Temp guage issue.

I have a 89 xj 4.0L auto trans.I have been battleing with this issue for a few weeks and tried many things to correct.Im at a dead end so please any help will be nice.My temp guage is reading 30-45 deg higher than it really is.I tested my block and cooland at operating temp and it read 195 deg but my guage reads 240.When its at 110 deg the guage reads 150 deg.I replaced the sender 3 times with the napa replacement,at first i thought it was a bad sender but not the case.Then i replaces the actual guage in the cluster,twice! Then last resort was make a new line for the sender so its direct from sender to guage,that did nothing.So what else can i do?All connections like sender wire and ground are perfect and guage and sender work and the engine temp is right just the guage is off.what to do???

Dumb question - have you checked the ground strap between the engine and the firewall? That provides the ground return for most engine sensors, and resistance here (due to corrosion, contamination, or just plain age) will cause false readings.

Later models provide a secondary ground path to the fenderwell via the battery - but RENIX does not. I'd replace that cable first - since most sensors depend on providing a resistance relative to ground, that's a good place to start.

5-90

I did check the ground and it was nasty but replaced the ground strap.The only thing i can think of is the senders from napa are incorrecty configured.everything else has been done and replcaed.I even replaced the other 2 cooling system sensors (block&rad fan)