Technical Ducato cooling fan

[Tom Hughes]

Today my 1998 ducato 2.5 diesel motor home cooling fan started running when the van had been idle for 24 hours

 

[Anthony489]

Hi Tom

Fan arrangements evolved over the years so I cannot be certain what you have fitted. The most likely arrangement has two fans directly switched (i.e. no relays) by a twin thermal switch screwed into the radiator low down. The switch comes electrically after the fan, i.e. it is the "earthy" side that is switched. One fan is meant to cut in at a certain temperature, and the other comes on as well if the temperature climbs even higher. If one of the internal switches has failed it would give the symptoms you describe.

These thermal switches are not overly expensive (say 15 Euros) so renewing it would be an easy first step. You will need a spanner with 29 mm jaws, and maybe a large cork to stop too much coolant escaping !

Another possibility is that the wire from the fan to the thermal switch is shorting to ground somewhere.

 

[Tom Hughes]

Hi Tom

Fan arrangements evolved over the years so I cannot be certain what you have fitted. The most likely arrangement has two fans directly switched (i.e. no relays) by a twin thermal switch screwed into the radiator low down. The switch comes electrically after the fan, i.e. it is the "earthy" side that is switched. One fan is meant to cut in at a certain temperature, and the other comes on as well if the temperature climbs even higher. If one of the internal switches has failed it would give the symptoms you describe.

These thermal switches are not overly expensive (say 15 Euros) so renewing it would be an easy first step. You will need a spanner with 29 mm jaws, and maybe a large cork to stop too much coolant escaping !

Another possibility is that the wire from the fan to the thermal switch is shorting to ground somewhere.

Thanks Anthony, that's really helpful. Very reassuring too

 

[Tom Hughes]

Thanks Anthony, that's really helpful. Very reassuring too

I should have said I have the two fans but after that I simply don't know what type of connection is used in this model. I better figure it out

 

[airwave]

Today my 1998 ducato 2.5 diesel motor home cooling fan started running when the van had been idle for 24 hours

Just some additional information here . As your van is only 2 years older than mine , it is possible you do have relays mounted , in the engine bay . Now if fitted , they will be inside a small black box , actually mounted to the top nearside fan shroud .

 

[Tom Hughes]

Thanks for the info. We've temporarily solved the issue by removing the cable to the problem fan a few minutes after we stop. So far there has been no repeat of the problem. So we will bring it back to our regular service guy when we get back

 

[airwave]

Thanks for the info. We've temporarily solved the issue by removing the cable to the problem fan a few minutes after we stop. So far there has been no repeat of the problem. So we will bring it back to our regular service guy when we get back

Yeah that sound fair enough , enjoy your trip my friend .

 

[Madmike]

Thanks for the info. We've temporarily solved the issue by removing the cable to the problem fan a few minutes after we stop. So far there has been no repeat of the problem. So we will bring it back to our regular service guy when we get back

I have the exact same problem myself today

My motorhome was off since Monday and last night, the fan started running with nobody near it, no keys etc

I unplugged the fan last night and have just now located 2 relays inside the black box on the shroud as mentioned by @airwave and the middle relay (or one closest to passenger side/same as fan that was running) was red hot, so I've unplugged the relay, but no idea where to go from here, so just posting a reply here to see if you ever got sorted afterwards

 

[airwave]

no idea where to go from here,

Well first things first , you say the relay was red hot ! , well my first move would be to replace that relay . It's not impossible that this could simply be your problem , relays can , and do go wrong themselves . The contacts are subject to constant arching , due to the constant off on function they provide , they are basically a switch when all's said and done . Not only can they fail to work , but they can fuse on as well . Being as hot as you say , would not have done the contacts any favours , so scrap it , but pay careful attention to the amperage . I don't actually know the rating off hand , but i'm sure i can find it out if it's needed .
Given that you have no manual means of controlling the fans , the most likely reason is you have a rogue earth somewhere , and that somewhere is likely connected to the relay affected .
Now let me explain a little about relays before i go any further . As i mentioned above they are basically a switch , a switch enabling a smaller switch to control a high voltage circuit such as cooling fans . Now that may seem confusing , so look at it this way . Many switches have a maximum amperage of 10 amps , put that into a 35 amp circuit , and it will likely melt . Failure is pretty much certain , but there is also a fire risk as well . A relay gets around that , the low amperage switch is connected to one side of the relay , and the high voltage circuit is connected to the other . Activating the switch causes the relay to complete the high voltage circuit , and operate the given function , in this case cooling fans . Now here you say , well that won't work , because the voltage will cross over , and yes you are quite correct . Except in this case it's the earth circuit that's used to control the relay . But now in the case of the cooling fans , we have the added complication in that , the switch is not only a two pole , it's basically automatic as well .
Now this is where i draw your attention to the thermostat , fitted in the lower right hand side of the radiator (looking into the engine bay from the front of the vehicle) . This is your switch , and it has two settings , one fan or both . I can't remember the actual settings , but as the temperature rises a single fan will activate first , and if this is unable to cope , the second fan will automatically kick in .
By the very fact , one half of the thermostat appears to be working fine , it's unlikely (though not impossible) , the other half has failed . But this is where the earth for the relay originates . Disconnect the harness plug from the thermostat and replace the relay , and see what happens . Nothing should happen , both fans should remain off , now replace the new relay with the old one you have already removed and test again , again nothing should happen . Now reconnect the thermostat , and see what happens now .
If the fan operates in the first case , you have narrowed the fault down , to between the thermostat and relay , examine that length of wiring carefully . In the second case , the relay is likely the culprit . The third is pointing towards the thermostat itself . Start there .

 

[Madmike]

@airwave Thank you for the reply

I had actually started a separate discussion on this initially, but while I was waiting on responses, I came across this thread and just said I would see if the OP ever got to the bottom of it.

The other thread is here and I tried plugging the fan back in and swapping the relays around, but it instantly ran again each time, so I'm guessing its the thermostat you've mentioned has failed, or possibly the wiring also and thats what I hope to try once I get back to it, but it could be Tuesday before I get to try it now