Faulty sender

[Paul Cairoli]

Took my 1987 Catalina 27 for a long motor , M18 after about 2 hours the temp guage showed about 215 degrees. Thinking I was overheating I checked the usual ie lots of fresh water , both pumps working and cool The motor was not overly hot anywhere I stuck my finger in the coolant it felt under 180 so mechanically the system is soundMy question is I suspect the sender or guage .... Does any one know how to check the sender thanks paul

 

[Monty]

Testing Gauges

Testing Fuel Gauges Testing Fuel Gauges:1. Disconnect Pink Sender Wire from Gauge, and turn power ON.The Fuel Gauge should read ZERO Scale (< Empty)2. Short the Gauge Sender Terminal to Ground.The Gauge should read FULL Scale (> Full).3. Measure resistance of Pink Sender Wire to Ground.American Floats: 240 Ohms (Empty), 103 Ohms (½ Full), & 33 Ohms (Full)European Floats: 10 Ohms (Empty), 95 Ohms (Half), & 180 Ohms (Full)Automotive & other Float Switches may use other resistances such as 0 - 90 Ohm, 73 - 10 Ohm, & etc.4. Disconnect Pink Wire from Sender on Fuel Tank.5. Test continuity of Pink Wire.Zero Ohms from Tank End to Gauge End - If not, repair or replace Wire.6. Measure Resistance from Sender Terminal (on Tank) to Ground on Tank.Should read as per (3) above - If not, replace Sender.Reply | Print Thread Gord May 48N x 89W 09/25 at 12:50AM General_interest Reply #7  Basic Engine Gauge Theory & Testing From a discussion @ http://cruiserforum.com/ENGINE GAUGES (Fuel, Pressure, & Temperature Instruments):Basic Theory of Operation:There are two basic types of Engine Instrument Gauges:a. The VOLTMETER, which requires an outside Voltage Source. This is the most common type Engine Gauge used on boats.b. The AMMETER, which does NOT require external power.The standard Voltmeter type Gauge receives it’s reference voltage from a Sender unit, mounted on the Engine. The Sender is a device, whose resistance varies with changes in Level, Pressure, or Temperature. As the sender resistance increases, the reference voltage transmitted to the Gauge decreases.Temperature Senders are often Bi-Metalic Thermo-Couple devices, whose resistance decreases as Temperature rises; resulting in a higher reference voltage at the gauge. Other Senders (Level, Pressure, Vacuum, etc.) employ differing methods of varying their resistance (ie: Varisters) in response to the measured stimuli.Alarm Switches are "On-Off" devices, either Normally-Open or Normally-Closed; which switch 'On' or 'Off' in response to a pre-set condition. Switches are utilized to operate Warning Lights and/or Buzzers.All Resistance values noted are for Single Station Senders.Dual Station Senders, operating two Gauges, will have One-Half the Resistance values noted below.If one Gauge (of a Dual Station Pair) failes, the Other Gauge will to read much Higher than expected.Pipe Extensions, Tees, etc., utilized to connect both a Gauge Sender & a Warning Light/Buzzer Switch to the same Engine Block Port are NOT recommended. Sender values could read Cooler or Lower Pressure than exists, and the added weight & moment could cause fatigue failures.Basic Troubleshooting of Gauges:All Gauges:1. Remove Sender Wire from “S” Terminal on Gauge, and Turn ON Instruments Circuit.2. Test Voltage between “I” Terminal (External Power Supply) and Ground Terminal “G”.Tested voltage must match nominal voltage of the Gauge (ie: 12V Gauge must test between 10 - 16VDC), and the Battery Voltage.If no voltage - check Ignition or Instrument Switch(s) and/or Fuses.If tests less than battery voltage, repair or replace (Violet) wire from Ignition or Instrument Switch.If a Sender fails “Open” (Infinite Resistance), one or both (if Dual Station) Gauges will read Zero Scale.If a Sender Fails “Closed” (shorted - Zero Resistance), one or both Gauges will read Full Scale.Other confusing Ohmmeter results, such as readings lower than expected, could indicate a poor Ground Connection at the Sender Body (Sender to Engine Block). Check for pipe dope or tape on Sender Threads.Temperature Gauges:1. Disconnect Tan Sender Wire from Gauge (Terminal “S”) and turn Instrument Power ON.The Temperature Gauge should indicate ZERO Scale (< Low Temperature).2. Short the Gauge Sender Terminal “S” to Ground Terminal “G”.The Gauge should deflect to FULL Scale (> High Temperature).3. Measure Resistance from Tan Sender Wire (disconnected from Gauge) to Ground.American Temp. Senders will read: 450 Ohms (Engine Cold @ 1000F)or 29.6 Ohms (Engine Hot @ 2500F )European Temp. Senders will read: 281 Ohms (Cold @ 400C) and 22 Ohms (Hot @ 1200C)4. Disconnect Tan Wire from Sender on Engine Block.5. Test continuity of Tan Wire.Zero Ohms from Block End to Gauge End - If not, repair or replace Wire.6. Measure Resistance from Sender Terminal (on Block) to Ground on Block.Should read as per (3) above - If not, replace Sender.Pressure Gauges:1. Disconnect Dark Blue Sender Wire from Gauge, and turn power ON.The Pressure Gauge should read ZERO Scale (Low Pressure).2. Short the Gauge Sender Terminal to Ground.The Gauge should deflect to FULL Scale (>High Pressure).3. Measure Resistance from Dark Blue Sender Wire to Ground.American Press. Sender: 240 Ohms (Zero Pressure) 33.5 Ohms (Full Pressure @ 80 psi)European Press. Sender: 10 Ohms (Zero Press.) & 180 Ohms (Full Press. @ 150 Bar)See 4, 5, & 6 above (but Dk. Blue Wire)Fuel Gauges:1. Disconnect Pink Sender Wire from Gauge, and turn power ON.The Fuel Gauge should read ZERO Scale (< Empty)2. Short the Gauge Sender Terminal to Ground.The Gauge should read FULL Scale (> Full).3. Measure resistance of Pink Sender Wire to Ground.American Floats: 240 Ohms (Empty), 103 Ohms (½ Full), & 33 Ohms (Full)European Floats: 10 Ohms (Empty), 95 Ohms (Half), & 180 Ohms (Full)Automotive & other Float Switches may use other resistances such as 0 - 90 Ohm, 73 - 10 Ohm, & etc.See 4, 5, & 6 above (but Pink Wire)HTH,Gord Related link Reply | Print Thread jmcclain Houston 09/24 at 10:13PM General_interest Reply #6  Plug the Gauge Hole and Move On! Our B321 had a fuel gauge, but

 

[Phil]

Engine hours

Thanks for the info. I'm having trouble with an engine hour meter that doesn't seem to work. I haven't found much info. It seems there is no "sender" other than the key switched on. The engine is a Universal M18, but there isn't much info in its manual either.

 

[Phil]

Old gauges, old problems

Well, it turns out that the digital engine hour meter (odometer style) is quite simply powered when the key is switched on and not powered when switched off. I checked 12V at the gauge when the engine is running, so I suspect either a bad motor in the gauge or mechanical gearing that is frozen/corroded. I suppose I'll take it apart and find out next.In the mean time, while tinkering about the gauge panel, I noticed that my fuel gauge was dropping steadily to nearly empty. It had always read full before. I had naively assumed that it was due to using the engine sparingly and keeping the tank full as the previous owner recommended. But it did seem strange that the needle didn't seem to budge at all. The gauge was powered with 12V and I had about 6V on the sender terminal. I haven't yet tried to put 12V on the sender terminal to see it read full or short it to ground to read empty. I'll check the resistance on the sender wire too. I don't have an easy way to check how much fuel is actually in the tank, so if the tests are seem ok I'm not sure what to conclude. Possibilities include1) everything is fine and someone sucked ~15 gallons of diesel out of my tank2) the float in the tank had been stuck high (reading full) and coincidentally dropped while I was working on the gauge panel3) a calibration knob on the back of the fuel gauge was disturbed (improperly fixed in place ?) so that what had previously been reading too high is now reading too low4) disturbing the wiring introduced a short to ground that I haven't noticedCan anyone think of other explanations?

 

[Phil]

Old gauges, old problems (2)

Check that.Open sender terminal to read full, short to ground sender terminal to read empty.