4200 Engine fans question

paul328

paul328

Member
Messages
132
When you start your 4200 from cold do one or both engine fans come on? The air con one should normally come on if it is switched on. I have only driven about 3 4200 and think I recall all had the fans running all the time,

I have discovered a problem I think is with the thermostat as the temp won't climb above 1/4 on the gauge. However this car has always had the fans run since I owned it and temp appeared normal.

I will change the thermostat shortly and possibly the temp sensor too, which appears a common pattern part.

Any guidance would be appreciated.
 
R

RJ237

Member
Messages
107
The low fan should not come on until the engine temp. is about 95 C, high speed a few degrees higher with the air off. I changed the thermostat in mine because it was dropping down to 70 C and even lower when moving. Now it holds 85. Use of a IR thermometer indicated the temp. sensor was correct.

I use a UltraGauge which plugs in to the OBD port to monitor temperatures, fuel trim, etc. It has the added benefit of a high temp. alarm.
 
doodlebug

doodlebug

Member
Messages
917
I had the same intermittent problem with mine about 6 years ago. It was diagnosed as a faulty temperature sensor in the engine (not the thermostat) so I had it replaced. It turned out to not be the sensor because the problem came back a short while later. From memory, Rob Grimaldi traced it to a fault in the binnacle gauge circuit board.

I never got to the bottom of how a fault there could cause the fans to come on, but it's been fine ever since.
 
spkennyuk

spkennyuk

Member
Messages
5,960
paul328 said:
When you start your 4200 from cold do one or both engine fans come on? The air con one should normally come on if it is switched on. I have only driven about 3 4200 and think I recall all had the fans running all the time,

I have discovered a problem I think is with the thermostat as the temp won't climb above 1/4 on the gauge. However this car has always had the fans run since I owned it and temp appeared normal.

I will change the thermostat shortly and possibly the temp sensor too, which appears a common pattern part.

Any guidance would be appreciated.
Click to expand...

I would look at the radiator fan resistor first. Its an alfa 147/156/166 part around £12 to buy.

If the resistance coil is breaking down then it will offer no resistance and your radiator fan will default to full speed regardless of the signal being sent to it by the thermostat / temperature sensor.

If its only just started breaking down you may find it starts to work normally once the car has warmed up a bit.

By the sounds of it yours is totally shot and so the engine isnt ever getting up to normal temperature as it on full cooling all the time.

The resistor is held in by two torx bolts on the back of the fan in the middle section.

82958


"SmartSense Radiator Fan Relay Resistor for Alfa Romeo 145/147/155/156/164/166… 5060426620997 | eBay" https://www.ebay.co.uk/itm/SmartSen...003090&hash=item1c51d68a4b:g:NrIAAOSwxmJf4gTB
 
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paul328

paul328

Member
Messages
132
Thanks guys. I have ordered the resistor. Thank you for the link. I don't think the fans could keep the coolant that low as has been happening for a while. I suspect the thermostat has stuck open.

Recently when I stop the car after a run it won't restart and overfuels, which I assume is due to the thermostat or temp switch sending a signal that the engine is still cold. I have to leave it 5 minutes till it cools a bit then it will start.

I have read the posts about the fuel vapour filters etc but can't see how these could make a difference as they are non service items.

I can't see the temp gauge can be controlling the ECU as it should simply record.

From previous threads I see these are quite common problems. I have always thought this car seemed to idle quite fast at about 1000rpm. however the two others I drove when I was buying mine were the same. I just thought it was the way they were.
 
doodlebug

doodlebug

Member
Messages
917
paul328 said:
Thanks guys. I have ordered the resistor. Thank you for the link. I don't think the fans could keep the coolant that low as has been happening for a while. I suspect the thermostat has stuck open.

Recently when I stop the car after a run it won't restart and overfuels, which I assume is due to the thermostat or temp switch sending a signal that the engine is still cold. I have to leave it 5 minutes till it cools a bit then it will start.

I have read the posts about the fuel vapour filters etc but can't see how these could make a difference as they are non service items.

I can't see the temp gauge can be controlling the ECU as it should simply record.

From previous threads I see these are quite common problems. I have always thought this car seemed to idle quite fast at about 1000rpm. however the two others I drove when I was buying mine were the same. I just thought it was the way they were.
Click to expand...
Those symptoms are identical to the fault mine had several years ago. It was only cured with replacement gauge PCB. Changing the temperature sensor (twice) and the fan resistors did not work.

Like you I didn't understand how the temperature gauge could be controlling the ECU but there is definitely something controlling the ECU via the gauge PCB.
 
T

tulit

Member
Messages
110
The symptoms don't sound like the fan resistor at all.

If the resistor fails, it simply prevents the fans from running in low speed, and they can only run at high. This would be the case whether the resistor failed open (basically they wouldn't come on at 95c and only kick in high at 100c) or fail short (in which case it would kick in high at 95c). Though its HIGHLY unlikely for it to fail shorted, only open.

Again though in either case it won't just make the fans run 100% of the time even from cold. You still need to pass the temperature thresholds.

Something else is going wrong.

I'd start by checking the fan relays aren't fused shut.

Sent from my SM-A515W using Tapatalk
 
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tulit

Member
Messages
110
BTW I wrote up a procedure to test the resistor

www.italianautotech.com

Testing Radiator Fan Resistor

The radiator fan on these cars has two separate speeds they can run at, LOW and HIGH. In the case of this 2006 Gransport, the low speed turns on at 95 deg C and shuts off at 90 deg C. Conversely th…
www.italianautotech.com

Sent from my SM-A515W using Tapatalk
 
doodlebug

doodlebug

Member
Messages
917
My take on it is it can't be the fan resistors. As mentioned previously, a failed resistor would only mean the fan would come on at high speed when the temperature was very high. The low speed wouldn't work at all.
My fans came on full speed even when it was below freezing outside, even on a cold start.
Rob Grimaldi suspected a faulty air-con controller because that controls the fans as well. After disconnecting the air-con controller from the ECU with no improvement, he came to the conclusion that something else was afoot.
My temperature gauge never went above about 70 degrees, but we both thought it might be because the fans were on full. It was in fact a problem with the gauge PCB which gave the problems and replacement cured it.
Weird.
 
CatmanV2

CatmanV2

Member
Messages
48,789
doodlebug said:
would only mean the fan would come on at high speed when the temperature was very high.
Click to expand...

Not quite true. Since the fans cannot come on at low speed, they always come on at high speed. Like when the aircon kicks in.....

But your ideas have distinct merit

C
 
T

tulit

Member
Messages
110
doodlebug said:
My take on it is it can't be the fan resistors. As mentioned previously, a failed resistor would only mean the fan would come on at high speed when the temperature was very high. The low speed wouldn't work at all.
My fans came on full speed even when it was below freezing outside, even on a cold start.
Rob Grimaldi suspected a faulty air-con controller because that controls the fans as well. After disconnecting the air-con controller from the ECU with no improvement, he came to the conclusion that something else was afoot.
My temperature gauge never went above about 70 degrees, but we both thought it might be because the fans were on full. It was in fact a problem with the gauge PCB which gave the problems and replacement cured it.
Weird.
Click to expand...

That doesn't make a whole lot of sense either... Both fan speeds are controlled directly from the ECM. Wondering if there's certain other faults that the system enters limp mode and part of that is to just run the fans. Maybe worth the poster pulling all ECM codes.

e.g. There's not much to it. The output of the ECM triggers the relays and power gets fed to the fans...



83003
 
S

spn

Junior Member
Messages
88
Have you checkd the fault codes?
Mine does this occasionally and as tulit has suggested, it enters a limp mode (no CEL though); the fans run when you start it, throttle is a bit dulled and gear changes are rough. There's a fault code stored (can't remenber the exact one - warmup issue), when the code is deleted, the fans go off and the car runs fine until the next time. Normally more of an issue in th winter.

I suspect it's an issue with the thermostat and probably temp sensor. I'm going to change them when I do the heater matrix.

Probably the thermostat sticks open or the temp sensor doesn't register an increase as expected so the car goes into a limp mode (overfuells, runs the fans) to protect the engine.

I think Chriss155 had a similar problem:

Cheers,

Simon
 
paul328

paul328

Member
Messages
132
This has happened a few times when the car wouldn't restart when hot due to overfueling. It was easy to smell. I haven't used the car much since late last year and when I did my first non short journey it came up with an engine management light and fault code PO128 or Thermostat. We reset it. It is still running cool. I don't recall if it was running cool late last year when I had the over fueling issue. Normally with old Italian cars I tend to watch if the car is running hot not cold so it is possible I missed it.

At present the issues are as above:

Both fans seem to be on immediately on start and run all the time. I think at fast speed. I think this has always been the case since I bought the car.
The car runs at about 1/4 on temp gauge and does not seem to want to get warmer.
When I stop after car should be at normal temp, say after 6-8 miles it is reluctant to start and there is a momentary pause and then it just wont start and smells of fuel. It restarts after about 5-10 minutes.
I have noticed the fuel consumption appears poor about 17mpg although it has mainly been short runs.
 
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