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Discussion Starter #1
Hi,
I recently read on alfa156.net (fun starts @3000) that the fan speed resistor (housed in the radiators cooling fan cowling), has two speeds in which the fan comes on in certain temperatures, as my one is faulty, the fan only comes on in high speed at 90degC and cools to around 85degC in traffic, reading on alfa156.net the fan is also meant to come on in slow speed at a much lower temperature, aparently the temp is not meant to go to 90degC!
I recently bought a used replacement fan speed resistor, and when the item arrived it looked different from the faulty one on my car,
I recieved a red colour plastic one with a resistance of 0.23 ohms,
The one on my car is black plastic with a resistance of 0.30 ohms,
When searching for new fan speed resistors I noticed that the one I recieved (red plastic 0.23ohms) is meant for the Diesel, V6 and JTS engines.

Can anyone shed any light on when the fan comes on on what temperatures? And am I right about the variants of fan speed resistors for specific engines.

Many thanks
 

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90degC is the perfect running temperature.

The resistor only has one "speed" (the reduced speed), when full speed is selected the circuit doesn't go via the resistor at all.

Your replacement resistor will result in a slightly faster "low" speed fan, but as long as your thermostat is working you will be fine. But if you want you can replace it with the correct rating.
 

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Discussion Starter #5
My engine takes 6 minutes to reach up to 75degC, (quarter of the way) then thermostat opens as a sudden temp drop to 55degC doing about 30mph in 4th at 1700-2000rpm and stays up to 65degC when poodling allong, in traffic it shoots upto 90degC after 5-10 mins in traffic then fan kicks in on high to cool to around 85degC, is this normal?
 

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My engine takes 6 minutes to reach up to 75degC, (quarter of the way) then thermostat opens as a sudden temp drop to 55degC doing about 30mph in 4th at 1700-2000rpm and stays up to 65degC when poodling allong, in traffic it shoots upto 90degC after 5-10 mins in traffic then fan kicks in on high to cool to around 85degC, is this normal?
No.
Points to your thermostat being stuck open.
It should stay close to 90degC all the time once warm no matter what speed you are doing and no matter how cold it is outside.
 

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Discussion Starter #7
But I tested my thermostat when re-newing my rad, I de-scaled the thermostat housing, and there is a temperature rating stamped on the thermostat itself inside the housing, think it was like 73degC, but when the engine reaches 90degC the engine feels a bit lumpy and idling is a tiny bit erratic, the fan comes on very fast over 90degC, when testing my thermostat, I put it in a cold pan of water and boiled it, with a thermometer in the pan it reached 73~degC and opened, I tested the seal of the thermostat when opened and closed, and it was definately shut all the way up to 73degC, but after driving off in traffic at 90degC the temp drops down to 65degC just poodling allong? This must me right surely because that's the wind cooling it down?
 

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Sounds like you may have the wrong stat which might have been fitted by a previous owner to hide the symptoms of a blocked radiator.
Like David said, it should sit rock steady at 90 degrees however you are driving it (mine certainly does).
 

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But I tested my thermostat when re-newing my rad, I de-scaled the thermostat housing, and there is a temperature rating stamped on the thermostat itself inside the housing, think it was like 73degC, but when the engine reaches 90degC the engine feels a bit lumpy and idling is a tiny bit erratic, the fan comes on very fast over 90degC, when testing my thermostat, I put it in a cold pan of water and boiled it, with a thermometer in the pan it reached 73~degC and opened, I tested the seal of the thermostat when opened and closed, and it was definately shut all the way up to 73degC, but after driving off in traffic at 90degC the temp drops down to 65degC just poodling allong? This must me right surely because that's the wind cooling it down?
83degC stamped on the stat.
Yes the wind is cooling it down BECAUSE YOUR STAT IS STUCK OPEN...!!!

You need a new thermostat.

I've been driving along at 70MPH with it well below 0degC outside and the gauge happily sat at 90degC, because my thermostat is working correctly....
 

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I told the mechanic I had a feeling I needed a new thermostat - I checked the large hose after reading a few threads - he said no, it's perfectly normal. Ignorant fool.
So even when driving say at 100km/h, the temp should stay around the 90C mark, regardless of outside temps?
 

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Yes, if the cooling system is working as advertised then it should stay at 90 regardless. Its possible your gauge is faulty however, but Alfa diag or similar should give a reading directly from the temp sensor.
 

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Discussion Starter #14
Oh okay, this all makes sence now, thanks guys, I didn't mean to be ignorant about it, its just that when I tested it I was sure about it, 83degC was the correct temp stamped on my thermostat, (dunno why I said 73) but it does make sence on when the fan kicks in and cools it down to above 85, 65degC does seem too low for running temp, but as my cooling system is running colder, does this effect performance/ ecomomy? Could it also damage running colder? I did test my fan speed resistor by connecting to a thermocouple reader, and the resistance is correct. Indeed mt thermostat is stuck slightly open, as it reaches to 70, thermostat opens and drops to 65 and stays there.
 

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Replace the thermostat.
Running cold isn't good for your pocket or the engine.

You are only seeing the problem now because your old rad lacked cooling ability and was masking the failed stat.
 

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What is the correct running temperature for the 1.9 JTD M-Jet? When running the air con the fan kicks in at 75-80 but without the air con on the engine reached about 90 the other day in traffic. It has recently had a new thermostat on it so I'm suspicious of the fan. Is there a low speed and high speed fan on a diesel?
 

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yea you have 2 fans and 2 resistors, both were badly corroded on mine though one was kinda ok so I refurbed it and got another...... I have coated them both in silicone spray to help stop it again :)
 

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I have weird issue. My car's temp stays at 90 if A/C is on. No matter what is the temp outside.
But if I switch off the A/C it goes up till 110 in traffic. Is it a resistor fault or something else?
 

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From a few owners of 156s Jtd / Jtdm including mine... my temp gauge stays at 70 steady... and thermostat is not broken... it's the same for other owners and it gets up to 90 dec only on a hot summer's day and stuck in traffic...
 
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