Art's write up w/pics
His site
Clean Flame Trap

240 Volvo Temperature Compensation Circuit
Here is a quick path to the truth in temperature.

http://cleanflametrap.com/tempFaker.html

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Temperature Gauge Failure in 86-93 240 Models

2011-03-09 - IPD Staff

If your coolant gauge is reading erratic or the needle doesn’t move at all, locate the coolant temp sender near the center of the engine block on the driver side under the intake manifold. The wire is yellow, and the connector is a female spade type. Disconnect the wire and touch it to ground and the needle should go to the hot range of the gauge when the key is in the run position. If it doesn’t, then the temp compensator board is most likely the cause.

We offer new replacement compensator boards or our money-saving bypass kit as well. Either repair will require that the instrument cluster be removed and disassembled. This is about a one-hour job that can be accomplished easily with common hand tools and a good service manual. Our bypass kit includes detailed instructions.


https://www.ipdusa.com/products/5670/Temperature-Board-Bypass-Kit-for-Volvo-Ipd-1363117-108262?


Pix ---the Jumper----
https://s3.us-east-2.amazonaws.com/prod.mm.com/uploads/2019/07/19/1563580027_dscn1801c_mmthumb.JPG