Thread: Thermofan over Viscous?

Good Morning guys and gals,

Before anyone suggests the search function – I’ve already had a look. I’ve done this test purely out of curiosity. I had the BF/FG Falcon thermofan at home doing nothing, and my cooling system (which had no issues and is unmodified) is in perfect working order. I have the same BF/FG thermofan on my 5 litre VS III Commodore Ute and it works the charm. I’m simply chasing opinions and thoughts from you. The fan is a 16” shrouded fan with curved blades. It operates at 1400rpm in low speed and 2800rpm in high speed. It draws about 18 amps in high speed (and much more on startup). I don’t know how much air it flows, but I have read somewhere that it’s around 2300cfm, I’m unsure what kind of flow the standard P38 Viscous Fan offers (but I would assume it to be much more being a 17” fan operated off the engine).

So what I’ve done is install a thermofan controller and temp gauge to the cooling system on my P38 Range Rover. I have established that the temp reading for the controller reads 7 degrees lower than actual engine temps. It’s simple, but complex – I can override the fan, either switching it off altogether or running manually at high speed if not using the temp controller to automatically control the fan speed. This is done with relay trickery, which I’ll show in detail once I’ve finished gathering the necessary photos and videos to back it up. The thermofan controller is designed to operate in a 7 degree band, so for example if I set the temp to 90deg for the fan to switch to high speed, the fan will drop back to low speed at 83deg. The thermofan (once installed) runs continuously at low speed when the controller is set to auto. This aids low-demand cooling, maintains airflow through the engine bay, and also reduces the initial current draw from the fan when starting or kicking into high speed, but can also be switched off manually – quite clever really. For an average joe, I’m impressed with how much I’ve been able to optimize this setup and how neat the install is. One switch controls the lot, with multiple relays covering the loads.

Establishing the baselines is very important, so here’s the vehicle info. The P38 is the last of the last, using the high compression 4.6 V8. It’s far from standard – 33” tyres, 2” lift, and at “everyday weight” it tips the scales at 2.7t with all the other junk that lives in the drawers and what not every day. It also has LPG, which for the purpose of testing, I did not use. I didn’t exactly offer this thermofan an easy introduction to rover life! The fuel consumption data is also very impressive, but I’m not here to discuss that today.

Before doing this series of tests, I cleaned the radiator and removed all debris from in front of the other radiators (condenser, trans cooler, oil cooler, power steering cooler, etc), had the radiator checked over professionally and reinstalled it, and I have a small set of Narva spotlights on the bulbar that may or may not be worth mentioning. I purposely did this testing at the height of the North Queensland summer, so the ambient temps were around 35 – 37deg, and humidity was through the roof. For the purpose of gathering temp data, I drove the car like Peter Brock setting a lap record at Bathurst aiming to get things as hot as I possibly could – I wanted to torture test the thing. I ran the air conditioning as cold as I could and had the electrical system working hard too. With this in mind, I grabbed bucket loads of temp data with the Viscous Fan still attached before putting the thermofan in so that I had data to compare to once the thermofan was installed. Once installed, I had the thermofan controller set to run the fan at high speed once the engine temperature reached 98deg. While noting the vehicle weight of 2.7t and the extremely hot ambient temps, etc., these are my findings:

Viscous Fan attached

• Urban Driving – Engine temp sits between 88 – 98deg, varying based on road speed.
• Idling – Engine temp continues to rise up to a highest of 110deg.
• Highway Driving – Engine temp sits steady at about 92deg, dropping to 82deg on a downhill, zero-throttle condition.
• Mountain Climb 1 – “Everyday weight”, 40km/h and very steep bitumen road. Engine temp rises to a maximum of 102deg while driven with much spirit.
• Mountain Climb 2 – “Everyday weight plus 1.7t trailer”, 40km/h and very steep bitumen road. Engine temp rises to a maximum of 104deg while driven with much spirit.

BF/FG Thermofan attached

• Urban Driving – Engine temp sits between 91 – 98deg, the thermofan bounces between low and high speed as necessary, without drama.
• Idling – Engine temp is stable at 93deg with the fan in low speed being sufficient to cool the engine.
• Highway Driving – Engine temp rises slowly with the fan in low speed, drops slowly with the fan in high speed, sitting between 91 – 98deg.
• Hill Climb 1 – “Everyday weight”, 40km/h and very steep bitumen road. Engine temp continued to rise to 110deg after a few km while driven with much spirit. Pulled over and allowed to cool to 91deg before proceeding again and pulling over again as necessary to cool the engine.
• Hill Climb 2 – “Everyday weight plus 1.7t trailer”, 40km/h and very steep bitumen road. Engine temp very quickly rose to 110deg while driven gently. Pulled over and allowed to cool to 91deg before proceeding again and pulling over again as necessary to cool the engine.

From the above data, it’s easy to surmise that the thermofan is not capable of cooling the engine when under extreme load, where the Viscous Fan was ‘adequate’ in all but idling conditions.

What I’m wondering (and this is where you guys really get to shine) is if I’ve overlooked something that might allow the thermofan option to offer the solution to all conditions. Do you think I could do something (such as include the two air conditioning thermofans into the “high speed” mix) to improve cooling under big demand situations? Do you think that I’ve set it up wrong (perhaps I have the kick-in temperature too high)? Do you think there’s a better thermofan that will do the job? Does the water flow at higher revs effect cooling ability (maybe I could do the hill climb in a taller gear and allow the coolant more time to get the chills)? Give me your thoughts!

I’m determined that there is something I can do to improve cooling at high-demand, without having to go to the bank or modify the cooling system to find it. The aim of this project was to keep the already-fine cooling system standard and achieve the results. I know that I can tow all day with the thermofan in, with the only limitation being low speed/high demand situations. I don’t plan to put a larger radiator in – this defeats the purpose of the test, I’ll put the Viscous Fan back in before I think of modifying other things. The fuel consumption benefits (especially when 4wding and around town) make this very viable, however, it was not the sole reason for the test.

I’d imagine if the P38 was completely standard and weighed its standard weight of 2,250kg, I probably wouldn’t have as much of an issue under load, if at all (and the around-town fuel consumption would be better than the highway consumption).

Cheers
Keithy

Just talking about fan draw on the engine, when you are driving at say 80 kms the wind through the grill is driving the fans and the viscous fan.
This came to me when I was driving in Saudi and there was this squeak that was driving me mad which turned out to be one of the aircon fans turning in the wind.

Jaguars have a system of flaps in the shroud which lets high pressure air out when travelling at speed.
regards PhilipA