No Temperature Reading

[victoryinerie]

I just bought a 1998 boat with with 5.7 Merc and temperature guage needle does not move, I assume it is the thermostat or the guage it self. Any suggestions on how to check the thermostat or the guage? If it is not one of these two things what else should I be looking at, the boat is running great.

 

[Brewman61]

Re: No Temperature Reading

Would either be the gauge or the temperature sender. Thermostat isn't part of the temp gauge circuit.

 

[Bondo]

Re: No Temperature Reading

Any suggestions on how to check the thermostat or the guage?

Ayuh,... Take the wire off the Sender,...
With the key on, ground it, the gauge should Peg, Hot...

 

[victoryinerie]

Re: No Temperature Reading

If the thermostat was not working wouldn't the guage read below 100? How could the themostat not be a the potential issue??

 

[CheeseCutter]

Re: No Temperature Reading

Have you cracked open the thermostat housing to know that there is a thermostat? Many people remove them to "solve" cooling problems.

 

[Rocky_Road]

Re: No Temperature Reading

If the thermostat was not working wouldn't the guage read below 100? How could the themostat not be a the potential issue??

Simple:

A thermostat stuck 'open' will read between 140 and 170, depending on the temp rating of the thermostat.

A thermostat stuck 'closed' will register over the thermostat rating...probably in the 200+ range.

A missing thermostat can be anywhere...but NEVER below 100.

You are not having a thermostat issue yet. You have a temp reading issue, and that has to be resolved before you go any further. Do what has been suggested and ground the temp lead to test the gauge. That will determine where to go next....

Happy boating!

 

[victoryinerie]

Re: No Temperature Reading

I took the wire off the sender unit and I grounded it and yes the guage pegged. I also looked and there is a thermostat, I replaced it however it made no change. I assume I have a bad sender unit?? It also seemed like the water in the left hose was hotter than the right hose, not sure if that means anything?

Thoughts before I replace the sender unit.

 

[pikiewicz]

Re: No Temperature Reading

Sounds to me like you should check the sending unit with hot water and see if it registers on the gauge. Good luck.

 

[victoryinerie]

Re: No Temperature Reading

I have not replaced the sender yet however I notice the sender threads are full of locktite or the red high temperature rtv. I was told there should not be nothing on threads and this is what creates the ground and this could be the issue. Would this be correct? Is there any way to test the sender?

 

[BAproject]

Re: No Temperature Reading

the threads should not be full of loctite, and for sure sounds like the sender is the problem.

 

[Brewman61]

Re: No Temperature Reading

I have not replaced the sender yet however I notice the sender threads are full of locktite or the red high temperature rtv. I was told there should not be nothing on threads and this is what creates the ground and this could be the issue. Would this be correct? Is there any way to test the sender?

I suppose it's possible to test a sender, but you've already eliminated the gauge itself as the issue, so why bother testing it? I don't think they're very expensive- in the US anyway, should be under $20. You put in a new thermostat knowing it hadn't shown as defective so toss in a new sender- problem solved.