actually I misspoke. They put the resistor at the sensor not at the circuit board.

I installed a new Bosch temperature gauge. However, the sending unit adaptor doesn't fit into the cylinder head threads. So, I ordered their metric adaptors. They should arrive shortly. This will tell me clearly what the actual temperature is.

In the interim, I used the existing sending unit and took out the series resistor.

So the original Volvo gauge reads 3/4 again when up to operating temperature and the Bosch gauge reads about 170 degrees F. However, since the sending unit isn't the one for the Bosch gauge, I can't really trust that reading yet. I'll let you know what it reads when I get the sending unit adaptors shortly.

One thing I may not have mentioned is that back in January, 2022 I got my turbo upgraded to a higher performing turbo.

I'm not exactly sure when this gauge issue started, but I don't think it was that long ago.

Another thing I noticed is that the existing tachometer was reading very low. A regular timing light showed the RPMs to be 850-900 at idle, but the gauge tachometer read really low. I can't explain that one. May have something to do with this?

So, I opened it up and adjusted the tachometer trimpot so that it read correctly.

But, this is suspicious along with the temperature gauge issue no?

See you.