4.8 Viscous fan

[AdrianPowrie]

Morning guys,

Busy prepping the van for a trip too Lesotho to go and hunt some trout when I took a hold of the fan blads and tested for play and there seems to be a wee bit of movement on the fan.
Not much, maybe 3 to 5 mm at most.

Will this be OK to do the lesotho trip? Baring in Mind we will be driving to Semonkong lodge and parking the vehicle to hike down the gorge for a week and then coming back out and driving home. So no more that 1200 kms round trip.

And on a side note, what if any are the benifits of changing to an electronic fan assembly and who/where and how can I/should I do it?

Lekker dag verder manne!

[AndriesS]

I don't think any play is good, but if you grab it can you move it in /out (axial) or up/ down(radial) . Is the play not just flex, can you see the pulley moving etc.

As for electric fans, I've not heard of many successful or reliable conversions.

[Peter Connan]

The blades can flex, but there shouldn't be any play. Are all the bolts tight?

If there is play, is it in the viscous coupling or the water pump? The viscous can temporarily be "gippoed" by firmly fixing the viscous coupling to the shaft. I would be hesitant to drive it like that, as I don't know if there is a possibility that the fan may come off and damage the radiator. If the play is in the water pump, that's a serious problem and needs fixing.

WRT electric fans: while it may well be a good idea to rig an additional electric fan or install wiring, relay and switch allowing you to force the electric fan already installed for the air-con on when the aircon is off, I would not recommend replacing the viscous with an electric setup.

I tried it, and it didn't work for me. I am well aware that electric fans come in various sizes and capacities, and that perhaps the ones I tried did not have the best efficiency around, but I had two fans of the largest size I could fit, and these did not keep the engine cool, and also killed my battery in about three months flat!

[ChristoSlang]

I did an electric fan conversion on my Sani, and it proved to be both successful and reliable!

The biggest hassle was finding a suitable temperature switch - I settled for one that had a very small variance between turning on & off, and that held the temperature tightly in check. The biggest disadvantage IMHO is that a failed electric fan normally stops working, whereas a failed viscous fan normally works all the time.

PS: I did a write-up with one or two photos on the Nissan 4x4 site many years ago...

[Gerrit Loubser]

One thing to remember is that a fan driven off the front of the engine could easily absorb as much as 2kW while doing its thing (i.e. 2kW absorbed in moving air through the cooling pack). If one wants to replace that setup with electrickery, the installation would have to be able to handle massive electrical current, in fact more than the alternator would be able to replenish (the electrical current required is equal to the power required divided by the operating voltage; in this 2000 W / 14 V = 142 A ). There is no way that the electrical fan installations normally fitted to cars are able to deliver that much power.

[ChristoSlang]

Gerrit, I honestly believe that you're over complicating things!

A cooling fan is only needed when you're moving slowly - once you're driving faster you've got sufficient airflow in any case. The electric fans on my Sani moved air at about 50km/h, fast enough to keep things nice and cool. If your vehicle overheats at higher speed you have other issues to deal with.

PS: Two 12" fans consume only as much electricity as a pair of 100w spotlights...

[Gerrit Loubser]

Christo, I am trying not to complicate things, but the simple physics of it is that 2 x 100W fans, while being easy and relatively cheap to install (current drawn by each will only be a little more than 7A, so relatively skinny cables are OK and the alternator will cope easily),are never going to match the ability to move air of a fan that can draw 2000W or more. In applications where the engine load is mostly low at low vehicle speeds (perhaps except for some transients) and the engine load is only high for long stretches at a time when the vehicle speed is high, the electrical fans might prove to be adequate, but if your usage includes something like towing an offroad caravan on long trips through sandy terrain where the engine load is high and the engine speed is relatively high (using, say 3rd gear low range), but the vehicle speed is low, then there is no beating that engine driven fan...

[AndriesS]

As PC said, not all electrical fans are equal- the cheapies just does not move enough air. Hot4Cold in Centurion has some decent one but I could not get the biggest one to cool my old Ford Magnums V6 3.0l enough. It did however work well enough for a sports car. You will either have to settle for 2 small ones or 1 big one and then you have to make a cowling as an electric fan without a cowling is useless. Most people advise to use a puller setup (behind radiator) rather than push set up(in front) . In my experience the number of failed installations is more than successful ones and as with any mod there are always issues at some point.

Christo, I know it's possible but a 4.8l is not the engine I would like to ruin in the process of getting it right.

[Peter Connan]

Christo, most road cars today use only electric fans. So, in theory, it should work.

My experience was that the two electric fans I had, kept the car quite cool under normal conditions.

Where I experienced problems were on one stretch in Botswana, from Xade gate to New Xade. This is a 50km stretch of deep sand, 2nd gear all the way, and in the mountain passes of Lesotho.

However, after I replaced them with a new viscous fan, I discovered something else: In all the time before, on long trips the transmission tunnel had gotten pretty warm, such that it was uncomfortable to rest my leg against it. But with a functioning viscous fan, that problem has been eliminated.

My feeling is that there are a lot of factors at play here that may not be immediately evident. One of them may be the length of the engine, and another may be the aerodynamics of the car and how air flows through the engine bay, but my experience with the Patrol (and I grant you that this might only be true in an older Y60, with an old radiator) is that there is not much safety margin in the cooling system, and that it needs all the help it can get.