Temp Gauges for 318bs

I have twin 318. '74 mode

I have twin 318. '74 model boat rebuilt in 2004. I had the mechanics "repair" my temp gauges. The gauges do not move and while running. I have heard from two different mechanics that the engines run extremely cool and may not be registering. That does not seem right. It is fresh water cooled. What should they be reading?

I'll bet you have the wron

I'll bet you have the wrong sender units. They are different for single and dual helm.

Jeff

"The only time the gauges move

"The only time the gauges move is when I have the port side key on and the starboard side key off. Thsi is on the upper station. As soon as I turn the satrboard key, they both go dead. Does that make any sense?"

"None. Got some bad grounds th

"None. Got some bad grounds there, I suspect.

Jeff"

Grounds under the gauges or do

Grounds under the gauges or down by the sending unit?

Both. Bad grounds cause all ki

Both. Bad grounds cause all kinds of electric nightmares.

Jeff

"Hook an alligator clip lead f

"Hook an alligator clip lead from the metal body of the sender to the engine chassis. If this works, look for teflon tape or some other insulation that is keeping the body of the sensor from making electrical contact with the engine chassis (ground)."

"You can also check the wiring

"You can also check the wiring. Typically, power flows from the ignition switch into one side of the gauge, then from the other side of the gauge it flows through the wiring harness and to the nut(or screw) terminal on the sender. The circuit is completed by grounding the sensor to the engine. If the ground is missing at your instrument cluster, many of your instruments will not work correctly. If the ground is missing at the sender (see my earlier post) then only that gauge will not work. If you have a test meter you can remove the wire from the sender and read the resistance from the case of the sender to the screw terminal. Many sensors work from around 30 to 240 ohms (different for dual stations)."

"In a dual station set up, wou

"In a dual station set up, would I start at the lower helm, or are they completely seperate? I have quite a few gauges that do not have power on my lower station(sync, depthfinder,RPM) just have not gotten around to chasing the problem since I tend to captain from the upper station. The only thing not operable on the upper station is the Temp gauges."

"Jason,
I would start by turn

"Jason,
I would start by turning off both upper and lower ignitions. Disconnect the wires at the temp sender. Then take and ohmmeter and measure the resistance of the sender terminal to its own case. It should read something like 30-240 ohms. (A dual station sender will read differenctly, but it should not be open or shorted). If you get a decent reading then move the lead from the case of the sender to the engine chassis where a clean ground can be obtained. If it now reads open, there is something insulating the case of the sender from ground. If it passes this test, hook the wires back up to the sender and disconnect the lead on both upper and lower gauges that does NOT go to the ignition source. Measure the wire you just disconnected against the ground bus in tour instrument cluster. You should see the same resistance you saw on the sender + a an ohm or two for wire reistance. Now reconnect the wire back to the gauge. If you read a high resistance, you will have to find out where the wire is open. Look for corroded lugs. Repeat the same for the other station's temp gauge. If the resistance was good, turn on the ignition and measure the terminal opposite the one you just tested on the temp gauge and you should see 12-14volts DC. Again, if not present, look at the lugs and crimps. Each station should have only the sender itself in common. Hope this helps...

From the various gauge problems you describe on the lower station, it sounds like a bad connection from the ignition switch to the common side of each gauge. Usually they are "daisy chained" together such that if the first crimp on lug fails, everything "downstream" will fail to. The best way to measure this is to turn on the ignition and start with the gauge closest to the ignition switch and take measurements at each gauge. If you see any voltage drop (assuming a digital meter) that is where to look. Untinned copper wire turns black over time in a nautical environment and will build up resistance. If you make repairs, I recommend cleaning and tinning the wire first, then soldering to the lug (even if it is a crimp type lug). The same could be true for ground although most gauges are not grounded (voltmeter excepted)."

"Ed,
Thanks for this info. I

"Ed,
Thanks for this info. I will get to work this weekend. The temp issue is one of my last hurdles on my to do list. Of course, there is always something that needs to get done on a boat!
Thanks, again."

Jason:

Ed's data is a g

Jason:

Ed's data is a great start - here's the supplement.

The dual station senders exhibit 50% of the 'resistance' values of single station senders. the low resistance value of a sender will provide the full scale reading on the gauge. You can measure the resistance of the temp sender to check it. fromm 550-750 ohms at room temperature and 55 ohm at 212 deg F.

You can also use resistors to verify the gauges are working. a 110 ohm resistor between the sender lead and ground should get mid scale on a single station gauge; use a 56 ohm one for a dual station install.

Teleflex specs their sender/gauge combination to be +/- 15 deg at 180 deg (F) - so don't expect them to be real accurate.