Cruisers Forum

Join CruisersForum Today

Thread Tools Rate Thread Display Modes
Old 07-07-2011, 08:35   #1
Registered User

Join Date: Jul 2011
Location: Indiana
Boat: Columbia 8.7 29'
Posts: 2
Testing instruments

My engine instruments have stopped working, i.e. oil pressure, temp and amp. How do I test to find the problem?

tom4754 is offline   Reply With Quote
Old 07-07-2011, 08:51   #2
Registered User
Astrid's Avatar

Join Date: Oct 2008
Location: Canada, up on Hecate Strait in sight of Alaska
Boat: 50-ft steel Ketch
Posts: 1,821
Send a message via MSN to Astrid Send a message via Yahoo to Astrid
Re: Testing instruments

Did they all stop at the same time, and how are they wired? If all went at the same time, I would suspect a fuze has blown or you have a short in your instrument panel.

Astrid is offline   Reply With Quote
Old 07-07-2011, 09:45   #3
Moderator Emeritus
GordMay's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 29,347
Images: 240
Re: Testing instruments

Greetings and welcome aboard the CF, tom4754.

See ➥ Basic Engine Gauge Theory and Testing

(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)

See also the graphics posted at:
Wiring Diagrams:
Testing Instructions:
Sender Resistance:
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

GordMay is offline   Reply With Quote
Old 07-07-2011, 15:13   #4
Registered User

Join Date: Jul 2011
Location: Indiana
Boat: Columbia 8.7 29'
Posts: 2
Re: Testing instruments

Thanks, I'll let you know how this works out
tom4754 is offline   Reply With Quote

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Navman 100 Series Instruments littleelse Marine Electronics 4 15-04-2012 21:19
Tacktick Instruments lancelot9898 Marine Electronics 19 02-08-2011 08:39
Advice on Upgrading Instruments cheoah Marine Electronics 2 11-07-2011 12:41
Yanmar Instruments Don't Work Yot Libertad General Sailing Forum 5 06-07-2011 05:00
Aruba cruising guide testing! Tranquilo General Sailing Forum 0 25-06-2011 08:11

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

Copyright 2002-2015 Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 18:43.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.