Ok here we go. I have been having an overheating problem. Just had car in shop the temp sensor in the block on passenger side in rear on block was replaced. NOW temp GAUGE on dash goes to 250 and ANALOG to left of speed O reads 200. WHO is right? Mechanic said  anolog is correct shot a hose with a sensor gun o heat gun.  Hesaid gauge need to be re placed $$$$$ part of gauge oackage BUT I read that there are two sensors for them Where are they found and how do I re place them Or test them /.  Any help  Thanks  guys

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Wingnut

Don't think this is going to fix your problem. It looks like you have a late model C4. There's also a temp sender on the water pump housing at the front of the engine. One of the senders is for the gage and the other is for the ECU. Don't remember which one does what, though.

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--  Mark

The one in the passenger cyl. head is for the temp gauge.  (single wire)  The one in the front near the thermostat housing (2 wires) is to the ECM and controls the fans. 

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Hi, have you tried to put a correct Automotive Thermometer in the cooling system when it is running & hot to determine what the correct temperature really is.  Then you address the real problem instead of relying on a gauge which may be faulty, then you can work out also which gauge is incorrect.

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just some thoughts...

The sensor located in passenger side head is for the analog gauge only. The digital temperature uses the ECT sensor in the water pump (below the throttle body)...this is the same sensor the ECM uses to control open and closed loop operation and fuel trim. The ECM also uses this sensor to turn on the cooling fans which run in tandom on either low or high speed depending engine temperature. At the point where the digital gauge is reading 250* both fans should be running on high....Are they ?? As "Adams Apple"  mentioned in another post you made about over heating these things are known for "air" in the cooling system and can be a PIA--be sure that's not your problem.