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Discussion Starter #1
I got a used 147 1.6 120hp a few days ago, and I'm currently on a small trip with it.

It was thoroughly tested by a specialized mechanic before buying so there's not an obvious fault with it.

I noticed on my trip that when cruising on the highway the water temperature was really low, around 70 degrees. I thought it was the way the twin spark engine was designed to run, but googled it afterwards and read about the usual thermostat issues.

I called my mechanic and he told me that its normal running temperature is near 90, but 80something was acceptable too, and to watch the temperature patterns for a few days, and if got lower temps consistently, to change the thermostat.

So, the car warms up normally when stationary or in city driving. The fan doesn't kick in. The temperature stays at 90 when driving in town or on harder back roads. Sometimes it drops to 80something when i drive super peacefully and then goes back to 90.

The low temperatures happen on open highway, especially when going really slow like 70km/h with 5th gear. I haven't had the chance to max out the car on the highway due to traffic, will do tomorrow and watch the temps.

So what do you think it's happening? Doesn't a broken thermostat mean that the fan should be constantly running? Can it be a "lazy" thermostat that delays the fan shutdown after opening?
 

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So what do you think it's happening? Doesn't a broken thermostat mean that the fan should be constantly running? Can it be a "lazy" thermostat that delays the fan shutdown after opening?
The thermostat has no control of the fan.

The fan is controlled by the engine ECU using temperature input from the coolant temperature sensor (which just happens to be on the thermostat housing).

Your issue does sound like the usual problem of the thermostat sticking open.
 

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Discussion Starter #3
So I tested it a bit more today, and I think I documented all the patterns the temperature moves in.

It gets to 90 normally when stationery, city driving, or on uphill twisty backroads. When I get to move without constant speed changes, It falls a little, and gets back to 90 after few seconds.

It fluctuates between 75 and 85 on more "easy" roads, and on really straight roads it gets as low as 65.
 

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Discussion Starter #5
Half open thermostat. Fan never kicked in, probably too cool due to water constantly flowing? Anyway, replaced now and works fine.
 

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Discussion Starter #8
Hope its not a Circoli thermostat you have fitted.............................
Didn't ask... The mechanic is my wifes uncle and he usually uses original parts, I trust him and believe he put whatever he things is better. (Lets hope he think the best thing is better though :p) Considering the price I paid and any applicable "family" discount, It's probably the original.
 
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