Stumped: can't get reading on temp gauge.

[OldNBold51]

95 7.4L in a 232 wellcraft. while this boat is new to me, it has never shown a reading on the temp gauge.

I've installed the following over the coures of 25hrs that I've owned it.

1) new temp sending unit 2) new thermostat.. No change.

I've tested the gauge per the manual by jumping a ground wire at the sending unit threads in thermo housing and pegged the gauge's needle all the way to hot.

The engine is running cool enough to lay my hands on the risers for 5 seconds.

I'm stumped and becoming paranoid . Any help would be appreciated.

 

[woosterken]

Re: Stumped: can't get reading on temp gauge.

can you get a multimeter and check the wires , between the gauge head (in dash) and the sending unit on the engine block?
the wire could be broken some where along the way

woosterken

 

[Bt Doctur]

Re: Stumped: can't get reading on temp gauge.

teflon tape on the sender?
This can result in a poor connection between the sender and what it screws into.

 

[Rocky_Road]

Re: Stumped: can't get reading on temp gauge.

teflon tape on the sender?
This can result in a poor connection between the sender and what it screws into.

My guess also.

The sender has to make solid ground to the engine block, using it's pipe thread (no sealer required) to operate. The fact that he grounded the sender's post and the gauge pegged tells me two things: the wire going to the gauge is fine, and the sender unit itself is not grounded.

Happy boating!

 

[fishinpa]

Re: Stumped: can't get reading on temp gauge.

Like Bt and Rocky stated

sounds like the place to look !



fish

 

[HT32BSX115]

Re: Stumped: can't get reading on temp gauge.

I've tested the gauge per the manual by jumping a ground wire at the sending unit threads in thermo housing and pegged the gauge's needle all the way to hot.

Howdy,

What exactly did you "short" to ground? The "threads" in the center of the sender or the case (I.E. BODY of the sender?)

If you shorted the "threads" that are screwed into the thermostat housing to ground, and the gage pegged, you need to replace the sender AND ensure that you have good ground connection from the sender (body) to the thermostat housing and a good ground connection from the thermostat housing to the manifold, AND a good ground connection from the intake manifold (if the housing is in the manifold) to the engine block.

See a pattern here? The sender (body) MUST be connected to a good electrical ground to work properly.

You can test your ground by using a little emory cloth, sand paper, file, etc, to "shine-up" the brass sender (body) and then just touch a wire from it to ground to test. If the gage pegs up-scale when you do this, the sender itself is SHORTED and must be replaced.


The center connection of the sender (the one that the sender wire IS connected to) must also have a good connection to the wire that goes up to the instrument panel/gage.


You test the gage by simply taking a wire with alligator clips on both ends and grounding the center connection of the sender (with the wire to the gage still attached of course) The gage should peg "up-scale"..........this is the same as DISCONNECTING the wire and touching it to ground........


If it does "peg" , the sender or the sender ground is faulty.



The sender is just a variable resistor. It changes resistance with temp............ one end of the resistor is connected to the gage, and other end is connected to ground. (.....the engine block....through the t-stat housing, intake manifold, block, bolt on the block, cable bolted to the block to the negative post on the battery)


All these connections must be clean and tight!


Cheers,


Rick

 

[jtmarten]

Re: Stumped: can't get reading on temp gauge.

This came up in another thread.

Make sure the body the sender is mounted in has a 'grounding gasket'. Apparently there are special gaskets for some units that incorporate a grounding source. Sounds like it may have a standard paper gasket.

 

[Rocky_Road]

Re: Stumped: can't get reading on temp gauge.

Howdy,

What exactly did you "short" to ground? The "threads" in the center of the sender or the case (I.E. BODY of the sender?)

If you shorted the "threads" that are screwed into the thermostat housing to ground, and the gage pegged, you need to replace the sender AND ensure that you have good ground connection from the sender (body) to the thermostat housing and a good ground connection from the thermostat housing to the manifold, AND a good ground connection from the intake manifold (if the housing is in the manifold) to the engine block.

See a pattern here? The sender (body) MUST be connected to a good electrical ground to work properly.

You can test your ground by using a little emory cloth, sand paper, file, etc, to "shine-up" the brass sender (body) and then just touch a wire from it to ground to test. If the gage pegs up-scale when you do this, the sender itself is SHORTED and must be replaced.


The center connection of the sender (the one that the sender wire IS connected to) must also have a good connection to the wire that goes up to the instrument panel/gage.


You test the gage by simply taking a wire with alligator clips on both ends and grounding the center connection of the sender (with the wire to the gage still attached of course) The gage should peg "up-scale"..........this is the same as DISCONNECTING the wire and touching it to ground........


If it does "peg" , the sender or the sender ground is faulty.



The sender is just a variable resistor. It changes resistance with temp............ one end of the resistor is connected to the gage, and other end is connected to ground. (.....the engine block....through the t-stat housing, intake manifold, block, bolt on the block, cable bolted to the block to the negative post on the battery)


All these connections must be clean and tight!


Cheers,


Rick

I see your concern, Rick...did he ground the wire, or the sending unit body?

Since the sending unit is new, my money is that he correctly grounded the sender post.

I have always felt that the easiest way to check your wiring, and gauge, is to simply take the wire OFF of the sending unit and place it to an engine ground...all simple! This isolates the sending unit in total, and narrows down your search by 2X.

Happy boating!

 

[OldNBold51]

Re: Stumped: can't get reading on temp gauge.

What exactly did you "short" to ground? The "threads" in the center of the sender or the case (I.E. BODY of the sender?) The threads in the T-stat housing. (not sender at all) I was testing the grounding of the t-stat housing.

If you shorted the "threads" that are screwed into the thermostat housing to ground, and the gage pegged, you need to replace the sender AND ensure that you have good ground connection from the sender (body) to the thermostat housing and a good ground connection from the thermostat housing to the manifold, AND a good ground connection from the intake manifold (if the housing is in the manifold) to the engine block.

See a pattern here? The sender (body) MUST be connected to a good electrical ground to work properly.

You can test your ground by using a little emory cloth, sand paper, file, etc, to "shine-up" the brass sender (body) and then just touch a wire from it to ground to test. If the gage pegs up-scale when you do this, the sender itself is SHORTED and must be replaced.


The center connection of the sender (the one that the sender wire IS connected to) must also have a good connection to the wire that goes up to the instrument panel/gage.


You test the gage by simply taking a wire with alligator clips on both ends and grounding the center connection of the sender (with the wire to the gage still attached of course) The gage should peg "up-scale"..........this is the same as DISCONNECTING the wire and touching it to ground........


the center connection of the sender I don't understand what you mean. Are you saying ground to the outside of sender?


If it does "peg" , the sender or the sender ground is faulty.



The sender is just a variable resistor. It changes resistance with temp............ one end of the resistor is connected to the gage, and other end is connected to ground. (.....the engine block....through the t-stat housing, intake manifold, block, bolt on the block, cable bolted to the block to the negative post on the battery)


All these connections must be clean and tight!


Cheers,


Rick

What exactly did you "short" to ground? The "threads" in the center of the sender or the case (I.E. BODY of the sender?) The threads in the T-stat housing. (not sender at all) I was testing the grounding of the t-stat housing.


the center connection of the sender I don't understand what you mean. Are you saying ground to the outside of sender?


Thanks guys. Surely this is something simple.

 

[HT32BSX115]

Re: Stumped: can't get reading on temp gauge.

What exactly did you "short" to ground? The "threads" in the center of the sender or the case (I.E. BODY of the sender?) The threads in the T-stat housing. (not sender at all) I was testing the grounding of the t-stat housing.

Ok,


You're saying that you were in fact testing the "ground"

If you did short the ground side of the sender to "ground"

Then your t-stat housing is probably somehow insulated from the rest of the manifold.........Didn't you also say that when you did that the gage "pegged"?


If that happened. The sender is SHORTED. The sender should always exhibit some resistance when it's cold. It should NEVER be shorted.

Your gage is just a simple ammeter (actually it's a MILLI-ammeter)

It's just reading current through the sender which isn't much when the sender is cold. (high resistance) when the sender gets hot, it's internal resistance become lower so the meter reads higher.

 

[carcraze]

Re: Stumped: can't get reading on temp gauge.

I do not have the manual for that motor so I do not know what the housing looks like. On mine I have the 1988 350 mag and I know in that era the 454 used a similiar housing per my manual to mine. My senders are mounted in an upper thermo housing which has a cover plate above that which the bolts go through. The bottom gasket between the manifold and the housing (which house the senders) has a gasket which has copper rivets in it so the housing will ground to the manifold. The gasket can not have sealant on it or the senders will not ground and not read.

I am not sure if that is the system yours has or not, the manual for mine has a note to not use sealant on the gasket so if your is the same I would assume the manual details that.

 

[OldNBold51]

Re: Stumped: can't get reading on temp gauge.

I do not have the manual for that motor so I do not know what the housing looks like. On mine I have the 1988 350 mag and I know in that era the 454 used a similiar housing per my manual to mine. My senders are mounted in an upper thermo housing which has a cover plate above that which the bolts go through. The bottom gasket between the manifold and the housing (which house the senders) has a gasket which has copper rivets in it so the housing will ground to the manifold. The gasket can not have sealant on it or the senders will not ground and not read.

I am not sure if that is the system yours has or not, the manual for mine has a note to not use sealant on the gasket so if your is the same I would assume the manual details that.

New gasket with the 4 copper rivets, installed w/o sealant. My housing is grounded as I jumped a wire from the housing to the wire to gauge which "pegs" the gauge.

 

[jtmarten]

Re: Stumped: can't get reading on temp gauge.

If you have a good ground to the housing, then just replace the sender. You already know the gauge and wiring is good.

 

[OldNBold51]

Re: Stumped: can't get reading on temp gauge.

Ok,


You're saying that you were in fact testing the "ground"

If you did short the ground side of the sender to "ground"

Then your t-stat housing is probably somehow insulated from the rest of the manifold.........Didn't you also say that when you did that the gage "pegged"?


If that happened. The sender is SHORTED. The sender should always exhibit some resistance when it's cold. It should NEVER be shorted.

Your gage is just a simple ammeter (actually it's a MILLI-ammeter)

It's just reading current through the sender which isn't much when the sender is cold. (high resistance) when the sender gets hot, it's internal resistance become lower so the meter reads higher.

Where is the "ground" side of sender? I'm assuming I have a ground "side" and the variable "side" of the sender, with the variable side culminating at the tip where sending wire hooks up.....right?

 

[OldNBold51]

Re: Stumped: can't get reading on temp gauge.

If you have a good ground to the housing, then just replace the sender. You already know the gauge and wiring is good.

I have a new sender installed.

 

[Rocky_Road]

Re: Stumped: can't get reading on temp gauge.

Where is the "ground" side of sender? I'm assuming I have a ground "side" and the variable "side" of the sender, with the variable side culminating at the tip where sending wire hooks up.....right?

You are on the right track: the threads of the sending unit are the ground, and the post and wire carry the variable current (that operates the gauge).

If you disconnect the wire...have your key in the "RUN/ON" position...and touch the wire to a good engine ground...the gauge should 'peg' full right (overheat).

If this happens, then your wiring and gauge are fine.

 

[HT32BSX115]

Re: Stumped: can't get reading on temp gauge.

Where is the "ground" side of sender? I'm assuming I have a ground "side" and the variable "side" of the sender, with the variable side culminating at the tip where sending wire hooks up.....right?

You're right. The ground "side" is the part screwed into the housing.

The variable side IS where the wire connects.

If it'snew, it should be ok. You can however test it by using a small cheepee DVM ( Digital Volt Meter that also has resistance measuring capability) like the type you could get at Harbor Freight or Radio Shack. The sender should be at approx 250 ohms cold and should drop to about 40 ohms or so when you heat it.


It's important to have good clean connections. (that the why of the rivets in the gasket, and the instructions NOT to use T-tape on the threads etc)

If the gage pegs when you touch a wire from ground to the sender wire, the gage is probably "ok"...

 

[carcraze]

Re: Stumped: can't get reading on temp gauge.

Or if you wish to check the gauge and the sensor ground jump from the center peg which goes to the gauge and the sensor body. If the sensor body is truly grounded and the gauge is good then the gauge will pin. If it does not and yet it pins when jumping to a known good ground the problem still lies in the sending unit being properly grounded either through the housing to manifold joint or the sender has some sort of sealant on it isolating it from grounding through the housing.

I have also been told enough corrosion on the gasket surface can also isolate it even with the copper rivets but I assume you clean the 2 surfaces up well.