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Old 04-08-2021, 11:45 PM   #1
84B23F
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Default Coolant Sensor: How Does it Work?

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Old 04-09-2021, 01:16 AM   #2
James M
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It's the level sensor in the reservoir right? No clue but pretty cool it doesnt touch the coolant. First time I replaced one I had a coolant bin ready and everything
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Old 04-09-2021, 01:35 AM   #3
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There is a ring shaped float with the magnet inside the coolant tank. At the low position it activates the sensor which is actually a switch.
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Old 04-09-2021, 01:51 AM   #4
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The "sensor" will have a reed switch inside the long black tip.




The tank should have a some kind of float inside (often donut-shaped, with a small magnet in it), that rides up and down on a molded-in, hollow waterproof tube. Here's an Audi tank cut open...



The switch usually inserts into the bottom of the tank, up inside the hollow tube.

When the coolant level drops, the magnet in the float gets close enough to the 2 "reeds", they are attracted to each other and close the circuit, turning on the warning light.

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Old 04-09-2021, 07:45 AM   #5
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Quote:
Originally Posted by MasterBlaster View Post
The tank should have a some kind of float inside (often donut-shaped, with a small magnet in it), that rides up and down on a molded-in, hollow waterproof tube.
Yes, Volvo 912997

93-940's owner's manual does not show idiot light for it, but it's shown in OEM parts for this sensor. Owner's manual does show a Low washer fluid level, so maybe I can rig something up if a ground circuit is used for triggering Low washer fluid level.

Thanks for responses...
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Old 04-09-2021, 11:39 AM   #6
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I think only V/S90's and may be late 960's had that switch wired. It's a great safety feature, I thought about adding a warning light for that too.
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Old 04-09-2021, 12:06 PM   #7
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Old 04-09-2021, 01:37 PM   #8
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Quote:
Originally Posted by PCH View Post
It's a great safety feature...
Problem with OEM vacuum controlled heater valve on 7s/9s is when it leaks, engine may be toast...history....just depends upon your situation, local, highway, etc.

I had just rebuilt my 1984-B23F, which is installed in the 93-940, and I was 180 miles away from home, and heater valve shot craps...lucky me, I saw the temp rising, and there was a Dollar General store, one block away.
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Old 04-09-2021, 02:10 PM   #9
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If I recall correctly Volvo was required by law to have that circuit for the Japanese market. Looks like a great addition to the car for safety.
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Old 04-10-2021, 12:52 PM   #10
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Quote:
Originally Posted by dl242gt View Post
If I recall correctly Volvo was required by law to have that circuit for the Japanese market.
On EFI based semi-trucks since around early 1990s, when coolant level was low or if temp too high, an engine could be shut-down if these parameters were turned on in ECM.
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Old 04-17-2021, 08:29 PM   #11
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My 1993-940 US did not come with coolant sensor, and the Expansion Tank did not have this float inside. Same Expansion Tank (9122997) in design.

I used a Coolant Level Sensor For Volvo Truck FH VN FL FM NH VNL VHD 630 670 780 21399626, which is cheaper than OEM Volvo, plugged it into a new Expansion Tank, and spliced wires so a LED would light up just below dashboard. Works fine


Quote:
Originally Posted by MasterBlaster View Post
The tank should have a some kind of float inside (often donut-shaped, with a small magnet in it), that rides up and down on a molded-in, hollow waterproof tube. Here's an Audi tank cut open...

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