Radiator fans not working

[swampy]

Hi all, this isn't quite as simple as the rad fans not working I'm afraid. I'm at my wits end! and any ideas would be most appreciated.
A few weeks ago when Marie and I nipped up to North Wales for a few days camping, I noticed it (calling the bongo 'it' as any affection is soon disappearing) seemed to be running a bit hotter than usual, not over heating, just slightly higher temp gauge. I modded the gauge last year to get rid of the 'sticking' point. Normally reads about 11-12 o'clock with occasional increases in traffic or steep hills up to 1 o'clock, just a bit higher on hols than this but not by much.

The next weekend I changed the coolant just in case as it hasn't been done since import and used the see saw method (works very well) no air locks, and not overheating afterwards, but noticed the radiator fans were not coming on after the revving and idling process. I would have expected them to as I'm sure the temp exceeded 96 degrees or even higher (tested this deliberately) Bongo is in very good mechanical condition and the coolant system is sound, water pump works, thermostat works properly, no leaks, head gasket OK, Radiator good etc. The rad fans do work, as when the engine temperature sensor is unplugged they come on, also come on for a while when air con is switched on.

So, did a bit of research and changed the engine temp sensor for an aftermarket from Bongo Bits- beld the system again - great, rad fans come on, but too soon (around 80 degrees) so the stat stays closed when driving and will not open as the fans are cooling the system too much to allow it. The fans are on nearly all the time just driving around and bottom hose is always cold. Spoke to Bongo bits (no probs with them BTW) they suggested it could be air, so bled again (twice) using a couple of different methods. Definitely no air locks, fans still come on at 80 deg.

Because I think it would be better to have the stat open under normal driving (unless it doesn't need to, which is most of the time at this time of year) I put the old sensor back in - bled again! No overheating under normal conditions, but no fans and ordered a genuine sensor from Mazda as Bongo bits suggested there could be a problem with the new sensor.

Changed to the new Mazda sensor (bled again - I'm getting good at this now - definitely no air) - and guess what, no fans! I ran it at idle with occasional revving until the gauge was nearly at hot and nothing. My guess is this is way over 105 deg. and I bottled it before it quite got all the way over to H. Again they come on when unplugged and when aircon switched on. (when aircon is on and fans are running the temp. fell quite quickly but they're not on for long so couldn't rely on this) The problems are going to arise if stuck in traffic on a hot day, wifey does some festivals, so there are often long queues getting in and out and you can't always stop/start the engine.

I'm flummoxed, spoken to a couple of mechanics, but so far no ideas, the ECU and all connections should be fine as one sensor operates the fans (at the wrong temp.), but others don't. I have thought about putting a switch on the dash to operate them manually, but not really sure how to go about it as you need to consider (I think) the relays, fuses etc.
Has anyone ever wired in a manual switch for the cooling fans? or maybe had the same problems with the sensor, any help would be gratetfully received.
Many thanks , Chris

[g8dhe]

I wonder if the new Mazda sensor is faulty, if you have a multi-meter might be worth checking that it has the correct resistance see this thread http://www.igmaynard.co.uk/bongo/forum/ ... ce#p532315 , you could also check the sensor that comes on at too low a temperature as well just to prove the situation ?

Oh and welcome to the forum!

[Northern Bongolow]

most aftermarket senders are inacurate. ive tried them. so that is what you were seing.
then you fitted a gen one and it works well, its just that you think its not.
how have you modded the gauge?? if its the 100 ohm mod, the fans will come on just at or very slightly before the line AT HOT, (just when your arse is starting to twitch) .
the reving to get them on actually slows the process as the waterpump is working and the stat is already open(check temp at bottom hose).
the way to get the fans on is to rev it till its as hot as poss, then leave it ticking over, the waterpump slows the flow, the hottest part of the system is the head-----where the sensor is, then just as you are about to give up, the fans will come on.

all the above applies if you have bled it properly, if not you may kill your bongo trying this so make sure your happy with this method.

[daveblueozzie]

Sorry cant really help more than the info given above, you say you've changed coolant and bled it, did you fit a genuine Mazda thermostat ?

[swampy]

Thank you for the replies, I forgot to mention that I measured the resistance of all 3 sensors at different temperatures, original fitted to Bongo, new aftermarket and new genuine in a pan of water on the gas, from cold right up to 90 deg. They are all within the correct range shown in the bongo manual. Although the aftermarket was slightly different, but still within correct parameters. The fitted original however did fall apart after removing and replacing and before that it did have a little play between the 2 pin plastic fitting and the sensor body, which is what I thought could have caused the problem.

Last night I got it hot by driving for a while, then revving in the drive and letting it idle for about 40 mins, for exactly the water pump reason you mention. The gauge was pretty near H and I just didn't have the nerve for any more!

I used a 100 Ohm reisistor on the mod, so full scale deflection should be 75 - 120 deg according to the factsheet, and the stat starts to open just before 12 o'clock on the gauge, I'm sure I got it above 105 if not 110.

With the aftermarket sensor, low speed started at about 80 deg. and high speed around 90. I tested this when bleeding using a probe thermometer, but when bleeding with the genuine fitted, as the fans didn't come on I stopped at 85 ish. As we were doing the bleeding with just the 2 of us, I rigged up a highly technical? string system so I can open the throttle myself and see saw at the same time. I don't have a thermometer to measure the temp on the hoses as you do in your vid. (brilliant help BTW) Perhaps I should get one.
What's weird is that the aftermarket does switch the fans, with roughly the same resistance values as the genuine sensor at a totally different temperature. I believe low speed should be 96 deg. and high speed 105. Do you think I'm really not getting it hot enough? As soon as I unplug so the fans come on (or use aircon) , the gauge comes back down really quickly, so the cooling system seems healthy overall. I hope this can be resolved as I'm hearing diesel clatter in my sleep now after bleeding so many times!
Thanks

[Northern Bongolow]

Thank you for the replies, I forgot to mention that I measured the resistance of all 3 sensors at different temperatures, original fitted to Bongo, new aftermarket and new genuine in a pan of water on the gas, from cold right up to 90 deg. They are all within the correct range shown in the bongo manual. Although the aftermarket was slightly different, but still within correct parameters. The fitted original however did fall apart after removing and replacing and before that it did have a little play between the 2 pin plastic fitting and the sensor body, which is what I thought could have caused the problem.


this is how they usually fail, the wobble on the end increases the resistance.



Last night I got it hot by driving for a while, then revving in the drive and letting it idle for about 40 mins, for exactly the water pump reason you mention. The gauge was pretty near H and I just didn't have the nerve for any more!

told you it sounds like you have a good efficient system there as its cooling well without the need for the fans, you have to take it past the point you are at to get them to work, that is normal. . be brave and go for it(if you can afford the fuel.)

[swampy]

Thanks for that, I'm sure you're right but I tried again tonight though and man was it close to the egde, virtually right on hot and no fan cut in. I had a word with a local garage this morning that regulary work on Bongos and they didn't know how to solve this, if it is a problem, as I've just done what they would have done. But they did say Bongo's come in with the fans running quite often after idling outside for just a few minutes sometimes, but that may be down to a less efficient cooling system.

What I find hard to reconcile is that the gauge range should be 75-120 deg. after the mod, so when it's close to H, it must be over the 96 degrees (or is it?) required to switch on the low speed fans. I could take out the sensor and check the resistance again, but it means a re-bleed and I'm running out of ear plugs.

Has anyone wired in a manual switch for the radiator fans? or carried out the temperature gauge mod as I have, if so, do the fans cut in before it feels like it's going to self destruct? I would be more comfortable knowing they do come on before the head gasket lets go and I would prefer not to put the aftermarket sensor back in as fan switch in at 80 deg. is not ideal either as the stat's always closed. Sorry to harp on about it.

[widdowson2008]

Has anyone wired in a manual switch for the radiator fans? or carried out the temperature gauge mod as I have, if so, do the fans cut in before it feels like it's going to self destruct? I would be more comfortable knowing they do come on before the head gasket lets go and I would prefer not to put the aftermarket sensor back in as fan switch in at 80 deg. is not ideal either as the stat's always closed. Sorry to harp on about it.

I seem to remember that mikeonb4c has his fans wired to a switch. Drop him a pm - he'll be glad to help out (if that's what you feel happy with).
Personally, I would suggest that you monitor the actual temperature at the top hose stub. That way you will actually SEE what the temperature is. Fans should come on at 96/97.

[Northern Bongolow]

just thinking,you arnt doing this with the heater fans switched on are you?.

do the front and rear heaters feel ok----hot.

what colour coolant are you using.

what stat have you in it, gen or copy.

mine has the resister mod.

just had another thought . get it as hot as poss then switch it off for 5 mins, all the heat will rise in the head, and no waterpump effect, then switch it back on again, this usually triggers them to come on.

[swampy]

I do put the heater on when bleeding for a couple of minutes to check they work, and both fr/rear blow hot, but they are not on when testing and getting the engine up to temperature.
Genuine stat which is behaving itself, using 5 yr Orange OAT coolant.

Thanks I'll drop mikeonb4c a line to ask how he wired them up, I'll try to obtain a thermometer to measure the temp. at the hose this weekend, you'd have thought just before H on the gauge was over 96 though, has anyone tested this?
Based on your gauge, have you had the fans come on stuck in traffic on a hot day, and if so at what point on the gauge did this happen?
Ta again, Chris

[widdowson2008]

Re-read through and I'm not convinced you have a problem other than the Mazda temperature gauge. However...............

Which of these have you replaced?

This one is located at the front of the head and is the sensor which operates the Mazda temperature gauge.



This one (located on the head - drivers side) is the sensor/switch that controls the fans via the ECU. If this one is faulty or has a bad connection, then the fans will not operated properly.


The way forward is to measure the TRUE coolant temperature as it leaves the head (top hose stub at the head). You may get a very pleasant surprise.


Re your question:
Based on your gauge, have you had the fans come on stuck in traffic on a hot day, and if so at what point on the gauge did this happen?
Dunno because I NEVER EVER look at the Mazda gauge. It's such a liar. Far worse than Tony Blair ever was. I rely totally on my TM-2 to tell me what's happening. (great piece of kit)
Never had the fans switch on in traffic. Temperature on mine normally stays 82/84 during normal running. On hills it may get up to 87. Stopped in traffic, maximum ever seen is around 87.

[rita]

Hi swampy,

You could fit something like this,it will bring on the fans at a preset temperature.


http://www.ebay.co.uk/itm/120897907308? ... 1423.l2649

Cheers.

[Northern Bongolow]

ive never had the fans on on mine in normal use, and i pull a caravan. but i have a manual box so the gearbox oil isnt being cooled in the rad like yours so mine runs really cool.

mine runs at around the mid 70's in normal running and only opens the stat for special occasions.
measured with 2 seperate gauges mounted at different places on the system, one digital with a voltage stabiliser on for accuracy, and one of the old capiliary type,again tested for true throughout its range.
plus the standard gauge modded with the resister mod. oh and the pressure measuring kit ive fitted.

im not paranoid just need to know what/where/how.

[widdowson2008]

Hi swampy,

You could fit something like this,it will bring on the fans at a preset temperature.


http://www.ebay.co.uk/itm/120897907308? ... 1423.l2649

Cheers.

That looks OK . TM-2 but cheaper.
Not too sure about using it to kick fans in though.
Wouldn't it be preferable to find out what's wrong and fix it, rather than sticking a plaster over the wound?

Hi Ady
Wadya mean 'not paranoid'?

[Northern Bongolow]

i think mike hot wired his scavenger fan not his rad fans, to cool his bum in traffic.