How to test 4.3 temp sensor?

smassey22180

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Apr 15, 2013
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I took my new to me boat out this weekend and temp gauge did not move above 100. IR thermometer said engine temp was good. My ohm meter say the sensor is an open circuit both hot and cold. What is the proper way to test?

Also, I grounded the tan wire and the alarm beeped but the gauge did not move (engine off). I tested the gauge and grounded the S post and it went to full hot. Does the wire to the gauge pass through the alarm somehow?

Thanks
 
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Thalasso

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Jan 18, 2011
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Try this
Remove wire to gauge. Connect an ohmmeter to terminal of sender and to engine block. Approximate values are: 75 (room temperature) = 600 to 800 ohms; 212 degrees = 55 ohms.
If sender is shorted (0 ohms) gauge will read above 240F.
If sender has infinite resistance (Open) gauge will read below 120F.
If the gauge reads lower than expected, was sealer used on the sender threads? Must remove the sealer.
The accuracy of the system (gauge, sender, voltage range) can vary as much as 16 degrees at 180F.
 

smassey22180

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Try this
If sender has infinite resistance (Open) gauge will read below 120F.
.

Sender is open so I am pretty sure it is bad. My next concern is when I ground the wire, I get the warning beeping but the temp gauge does not move. The gauge does move a little bit when I switch on the ignition. If I disconnect the brown wire at the gauge it does not move when ignition is switched on. So based on that I think the brown wire is good to the back. This is my first boat with a a warning beeper.

I actually made a pot out of my trim sensor and was able to get the beeping to vary in intensity. A trim sensor puts out between 600 and 0 ohms. The gauge still did not move.

thanks
 

smassey22180

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Ok figured it out. There are 2 of these things. There is a switch on the front of the thermostat housing for the alarm system (single wire spade connector). The sensor for the gauge is in the intake manifold just to the left of the thermostat housing (single wire loop held on with nut). It is under the hoses and hard to see. Just to confuse us Volvo parts lists the switch in the Cooling section. The sensor is listed in the Manifold area.

Grounding the sensor wire makes the temp sensor go to full hot. Part number 3852029 for $23.
 

Fun Times

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Also, I grounded the tan wire and the alarm beeped but the gauge did not move (engine off). I tested the gauge and grounded the S post and it went to full hot. Does the wire to the gauge pass through the alarm somehow? Thanks.
You should have one wire and one sender for the gauge and one wire and one switch/sending unit for the warning horn.

They should look like these,

mLb6mxDKQg6-0KxZzLHLiFw.jpg

Volvo part number 3852029
$_12.JPG

And I don't believe you'll have this style on your engine model,
$(KGrHqZ,!poE+oSwPGWeBQBbPWvslw~~60_35.JPG
 

smassey22180

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Fun Times, yes my sensor is like the one on the top. The last sensor is not mine as it has 2 connectors. Mine has a single spade connector.

Now that I have found the correct sensor tested it and it is fine. I then removed the thermostat and is was pretty rough looking. My 10 year old son was playing around scraping rust off the thermostat housing. When he was done I decided to blow the rust out. When I blew on the bypass it sounded restricted. Sure enough there was a piece of old impeller buried deep within the housing. There was no way to see or feel this blockage. It took me almost an hour to get it out but I am now confident the engine will get to the right temperature.
 
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further

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While you're at it, I'd take off the Tstat housing and clean out all the passages with a wire. I had a similar issue and turned out that the bypass passage/port was blocked with remnants of the casting process (new Tstat housing).
 

Tail_Gunner

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You should have one wire and one sender for the gauge and one wire and one switch/sending unit for the warning horn.

They should look like these,

mLb6mxDKQg6-0KxZzLHLiFw.jpg

Volvo part number 3852029
$_12.JPG

And I don't believe you'll have this style on your engine model,
$(KGrHqZ,!poE+oSwPGWeBQBbPWvslw~~60_35.JPG



He should have the bottom sender unit...
 
Last edited:

Fun Times

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He should have the bottom sender unit...
The bottom sender is typically used for digital reads. The ones above it are more for analog reads. The OP has a carbureted engine so it's more common to find the analog units on them. Mercruiser has started using the digital sender in carbureted engines to sound the warning horn through the ignition module. I don't believe Volvo went that route with their carbureted engine models.
 
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