look carefully at your guage's behavior. As you add accessoy load does your temp guage creep up? then does it slowly drop back down to where it was? If it creeps up as you add a load and stays up you could have a resistance problem or an alternator working a bit too hard. Especially if you have a stock alternator, external regulator and a heavy electronics (stereo/ignition) loads.

The cheapest thing is toCheck grounding first but also make sure your Alt can handle the additional loads.(Do the math). If your alt is rated at 42 amps and your max load is up around there (37-42 amps). you may want to go with a 60 amp. But befor you spend any money check your grounding. and if you do spend money add aditional grounds. I ground the base of my distributor to the intake and from there to the firewall and also to the cylinder.

[AG]

Check your coolant temp in the radiator with a good thermometer and compare it to your gauge.