Scavenger fan sensor test

[mikexgough]

Think from the way the thread is going .............I will leave well alone......

My dad always says..............if it aint broke...........don't fix it...........

[Lewy]

I think I may well try the hot air test on the sensor and see if it activates the fans. Does anyone know of a way of testing the water temp rad fan sensor? And is putting the AC on activating the same rad fans that the water temp sensor activates?

[dandywarhol]

Same fans Lewy but different input from the ECU and relays.

In the centre of the head on the driver's side there's a 2 wire sender switch for the fans - disconnect it and check the resistance:

@ 20 deg.C 2300 - 2600 ohms
@80 deg. C 290 - 340 ohms

[mikeonb4c]

Okay, I don't have a wiring diagram but the sensor switch has a 5v supply going to it and when the switch momentarily triggers for around 1 second then thats going to be 5v going BACK to the ECU - not directly to the scavenger fan. So you're supplying 12v to the "safe" side (by luck presumably ) of the ECU. Whenever your engine bay gets hot enough to allow the sendor to become a closed "switched" circuit you're going to put 12v down to the "unsafe" side of the ECU - PHUTTTTTT

"Ermmm Bongobits - could I have a second hand ECU please?"

Plausible????

But that surely can't be right as the supply to the scavenger is 12v as standard, which suggests to me that the 5v is a switching side voltage, and that the switch then makes a circuit on the 12v supply side which is (has to be) a completely different circuit

[dandywarhol]

Yep, agreed but you're feeding 12v into a 5v circuit i.e. into the ECU. I don't know a lot about it and haven't got the diagrams but I would expect fireworks when the scavenger sensor becomes a closed circuit. There's no reason why a relay can't be fed by th ECU's 5 volts and switch the scavenger 12v circuit on.

Maybe I'm totally wrong and paranoid about this but I'll never forget a Service Manager's look of despair with his head in his hands when a mechanic spiked a brand new SAAB 9000 ECU when fitting and wiring a towbar. That replacement ECU cost a few quid short of £2000 and that was 16 years ago.
The mechanic didn't do as SAAB advised and ground the electrics - he thought he knew better!

Funnily enough, I recently saw him driving a Lothian Transport bus - mind you he probably gets more for doing that than a mechanic with 3/4 years training

[mikeonb4c]

Yep, agreed but you're feeding 12v into a 5v circuit i.e. into the ECU. I don't know a lot about it and haven't got the diagrams but I would expect fireworks when the scavenger sensor becomes a closed circuit. There's no reason why a relay can't be fed by th ECU's 5 volts and switch the scavenger 12v circuit on.

Maybe I'm totally wrong and paranoid about this but I'll never forget a Service Manager's look of despair with his head in his hands when a mechanic spiked a brand new SAAB 9000 ECU when fitting and wiring a towbar. That replacement ECU cost a few quid short of £2000 and that was 16 years ago.
The mechanic didn't do as SAAB advised and ground the electrics - he thought he knew better!

Funnily enough, I recently saw him driving a Lothian Transport bus - mind you he probably gets more for doing that than a mechanic with 3/4 years training

Nah, you're right to be cautious. I'll just pray to Allah and keep an eye out on ebay for a spare ECU to have handy (you know who in you know which county were actually selling some 2nd hand ECUs for £15 a while back )

[dandywarhol]

If you want to feed the fan seperately you could take a 12v feed directly to the relay which operates the fan - that way you have no chance of frying the ECU.

[teenmal]

If you want to feed the fan seperately you could take a 12v feed directly to the relay which operates the fan - that way you have no chance of frying the ECU.

I seem to remember that Mike took a feed direct from the battery via a switch and fuse to the fan motor.

I have done this myself,but only when there was a problem with the cooling systems.

I would not recommend Fitting any type of by_pass system unless it was a get you home(emergency situation)

Thats only my opinion.

Malc..

[not so old]

I am totally confused about this temp thing. Can anyone please tell me what the normal engine temp should be when not towing or taking on hills. I really worry about this and would be so grateful for anyone who can relieve this worry, so that I can just enjoy the Bongo again.

Cheers Anna

[g8dhe]

Anna - Please don't get concerned!
First you only get to hear of the problems on here, there are thousands out there who don't have any problems!
Most of this thread is us boys playing with our bits
The more you play with a vehicle and its engine the more faults you will have !

Coming from an electronics engineering background the best way to avoid problems is NOT to touch at all, when BT engineers were locked out of the exchanges in a trial the fault rate dropped to 1/10 of the previous level - the trial only lasted a few months before it was put into practice across the entire network (this was a back about 20 years ago).

[dandywarhol]

I'm probably the person causing the angst here.

Mike - could you clarify how you rewired the scavenger fan on yours. I was under the impression you'd fed a supply into the sensor circuit but looking back through the thread I could've misinterpreted that...............

[not so old]

Anna - Please don't get concerned!
First you only get to hear of the problems on here, there are thousands out there who don't have any problems!
Most of this thread is us boys playing with our bits
The more you play with a vehicle and its engine the more faults you will have !

Coming from an electronics engineering background the best way to avoid problems is NOT to touch at all, when BT engineers were locked out of the exchanges in a trial the fault rate dropped to 1/10 of the previous level - the trial only lasted a few months before it was put into practice across the entire network (this was a back about 20 years ago).

Thanks, I know you boys like to play with your toys and all clever stuff too! I had my alarm go off last week and was given advice earlier on this thread , but I still worry and just wondered what the temperature should ideally be on a straight road -no towing. Thanks for the very interesting BT bit

[g8dhe]

when BT engineers were locked out of the exchanges in a trial the fault rate dropped to 1/10 of the previous level - the trial only lasted a few months before it was put into practice across the entire network (this was a back about 20 years ago).

I had better add, in case someone thinks otherwise, that it wasn't that the BT technicians were putting faults on as such, but the simple process of removing covers, jacking selectors in and out, routine testing (one of the biggest causes of faults) were the cause, the regime then became that only when there was a likely hood that service would be affected would an technician be sent out, and deal with all the known problems.

[mikeonb4c]

I'm probably the person causing the angst here.

Mike - could you clarify how you rewired the scavenger fan on yours. I was under the impression you'd fed a supply into the sensor circuit but looking back through the thread I could've misinterpreted that...............

Mine's a direct feed from battery (via a switch) to the fan so does not touch the sensor circuit. So I'm reckoning what I've done is as safe as could be.

This is as good a time as any to reveal one of the main reasons I fitted a scavenger over-ride (you'll laugh at this). Well, I had (still have in fact) a leaky diesel pump. Nothing serious, but if sat in traffic after a session at speed (when it seems to drip - why? no idea, but maybe excess head of pressure) you could sometimes get a whiff of diesel in the cab. And since 'her indoors' would be straight on the case if she whiffed it ("your bl**dy father had to get an old smelly van that stinks of diesel") I thought a quick means of scavenging the engine bay might be handy. And by jingo it has been. And the switch is out of her line of site so any concerns and I just flick it on and hey poncho - no whiff.

Brilliant or wot

[dandywarhol]

Wot.............