Technical Rad Cooling Fan Running Constantly, and Fast

[Steve148]

Hi -

A few previous topics about this, but I'm not sure what applies to my 2004 JTD. Apologies for going over old ground...

With a totally cold engine, the rad cooling fan starts running at max speed as soon as the engine is started. This continues for about 5 seconds after the engine is turned off and key removed.

If my browsing so far is reliable, this is likely to be a relay problem? Would be really grateful if someone could tell me which relays, located where, need checking?

Thanks!

 

[Davren]

Relay T7 in the engine compartment fuse box is for the engine cooling fan at high speed. However, for early 1.8 and 2.4 petrol, and 1.9 diesel engines, the cooling fan speed is continuously variable and controlled by an ECU mounted behind a panel in the radiator cowling.
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[Steve148]

Thanks Davren - I'm a bit confused then, because Decks said in another topic that the JTD's changed to relay/resistor control after 2003 (https://www.fiatforum.com/stilo/245310-help-cooling-fan.html?p=2565125).

Maybe I need to start by having a look at what's there, and then report back with some photos.

 

[Davren]

No confusion, I posted above that early engines have the ECU, Decks posted much the same:

It looks like around 2003 JTD’s both 8v and 16v changed over to the more reliable system of relays and resistors

I have 2 Stilo JTD MWs. One was built in March 2003, the other in October 2003. The earlier one has the ECU, the later one doesn't, so the change over was sometime between those dates.

As you say, check which system you have. The plastic panel in the radiator cowling is held on by one screw. The ECU (if fitted) attaches to the back of the plastic panel.
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[Steve148]

Thanks Davren -

The plastic panel only has two wires connecting to the back. The retaining screw wasn't in a co-operative mood, so it got Dremmelled...


The panel then lifted out neatly, and looked OK from the outside....


Inside wasn't so good. There's a large ceramic tube with a coil around it - looks pretty flaky, and has probably gone bad.


Underneath the tube is a some kind of in-line resistor, which is looking pretty scabby too.


I put a multimeter across the terminals and it was giving about 1.6 Ohms. Applying a hot air gun didn't change the reading.


Starting the car without the thermostat / resistor wasn't a problem, and no fault light came up. The rad fan is still whining at full speed though.

I tested the red and white cables which connect to the thermostat / resistor. When the engine is running and the fan going at full speed, they have a small voltage potential between them. Removing Relay T7 causes the voltage to jump to approx 14v with engine running, approx 12.5v with engine stopped, and 0v with key removed.

I checked Relay T7 with a multimeter, using my cordless drill battery to actuate. It switches neatly from 0 to 1 resistance, there's no indication of fault there. When Relay T7 is removed, the fan stops it's awful howling - so that's a short-term win while the weather's still cool.

 

[Steve148]

Assuming that the fan motor resistor assembly has failed, the Eper (2005 version) part number is 51738171. I can see a used one on eBay for £20 (item 181329358846), which seems a bit steep. (http://www.ebay.co.uk/itm/Fiat-Stil...846?pt=LH_DefaultDomain_3&hash=item2a38126ffe)

There's a new Bravo OEM part listed for £30 by another trader (item 181232102722) which looks identical, but has part number 51736774. (http://www.ebay.co.uk/itm/Fiat-Brav...722?pt=LH_DefaultDomain_3&hash=item2a32466d42)

Another listing appears identical (item 281631345568) and only £20, but not a factory part. That listing is for a Fiat Ducato. (http://www.ebay.co.uk/itm/Peugeot-B...main_3&fits=Car+Make:Fiat&hash=item4192894ba0)

Finally an OEM Alfa part is listed (item 181428051145) and also appears identical, but has part number 51736821. (http://www.ebay.co.uk/itm/Alfa-Rome...145?pt=LH_DefaultDomain_3&hash=item2a3df45cc9)

I'm guessing that there's a good chance these parts are all interchangeable, but I don't have access to Eper or other part catalogues after 2005. Can anyone help?

 

[sussexa]

not sure what you want to check but I have 2014 eper
heres some screen shots of the part number you listed



anything particular you want me to look for ?

 

[Steve148]

Thanks sussexa -

Really appreciate that, I can see from your second pic that 51738171 is still a valid part number for this item, and also there's an alternate part, number 51729494. That's helpful.

I suppose I was hoping someone could say whether 51738171, 51736774, 51736821 and 51729494 are interchangeable. They are physically identical, but obviously that doesn't mean they function identically. I probably need to go to a Fiat dealer or a specialist parts firm.

Thanks again -

 

[Steve148]

I put a multimeter across the terminals and it was giving about 1.6 Ohms. Applying a hot air gun didn't change the reading.
View attachment 152624

Sorry, one final point. As I was putting away the multimeter, I idly shorted the test leads together. And discovered that there's about 1.6 Ohms of latent resistance in the testing apparatus.....

So in fact the Fan Motor Resistor is providing no resistance at all, at room temperature. Which makes me wonder if it has actually failed.

(Off to buy a decent multimeter now, after years of cheap eBay tat...

 

[Davren]

A faulty resistor will not cause the fan to stay on, and it is only in circuit for the low speed, you say yours is running at max speed. About 1.6Ω is correct for a fan speed resistor, so you can discount it as the cause of the problem. Either relay T7 is shorted, or it's getting an unwanted ignition switched earth to pin 86. This could be from pin A19 of the engine management ECU, or possibly because of water in the engine compartment fuse box.

I checked Relay T7 with a multimeter, using my cordless drill battery to actuate. It switches neatly from 0 to 1 resistance, there's no indication of fault there. When Relay T7 is removed, the fan stops it's awful howling - so that's a short-term win while the weather's still cool.

How are you testing the relay? Do you mean it's switching from 0Ω to 1Ω?

If testing the relay off the car with a battery; when the battery is connected across pins 85 and 86, pins 30 and 87 should show 0Ω resistance. When the battery is disconnected, pins 30 and 87 should show infinity resistance (open circuit).
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[Steve148]

A faulty resistor will not cause the fan to stay on, and it is only in circuit for the low speed, you say yours is running at max speed. About 1.6Ω is correct for a fan speed resistor, so you can discount it as the cause of the problem. Either relay T7 is shorted, or it's getting an unwanted ignition switched earth to pin 86. This could be from pin A19 of the engine management ECU, or possibly because of water in the engine compartment fuse box..

Thanks Davren - yes, I have been looking at the schematic (attached) and I realise now that I have completely misunderstood the function of the radiator-mounted resistor. I thought it was there to detect the radiator temperature, and that it's resistance would change as it became hotter (this data being sent to the ECU).

Now see I was utterly wrong. The only function of the resistor is to reduce the power supplied to the radiator fan at low setting. The resistor is only positioned in the radiator area because it becomes hot when operating.

I refitted the resistor, and removed Relay T7. The engine ran fine, but the fan started operating immediately at low speed. So the problem is (I think) related to the the signal being sent to operate it. I need to find and check the coolant temperature sensor, which I assume is tapped into the block somewhere? If that isn't faulty, then there must be a malfunction in the ECU or fusebox.

Thanks for help, I'll get onto that tomorrow -

 

[Davren]

If the fan is running at low speed, check that relay T6 isn't shorted..

The coolant temperature sensor is on the engine thermostat at the gearbox end of the engine.
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[Steve148]

Thanks - T6 operates normally under test. I'll have a look around for the coolant temperature sensor next.

 

[Imeraan]

Thanks - T6 operates normally under test. I'll have a look around for the coolant temperature sensor next.

Hi. I have the same problem. Did you get yours fixed? And how? Please assist. Thanks