Join Date: Jul 2007
Location: New Zealand
I was noticing this particularly last night during a fairly long drive. Outside temperature was 6 degrees and the gauge temperature was swinging from 70 to 90 degrees (and back) over and over again. You'd expect this a little during the engine warm-up phase (the thermostat opens, the cold radiator coolant is released into the engine, the thermostat closes, etc.) but to get it all the time suggests that the thermostat is not gradual enough in its opening.
I like the idea that it is a dodgy wire but I can't see that being so regular and repeatable, let alone cropping up on so many different cars. Plus, I think you'll find the sender is a four-wire type, so the gauge has its own sender (the ECU has the other). I checked my gauge reading against Alfadiag and they seemed to agree fairly well - gauge read 80 when Alfadiag said 85, gauge read 90 when Alfadiag said 92. However, the ECU thinks the outside air temperature is 42 degrees C, which is hardly accurate!
If the thermostat is stuck open, the engine runs ridiculously cold (50 degrees) even on a long trip, so that suggests the radiator is over-efficient for the job it has to do. I wonder if it is worth fitting a restrictor into the thermostat so that when the thermostat opens, the flow of coolant through the radiator is restricted. You may have noticed that the thermostat has a very large hole where it bolts to the cylinder head, much larger than usual on other engine designs.
Somebody local reported that fitting an undertray made a difference, but another idea would be to get a genuine Alfa Romeo thermostat. I bought a Behr thermostat, since the one that came off my car had the Alfa Romeo logo as well as the Behr logo, but I wonder if there may be an improved design available.
'00 GTV V6, '08 FIAT 500, shell and parts for a '71 FIAT 850 Coupe
Last edited by alexGS; 15-07-10 at 23:40.