Coolant Temperature Sending Unit
Thread Starter
Instructor
Joined: Dec 2005
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Coolant Temperature Sending Unit
I have a 94 LT1.
Both instrument gauges on the dash don't 'match' with the same accuracy.
The digital gauge appears to be right on.
The analog gauge gauge always seems 40-60 degrees higher if not reading off the chart even when the engine is cool.
I've always ignored it as I knew the digital was telling what was going on.
I've never replaced the Coolant Temp Sending Unit on the r/s head. I was wondering if this sensor is the one responsible for sending information to the analog gauge? Granted, I know there could be other variables like a grounded wire, but, I am just trying to figure the correct area to trace.
I have the Big Corvette GM manuals...but somehow in the last 2 months packed them somewhere in my house.
Does anyone have some good first hand knowledge of this?
Both instrument gauges on the dash don't 'match' with the same accuracy.
The digital gauge appears to be right on.
The analog gauge gauge always seems 40-60 degrees higher if not reading off the chart even when the engine is cool.
I've always ignored it as I knew the digital was telling what was going on.
I've never replaced the Coolant Temp Sending Unit on the r/s head. I was wondering if this sensor is the one responsible for sending information to the analog gauge? Granted, I know there could be other variables like a grounded wire, but, I am just trying to figure the correct area to trace.
I have the Big Corvette GM manuals...but somehow in the last 2 months packed them somewhere in my house.
Does anyone have some good first hand knowledge of this?
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
According to my Owner's booklet (96), the coolant sensors are made to work accurately with a 50/50 mix of anti-freeze and water. That changing that ratio can effect the accuracy of the readout.
Jake
Jake
Le Mans Master
Joined: Dec 2004
Posts: 5,789
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From: Myrtle Beach SC
St. Jude Donor '05-'06
On most cars they never will match. The gauge is analog the LCD is digital. Analog gauges change over time digital ones work off a resistor and 5V. Believe the digital and forget the analog unless it gets burried then check the digital.
Melting Slicks
Joined: Oct 2006
Posts: 2,238
Likes: 10
From: College Station TX
To the OP, I'd start by replacing the sending unit and see where that gets you. My money is on either the sending unit or the cluster not working properly.
Thread Starter
Instructor
Joined: Dec 2005
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Thanks
I'm still pissed because I can't find my books. Those of you that have them, know they're pretty big to just misplace. They must of been packed in a box somewhere.
I was pretty sure that the sending unit on the right side head was the culprit.
One of these days when I get bored I'll replace it. It's just weird when you see it creep slowly up & then gets pinned over to the hot mark.
It's just one of those things that bug you.
I'm still pissed because I can't find my books. Those of you that have them, know they're pretty big to just misplace. They must of been packed in a box somewhere.
I was pretty sure that the sending unit on the right side head was the culprit.
One of these days when I get bored I'll replace it. It's just weird when you see it creep slowly up & then gets pinned over to the hot mark.
It's just one of those things that bug you.
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
To the OP I doubt the sensor will change much of anything they are pretty reliable it is the gauge that is not thus why digital is better than analog(mechanical).
Last edited by Redeasysport; Jul 25, 2008 at 09:55 PM.
Thread Starter
Instructor
Joined: Dec 2005
Posts: 101
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I hear what everyone is saying.....
but I doubt when this car was brand new the gauge was all over the place. Otherwise, why have it there & for what purpose?
It has to be a series of things from the sensor, wiring, gauge, & etc....
My experience is you start at one end & look at all the components until you get to the other end. Which is why I wanted to make sure I was starting in the right spot.
The gauge could very well be bad....so could the sensor. I hate replacing good parts so I will make sure the wiring looks good to start with. From there....I will then start with the cheapest & easiest part to get to & go from there.
but I doubt when this car was brand new the gauge was all over the place. Otherwise, why have it there & for what purpose?
It has to be a series of things from the sensor, wiring, gauge, & etc....
My experience is you start at one end & look at all the components until you get to the other end. Which is why I wanted to make sure I was starting in the right spot.
The gauge could very well be bad....so could the sensor. I hate replacing good parts so I will make sure the wiring looks good to start with. From there....I will then start with the cheapest & easiest part to get to & go from there.
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Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
I hear what everyone is saying.....
but I doubt when this car was brand new the gauge was all over the place. Otherwise, why have it there & for what purpose?
It has to be a series of things from the sensor, wiring, gauge, & etc....
My experience is you start at one end & look at all the components until you get to the other end. Which is why I wanted to make sure I was starting in the right spot.
The gauge could very well be bad....so could the sensor. I hate replacing good parts so I will make sure the wiring looks good to start with. From there....I will then start with the cheapest & easiest part to get to & go from there.
but I doubt when this car was brand new the gauge was all over the place. Otherwise, why have it there & for what purpose?
It has to be a series of things from the sensor, wiring, gauge, & etc....
My experience is you start at one end & look at all the components until you get to the other end. Which is why I wanted to make sure I was starting in the right spot.
The gauge could very well be bad....so could the sensor. I hate replacing good parts so I will make sure the wiring looks good to start with. From there....I will then start with the cheapest & easiest part to get to & go from there.
Thread Starter
Instructor
Joined: Dec 2005
Posts: 101
Likes: 0
The way to check the sensor is to use 2 pins in the harness near it and check the voltage across those 2 pins if it is steady the sensor is fine.It should read between 0-5 volts. The gauge is a whole other thing and will require sending it off to be repaired. There are no replacement gauges available. Yes it could be a wiring issue good luck with that one.
only place I would be checking the wiring is near the exhaust manifold. If it got burnt or grouning out....that could cause some issues.
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
The LT1/LT4 has a "reverse flow" cooling system as compared to most other vehicles.
There are a couple of things to keep in mind:
1) The analog sensor is in the right side cylinder head and the digital sensor is in the water pump. The heads, and therefore the analog sensor, gets the coolant from the radiator first and then the coolant flow is "down" through the block and out to the radiator after flowing past the digital sensor. Therefore, the analog gauge should always read cooler than the digital gauge simply because the coolant should be cooler in the heads.
2) The analog gauge is "non-linear." At best, you are extrapolating a reading from some dividing lines that do not have the same temperature span between divisions -- good luck trying to read it with any accuracy.
Tom Piper
There are a couple of things to keep in mind:
1) The analog sensor is in the right side cylinder head and the digital sensor is in the water pump. The heads, and therefore the analog sensor, gets the coolant from the radiator first and then the coolant flow is "down" through the block and out to the radiator after flowing past the digital sensor. Therefore, the analog gauge should always read cooler than the digital gauge simply because the coolant should be cooler in the heads.
2) The analog gauge is "non-linear." At best, you are extrapolating a reading from some dividing lines that do not have the same temperature span between divisions -- good luck trying to read it with any accuracy.
Tom Piper
