Temperature Guage Problems

[Limestone]

Hi, I have a 12 year old boat with a Mercruiser 5.7L engine. The temperature guage seems to have stopped working and we notice the following symptoms:<br />- guage used to work fine a few weeks ago<br />- guage started cutting in and out but is completely dead now.<br />- at one time, turning on the guage panel lights made the guage work (no longer true)<br />- sometimes the voltmeter cuts out and the tachometer reads 50% higher then the actual revs for a brief period of time<br />- I measusured the voltage at the temperature guage leads and it seems to exist (10-12 volts it was hard to reacg the guage though). Could we have a grounding problem ?<br /><br />Any help would be appreciated - I'm not sure what to do next.<br /><br />BTW: Has anyone had experience adding an exhaust or oil temperature guage to this type of engine?

 

[mikeyb]

Re: Temperature Guage Problems

Hey Limestone,<br /><br />Does sound like you may have wiring probs. If you're getting power to the guage try the wire from the temp transmitter on the engine to guage. You may have a continuity problem. There will probably be an earth wire leading back to the boat battery, check the continuity here also.<br /><br />Boat electrics are so prone to bad continuity through corrosion eating away at connections and also inside the insulation of the wiring. Even if the connection is okay the wire could be rotting away somewhere along its length.<br /><br />Good luck, I'll keep an eye out for a progress report <br /><br />Mike.

 

[Limestone]

Re: Temperature Guage Problems

Perhaps I need a better understanding of how these guages work - here is my current understanding:<br />- The guage itself requires 12v power in the form of a positive and a ground. This in theory should be seen as two wires to the guage which I can measure the power on.<br />- The guage also has a wire from the sender probe (or is it two wires?). I should be able to do a continuity check between this wire and ground (or the two wires if there are two wires). <br />- Would it be correct to say that the resistance betweem the sender wire and the ground changes with the engine's temperature?<br /><br />Thanks.

 

[fone_man]

Re: Temperature Guage Problems

Sounds like a bad connection at battery... but I have seen guage area butchered by someone wanting to hook up accessories... START there!!!

 

[Walter]

Re: Temperature Guage Problems

I suspect your gauge is very similar to mine...and mine works as most temp gauges I've encountered do. I think Fone_Man has you on the correct path considering you have other electrical issues other than just your temp gauge. But if you're interested, here's how it works:<br /><br />A 12 volt source (controlled via ignition cicuit) is provided to your gauge and the ground side is "regulated" by the resistance within the coolant temperature sender. The warmer the engine coolant...the less resistance to ground...thus moving the needle further around the gauge. Testing your circuit is simple:<br /><br />1) Turn key switch to run position (Do NOT start engine) and insure you have a good 12 volt source at the positive post of your temp gauge.<br /><br />2) Remove the ground wire from the coolant temperature sender (should be located on your engine's intake manifold) and put it to ground by touching the ring terminal to the engine block. <br /><br />If your sender circuit is good...your gauge should peg to the max. temp reading. If it doesn't, the sender wire itself...or either connector at it's ends are faulty. If they check out ok...then double check your 12 volt source at the gauge. If that checks out ok...then your gauge is most likely the problem.<br /><br />Like MikeOman said...boats are notorious for poor connections etc. The fact you have multiple problems...I'm betting on Fone_Man's suggestion that you have a poor ground somewhere. <br /><br />Good luck...<br /><br />Walt

 

[Limestone]

Re: Temperature Guage Problems

Thanks everyone for your help. Using my multimeter and the suggestions posted here, I was able to track down the problem. <br /><br />All wiring to the engine goes through a large, circular multi-prong connector which is mounted to the engine block. It seems that the some of the connections are intermittent in this connector as wiggling it caused the temp guage to work/not work. One time, when I wiggled too much, the boat wouldn't start. I suppose I could get and rewire a new connector or try to clean the contacts on the existing connector. What is the BEST solution for this problem? Doesn't anyone make connectors with gold plating? Do I need a connector at all?<br /><br />Thanks again.

 

[ODDD1]

Re: Temperature Guage Problems

Limestone,you are correct in assuming the umbilical harness connector on the motor is a weak point....the original merc equipment was silver plated brass pins...many boat harnesses are nothing more than rolled tin plated steel pins, and corrode badly....open the connector, spray with battery terminal cleaner [caustic stuff, be careful] flush with water, dry with compressed air and assemble, WITH a hose clamp around the connector to maintain tightness...hopefully will help with your erratic guages....