My 355 on a recent drive had the water temp gauge rising to about 3/4 from max when standing still then falling back to midway when on the move. Any ideas what causes this....normally she is rock sold on midway at all times.
Check your fan fuse under the passenger footplate. They blow easily and you will get that exact behavior. If it blows again soon or often time to replace the fan with a sealed unit (search for this, an old issue that is well known.)
If fuses are good, check to see if the passenger side fan is coming on. If not, and the fuse and fan are good, check the coolant temp sensor. It is forward and to the right of the oil filter. You can pull the connector off and measure the resistance of the sensor. It should be about 2k ohms when cold, dropping to a few hundred ohms as it warms up. If the resistance doesn't drop the fan will not come on.
Hope the problem is fixed. If everything works as it should and you still have an issue, check the clamps to make sure they are not loose. If they are, 355s are notorious for sucking air in the system, creating air pockets, not letting the water circulate properly--unless you push on the throttle, rev the engine and force the pump to do the work.
Am thinking of replacing both fan units with the SPAL ones that use less current and have a sealed motor. My fans are original and have done 52,000 miles.... Will check the fuses later this week...but i fancy replacing the fans myself in my garage.
Understand how the fans work. Left hand side fan is controlled by a sensor in the left side radiator. The fan come on when the coolant temp gets to about 190F. The right side fan is controlled by a coolant temp sensor located in front of and to the right of the oil filter (there is one on each side on a 95 355). The right hand fan comes on when the coolant temp in the water manifold reaches 212F. So let your car heat up and make sure both fans come on (they may cycle on and off). If one or the other does not, check the fan fuses. If the right hand fan fails to come on even when the car gets hot you can either pull off the wheel and check to see if the fan works when directly connected to a battery or you can pull the connector off the afore mentioned coolant temp sensor and check it's resistance. It should be around 2k-3k ohm cold dropping to a few hundred when hot. If it doesn't it's bad and should be replaced. Your choice as to which you do first. For the left hand fan you have to pull off the wheel and then test the fan when directly connected to a battery. To check the temp sensor in the radiator you can just place a jumper across the terminals and the fan should run whether the coolant is hot or cold. If the fan doesn't run with a jumper across the temp switch in the radiator the problem is elsewhere. Again, which you do first is up to you. As fro replacing the fans, remember that the lower amp fans push less air. You might also want to check the fault coded stored in the ECU. A bad coolant temp sensor is supposed to set a 1112 code and turn on the CEL on a 1995 car. I had a bad coolant temp sensor on my car and the code was stored but there was no CEL.
