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MG MGB Technical - Electric Cooling Fan Direction?
|I have just purchased a '78 MGB.|
The electric fan is forwards of the radiator.
When the electric fan runs, it sucks air from the engine and blows it out of the grille- the air is going forwards!
Looking at the blades, this is what is supposed to happen, the round part of the blade section is nearest the radiator, so the motor isn't going backwards.
Is this right?
When sttionary, it won't make a difference, but moving slowly forwards surely the air is going the wrong way?
|Is this an aftermarket replacement fan? All the cars I have worked on have always brought fresh air into the engine compartment, either with a puller fan located between the motor and the radiator, or a pusher fan located between the grille and the radiator.|
If the fan motor is turning the right way, then it sounds like it is mounted on the wrong side of the radiator.
|Are you sure? because that's wrong. Watch closly and see which way the blades turn.|
Some one may have wired it up backwards. Easy to do, and fix.
The fan should rotate in the direction of the most forward part of the blade, so as it turns it is scooping air up and shoving it backwards.
Just swap the wires around so it turns in the correct direction.
You're right, Fans do have an optimum shape for the direction that they are turning in. Some fans are made so you can unclip the blades, turn it around and then reclip.
Even if you can't do this it is obviously still better to get the thing turning in the right direction.
Or, shift the fan to the back of the radiator. It's actually better there as it works slightly more efficiently and the motor is kept warm and dry.
|The fan will always blow in the same direction regardless of which way round the blades are fitted, but if the power connection is reversed the motor will run backwards. For the fan blades the leading edge is rounded and the trailing edge sharp, just like an aircraft wing. If that is what is happening but it is *pulling* air from the radiator instead of pushing air through it, then both the connections and the fan blade need to be reversed. Could be a replacement motor/fan from a scrapper but a puller instead of a pusher, but having said that it should be fitted in pushing mode on an MGB. The connector should be a 2-pin plug and socket meaning you can't get it the wrong way round, but if you get a bit of tubing that just fits over a pins it will depress a tang at the base and allow you to pull the pin out of the back still attached to the wire, thus you can swap the pins over in one (!) connector without having to cut and solder. Metal brake pipe for example, can be swaged down by tapping gently with a hammer while rotating it, to a snug fit over the pin.|
|Paul Hunt 2|
|Thanks everyone. Paul is correct. The fan was a "puller". (There is an arrow on the blades to show which way it has to go, but it confirmed my own idea about the wing shape)|
Working through the grille apperture I was able to remove the blade, (grubscrewed on) and then remove the motor from its bracket and get it out.
I have now reversed the blade, and swapped the pins in the motor plug, and it pushes. Everything is back together, but the feeble amount of air coming through the radiator makes me wonder if it was a deliberate mod to get more airflow when standing. A lot of air spills out sideways though.
I'm aiming to fit a shrouded fan on the engine side when I can get metal to make up some bracketry.
My next job is getting the engine to run right. It is very rich at idle, but it has K&N filters. It doesn't help that it has HIF carbs fitted either. (But that can be another thread )
|It shouldn't really need extra cooling, especially in the UK. Several things can contribute to extra heat production like incorrect timing as well as poor heat loss like clogged up radiator. The biggest improvement I made to the twin cooling fans on my V8 was to provide an additional local ground to each fan where its mounting gracket bolted to the bonnet slam panel, and a direct connection from a spare output spade on the alternator to the relay that powers the fans. That made a difference of 2 or 3 volts on my car, and now it keeps its cool in temps of 40+. Don't forget that the temp gauge is *supposed* to go up as high as mid-way between N and H before the fans cut in, and even if it goes higher it isn't necessarily a problem if it isn't steaming or losing coolant. I've seen my V8 in the red before I fixed the fan electrics, with no actual running problems. All Bs have to push air out of the bottom of the engine compartment as that is the only exit. At a standstill at least 1/3rd of this comes forward and is picked up by the fans and pushed through the rads again! Under way a Sebring valance helps a great deal. The standard valance tends to compress air under the car which as well as causing unwanted lift at speed also prevents air coming down from the engine compartment. The Sebring valance results in negative pressure behind it which as well as sucking the car down at speed also sucks air out of the engine compartment i.e. through the radiator and aids cooling even at slow speeds.|
|Paul Hunt 2|
I"m a bit late coming in on this one but i have come across this many times where the fan blades are on the wrong way round. I believe some fool at the factory was having a laugh. It is perhaps o0ne of the reasons why some owners are having trouble with over heating.
This thread was discussed between 10/08/2006 and 11/08/2006
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