Temp sensor and sender needed for Yanmar

[dougtheslug]

I have a Yanmar 3QM30FG motor (early 1980s) and the temperature gauge is not reading correctly. Can someone suggest a replacement sender and analog gauge replacement?

I don’t know the threading on the sender, or even which of the 3 senders I see threaded into the block the temp sender is.

Any ideas would be appreciated!

Thank you

[TheOffice]

Start by checking the electrical connections if it is reading low and check the temperature with a cheap laser thermometer.

[dougtheslug]

I'm looking for anyone who has put on a sender and temp gauge and can send info on what they bought. I'm going to replace both and need to know what works. Just knowing the threading on the sender would be great.

I'm not at the boat now and would love to buy a sender/gauge assembly and bring it to the boat the next time I go.

[charliehows]

replaced my in head sensor on 2qm20 recently with a $20 car unit - found one that looked like it would fit online and a local carspares chain store - supercheap i think - had it in stock. Threads were close enough with some threadtape. I was a bit surprised when i started the eng the first time and the temp gauge started reading perfectly.

[GordMay]

Basic Engine Gauge Theory and Testing
➥ http://www.cruisersforum.com/forums/...sting-645.html

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.”

[Cpt Mark]

Originally Posted by charliehows

replaced my in head sensor on 2qm20 recently with a $20 car unit - found one that looked like it would fit online and a local carspares chain store - supercheap i think - had it in stock. Threads were close enough with some threadtape..

That is super scary and quite frankly ridiculous.

[Cpt Mark]

On my Yanmars they are British Tapered Pipe (BTP). Threading in anything but the exact thread is inviting permanent damage to your head.

Of course you could go to Yanmar, they will have new sensors, gauges etc.

Gauges are notorious for doing this and usually, almost always, ok, virtually always, it is the wiring. Pop a new gauge/sender in and you may still have the same problem. Remove and clean all the ends with crocus cloth, emery board , fine grit sandpaper. Get them super shiny clean. Run the tests Gord laid out and you should fix your problem.

[dougtheslug]

Thank you for the thought on the BTP thread. My gauge is old and sticky (tapping it really is the only way to get the needle to move consistently) so I'm very interested in replacing the whole lot - including the wire.


Thank you for all the testing ideas (GordMay)!

However, due to the age of gauge and sender and now thinking about the wire, I am even more set on replacing the whole package.

Yanmar hasn't exactly been helpful since my local Astoria Oregon guy didn't know the specifics and Tacoma Marine didn't know offhand about the threads, although Tacoma is looking into it. Any Yanmar people you guys know of that can take an engine model number and know exactly what I'm looking for on head threaded senders and a gauge?

Doug

[charliehows]

Originally Posted by Cpt Mark

That is super scary and quite frankly ridiculous.

yep - kept it a bit vague cos its not a solution for the inexperienced mechanic...I think i'm about 2 years down the road with my fix and no probs - not for the easily scared tho'...you guys get to pay 10 times the price to yanmar.
( little hint - find a BTP-mm adaptor)