And now the Fans

[Grady]

I have a 86 280i with a nose radiator and twin fans. The fans appear to be original. The only change (in 2004) has been to replace the otter with a threaded fitting and this weekend to replace the previous thermostat switch (which worked fine for many years) with a cooler one.

The car has been off the road since 2012 and I've been getting it running again. After I got the engine running, I noticed that the fans were not coming on and determined that the 20 amp fuse was badly blown - almost melted. I replaced the fuse, bypassed the thermostat and the fans ran just fine, off/on several times, no extra noise, wobbling, etc. After I installed the new thermostat (and resolved the coolant issue) the fans came on for a few seconds(I not sure how long but enough to get up to speed)and then shut down. I checked the fuse and it had blown. Being out of 20 amp fuses that's as far as I got.

My thought is to disconnect one fan at a time and see if one is shorting. Otherwise I guess it is some kind of surge/load issue. Any suggestions on trouble shooting? Thanks Grady

Edited by Grady on Wednesday 27th April 16:23

[mrzigazaga]

Hi mate...Im no electrical wizard but a single 20amp fuse running two ...What are they 30w fans?...You might need a switching relay in there if you haven't already?...

Sorry I'm not much help on this one.


Ziga

[Number 7]

Have you tried turning the fans by hand to see if there is any physical resistance which might indicate that the motor is corroded?

[voltage_maxx]

20 amp is unlikely to be sufficient to withstand the initial turn on current.

I have a big pair of fans salvaged off an Audi on my 350i.
Connecting up an analogue AVO meter, I could clearly see the turn on current spiked at well over 30AMPS, even though the continuous current draw was below 30.

I stuck a 40AMP fuse in and forgot about it. Not had any problems since - and on a V8 wedge those fans run every trip out!

[Grady]

I'm away from the car until the weekend, but looking at my handbook I see there are two 20 amp fuses, 1 listed as "Air Condition Pump, Air Condition Cooling Fan, 20 Amp" and the other as "A/C Cooling Fan, 20 Amp". The fuse that blew is the 2nd one which is one above the bottom of the fuse stack. But I didn't check the 2nd one as I thought I found the culprit. I wonder if the 2 fuses split the starting load.

Because of the fans' power draw I figured there was a factory relay. But looking at the relay board, the only thing I see is a relay (or space?) labeled "Cooling for Relay" - What is that?

I think the fans spin OK but I'll check that.

I'll check the amperage draw. A quick check of Amazon shows a couple of 12vt delay modules so I might also stagger the starting sequence so both fan's don't kick in together.

Thanks Grady

Edited by Grady on Tuesday 26th April 21:52

[Wedg1e]

Grady said:

I'm away from the car until the weekend, but looking at my handbook I see there are two 20 amp fuses, 1 listed as "Air Condition Pump, Air Condition Cooling Fan, 20 Amp" and the other as "A/C Cooling Fan, 20 Amp". The fuse that blew is the 2nd one which is one above the bottom of the fuse stack. But I didn't check the 2nd one as I thought I found the culprit. I wonder if the 2 fuses split the starting load.

Because of the fans' power draw I figured there was a factory relay. But looking at the relay board, the only thing I see is a relay (or space?) labeled "Cooling for Relay" - What is that?

I'll check the amperage draw.

Thanks Grady

You sure it didn't say 'Cooling fan relay' but it's rubbed away?

Most fan motors would probably take a good 10A when running and a start-up spike of 20A+, so I'm not surprised the fuse blows if running two fans.

Delayed start-up... a better idea might be staggered switch-on temperatures, so you get one fan at say 80 degrees and both of them at 85-90 or whatever suits your engine.

[RCK974X]

Yeah as above, first check you can easily turn the fan blades with your fingers - this checks they aren't gummed up....

Some of the fans are 10A draw [each] so a 20A fuse is a bit marginal. Make sure all your wiring and fuse connectors are good,
otherwise they will overheat pretty quick.... try a 30A fuse... most 'square' type plugin relays are rated at 30A...

[tofts]

Indeed, most fans will require a minimum of 20 amp, and will probably draw more with start up in-rush current, so 30 amp is selected on the later cars.

voltage_maxx said:

I stuck a 40AMP fuse in and forgot about it. Not had any problems since - and on a V8 wedge those fans run every trip out!

I would NOT recommend fusing higher than original specifications in any case, especially on such a high draw. What people don't seem to realise is the fuse is selected for the appliance connected, then the CABLE is selected to support the fuse. By increasing the fuse, means the capacity of the wire may not be sufficient to withstand overload current in the even of a short circuit. In short, fire.

This is not always the case, but unless you know what wire gauge the fuse is protecting and its Current carrying capacity, I would be wary about putting in a 40a fuse instead of whatever it was before! You must also take in to account external factors, such as heat and de-rate cable accordingly so even if he cable can withstand 40 amps. Can it still withstand 40 amps in a hot engine bay?

TVR wiring is marginal at best, coupled with 30 year old joints and corroded wire, just be careful and make sure its safe, don't want any more dead cars

Jody

Edited by tofts on Wednesday 27th April 00:15

[GBinUSA]

Remove the battery from the car and unplug the fans. Test each fan individually by rigging a 20 amp circuit direct to the battery. Make sure you make the circuit out of the correct gauge wire. If both fans run without blowing the fuse then the problem is obviously elsewhere. It would be relatively simple to remove the fans from the original wiring loom and create a new separate loom with a fused relay for each fan. I did this with my Lotus Esprit S1 and it worked very well. The Esprit had three fans, so I had thee relays and three fuses. What's nice about this, is that if one fan fails the others are protected and still function because they are on a different circuit. I used 50 amp relays triggered by a 10 amp fused wire. You can use the existing otter switch to trigger the relays, or add a trigger probe in the top hose of the radiator. I also added a manual switch on the dash to override the otter switch when desired, sitting at lights / in slow traffic etc....

[mrzigazaga]

Definitely make sure the wire is rated...This is what happened to mine...This was a 30amp fuse to my cooling fan, I think the wire was about 20amp...

I replaced it with some 30amp wire and soldered it together with some heat shrink tubing on....

[Grady]

Wedg1e said:

You sure it didn't say 'Cooling fan relay' but it's rubbed away?

That got me out of my chair but no, it clearly says FOR. However I am now sure it's just a typo in the USA Spec 280i edition of the Owners handbook (page 20). The Service Manual refers to it as FAN.

But wait, there is more...

This lead to some interesting discoveries: My Owners handbook is not model year specific (it is dated as copyright July 1985) and includes fuse/relay diagrams for Series I and II models, sort of an evergreen handbook. And while (I believe) it came with my 1986, it does not picture the fuses and relays for a 1986 models with a G in the VIN. And I am quite sure the diagram on the fuse box is for a late 1985 model with an F VIN (same as the handbook).

FYI - Per the handbook, there was a major VIN change in mid-1985 with the first of the new VINs (with the SA9 prefix) being #19433. For model year 1986, the VIN changed: the F (1985 model) became a G (1986 model) and the VIN count started over at 19001.

However the Service Manual (September 1985) does cover 1986 models. It shows the 2@20 amp fuses noted above have the changed to a 10 Amp for the a/c pump (only) and a 30 amp fuse for the Engine, A/C cooling fan. Further, it shows 2 separate fan relays.

I need to check the car but it looks like I have the wrong fuses information in the handbook and fuse cover and should have 2 fan relays powered off a 30 amp fuse. Which would explain why it was blowing the 20 amp fuse. So this weekends chore (among others) is to add the correct fuse information and see what else may be over/under fused. Grady

Edited by Grady on Wednesday 27th April 16:54

[Grady]

Just to follow up - my 86 USA 280i wiring doesn't match the handbook diagrams but does match the service manual for an 86. The fuses are the same except for the 30 amp fan fuse. The relays are different with 2 fan relays.

I think the fans are now working but I got rained out. I also discovered a small coolant leak at the overflow tank and later a pool under the car that may have been an overflow/burp from over-filling. Grady