156 V6 Cooling Fan Puzzle (temp sender?) - Alfa Romeo Forum
You are currently unregistered, register for more features.    
 
Thread Tools
(Post Link) post #1 of 9 Old 28-09-08 Thread Starter
Status: -
AO Member
 
Burnsy's Avatar
 
Join Date: Dec 2004
Location: Bath, UK
Posts: 222
156 V6 Cooling Fan Puzzle (temp sender?)

I'm after a pointer on where to find the temp sender that drives the ECU cooling fan control input - let me explain... in case someone has a better idea!

My 156 2.5 V6 normally runs at between 80 and 90deg whatever the traffic/use, however it has recently started to get to over 100deg in traffic, fans cut in and bring it down again. With the a/con on and stationary it sits nicely at 90deg (fans pulse on and off) and at any speed above about 40 it also sits below 90deg.

Did a bit of diagnosis at the weekend and found a few things out:

1. Both fans should run together, whether slow or fast, and whether driven by the a/con or coolant temp.
2. There are 2 x 50A black relays (in the group in front of the battery) that drive the fans - 1 for fast (the rear left hand relay) and 1 for slow (the one to the right of it). Each relay drives both fans.
3. There are two resistors on the panel behind the radiator, one in each of the fans' slow speed circuit (to regulate the speed) - the upper one of mine has failed, so until I shorted across it, I had no n/s slow speed fan.
4. Whilst my slow speed fans used to cut in at just over 90deg (a/con off), they now cut in at around 105-110deg.

My diagnosis: I only had one fan working at slow speed so need to replace a resistor, but without the a/con on (which I understand uses an a/con gas pressure sensor switch to drive the ECU to turn the fans on) there is no drive signal to the fans until coolant temp reaches 105-110deg (on the dial).
From other threads it seems the V6 has 2 temp sensors, one feeding the temp display dial and the other the ECU uses to drive the fans. So my conclusion is that the one feeding the dial is ok, the one feeding the ECU is on the way out and is under-reading.

Problem is, I can't find them - anyone help?? Thanks
Burnsy is offline  
Sponsored Links
Advertisement
 
Status: Busy busy busy!
Club Member
Membro Premio
 
Pud237's Avatar
 
Club Member Number: 71
Join Date: Apr 2006
Location: United Kingdom
County: Cumbria
Posts: 44,678
Re: 156 V6 Cooling Fan Puzzle (temp sender?)

Intersting reading for you from here onwards..
Pud237 is online now  
(Post Link) post #3 of 9 Old 29-09-08 Thread Starter
Status: -
AO Member
 
Burnsy's Avatar
 
Join Date: Dec 2004
Location: Bath, UK
Posts: 222
Re: 156 V6 Cooling Fan Puzzle (temp sender?)

Thanks Pud237 - nice carpet!

Read the thread the other day before I started digging around on my own car and it helped work out where to start, but I still come back to needing to find the temp sender.

I'd already jumpered between the resistor terminals so at "slow" speed drive the fan with the failed resistor runs fast - the problem is the ECU isn't turning them on a slow speed until about 105deg!
Burnsy is offline  
Status: Busy busy busy!
Club Member
Membro Premio
 
Pud237's Avatar
 
Club Member Number: 71
Join Date: Apr 2006
Location: United Kingdom
County: Cumbria
Posts: 44,678
Re: 156 V6 Cooling Fan Puzzle (temp sender?)

Not sure where the temp sensor is - I never got to that stage as I found my problems was due to a wire melting on the exhaust and shorting out.

Really not sure what you should try, the temp sensor isn't a usual fail item though.
Pud237 is online now  
Status: -
AO Platinum Member
 
156Chris's Avatar
 
Join Date: Jul 2007
Location: United Kingdom
County: Surrey
Posts: 12,881
Re: 156 V6 Cooling Fan Puzzle (temp sender?)

Consulting eLearn I've gleaned the following information ...


The V6 has 2 temperature senders...
1. the first is on the thermostat, this only drives the temp gauge.
2. the second is in/on the injection unit which drives the ECU

If you disconnect the sender on the injection unit this should put the ECU into "panic mode" and switch on the fans all the time ...
156Chris is offline  
Status: -
AO Platinum Member
 
156Chris's Avatar
 
Join Date: Jul 2007
Location: United Kingdom
County: Surrey
Posts: 12,881
Re: 156 V6 Cooling Fan Puzzle (temp sender?)

I know on the JTD that the pipe that passes the coolant from the stat to the injection unit is very small (in comparison to the other coolant pipes) ... I presume it's only purpose is so that the sender in the injection unit can do it's job ... so maybe it's become a bit blocked (just clutching at straws though ...)
156Chris is offline  
(Post Link) post #7 of 9 Old 29-09-08 Thread Starter
Status: -
AO Member
 
Burnsy's Avatar
 
Join Date: Dec 2004
Location: Bath, UK
Posts: 222
Re: 156 V6 Cooling Fan Puzzle (temp sender?)

Thanks for that Chris.

Will have a look round for the Injection Unit, though not sure exactly what I'm looking for - presumably the electronics until that controls the injectors, so tracing the wiring back from the injectors should find it?

From what I could see, there was NO electrical connector coming from the thermostat housing, though I really ought to take off the intake plenum chamber to get a proper look. I do remember seeing a small hose around the area of the thermostat housing though, so hopefully that is the feed for the injection unit temp sensor and I can trrace it along to find it - again will need to take off the intake to get a proper look.

That's the problem on the V6 - it's so tight under the bonnet that finding or inspecting anything is a job in itself!
Burnsy is offline  
Status: -
AO Member
 
maxitore's Avatar
 
Join Date: Apr 2009
Location: Serbia
County: -
Posts: 59

Member car:

Alfa 156 2.4 JTD

did you resolve it?
maxitore is offline  
(Post Link) post #9 of 9 Old 19-07-09 Thread Starter
Status: -
AO Member
 
Burnsy's Avatar
 
Join Date: Dec 2004
Location: Bath, UK
Posts: 222
Hi Maxitore.
Yes I did get it sorted, eventually - with the onset of autumn and cooler weather I never seemed to get stuck in traffic long enough for the temp to rise a lot - so I left it. Then a few months ago my cambelt was due replacement, so when it was in at Benalfa I asked Alan to change the sensor and slow speed resistor. Back to 90 on the button now in the hot weather.

I should also mention that after that last post I had another good dig around the fans etc and found that the 2 bolts securing the O/s of the fan mounting frame to the radiator has fallen out!
This allowed the fan frame to flap about, no doubt reducing the effectiveness of the fans, and a bolt had chafed one of the fan supply wires so I think I also had an intermittent open-circuit. Impossible to be sure exactly what was going on with the combination of factors, but am fairly sure the fans had not been loose all the time and that they didnt even switch on before 95deg, so the new temp sender sorted that and the wire repair, new bolts and resistor mean it all works all the time now too!
So with that done, new cambelt and having had bonnet, roof and sills repainted - dulled finish, rust and rust respectively - I'm now hoping to keep her going for another 136k!!

or til the next 'belt change at least :-)
Burnsy is offline  
Reply

Go Back   Alfa Romeo Forum > Supported Alfa Romeo Models > Technical & Vehicle Assistance > Alfa 147, 156 & GT

Tags
156 , cooling , fan , puzzle , sender , temp

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome