Bongo Fury

Hi guys , my radiator fan is running after a shortish commute , temperature gauge is normal, though I know this is not a great indicator, the bottom hose is cool to touch even though the fans are running, leaving it to idle before I switch the ignition off doesn’t seem to allow them
To stop , I changed the thermostat as I though it was opening too late , and bled the system as I have done many times on this and a previous bongo, the bottom hose got hot , so I know all is good with the stat (genuine Mazda ), so I’m suspecting the sensor it’self , I think it’s the one under drivers seat on block near FIP , what do you guys think ?, anything else I should check ? Air con is off by the way . Interested in fitting a digital temp gauge , can someone advise on which is best . If it is the sensor in the block , do I need to bleed the system after ? In other words will coolant come out when I remove it !
Thanks in advance
Paul

Yes the coolant sensor for the ECU and hence the fans is on the side of the block a 2-wire device.

Thanks Geoff, is it likely to be causing my symptoms , turning the fan on but not off ?

You don't say which engine ? The fan will continue running till the engine has cooled down even with the ignition off as I recall.
Are you certain its the radiator fans and not the scavenger fan which keeps the engine housing cool that's coming on, this will fire up if your static at all and the engine housing heats up, the sensor for that is directly below the handbrake handle poking into the housing, this continues after ignition is switched off as well.
Otherwise I wouldn't be too worried it would seem to be doing its job too be honest ?

Hi Geoff , apologies, it’s a diesel, it’s definitely the radiator fans and not the scavenger fan , the fans do turn off with the ignition, however they come straight back on if I put the ignition back on and don’t start the engine. I’m probably being paranoid , but after my last Bongo had head gasket problems...... my concern is that the bottom hose is not hot , so the stat is not opening , the hoses do seem to pressurised after a run , I appreciate they will get harder as the engine is warm , but not sure how hard is normal, and I’m guessing the radiator cap would release the pressure if it’s too much ?!
I looking at other posts to see the best/ easiest way to add a temperature gauge that is more accurate, I’m off on a long trip to Wales next week and just want to make sure all is good,
Thanks again for your replies

That sounds ok to me.

When you switch off the engine continues to dump heat into the coolant so the temperature rises, hence the fans come on if you switch on the ignition. With an accurate gauge that would also rise.

They should stop after a couple of minutes.

Firstly check the system for coolant leaks, check the rear heater pipes and the one over the starter motor, these are prone to leaks and could let air into the area of the switch, is it loosing coolant.
The front rad fan switch is the one you say, just in front of the starter motor and behind the pump. This is a service part and should be changed if you doubt it. Make sure you use a gen Mazda one as they are better quality than the copy parts.
You need a good fitting deep socket to remove and refit as the last inch is plastic, this plastic bit is liable to become loose when knocked. If the plastic end wobbles or is at all loose replace it as the trigger temp start to go out of true as the resistance increases because of poor internal connections in the metal bit. This can make the switch work ok but trigger at weird temps.
Take the cap off, let pressure go, then remove the plug wires, deep socket off quick, stick her finger in the hole, watch out for the crush washer between the switch and block face, replace with new one, if any doubt rebleed system until really hot and you should notice a new fan trigger point. WARNING, when bleeding up to fan switch point, cap everything off then keep going revving on and off until you think they aren't working and the thing is going to explode, the fans will come on when you then let it tick over for about a minute, but it is hard to get too so keep going. This point is a lot higher than your seeing at present so the difference should be obvious.
Be brave, it's scary, but go for it.

Thanks , for both your posts , I’m pretty sure I don’t have any leaks , I’ve replaced pipes previously, it’s reassuring what you say about the temperature sensor and I suspect/hope that this is the cause , I will replace with genuine, I know what you mean about it being scary to get the fans to come on ! Just a thought but would a resistance test on the old sensor give an indication to its condition?
Thanks again
Paul

Surely you expect the pipe from the radiator to be cold ? Its the cross flow over the top of the thermostat that is the flow to be cooled down ? Click the image for animation ....
http://www.g8dhe.net/bongo_images/widdo ... ration.gif

PaulD wrote: ↑Mon Jul 27, 2020 4:51 am Thanks , for both your posts , I’m pretty sure I don’t have any leaks , I’ve replaced pipes previously, it’s reassuring what you say about the temperature sensor and I suspect/hope that this is the cause , I will replace with genuine, I know what you mean about it being scary to get the fans to come on ! Just a thought but would a resistance test on the old sensor give an indication to its condition?
Thanks again
Paul

I've tested these in the past and you can get weird readings when tested if the sender is loose between the plastic connector and the metal end, any movement on this the sensor and
it should be binned, as said it is rare but as you've done most other control items it makes sense to swap out as this controls the temps seen at the ECU which controls cold start, egr, fans,