Basic fan operation

[gazza]

Still having problems with low speed cooling fans

Following loss of coolant many years ago, my Bongo 2.5 TD Auto started to smoke badly every now and then after a cold start.
I suspected a cracked head or head gasket failure, but was loathed to spend all that money without being certain, as performance was unaffected.
I continued to use the vehicle over a 2 year period, occasionally having to top up the coolant. I had top up the coolant following lots of short journeys, but never after a long journey.
During this period , I carried out the temp gauge mod from the fact sheet, fitted a low level coolant sensor , replaced the radiator, thermostat and ECU coolant temp sensor (the one in the middle of the head).

Finally, I decided to have the head checked. The head was cracked on one of the exhaust ports.

Engine has been put back together with new head, water pump, belts, etc……..

Now it's all running fine , but the low speed fans don't come on.

When the ECU coolant temp sensor is disconnected the high speed fans come on. Therefore, a new sensor was tried.
First of all the sensor tip was put in boiling water, still no low fans.
Secondly, new sensor was fitted to the head, fully warm , still no low speed fans.

Relays , in turn were switched to ground, both low speed and high speed fans work.

All fuses and relays checked as OK.

Does anyone have any advice. Have you seen this before?

I can only assume it's either the engine ECU or wiring from the engine ECU to relays / temp sensor.

Are we still missing something still? Another module somewhere?

Would be good to have another ECU to see if it cures the issue.

Any advice gratefully received.

Garry

[missfixit70]

Just wondering if the body of the fan switch should be earthed to the vehicle body for it to work when testing? Did you test the sensor's resistance values as per the manual in my earlier post? Have you tried disconnecting the relay for the high speed fans to check the low speed circuit works when the switch/sensor is disconnected?
Have you tried it in situ, running the engine up to temp? Just make sure you are monitoring engine temps if you go this route, but as it seems the high speed fans seem to work, you should be ok.

[missfixit70]

Do the low speed fans kick in when the ac is on (if your ac works)?

[gazza]

Hi, the body of fan switch does not need to be earthed, it works on varying the resistance.
Sensors Resistance values are the same at given temps for both sensors we have tested.
Already know that both high and low speed circuits work by switching the ECU wires to ground.

The problem is the engine ecu is not calling for either of the fans to come on at the temps (96 and 104).

Fan does not come on with AC but then does it need the AC on in order for the fans to come on?

[missfixit70]

Hi, the body of fan switch does not need to be earthed, it works on varying the resistance.

I would tend to agree (but I have not checked the wiring diagrams), but is it worth a try?

Fan does not come on with AC but then does it need the AC on in order for the fans to come on?

It does not need the ac on in order for the fans to work, BUT it should kick the rad fans on when the ac is on & loaded up (not when just the internal fans are on), so if it is not kicking the rad fans in, that may help in diagnosing the fault.

Just trying to help, seems you know all the answers so I'll leave you to it.

[dave_aber]

What temp are you expecting the low speed fans to come on at Gazza & how/where are you measuring it? Not supposed to kick in till 96 degrees at the sensor, which you'll have to push it pretty hard to reach.
To test the sensor itself,
at 20 degrees, resistance should be 2.3 - 2.6 ohms
at 80 degrees, resistance should be 0.29 - 0.34 ohms.
I guess if you removed the sensor (or use the old one if it's within range) & stick the sensor end in a boiling kettle while connected to the circuit, it should switch the fans on, not gona be that simple to do, due to the location of the wiring.
Only way to properly test it it is to run it up & get it up to temp, just needs a bit of patience, but you need to have sumat to monitor the temp with.

Any idea what 96° should look like on a Mason-modified gauge?

I've just swapped the stat and rad, and everything seems fine - however I've not managed to get the fans to kick in. I'm going to measure the ECU sensor resistance whilst monitoring the gauge to be comfortable that the ECU sensor is OK. I've not pushed the temp up past about "2 o'clock" (wildly inaccurate description!) so maybe I've not been brave enough to get the temp to 96° yet.

[jaylee]

What temp are you expecting the low speed fans to come on at Gazza & how/where are you measuring it? Not supposed to kick in till 96 degrees at the sensor, which you'll have to push it pretty hard to reach.
To test the sensor itself,
at 20 degrees, resistance should be 2.3 - 2.6 ohms
at 80 degrees, resistance should be 0.29 - 0.34 ohms.
I guess if you removed the sensor (or use the old one if it's within range) & stick the sensor end in a boiling kettle while connected to the circuit, it should switch the fans on, not gona be that simple to do, due to the location of the wiring.
Only way to properly test it it is to run it up & get it up to temp, just needs a bit of patience, but you need to have sumat to monitor the temp with.

Any idea what 96° should look like on a Mason-modified gauge?

I've just swapped the stat and rad, and everything seems fine - however I've not managed to get the fans to kick in. I'm going to measure the ECU sensor resistance whilst monitoring the gauge to be comfortable that the ECU sensor is OK. I've not pushed the temp up past about "2 o'clock" (wildly inaccurate description!) so maybe I've not been brave enough to get the temp to 96° yet.

This may help Dave..? http://www.igmaynard.co.uk/bongo/forum/ ... ason+gauge

[Northern Bongolow]

dave the mason switch point for the fans on is on or just below the line before the hot block, if that makes sense.
the best way to get them on is rev at 2500 once warmed up, and let the gauge rise to near the hot line then let the motor tick over, this allows the water pump to run at its slowest so heat in the head builds so triggers the fans.
they should pull it down to the half way point on the gauge.

little tip.
they always come on after you have reached the ar*e twitching point

[dave_aber]

Ahh....

That's encouraging then. I've not had it anywhere near that point. Bottom hose nice and hot, but not as far as the line. TBH, I don't know if I've ever had the fans come on apart from with the A/C.

Thanks for your replies - I must try harder to get it really hot!

[g8dhe]

You need to look at this animation which shows the temperatures the fan come in at on the diesel

[g8dhe]

Ah yes, I see where your coming from now I'd forgotten the context of the this old discussion!
I guess no one came up with an answer unless the ECU's have changed at some time, when you say it triggered at 0.032 that sounds rather small voltage to be able to adjust the resistor to ? What type and max. value was the variable resistor you used ?

[g8dhe]

They're dual wound motors, you don't go to that expense just for resilience on a radiator fan! If you manually operate the two relays then you will see that there are two speeds available, why your ECU is not doing what Steve originally recorded I can't say, its only the diesel that has the function.