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Water temp. indication problems.


Chaz8's Avatar
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06-28-04, 08:42 PM   #1  
Chaz8
Water temp. indication problems.

I have a 1998 Caravelle 209BR, 5.7 liter Mercruiser. My water temp. stopped indicating, so I replaced the temp. sender. That did not help, so I replaced the temp. gauge and senser. The temp. is still not working. The continuity is good from the sender to the gauge. I have electrical power to the gauge.
The needle on the gauge normally sets about four needle widths from cold, then after you start the engine, the needle moves to full cold and will not move the entire time the engine is running. Once you turn off the engine, the needle returns to it's normal position. I can tell the thermostat is working by feeling the water temp. changes on the water hoses.

The last two years, the gauge worked fine until the above mentioned problem.

Any thoughts or ideas would be very much appreciated. Thank you!


Last edited by Chaz8; 06-29-04 at 03:53 PM.
 
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06-29-04, 07:12 AM   #2  
Possible Causes and Solutions

Hello Chaz8. Welcome to our Boats, Sailing, Pwc's & Navaigations topic and the Do-It-Yourself Web Site.

The problem may not be with the gauge or sending unit. May be a high electrical resistance in the wiring and connections. Clean all terminal ends and check those at the fuse and the connections in the fuse box, etc.

The voltages are very low in the circuitry. Any small amounts of rust or corrosion at connection points, terminals and under the coating of the wires, etc creates resistance to the flow of electrical current.

Changing out the gauge and sending units simply puts the new parts back into the same defective electric system/circuit. Therefore, the new parts react like or similar to the old units and nothing much, if anything, is gained.

If all else fails, there may be rust or corrosion under the wire coating. Replacing all the wire from the main fuse box to both sending unit and gauge may be required.

Continuity only determines a connection is present. Resistance to flow of current is not factored in. A resistance test than would be required. A weak or defective fuse or fuse holder, etc, creates a resistance also.

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07-01-04, 05:18 AM   #3  
Let's see if I understand what your saying.
If the key is on and the engine is NOT running, the gauge reads correctly. When you start the engine is when the problem occurs. Is that what is happening? That would incicate something bleeding into the temp wire, possibly alternator voltage traveling back through one of the cables.
To test the dash gauge and circuit, (assuming it's a 1 wire gauge) take the wire and ground it with the key on. The gauge should go full hot.

 
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07-01-04, 02:27 PM   #4  
Chaz8
Posted By: Desi501 Let's see if I understand what your saying.
If the key is on and the engine is NOT running, the gauge reads correctly. When you start the engine is when the problem occurs. Is that what is happening? That would incicate something bleeding into the temp wire, possibly alternator voltage traveling back through one of the cables.
To test the dash gauge and circuit, (assuming it's a 1 wire gauge) take the wire and ground it with the key on. The gauge should go full hot.

Yes. The problem occurs after you start the engine. I have also tested the circuit as you have mentioned, and yes the gauge goes full hot. I am going to the lake tomorrow. I am planning on double checking all connections and I will run a new wire from the sender to the gauge. I will let you know next week with the results. Thanks for you help!

 
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07-09-04, 06:47 AM   #5  
Chaz8
I have rechecked the connections, and ran a new wire (the new wire did not help) from the sender to the gauge. The gauge still goes to full cold after you start the engine. Although the gauge at one moment started to slowly move off of 120 degrees to about 140 but only return to 120, where it stayed the remainder of the weekend (with the engine running). The next time down I will try to replace the other wires, unless somebody has a better idea. Note: all the other gauges are working fine except the fuel gauge only indicates properly when it is full or empty only. In other words the fuel gauge, reads full the entire time until you are about out of gas then it will snap down to empty. The volt gauge reads 14v while the engine is running. Is there any other information I can get that would help diagnose this problem? Again thanks for your help!

 
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07-10-04, 02:47 AM   #6  
save yourself all this trouble & replace the gauges. they don't last forever & are fairly inexpensive.

 
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07-26-04, 07:14 AM   #7  
Chaz8
I have already replaced the gauge, sender and sensor, last summer. I am now trying to figure out why it is still not working. Thanks

 
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