Engine cooling fans confused

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JulesMartin
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Engine cooling fans confused

Post by JulesMartin » Sun Jan 19, 2020 1:28 am

I'm a bit confused and wonder if you guys could answer this question? All is going well since the head gasket rebuild the temperature at the back of the head on long runs sits between 90 and 96 depending on speed and engine load. I thought I would knock up a jury rig to see what was happening with the cooling fans and when they were coming on so ran 4 wires one from each of the two lives on each of the fans to 4 led's inside the cab. I was expecting to find that two would come on if the Bongo was sitting in traffic with the other two coming on if it got really hot. What I did find is that all 4 come on at 40mph regardless of engine temperature. The lights come on at that speed and stay on until the van comes to a halt. Under 40mph they don't light at all. I can't obviously see if the fans are actually coming on or not. I expect the cooling system is much more complex than i have anticipated but was not expecting this result. I'm taking the live feeds from the two 4 wire sockets going directly into the two fans. Plonkatronix had said that they are earth switched, I have no doubt he is right but I found that the 4 earth wires are constantly to earth. I'm obviously missing something and the cooling system is way over my head. any help as always much appreciated
Martin
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Re: Engine cooling fans confused

Post by g8dhe » Sun Jan 19, 2020 10:43 am

If your going to play with the electrical then it would benefit you to visit the wiring diagrams site and understand that the motors are not your general single speed devices on a diesel! You will need Flash installed and if using Chrome then you need to enable Chrome to use Flash for the site
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Re: Engine cooling fans confused

Post by JulesMartin » Sun Jan 19, 2020 11:10 am

Cheers Geoff thanks for the diagram and advice. I'll have a look into it a bit deeper but I was interested if anybody could suggest a reason why the fans are apparently switching on at 40mph regardless of temperature. I'm not sure they are of course but the circuit is becoming live at that speed as testified by the led's. I'm not aware of any speed monitoring module in the cooling system or at least not seen one as yet.
Martin
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Re: Engine cooling fans confused

Post by g8dhe » Sun Jan 19, 2020 11:42 am

Are you sure your not just seeing the fan's turning in the breeze and powering the LED's up rather than seeing when 12 volts are being applied ?
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Re: Engine cooling fans confused

Post by JulesMartin » Sun Jan 19, 2020 8:41 pm

Thanks guys as always for your replies. i did ponder if it would be possible for the motors to motor up with the wind but wouldn't the lights go out once the motors stop motoring? The LED's stay on for a couple of seconds after the van comes to a stand still and all go out together. I'll give the wiring a second check over and see if I can fathom the earth switching of the relays and light the LED's from there. I understood about using LED's and not bulbs to prevent the reverse current so I got something right! Thanks guys, I'll be back.
Martin
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Re: Engine cooling fans confused

Post by windywatson » Thu Jan 23, 2020 12:01 pm

I've come across this before, a friend tried to do the same. Found that the fan motors being DC acted as generators & illuminated the lamps he'd installed. As the fans can still be spinning down when coming to a stop, the lamps sometime stayed illuminated for a short while.
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Re: Engine cooling fans confused

Post by JulesMartin » Fri Jan 24, 2020 5:26 pm

Well done Geoff, Plonkatronix and windy. you clever people! The fans do indeed spin up in the wind. I was given an endoscope for Xmas and I'd recommend it for use around the Bongo. Today I stuck it under the bonnet pointing at the two fans and took it for a run up the road. Annoying the video can't be saved as the software that came with it is next to useless. it does however show that on acceleration up to 40mph one fan then the other stutter then spin up. I then slowed down to a stop and the fans can clearly can be seen slowing and stopping after I have stopped. So conclusive proof that they do motor up and that you can't therefore cut into the loom on the fan side of the relays to monitor their action. i have done as Plonkatronix said and wired into the switching earth at the first relay on the right looking down on them. I've run a light gauge wire from this earth to a single LED on the dash and run an ignition switched live feed through a 1amp inline fuse to the other side of the LED. this I've tested by pulling the wires off the temperature control sensor under the manifold. I'm out for a run down to the coast tomorrow so will be able to see it in action for real then. Thanks as always for your great help and assistance.
Martin
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Re: Engine cooling fans confused

Post by JulesMartin » Sat Jan 25, 2020 2:18 am

As long as I keep the curly blue smoke in the little black boxes it should be ok :) . I'm going to give it a run out over the weekend to get it to switch on under it's own power rather than forcing it on by pulling the plug but in this weather it does take ages to reach their switch on temperature. It's funny that I've got a lower water sensor, a digital thermometer and now a fan indicator all to ensure that it doesn't get too hot without me knowing about it and now I actually want it to get to the point of overheating!!
I was thinking about the fans again and although I've witnessed them running up it didn't really prove that they were spinning by wind pressure only. I'm going to repeat the test with the wiring plugs unplugged and see if they still do the same thing. I'll keep you updated.
Martin
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Re: Engine cooling fans confused

Post by JulesMartin » Sun Jan 26, 2020 4:07 pm

Just an update. Took it for a run yesterday with the fan LED wired up from the switched earth from the first relay and all went really well. It flickered on with the ignition as predicted by Plonkatronix then went out and stayed out until after about 30 minutes of dual carriageway and on deceleration it popped on for about 15 seconds. Parked up for about 15 minutes and on start up the light came on for maybe 30 seconds then went off. Coming up from Canvey Island there is a lovely long hill which I pushed up to give it a good test and after reaching the top and about 30 seconds the light came on and stayed on for about 10 minutes. The digital temp gauge also showed an increase in temp of about 6 degrees. The temp gradually came down and as it did the light went out. i would assume from this that all is working as it should and I'm happy with that. I guess in the summer months I can expect it to pop on and off more regularly but I'm happy with that now. Thanks again for all your help.
Martin
1996 2.5 TDi Silver pop top unconverted
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