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4JB1-T viscous fan not freewheeling

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4JB1-T viscous fan not freewheeling

Postby bedford4x4 » Sun Oct 04, 2009 5:05 pm

G'day folks,

My viscous fan is stuffed - it won't freewheel under any conditions, and I was wondering if anyone noticed an increase in power by going to an electric fan. I know that a plastic fan doesn't have the mass of a steel one, but at highway speeds it won't be doing anything except creating a lot of turbulence or wind resistance under the bonnet. It is supposed to freewheel at high speeds unless the engine temperature goes over normal, but it's not doing that.

Has anyone found that they got a bit more power from changing to an electric one? I know it works well with old Land Rovers - the fan on those things sucks about 7-10hp from the motor.

Thanks everyone.
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Re: 4JB1-T viscous fan not freewheeling

Postby geeves » Sun Oct 04, 2009 6:00 pm

On a dyno you can see some gain but in real onroad situations at over 50kph the fan isnt doing any work or useing very much power.
The isuzu fan is fully interchangeable with a hilux fan. In fact the hilux is better as it sits about 5mm furthur away from the radiator so doesnt eat it as often.
Untill you fix it avoid water as the viscous unit lets the fan stop in water but without the viscous part the fan will get dragged right through the radiator
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: 4JB1-T viscous fan not freewheeling

Postby bedford4x4 » Sun Oct 04, 2009 6:29 pm

geeves wrote:On a dyno you can see some gain but in real onroad situations at over 50kph the fan isnt doing any work or useing very much power.


Sorry, I'm not really following your reasoning here. If the fan isn't doing any work over 50 km/h, then surely vehicle manufacturers wouldn't put them on in the first place, but would stick with the old tried and true fixed mechanical fans, which are a lot cheaper to make.

Unfortunately, the problem with mechanical fans is cavitation as the fan blades are designed to cool the engine adequately at low engine speeds, and are inefficient at high engine speeds.

The whole idea of the viscous fan is to let them freewheel at highway speeds at normal temperatures, so as not to rob power from the motor.

Have you tried going to an electric fan, Geeves? Did you notice any difference?
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Re: 4JB1-T viscous fan not freewheeling

Postby geeves » Sun Oct 04, 2009 7:05 pm

Still useing viscous. I had a cortina a lot of years ago that I took the fan off in the quest of more power. Only time it ever got hot was following a bus up the Rimitukas (similar to your Hunterlies) at 20mph (old cortina) Overtook the bus and temp was normal by the top. Anouther more modern example is the Buggati Veron. This only has electric fans but the whole cooling system at full noise uses 1000hp. Take away the cooling system and it would be a 2000hp car.
A lot of design goes into fans so that even a well made solid fan doesnt have to use much energy at open road situations. Even electric fans use electricity to work and this comes from the alternator which takes it from the engine.
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: 4JB1-T viscous fan not freewheeling

Postby bedford4x4 » Sun Oct 04, 2009 7:34 pm

geeves wrote:Even electric fans use electricity to work and this comes from the alternator which takes it from the engine.


True, but at motorway speeds the fans don't work because airflow through the radiator is more than enough to keep the engine cool, therefore they don't use any power as long as the airflow provides sufficient cooling.

I had an old Cortina too. My one had a viscous fan which would freewheel at high RPMs, regardless of how hot the engine got. Very annoying when trundling about in 1st gear.

Maybe I should take the viscous fan off temporarily and see whether I can notice the difference?
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Re: 4JB1-T viscous fan not freewheeling

Postby wbski007 » Sun Oct 04, 2009 11:01 pm

I replaced my stock fan for an electric and it does a great job,I pull a 15' camper and have had no cooling problems,its done just as good of a job as the stock one without robbing the horsepower.There's less engine noise also, See photo
cheers,Wayne
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Re: 4JB1-T viscous fan not freewheeling

Postby bedford4x4 » Mon Oct 05, 2009 6:29 pm

wbski007 wrote:I replaced my stock fan for an electric and it does a great job,I pull a 15' camper and have had no cooling problems,its done just as good of a job as the stock one without robbing the horsepower.There's less engine noise also, See photo
cheers,Wayne


Did you notice any difference in power when you changed to the electric fan?
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Re: 4JB1-T viscous fan not freewheeling

Postby wbski007 » Mon Oct 05, 2009 10:45 pm

To be honest with you no I didn't but then it would be hard to feel maybe a 3 to 5 HP gain,what I did notice was a quieter engine,my viscous fan seamed to be running all the time and it was very noisy and I'm sure it was robbing some HP,the only time the electric fan comes on is if I idle for awhile or pulling a long hill with my camper other wise it never comes on
cheers, Wayne
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1949 Dodge 2 1/2 ton pumper fire truck, 15,000 original miles, with a 1991 Cummins 5.9 diesel, turned up fuel, 5 speed trans, two speed rear, also added P/S, P/B.

Re: 4JB1-T viscous fan not freewheeling

Postby iananita » Tue Oct 13, 2009 3:12 pm

I've done a retro fit Ford Mondeo twin electric fans on my 2.8 Rodeo.

Made no power difference or temperature difference.

Piece of mind for water crossings only. Radiator already bears scars of deep water plunge from plastic fan.
Interesting comment from Geeves re Hilux fan maybe better option.

Other thing air conditioner works better, my fans cycle with compressor.
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