Temperature guage question?

[lyrikz]

Well, the exterior of my truck is done. And i was driving it today and i ran into an issue.

I have aftermarket electricla fans that are ran off a 185 degree switch. well, while driving my temp guage (which is stock) ran all the way to high. But my fans were not coming on. The truck was not overheating. Eventually the fans kicked on but the guage stayed pegged at H.

Any ideas???Just one wire from the temp sender in the side of the head to the cluster. Any thoughts??

[Lee H]

Bad or wrong sender. Verify temp with a know good gauge or IR sensor to be sure.
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[VetteVet]

The sender may have failed or the wire from the sender may have grounded itself to the block or cab. Disconnect it from the sender and see what it reads.

[lyrikz]

With the key on, when i disconnect it the reading stays. After awhile it drops back down.

I dont really no.. Im thinking of buying a cheap guage and sender and see whats going on.

[lyrikz]

Originally Posted by VetteVet

The sender may have failed or the wire from the sender may have grounded itself to the block or cab. Disconnect it from the sender and see what it reads.

I used an IR guage. The radiator/intake/thermo housing/ coolant hoses are all under 195 degrees. I point the IR at the sending unit thats located in the side of the head near the headers and it reads 235.

So, where do you guys put your guage sending unit to get the right temp??

[landsurvey1]

It sounds like the sensor is in the correct place. I have noticed some guys put it on the intake, but I think the temp. gauge would show the engine a little cooler there.

[MagmaJct]

Check your coolant level.

I didn't see where you stated the fan thermostat is located. If the coolant level is low, and your fan thermostat is in the radiator, then it won't come on because it needs heated water from the engine to sense the temp.

[lyrikz]

Originally Posted by landsurvey1

It sounds like the sensor is in the correct place. I have noticed some guys put it on the intake, but I think the temp. gauge would show the engine a little cooler there.

I moved the coolant temp guage and put it in the intake. I drove the truck 25 miles. On the freeway it stays a little bit in front of the middle mark. As soon as i stop it starts to climb. So i let it climb until the fans kicked on. I then shut the truck off and measured all areas. I measured radiator/ hoses/ heads/ temp sensor. Nothing was over 200 degrees.

Im going to just buy an aftermarket guage and mount it in the stock location. I need to see what the heck is going on.. If the water was 240 degrees wouldnt it overheat or the hoses get hotter then 190 and 185?

Originally Posted by MagmaJct

Check your coolant level.

I didn't see where you stated the fan thermostat is located. If the coolant level is low, and your fan thermostat is in the radiator, then it won't come on because it needs heated water from the engine to sense the temp.

Coolant level is topped. Fan thermostat? I have a fan switch that turns my fans on and its located in the intake manifold. My fans come on fine. Its the guage im having issues with.

[lyrikz]

anyone know what the ohm spec should be on the sending unit. I dont know what the hell is going on.

Or anyone recommend an aftermarket coolant guage that i can modify easily and put in there/?

[MagmaJct]

lyrikz,

One of us is confused. At first you stated that your fans were not coming on. That implies that you have some automatic device that turns them on, likely when a temperature is reached. That device is called a thermostat. It's similar to the thermostat in your home that controls your furnace and/or air conditioner. (Not to be confused with the thermostat in your engine). It has to sense heat to work, if the coolant level were low, preventing coolant from flowing to the thermostatic switch the fans may not come on. I have witnessed this in a vehicle with an electric fan. The engine would overheat without the fan coming on. The cause was low coolant level. However, as stated, this was found NOT to be the case in your truck, moving on...

You're not sure if the problem is the gauge, or how to test it. Then you say that you're sure it's the gauge. When troubleshooting anything, a theory is proposed that matches the symptoms present. Then the troubleshooter develops a test to prove or disprove the theory. My theory is low coolant level, which was partially based on the stated symptom the fan wasn't coming on, that was tested and proven to be incorrect, so we move on.

Next theory, is the engine thermostat good? Does it open when it should? If the thermostat sticks closed, NO coolant will flow into the radiator. In fact, the hose and radiator will remaining amazingly cool to the touch. The thermostat can be tested outside the engine. Remove it, and plop it into a pot of water and heat it on the stove. Make sure you have a thermometer in the water to know the water's temp. What temp does it open?

I really want to help solve your problem, but you have to be open to any root cause until it's proven not to be the cause. I don't know the correct resistance of the sensor at one temperature or another, otherwise I'd provide it.

Good luck, I want this problem solved too.

[Legolas894]

I think as well that you have to decide what you are going to be measuring: the coolant temperature or the block temperature. I believe the stock locations expose the temperature senders to the coolant not to the metal block. The coolant is supposed to be circulating throughout the engine. By sensing the temperature of the coolant, you are monitoring the overall heat of the engine cooling system (including the rad which is trying to remove the heat).
I'm thinking if you just put a surface mounted sensor on the block, you are measuring the temp of just that one point. The stock temp gauges are designed to work with the coolant temperature which can only reach a certain temp before boiling.is why you might be pegging the gauge if it's in direct contact with metal only.

I'm not an expert by any means but I think you should be monitoring the coolant (water) temperature and not the "engine" temp.

[Shyguy]

This may be a little different because it is in a '92 K-3500 I own, but here is the temperature sensor setup. The temperature gauge is in the driver's side head and the temperature sensor for the electric fan is in the passenger side head.

I would first verify the temperature the engine is getting up to using a cheap gauge installed in the engine in the place of the stock sensor.

[lyrikz]

Originally Posted by MagmaJct

lyrikz,

One of us is confused. At first you stated that your fans were not coming on. That implies that you have some automatic device that turns them on, likely when a temperature is reached. That device is called a thermostat. It's similar to the thermostat in your home that controls your furnace and/or air conditioner. (Not to be confused with the thermostat in your engine). It has to sense heat to work, if the coolant level were low, preventing coolant from flowing to the thermostatic switch the fans may not come on. I have witnessed this in a vehicle with an electric fan. The engine would overheat without the fan coming on. The cause was low coolant level. However, as stated, this was found NOT to be the case in your truck, moving on...

You're not sure if the problem is the gauge, or how to test it. Then you say that you're sure it's the gauge. When troubleshooting anything, a theory is proposed that matches the symptoms present. Then the troubleshooter develops a test to prove or disprove the theory. My theory is low coolant level, which was partially based on the stated symptom the fan wasn't coming on, that was tested and proven to be incorrect, so we move on.

Next theory, is the engine thermostat good? Does it open when it should? If the thermostat sticks closed, NO coolant will flow into the radiator. In fact, the hose and radiator will remaining amazingly cool to the touch. The thermostat can be tested outside the engine. Remove it, and plop it into a pot of water and heat it on the stove. Make sure you have a thermometer in the water to know the water's temp. What temp does it open?

I really want to help solve your problem, but you have to be open to any root cause until it's proven not to be the cause. I don't know the correct resistance of the sensor at one temperature or another, otherwise I'd provide it.

Good luck, I want this problem solved too.

First off, Thank you. Thanks for taking the time to explain all that stuff. I learned what i know from listening to guys on this board.

I do have a switch that activates the fans, those are coming on.

Yesterday i drove it home, and today i drove it to work. About 25 miles one way. On the freeway doing 55 ( 3 speed auto th400 SUCKS) the temp stays BELOW the middle point. As i slow the guage moves up, i can be doing about 25 in traffic and the guage will move up. So today, as soon as i got to work i gunned everything and the temps on the heads were 200, and everything else on the truck but the headers were at or under 190. But the temp guage moved up to the first hot line. Coolant is 100% topped off also.

Thermostat is new and is opening. One hose gets up to about 185 the other is about 100 then they equal out. One is 190 the other about 185.

One thing that was brought to my attention is what if the guage in the truck is just old and has a loose spring. I have put in two sending units and it does the same thing. Today i am going and buying an aftermarket coolant guage and am going to test that side by side with the stock one at the same time to see what is going on.

Originally Posted by Legolas894

I think as well that you have to decide what you are going to be measuring: the coolant temperature or the block temperature. I believe the stock locations expose the temperature senders to the coolant not to the metal block. The coolant is supposed to be circulating throughout the engine. By sensing the temperature of the coolant, you are monitoring the overall heat of the engine cooling system (including the rad which is trying to remove the heat).
I'm thinking if you just put a surface mounted sensor on the block, you are measuring the temp of just that one point. The stock temp gauges are designed to work with the coolant temperature which can only reach a certain temp before boiling.is why you might be pegging the gauge if it's in direct contact with metal only.

I'm not an expert by any means but I think you should be monitoring the coolant (water) temperature and not the "engine" temp.

The stock sending unit goes into the water ports. Hopefully when i put in a different guage it will tell me whats going on.

Originally Posted by Shyguy

This may be a little different because it is in a '92 K-3500 I own, but here is the temperature sensor setup. The temperature gauge is in the driver's side head and the temperature sensor for the electric fan is in the passenger side head.

I would first verify the temperature the engine is getting up to using a cheap gauge installed in the engine in the place of the stock sensor.

it will be here at 8 this morning and i will let you know.

[lyrikz]

Ok, installed an autometere. Never goes over 200 degrees. Fans kick on at 195.

So it appears that guage spring or whatever holds the guage is a little weak.

Thanks for all the responses and help.

Only issue im dealing with now is it smelling like RAW GAS. it has a quadrajet on it that is stock and rebuilt. I dont know if its normal smell or not. ahah. I adjusted the idle and the idle mixture down a bit, but still strong gas odor.

[Legolas894]

Originally Posted by lyrikz

Ok, installed an autometere. Never goes over 200 degrees. Fans kick on at 195.

So it appears that guage spring or whatever holds the guage is a little weak.

Thanks for all the responses and help.

Only issue im dealing with now is it smelling like RAW GAS. it has a quadrajet on it that is stock and rebuilt. I dont know if its normal smell or not. ahah. I adjusted the idle and the idle mixture down a bit, but still strong gas odor.

Mine smells gassy too. After the engine warms up, it usually is hard to start (flooded). A few cranks and it will go fine but I think it's leaking gas into the intake when it's warm.