Thread: Thermofan over Viscous?

On D1 V8s the A/C fans kick in around 104 deg. And the factory temp “gauge” might as well be an idiot light. Stupid thing.

Originally Posted by DiscoClax

On D1 V8s the A/C fans kick in around 104 deg. And the factory temp “gauge” might as well be an idiot light. Stupid thing.

Yeah, I think on my tdi D1, I notice they come on at 103 on my aftermarket temp gauge.

I thought that as revs rise, the VC hub begins to decouple the fan so to not allow the fan blades to spin too fast too.

Originally Posted by PhilipA

It was posted somewhere long long a go in a faraway galaxy, that the VC took 11BHP to run when fully engaged.

My calculations then were that it was the equivalent of 200amps or 2400Watts.

Someone may correct me as it was along time ago.

So you can see that 18 amps doesn't go very far even if the two fans are more efficient..
Regards PhilipA

As gentle a correction as I can!! ...11BHP is equivalent to 8.25Kw, which at 12V would require 688 Amps...
So it's no surprise that the thermo fan, by itself, is inadequate for the task...

I'd argue that the 11hp figure quoted by Philip will be variable depending on the fan itself.
Judging by sound alone, 11hp probably sounds about right on a V8 landrover!

Does the P38 use the same fan as the D2 v8?

I'm fairly confident that a fan for a tdi .. much much smaller and almost inaudible(ie. much less air movement), probably won't draw that much power itself.
Damn I think 300 tdi only has 11hp in totality! ... damn feels like it sometimes.

IMO when it comes to a fan what ever type it is the CFM is relevant and that's based on it's constructional efficiency, other values can be considered just for very rough comparisons

I'm fairly confident that a fan for a tdi .. much much smaller and almost inaudible(ie. much less air movement), probably won't draw that much power itself.
Damn I think 300 tdi only has 11hp in totality! ... damn feels like it sometimes.

I can tell you that a tdi fan moves more air than a 3.9RRC one. And a good VC certainly moves tonnes of air and is noisy.

Graeme Cooper gave me one once for my 91 , saying it wouldn't cool a Tdi but was fine on a V8.

I fitted it and it was great and I eventually replaced the VC, except I broke a blade off on the OTT. The Tdi ones are fibre filled so you dont lose blades like a white plastic one. They have to be trimmed about 5MmM to fit a v8 shroud. So the blade stayed in place and just grazed the radiator.
Regards PhilipA

Originally Posted by PhilipA

....

Graeme Cooper gave me one once for my 91 , saying it wouldn't cool a Tdi but was fine on a V8.

....

Interesting to know.
Tdi fan has something like 11 blades .. maybe this is why .. no experience with 3.9 RRCs.

I did find an article done for the SAE, where the study found that on a 180hp commercial vehicle the average power draw was between 7-9%
Didn't say what vehicle/motor, and it was dated 2019. It was only the summary, and not the full article.
So your comment about 11hp sounds about right.

Dad used to have a '73 Cadillac. Had a enormous radiator, etc. The fan wasn't viscous coupled tho just hard bolted, but the fan blades themselves were flexible, so as revs rose the fan went from a fan to a less aggressive fan pitch and finally to a basically flat surface.
So CFM would have got lower as revs rose, as the pitch of the fan blades decreased. You could easily feel it with bonnet open, that it sucked tons of air, but then slowly less as revs rose.
Interesting idea.

Originally Posted by AK83

I would have thought that by 110°C, the ac condenser fans would have well and truly kicked in automatically, no matter if the ac is used or not.
I think they auto kick in once coolant temps hit the low 100's, so I don't think the AC fans question you raised will be of any benefit.

Also on the topic of fuel consumption:
Many many moons ago I converted my 79 RRC to twin 10 or 11"(can't remember exactly) thermos. I just go sick of replacing the useless viscous every 6 months or so.
Came as a kit(Davies Craig) and a variable controller. I set it up the way I thought best, never had any cooling issues, much of the RRC life spent in Lake Eyre country sandy conditions, in close to 40°C temps.
Never over heated(that I knew of).
But fuel consumption saving alone made it worth the effort. On a regular trip easily 0.5 - 1klm /lt saving, that gave close to 50-100km additional range on the highway.
Around town I don't recall it being so dramatic tho.

I can’t see how a viscous fan fitted vehicle would consume more fuel on a trip. If that trip had any part at highway speeds the viscous would not be coupled to the engine therefore not consuming additional fuel. The airflow through the radiator at highway speeds is more than enough to cool the engine. Viscous fan only couples when it has air that is hot enough, when cooler than the trigger temperature the air is not hot enough to couple the fan via silicone oil.

If there was a lot of slow speed driving where the natural airflow through the radiator was too slow to provide sufficient cooling then perhaps you would get a fuel saving with electric fans.

The energy consumed by an electric fan does not come for free, the alternator will be pulling power out of the engine.

It might be that electric fan blade are so much more efficient that you do get a saving but I doubt it. Electric fans are quieter because they move less air. The sound levels are one reason they are used on modern cars. You don’t get anything for nothing when it come to power and the conversion of energy.