Radiator Fan - 20 sec on then off

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Radiator Fan - 20 sec on then off

Post by aknapper »

1987 Komet DG High top: So the radiator fan does work. but just not very long - maybe 20-30 sec at a time. Coolant temp has always run a bit hot (between half and 3/5 on the gauge). Fan comes on as gauge nears 2/3 so I've not really worried about it, but always watch it if you know what I mean. It does seem to cycle on - off. Coolant reservoir is full to the brim. Coolant level sensor works. Coolant light flashes a few times when ignition on.
But I suspect that there isn't something quite right and that radiator cooling is done more from driving than the fan coming on. I haven't made the effort to change out sensors, switches, hoses etc as that will be a major effort and I'd have to drop the coolant. I am thinking of 3 replacements: radiator fan switch (3 prong), radiator fan relay (if I can find one in stock), and thermostat. And if I do those, then I guess that'd be the time to renew the engine bay coolant hoses and clips...
So, I thought I'd ask for feedback before I start thinking about tackling the problem. Thanks!
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Re: Radiator Fan - 20 sec on then off

Post by Mocki »

The fan shouldn’t really come on when moving , the airflow should be enough.
Normally on my 2.1petrol the fan only comes on in traffic and only for maybe 30 seconds at a time , maybe a minute if it’s exceptionally hot weather , then cycles on and off as the coolant travels by the sensor on its way from the engine .

The gauge is only telling you a representation of the coolant temperature at the thermostat housing , the fan is totally independent and only triggers when the radiator temperature is high enough , there is no electronic connection between the engine and the rad .

I suggest it’s working as it should , but you would need a accurate temperature reading from a infrared thermometer at the rad to confirm that the temperature is rising , fan switching on and then dropping .

You don’t need to drain th system to change the switch , just a stone cold cooling system and be fast !
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Re: Radiator Fan - 20 sec on then off

Post by aknapper »

thanks Steve - that's sort of what it does - certainly when hot and stationary it cycles on off - I guess I've been used to the later models of VWs Jettas Golfs etc that the fan stays on longer.
How can you tell when the second fan comes on? I have the 3 prong sensor and have tried to test it but that was last year and I've forgotten if the fan actually came on...

I'll do my best to figure out how to do some temperature recording of the rad.

I'd actually thought about doing the cold swap out of temp sensors...

A
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Re: Radiator Fan - 20 sec on then off

Post by Mocki »

You don’t need to change the temp sensors , o ly the temp switch in the radiator.
Easy to read actual temperature of the radiator with a infrared thermometer, point it at the top of the radiator take a reading and then take a reading at the lower half near the switch before or during fan operation and again after to see difference
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Re: Radiator Fan - 20 sec on then off

Post by aknapper »

because I follow Mocki's advice I have bought a temperature gun and will do some self-testing on the van when it arrives in the post.
Steve, the trip up and down to Mull of Kintyre late last week went without a hitch.  Temp gauge was sort of in it's normal 'to the left' of the middle when driving, easing higher in stop and go traffic, and going to just under3/5 when climbing in 4th (!) to Rest and Be Thankful.  Fan kicks in at 3/5 for 20-30 sec.  So, I am now officially considering this to me what it does.
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Re: Radiator Fan - 20 sec on then off

Post by Mark S »

For your model year the fan is probably two-stage: that is to say that it operates at two power levels (and hence airflow volume) depending on engine temperature.  Stage 1 (low-power mode) is designed for sustained cooling and is supplied directly via the coolant sensor in the rad, while Stage 2 (high power/rapid cool) operates via a relay system owing to the higher current involved.  When stage 2 is in you will know about it as it really roars away.

It sounds from your description as though your stage 1 fan is not working, hence why your engine is running hot from time to time.  Then it kicks directly into stage 2 at a higher threshold, which cools the system very effectively in seconds and so then cuts out again.  This is what was happening on my bus.

I recommend pulling the plug off the temp sensor and you should see three contacts.  One should be live all the time (test with bulb).  If no live found then that's your first problem right there.  Then, using a piece of wire, join the live contact to the other two in turn.  If stage 2 works but not stage 1, the problem most likely lies with the fan motor.  If stage 1 works but not stage 2, it could be the motor but also the relay (on main fuseboard under dash).  If both stages work, the sender could be faulty or there might be a problem with your cooling system (airlock etc).  Bear in mind that the sender for your temp gauge is actually in the cylinder block so there is a disconnect between what is happening at the front and back of the bus.  If neither works, it could be the motor again or dodgy earth.

It looks as though you've got a fan so your live and earth are OK.

I found my stage 1 fan motor was shot.  You can buy replacement motors but they are rare for certain models.  Solution I used was to join stage 1 to the stage 2 circuit after the sensor, so I only ever get stage 2 even when stage 1 is called for.  This still only comes in on an occasional basis (steep hills, traffic on hot day etc) and is probably preferable to running hot.
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Re: Radiator Fan - 20 sec on then off

Post by aknapper »

Mark, thanks for the testing advice for the stages.  Stage 2 definitely comes on.  I'll need to have a look at Stage 1 testing.  Did 350 miles this past weekend and for first half of M6 journey south temp gauge was in the sweet 'halfway' spot.  We hit motorway works so crawled for 5 minutes with fan cycling off and on as you'd expect.  Funny thing tho was afterwards the gauge was reading cool - about a third - which I haven't seen really ever.  Outside temp was cooler after the rain which preceded us.  On the run back it ran cool again the whole way, but then waiting for offramp lights to change it went to halfway and fan kicked in.  So, as Steve said above, the main cooling works through the rad.  I did discipline myself to stick to 60 mph which also may account for something.

Did find a slow drip from the rad once we arrived at our destination.  I had forgotten about it but now surmise that's the source of my coolant header needing top-ups and why the top-up tank doesn't seem to get reliably sucked back to the header tank.  The source is unhelpfully on the passenger side bottom run underneath the grommet/bracket.  The rad fins are a brittle as anything so yes it's time to replace.

New radiator and gubbins all ordered today from BW for some August DIY fun.   Still going to take it up north on the SC500 beforehand and take extra coolant since I don't have time to replace beforehand.  I'll test the 1st stage before I rip out the old rad and see what's up.  Best to replace fanny bits if necessary when doing the rad.  At least the rad replacement looks fairly straight forward :lol:
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Re: Radiator Fan - 20 sec on then off

Post by Mark S »

Yes, your fan behaviour seems consistent with Stage 1 being absent (as was the case with mine).  The motor windings seem to be a weak point considering how little work it actually does.  I did buy a new motor from BW but it was the wrong model and had to go back.  The right one seemed as rare as rocking-horse droppings and so I gave up.

Ironically, there can be an inverse relationship between speed and temperature because of airflow.  In my experience the fan tends to come on when the bus finds itself static following a period of high-speed running (coming off the motorway to traffic lights etc), or in stop-start situations.  I cannot remember many cases of the fan coming in on the open road.  I drove over some passes in the Dolomites during summer once, and I recall it kicked in more than usual then - but we're talking about sustained gradients at low speeds in hot conditions.

I fitted a toggle switch under the dash, linked to the relay so I can bring in Stage 2 fan manually if desired.  I rarely use it while driving but it is a useful test tool and I often give it a flick as part of my 'first parade' checks.
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Re: Radiator Fan - 20 sec on then off

Post by aknapper »

Mark that's been consistent with mine - rarely comes on during highway or constant driving - but will come on at lights or motorway works - doesn't typically come on for long.  it works so I am not complaining but will look into what's up with stage 1.  I'm going to pull it out during the rad changeover since I can do some clean up and repaint the fan housing.
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Re: Radiator Fan - 20 sec on then off

Post by silverbullet »

FWIW its not the fan windigs that are the weak point: its the old-fashioned high wattage dropper resistor that is used for the low-speed first stage.
Remove upped grille and look on the far right (as you look at the van) outboard and below the headlamp.
Thats where the resistor lives, wound on a pair if ceramic bobbins.
If it looks all brown and split on one half, that will be the failed winding.
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Re: Radiator Fan - 20 sec on then off

Post by silverbullet »

85 syncro Caravelle twin slider Oettinger T3200E-6
90 SA Microbus supercharged wbx/UN1 project

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Re: Radiator Fan - 20 sec on then off

Post by aknapper »

@silverbullet - thanks for the intel on the resistor!  I'll have a look later today.  And for the BW link!
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Re: Radiator Fan - 20 sec on then off

Post by Mark S »

That's handy to know, thanks.  I'll see if mine's got a resistor in line as that could explain the loss of Stage 1 (it was built an N/A diesel with a two-speed fan, now TD but fan not changed).  IIRC on mine, the red goes straight from the switch to the motor with only a spade-connector block in the interim, but this has motivated me to check again.
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Re: Radiator Fan - 20 sec on then off

Post by aknapper »

took the upper grill off last night to have a look for the resistor.... nary to be found in suggested area.  Prob didn't look hard enough.  I'll have to track and trace from the fan wires once I drop the rad out in August.  at least the part is available...but low stock 
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Re: Radiator Fan - 20 sec on then off

Post by Mocki »

It will be up the ledge on the outer side of the headlight , in the inner wing . 
not to be mistaken for the dim dip resistor for the headlights ( normally has a yellow wire ) on later vans 
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