why? plse explain. some cars are designed with push fans, are they not?
surely its air volume thru radiator that matters?
so why do some manufacturers put the fans at the front?
I cant see that one at the back will be any better, or worse than at the front. I still maintain it is airflow thru the rad that matters and the thermal efficiency of the radiator, not just fan positioning. Where are the facts, rather than postulation.
bennybenny
Active Member
i agree with you it would seem that it wouldnt matter where the fan was aslong as it gave the correct amount of air .....but i work for vauxhall and they dropped the front fan in favoure of the rear fan they said it was to remove the houseing and fan kit on the front allowing the rads (weather they be a intercooler or aircon) to have more ambiant air from the air flow from the front end ......weather it is right i have no idea maybe they were just saveing a few pennys on each car sold ......
bennybenny
Active Member
true but most fan houseings act like a funnel ........so the air flow maybe greater
blue beasty
Leaks an prone to bits dropping off
You will also be restricting air flow by putting a cowl over one side of the radiator. Air conditioning fan(s) will also restrict the air flow. I can only assume that a fan that is fitted must be designed to ensure enough air flow to counteract these restrictions. If this is the case then a fan would be capable of pushing or pulling air, providing it is capable of moving the requisite volume of air through the radiator, to ensure the correct temperature difference across the radiator.
I concede that if, what you say is true, then a smaller fan (and therefore cheaper to a manufacturer) would be an advantage, but that doesn't mean that radiators are "designed" to have air pulled through them and that it is a "no-no" to front mount a fan, a several people have done, without any problems.
V8jon
Well-Known Member
My fan is in front of the rad on the series and it works fine, simply because there is no room to fit it behind
Oldseadog
Well-Known Member
OK folks, a quick experiment. Take a piece of ordinary tissue paper and try blowing through it. You will find that it will try to move away from your mouth.
Now put the piece of paper up to your mouth and suck through. The shape of your mouth becomes the fan cowl and will allow more air to pass easly through.
Technically, it is all due to simple fluid dynamics and the resistance to the flow in a given direction. Why do you think that air is sucked through the air filter rather than trying to blow it through?
You need x% of pressure to deliver an air flow through the rad, and you need only a very small vacuum to deliver a similar amount of through flow.
OSD
Now put the piece of paper up to your mouth and suck through. The shape of your mouth becomes the fan cowl and will allow more air to pass easly through.
Technically, it is all due to simple fluid dynamics and the resistance to the flow in a given direction. Why do you think that air is sucked through the air filter rather than trying to blow it through?
You need x% of pressure to deliver an air flow through the rad, and you need only a very small vacuum to deliver a similar amount of through flow.
OSD
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Still not convinced by your argument. The reason air is sucked thru an air filter is because the engine sucks the air through. It would be difficult to blow air through, but then again, your proposition fails down immediately you consider a turbo or supercharger, which both "blow" air into the engine. You are suggesting that it would be more efficient to suck the air flow into the exhaust. Not something many manufacturers do, I think you will find.
jamesmartin
Well-Known Member
behind the rad is better in that the whole area of rad is cooled evenly as near as can with air from forward motion on the road .and a fan with a reasonable tunnel length would be better front or back with back been preferable ,but for offroading with lower speeds and the nature of close fitting electric fans i wouldnt think there was much difference and fit both .both have worked equally well
Blimey, talk about a heated debate...
A ducted fan in front of the radiator will impede flow when the fans not running, and you are moving along at a reasonable speed, as you are blocking certain areas of the rad with the mechanism. However, the ducting will create a funnel effect, meaning that a high pressure area will be created in front of the rad in the duct, which will escape through the radiator to the low pressure area in the engine compartment.
An unducted fan will do the same, but to a lesser extent as there is no cowl to block the rad so much, and air will try and escape around the sides of the rad, down underneath the chassis rail etc
The same would apply if the fan was behind the rad in both cases, but to a lesser extent, as the airflow from the motion of the vehicle would push the air through the rad, but the exit of the air from the back of the rad will be impeded.
When the fan is running, a ducted fan is way more efficient as you create a high pressure area between the fan and the radiator, which forces the air to go through it.
For low speeds, either in front or behind should be fine, as long as the fan can shift enough air through the radiator. At higher speed, where the fan is in relation to the rad is irrelevant, as the speed of air from vehicle speed is way in excess of what the fan could shift, as long as your fan and cowling don't block off so much of the rad that would mean the air couldn't get to it..
A ducted fan in front of the radiator will impede flow when the fans not running, and you are moving along at a reasonable speed, as you are blocking certain areas of the rad with the mechanism. However, the ducting will create a funnel effect, meaning that a high pressure area will be created in front of the rad in the duct, which will escape through the radiator to the low pressure area in the engine compartment.
An unducted fan will do the same, but to a lesser extent as there is no cowl to block the rad so much, and air will try and escape around the sides of the rad, down underneath the chassis rail etc
The same would apply if the fan was behind the rad in both cases, but to a lesser extent, as the airflow from the motion of the vehicle would push the air through the rad, but the exit of the air from the back of the rad will be impeded.
When the fan is running, a ducted fan is way more efficient as you create a high pressure area between the fan and the radiator, which forces the air to go through it.
For low speeds, either in front or behind should be fine, as long as the fan can shift enough air through the radiator. At higher speed, where the fan is in relation to the rad is irrelevant, as the speed of air from vehicle speed is way in excess of what the fan could shift, as long as your fan and cowling don't block off so much of the rad that would mean the air couldn't get to it..
