Thread: Thermo Fan vs Viscous Fan v6.023.455

I was thinking about it more last night. My thought would be, a V8 Commodore or Falcon will predominantly sit sub 2500rpm under most driving condition, even when being thrashed its not continually being kept at high rpm under the same load. Load seems to be the big cause of heat in the LR, in low range crawling along at 2000rpm and above, and upwards of 110kph on the motorway sees the temps start to rise (aerodynamics of a brick)

I find under normal driving conditions the electric cooling system has been great, both for noise and power and i can happily sit in traffic jams for ever.

The big BUT is when used off road. Over here in NZ if you join a group outing, you will likely have your headlights on under convoy and beach driving requires headlight use too. The alternator will be taking a big draw causing more engine load, leading to excessive heat generation that the fans can struggle to keep up. I have two 1500cfm 12inch fans in a shroud, these are not enough to cover all areas of vehicle use, so keep that in mind. If you go down this path you need to find something in my opinion upwards of 2000cfm, however this will put more load on the motor which will also produce more heat.

In my opinion, if i was living in a country like Australia and plan on going wild on dusty sandy roads, electric fans wont be ideal. The only work around might be big cfm and possibly dual batteries to ease the strain on the alternator.

Originally Posted by Landyv8

.... The only work around might be big cfm and possibly dual batteries to ease the strain on the alternator.

I don't know about strains on alternators, but if an alternator is capable of X Amps, then I'd guess there's no more strain on it at X amps, as there would be at say (X-20) amps.
That is, if your alternator is capable of 100 amps, and your total electrical needs for a situation is 80 amps, there's no issue with any strain on the alternator.
(maybe someone will correct me on that).
Anyhow, I had this issue on my RRC, which I didn't really expect.
Once I was at Ayres Rock, and the RRC just suddenly started heating up too much. Dash gauge on the red line. Of course I panicked .. but I just checked stuff. Even tho it was showing red hot, I could still squeeze all coolant hoses, so no over pressurising.
2700klms from home, I still had a bit of a drive to go.
Fans on 100% of the time, and having lots of night driving to do I still wanted to run the 135w spotties.
I could see the current draw on the ammeter, so I had to manage it. First I didn't use high beams nor spotties. Then had the idea to prop the bonnet open somehow. Found an old box in a wayside bin, wedged under bonnet, wired down bonnet and now the poor old 3.5 running cool, no fans. Spotties back on.
I think the original .. USELESS .. alternator was only 40 amps maybe.
And because they were dependable only in their unreliability(like the VC hubs!), had to fix it. Elec mate found me an 80 amp alternator off a 280Z that fit well, changed my plug for it, all I had to do was find a longer adjustment arm for it(easy).
Then with 80 amps, never had a problem running fans and lights.
Dual batteries didn't help as much as you'd think they would, unless connected 100% .. ie. not with a VSR type relay system.
All they did was give you a little bit longer run time before the battery depleted too much. The upgraded alternator was what's needed(and never failed in the 10 odd years henceforth).

What I learned: air through to the engine!
Drive was about 30 hours, and the overheating being a new issue didn't want to push my luck. So bonnet stayed propped. Can't remember exactly but maybe 2 or 4" .. not open.
Gauge shoewed cool all the way, even tho I had a problem. Issue turned out to be a rotted radiator core, even tho it 'was checked'. New rad solved the problem, but showed that with good venting even with a sub optimal cooling system you can still get it cool.

I had cooling issue with my D1(tdi) recently which I posted about. Normally in any heat, D1 runs fine, so cooling system appears fine and dandy.
But with AC on, not! I'd see far too hot temps than I'd prefer. Tried a few things, then it stuck me that I'd removed a plastic splash air directing cover forward and under the radiator. Removed as the auto trans cooler pipes melted it.
But I thought with this plastic panel gone, the air being forced at highway speeds maybe directing down and under the rad, where the panel should stop that.
Got a metal sheet panel, cut(trimmed) to size and I fitted it now as a scoop under bullbar up to where the plastic panel should be. Now I'm forcing just a small amount of extra air from under the bullbar(20mm gap) AND air through grille not being deflected down and under the rad too.

I saw a small benefit in having the grille off(just a few degrees) .. but not the 20°C or more I'd prefer to deal with. Before home made scoop I used to see 110 and more with AC on, now with the scoop max I've seen in 38° ambient has been 94, hard(ish) up an incline where I could only get 90k/h.
No grille, didn't help that much .. maybe 5 degrees max(but something). Before plastic panel/scoop idea, I found a D1 grille I could hack to pieces and turn into a hacked Saudi type grille. Made no difference at all.
Just too slack to remove it and use original!

One thing tho. no grille did help with EGTs(on a turbo) 50 or more degrees with no grille, can't say I noticed a lot of diff tho with my home made Saudi grille tho.

I'm toying with the idea of trying elec fans myself on the tdi.
Got a new VC a while back now, and about 14 months later it died .. or stopped VCing properly. Found out the hard way climbing up into the high country 3 hrs from home.
IN every day driving/commuting/touring easily .. no problem! In winter I actually remove the fan completely(easy with these spin on fans) .. chuck it in the back. Never seen hot temps in my tdi running like that in colder weather.
But I don't to repeat the drama with the RRC all those years ago, renewing VC hubs every year.

Originally Posted by AK83

I don't know about strains on alternators, but if an alternator is capable of X Amps, then I'd guess there's no more strain on it at X amps, as there would be at say (X-20) amps.
That is, if your alternator is capable of 100 amps, and your total electrical needs for a situation is 80 amps, there's no issue with any strain on the alternator.
(maybe someone will correct me on that).

sorry i wasn't very clear on this, i should have said the extra load required of the engine to drive the load coming on the alternator.

Often when i have been on group runs, i tend to place myself towards the front of the group, it gives me the chance to pop the bonnet whilst waiting for everyone to catch up
It certainly cools rapidly with the bonnet open. I often wonder if this would be such an issue if i didn't have a winch and spotlights taking up half the radiator area in front of the grill.

Originally Posted by Landyv8

sorry i wasn't very clear on this, i should have said the extra load required of the engine to drive the load coming on the alternator.

....

Yes of course.
As most folks will say, and makes sense .. all you're doing is changing where the load on the engine is coming from.
But if the cooling system is in top nic, and the fans set right so that they don't cycle on much on the highway, then load on alt/engine will be lower or whatever.
And again heavy load on engine when say towing, or in heavy going sand/mud/bog or whatever, then of course hotter running and fans come on etc.

I can't ever remember them coming on worryingly so in my '79 in normal high country type off roading, eg. steep climbs or slow tracks like others have said.
But definitely in soft sand they seemed to be on more than not.
Not having accurate way to measure coolant back in the day(90's), I just went off gut feel and temp gauge(which we all know tells you nothing in reality).
Can't recall exactly how many klms I had them in my 79, but the overheating Ayers Rock trip was '92, they were on well before that, maybe 90-ish.
But never seemed to cause the 3.5 any more wear or stress, or blown stuff over the next umpteen years and approx 200-400K klms I ran the RRC.
Motor was pretty worn from the start, about 100 or 150 K klms and I had to stop using it at about 650-ish K klms.
All original motor.

With the overheating issue finally found about a year or more later, turned out to be the rad.
Even mechanic couldn't understand, why gauge says so hot, but no excessive pressure on hoses and whatnot. Never lost/used/ejected coolant or nothing.
Like nothing was wrong, but something was wrong, and fans (were set to enable at about 85) were on all the time and gauge showed hot.
And I still drove it around the country like that thinking ... just a damn gauge issue!

Probably was the gauge The gauge in my 110 starts to climb past midway once it starts heading into the 90's, by 100 its almost at the end of its travel. I guess the fun in these vehicles is playing about and working out what works and doesn't. Its good see see other peoples feed back on the topic.

Originally Posted by Landyv8

Probably was the gauge ....

LOL! yeah, gauge in a Landrover .. works perfectly
But no, it was the rad. Once new rad went in gauge did read normal again.
The old rad was rotted on the front side. Why mechanic didn't notice it, dunno.
But as it was front, and I rarely ever needed to touch anything from the front, couldn't see/feel it. Engine side was fine and solid. Fans were fixed to bracketing I made up, not the hack through the fins hardware most fan come with.
But one day well after the event started I doing stuff up front. Removed grille and had hand hard up against the rad fins, and all I got was copper dust all over my hand!

Ah! .. penny then dropped.

I got the temp guage up over 100degrees with EL falcon fans pulling up that big climb coming back from QLD .... can't remember what the moutain range is called at this particular minute. The radiator has never been checked in my ****box. but this is the only time I've seen it over the low 90's. A solid 10+ minutes of 2nd gear wide open throttle with the ****box pulling its guts out dragging the block of flats up a very steep climb the entire time ( as it hit 105 I found a spot to pull over .... literally 90seconds of waiting and the howling fans dragged the temp back to 85degrees). I pulled back out to find the crest and downhill around the next corner I ran into someone the following day towing with a modern turbo diesel range rover in the local caravan park... He reckoned he went over the climb in top gear at 85km/h (how many way can you not say "You are full of merde" ) ..... Not because the modern v8 turbo diesel probably wouldn't do as he suggests ( what 800Nm @ low revs) ... but the corners would restrict you to less than 40km/h!

seeya,
Shane L.

The important and missing factor in the discussion is what as known as de-rating.

As the temperature in the engine bay climbs, the efficiency of the alternator is reduced.. and it's not a trivial amount either.

Heat-soak, from high ambient air temps and airflow provided to the unit (the alternators cooling fan), will bring the unit to above engine bay ambient temps in most cases.

The harder you run, the hotter the engine, the harder the cooling system works the more the alternator de-rates. It's a decreasing spiral effect.

It's quite possible for an alternator to de-rate to as little as 60% of rated output when the temps approach 90-95ºC ambient. Remember, heat soak is an issue.

The alternator is generating heat through operation as well as having it's cooling efficiency compromised with higher ambient engine bay temps.

The optimum solution is a ducted cool air source to the back of the alternator, but in 4x4 applications there are so many possibilities where that could actually contribute to failure through water or dust or mud ingestion, that it's best to simly shield the alternator from any heat sources in close proximity. On a v-belt motor, the pathetic little sheetmetal shield does nothing to isolate the exhaust headers from the rear of the alternator, so that's one obvious source right next to the alternator. Then the radiator itself, which is in close proximity, and the top hose.

Obviously the alternator is not in the best spot.... but it is up high and that's a good thing... most of the time.

Still, if you have one of those open cage internal fan type alternators, do not be surprised to have it fail on you if you go splashing through puddles.
I lost a brand new one driving on bitumen roads through a tiny wash that barely covered a tyre sidewall.
The external fan variety - aka denso / bosch / leece-neville etc are far superior in general protection of the stator and brushes in this type of scenario.

If you look for a replacement alternator, these days it is hard to find a correct rated off-the-shelf unit which is brand new (not reconditioned) and of high quality.

Also, the 100A rating is barely enough to keep a Range rover going on a 'trip' offroad, where you have a second battery, isolator / bcdc etc and say a fridge and some LED spotties / camping lights etc.

If you then decide to "upgrade" your cooling system with twin electric thermofans, be aware that the current draw at full load on the fans alone, can be as much as 60A. If you're doing lots of hard low-range crawling or mud-plugging, you might wish to think about whether or not the cooling system actually IS of sound serviceability.

Now let's say you have really efficient LED headlights, a pair of driving lights and a light bar - all LED>. that's enough to consume anywhere from 7-25A depending.... and we haven't even considered the power requirements for the ECU, the Ignition, Interior electrics etc....
Let's say that's about 15-40A depending.

with everything going flat biccies on current draw, you have a 120A current draw requirement, and an alternator only capable of 100A - at it's OPTIMUM rated temperature and engine RPM.

So it's not hard to see how the alternator gets hot so quickly and de-rates, due to the heavy load.

There are a couple of ways to "ease" the problem, but simply put, they are not solutions.

1. Upgrade the battery to a much higher capacity, or if possible install two higher capacity batteries in the engine bay, AND an auxillary battery managed with a smart isolator. That's the cheapest way out. More battery capacity reduces the extreme demand on the alternator, but does not mean you have solved the issue of consumption versus replenishment.

2. Use a battery management system.
These buck/boost type chargers have the ability to take alternator output and boost the voltage, so that the batteries are seeing a higher voltage, which assists in mantaining a more optimal charge state for the batteries, despite the electrical system load being a little heavy. Again, not a 'solution' per se, but a great way to minimize the SOC problems when you need to use heavy current consumption devices for short periods and frequently (e.g. a winch) the BCDC/manager type charge controllers also help you manage solar inputs etc and manage disconnection etc etc. to ensure your starting batteries are not flattened by excessive draw on the auxillary battery (fridge, lights etc)

3. Bigger alternator.
Sounds simple, but it's not. To effectively upgrade to a decent high output alternator, a few things need to be understood.

a) output at idle
b) output at cruising rpm
c) output at max rpm/heavy load/high temps.

Aftermarket 'upgrade' alternators usually ship with a power rating curve, which comes from the test of the alternator you purchased.
All manufacturers supply the de-rating curve as part of their literature, but you may have to crawl a website to find it.
These are important factors in choosing the correct pulley diamater, and matching the alternators useable RPM to the engines operating RPM range. Failure to correctly match will result in not only poor performance, but possible premature wear or damage as a result of over-rpm or excessive load form the electrical system which cannot be matched due to inadequate alternator rpm.
Bearings brushes and rectifier diodes are all under stress when the alternator is not correctly matched.
Also bear in mind, the existing pulley size from the 'old' alternator may not be the correct size for the new one.

Wiring upgrades are important. Especially with regards to reducing bottlenecks.
fit the biggest cross-sectional cable you can between your alternator and your start battery / main distribution post. This gives you the best possible efficiency for charging the battery and delivering the required energy to the electrical system with the minimum losses.

It's simply not enough to upgrade the alternator to battery wiring.
The main earth(s) should be upgraded to the heaviest possible cable within reason - 00 B&S is a bit of an 'overkill' standard, but the rules on cable sizing are widely available and should be considered with an overhead for any future modifications.... e.g. winch, camping requirements, additional lights etc. always go one size up if you can, especially if you are planning modifications.
Fuses should be waterproof, and of good quality and correct rating for each circuit and not overloaded.

So why are we talking about all of this electrical stuff, if all we want to do is chuck in a couple of electric fans???

It's simple.

Electric fans are a heavy and semi-constant load on the electrical system, a system which operates from the engine, which generates heat through manner of operation, which the fans reduce...

So, if you have a robust electrical system, and your loads are not exceeding the rated output of your alternator, then you should be fine installing thermatic fans.

But there is no point in doing so, if your cooling system is not fully cleaned and serviceable. If your water pump and radiator aren't at their maximum efficiency, no amount of thermatic fan will improve the cooling situation. They may be (are) more efficient at mantaining optimum stable engine operating temperatures when the cooling system is serviceable, and certainly moreso than a clutch fan, but they are a parasitic loss, just like the clutch fan, and while the loss is not direct mechanical frictional loss, it is an indirect frictional loss, because the alternator has to supply the power to keep the batteries charged, The batteries that supply the power to the fans which makes the system work.

electric direct driven clutch fans are the most efficient and draw the least amount of current, but they are difficult to implement as an aftermarket solution and expensive. They do have the least number of moving parts (and electromagnet and a spring friction disc) and the lowest parasitic losses, but retrofitting one to a vehicle which was not designed with one as an option or original equipment, is a waste of money.

If you are going for thermatic fans, the most efficient are brushless sealed motor types (and for a 4x4 this is what you want). You also need them to be PWM controllable, rather than a relay/ two step sensor drive.

If you can find a solution which has the controller, sensor and fans in a shroud which matches the radiator, you are MILES in front. It may not be the ideal solution, it also may not deliver the required airflow, or it may have it's own inherent issues due to it being a used part from a wrecker etc, but even with that said, retrofitting better quality fans to a shroud that fits and has the controller and temp sensor, is cheaper than doing from scratch.

Again, it depends on how much effort you want to go to, and if the fans are part of a 'bigger picture' project build, or if you are simply facing a scenario where you have catastrophic damage due to failed cooling system components..

My fan failed, catastrophically, and it took out the shroud, the clutch, the radiator cores and sliced through the top hose, as well as launching at terminal velocity through the bonnet.
All because of an invisible stress crack in the little alloy ring that the plastic fan uses to mate to the clutch.

So my example is the 'extreme failure' scenario.

it cost me a new radiator, hoses, waterpump, fanbelts and a sheet of epoxyglass ($$$) from which I fabricated a shroud for the two 16" spal 3000cfm fans, and the pwm controller with sensor.

So over 3K to overhaul it all, with the upgraded 4 core heavy duty all-brass core radiator being more than 50% of total costs.
Zero labour costs since all DIY, but it's easy to see how you could drop $5K on a 'thorough' and complete cooling system overhaul.

Now the funniest thing about all of this, is that I've had to adjust the hysteresis loop on the PWM controller to actually increase the base temp at which the fans commence. Currently that is around 95ºC.
I have a redarc sensor in the inlet manifold right before the thermostat, so I have an accurate temp for engine, and the derale sensor is placed at the radiator outlet on the side tank exactly as prescribed.

At full RPM, both fans draw about 50A, and although I have never encountered this during normal vehicle operation, the manual override switch (ON) which is like an 'emergency' on will deliver the full 50A to the fans. (each fan rates 25A max load)

50A is a lot of current to pull fom a battery, which is why correct cable sizing is so important. Furthermore, if the sensor and controller are not optimally set, then the fans can actually be 'on' longer than they need to be or for longer duration.

It is very hard for me to get the operating temp of the RRC to anything above 95ºC in normal operation (including heavy traffic / low range crawling) but the controller is precise, and efficient.
Oversizing the fans and ensuring the shroud was not posing an airflow restriction were the key critical elements to ensuring rapid efficient cooling.
I have approximately 95% free flow through the shroud and fans, by design - first and foremost removing any flow restriction to the radiator core should be the primary goal.

I'll go down and get some pics to give you an idea of my solution. It seems I never took any, which is unusual for me.
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Edit: added pics (large, click on thumbnails)