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MG MGB GT V8 Factory Originals Technical - fan question
| I just wanted to check that my fan set-up is correct as it has not been as effective since coming back from the garage where it was replaced as a result of a new V8 shelf being fitted. I have a single 14" fan sitting in front of the rad (ie between rad and grill). The fan blades sit at an angle from southwest to northeast. The fan rotates clockwise (when looking at the car). The air flow when I put my hand between grill and fan feels as though its acting as a puller rather than a pusher. Chris. |
| Chris Holmes |
| Chris What is a V8 shelf?? Unless I have misunderstood your description the fan is rotating in the wrong direction or the blades have been installed the wrong way around. cheers |
| Ian G Buckley |
| From my understanding reversing the fitment of a fan or propeller blade only changes the section or presentation of the blade or aerofoil, the angle of attack and direction of airflow remain unchanged |
| N Griffiths |
| by shelf I mean in front of the rad where the oil cooler sits. I have a 65 roadster that had a poor conversion at the front end - hence the reason for the body work. I'm convinced that my fan should be running anticlockwise given the blade angles. Is changing the rotation direction of the motor easy to achieve? |
| Chris Holmes |
| Chris, maybe they reversed the wiring or something. The way you've described it sounds backwards. I'd just reverse the wires and see if life doesn't immediately get better. |
| Ted |
| Chris, try gently blowing smoke into the fan, if it blows it back its round the wrong way..... Frank |
| frank swinton |
| Chris Just put a wet finger between the rad and engine - you will certainly know if the fan is not blowing. The setup is different to the GTV8 which has two smaller fans (for redundancy) with the blades mounted very close to the rad block - the grub screw fixing for each faces the rad. |
| Roger |
| From your description it sounds like the wiring is reversed and causing the fan to blow forward. The way I confirm the airflow is with a strip of tissue paper. |
| George Champion |
| When you *do* get it pushing instead of pulling examine the blade edges, for best effectiveness the rounded edge should lead and the sharp edge trail, just like a wing profile, and this *is* changed by reversing the blades on the motor spindle. |
| Paul Hunt |
| Just changed the wires round so that it rotates anticlockwise. Air is now definitely being pushed into the rad. Did some stationary tests with the bonnet down and getting the water temp halfway between N and the white. With the fan on, the temp stopped rising but did not fall. When turned off, the temp continued to rise slowly. Should I expect the water temp to fall with the fan on? |
| Chris Holmes |
| Chris, Your thermostat will stop your engine cooling excessivly. When the water/engine gets warm enough the mechanical thermostat (on the front of the inlet manifold)will open and let the water into the radiator, after that its up to the fan and radiator to cool the water. If the fan were to run non stop ( if you had a good radiator) then eventualy it would cool the water to the point where the "manifold thermostat" would start to close off the water flow again in order to maintain a constant operating temperature. How-ever most people prefer to run an addittional electrical thermostat/relay to switch the fan off before that point. Every one, on this subject I'm getting to the "instal giant aluminium radiator and fan" part of my conversion. I would like to put a fan behind the radiator as per RV8 as I figure a puller (with ducting) is going to suck air through the entire radiator, where-as a blower will only blow on the part of the radiator directly in front of it. I've got more space than usual as I've pushed the motor about 2 inches futher back that std., does anyone know of a suitiable big flat fan?, I've read somewhere that a volvo one is suitiable. |
| Peter |
| Chris, As Paul says, check blade shape, I ran mine for a couple of years rotating in the right direction, but with the blades wrong way round, switching the fan in the spindle made a lot of difference. Mike |
| Michael barnfather |
| If the temp is maintained close to the N when under way, then if the fan is left running long enough it should reduce the temperature to, and maintain it at, much the same. If you have the fan stat on the engine and it is set too low than it can keep the fans running even after the stat has closed and hence is just wasting fuel and wearing the fans out. With the stat or sensor in the rad the fans should always switch off, even if the 'off' temp is set below that of the stat. |
| Paul Hunt |
| Peter..I'm in process of fitting a TR7 fan modified to fit over my Rover water pump on my V8 engine...I'll use it in conjunction with the 2 original electric fans in front of the radiator....photos can be found at http://www.theautoist.com ....just click on the latest changes to 'garage' section & wander around the build plan or go directly to some photos at: http://www.theautoist.com/poorb.htm#5 September 2002 http://www.theautoist.com/poorb.htm#17 September 2002 http://www.theautoist.com/poorb.htm#14 October 2002 |
| anthony barnhill |
| FWIW: I now have basically the same setup as Tony and I can confirm that even with the motor in the standard V8 conversion position, there's simply all kinds of room. It's not at all a tight fit. Having tried all sorts of combinations, I now think that the most bulletproof setup is to have at least the one fan that's pretty much guaranteed to turn so long as the motor is ... those electric fans, while admittedly moving huge CFMs under no load, only have about 1/10 of a horsepower or even less. |
| David |
| Fan performance is a small part of the equation. Utilising all the work done by the fan to move air is usually overlooked. The big problem is that are will not easily pass through the rad core as the very function of heat exchange requires contact between the air and rad core, and thus this generates a resistance. If there is another easier course for the air to travel then it will and this will not be through the fan. For this reason this is why fans are usually mounted as close to the rad core as possible so that the air has less option to find another path. In cases where the fan is further away thebn there is comprehensive cowling to ensure the air passes the intended course. In the case of the standard MGBV8 set ups the common problem is that the fans have not cowling, not even a built in rim that helps in this job. They also can easily be mounted too far away from the rad core so whilst they can actually move more then enough air to cool the V8 comfortably they often don't as the air path control is damn awful. Even the finger guard over the top of the fan blades is wrong as this should be solid, not a grille, and then adding a crude cowling down either side to force more air through the rad core adds to the benefits. Rog |
| Roger Parker |
| If of any moment: I swapped out my two yellow factory pushers -- which were totally and unequivocally useless items -- for a pair of 8" Perma-Cool pushers I got from JEGS' mounted hard up to the core (so their cowls touch the face) and life has been a lot better. Sorry about the originality, but I've seldom run into anything more ridiculous than those OE fans! |
| Ted |
| I had been pondering the cowling Roger mentions for some time, for a factory V8, a hand anywhere near to the spinning blades showing just how bad the losses are. Cooling was OK except when stuck in traffic in high ambients when having the heater on full blast became a normal event to stop the temp gauge going more than half-way to the red, and this was with the fans mounted as far forward as I could. But after helping out a friend with his fan electrics I decided to go through mine. I took a series of voltage measurements through the circuit and found I was losing about 3v at each fan motor. Some of this was down to iffy PO spade connectors on the supply side, but a major part was the factory grounding which uses a long run of thin black which gives significant volt-drop. Adding a heavy gauge wire from the fan connector to a lug secured between the fan bracket and the bonnet slam panel gave a noticeable increase in fan speed. But the biggest gain was adding a thick brown between the spare output spade on the alternator and the fan relay, a distance of a few inches rather than the several feet of wiring and many connections current normally has to travel through, again giving a distinct increase in fan speed. At Le Mans this year, which was pretty warm and ever since, the fans on their own have maintained the temp only slightly above N when stuck in traffic. |
| Paul Hunt |
| It seems that the best bet, for those with "pushers" is to put ducting /cowling around/in front of their fans, a bit of sheet metal, plastic or fibreglass with two fan sized holes. Ideally (but not essentially) these holes should have circular surrounds to minimize edge effect, essentially putting the fans inside 2 very short tubes The "fan edge circles" would also stiffen the flat sheet surround) You could attach this sheet to the slam panel. Then completely seal off between that panel and the radiator.. That is that part of the radiator behind the fans and above the front "oil cooler tray", if your radiator (like mine) extends below. This arrangement would allow the pusher fans to establish and maintain a high pressure area in front of (the majority of) the radiator. You would lose a little cooling efficiency at speed of course, but not much because then there's plenty of fresh air , ...and you don't care. If you didn't want to commit your self you could always experiment with cardboard and duct tape I suppose, either way it would be a cheap easy change to make. If any one wants to try it let us all know, I'm agog. |
| Peter |
| The stock fans have been "ok" for me with the 302. Until now I had NO room behind the radiator for any fan of any kind. I had one of those fans shut of one day and I definitely saw a spike in temp! I am currently changing out the front end of my motor for a newer sort pump set-up which should gain me 1.5-2" clearance and I plan to install a big 16" puller which should solve my heating worries completely. I will keep you posted on the website.. |
| Larry Embrey |
| I've had a new thermostat fitted as well. I've noticed that the water temp has to get half way between N and H before it opens and the temp rapidly falls back to N. I haven't tested this stationery with the rad cap off to see exactly when the stat opens but I expect something is not quite right. I presume it should open/close at 82C which is around the N level? Also, doing a long run to Cambridge yesterday in quite cold temps on the motorway, the water temp sat quite a way below N. I'm wondering if the stat was still open, or the cold air coming into the engine bay was keeping the water temp at this level. I still have a manual switch for the fan so that I know when they are on or off (they were off for pretty much the whole journey), although it does mean I have to constantly have one eye on the water temp guage. |
| Chris Holmes |
| I was interested to see Tony Barnhill's project of adding a fan to the water pump. I asked Tony for more info but he hasn't visited this board again since his post. Anyone any ideas about his suggestion? I realise that of course it would use some power but other than that it sounds like a good idea but how is it accomplished? |
| Marc |
| The stat should only start opening at the stated temp, but by that time the temp should be rising quite rapidly. Both my MGs exhibit a clear point at which the stat opens and a number of cycles up and down before it stabilises, and again on the V8 as the electric fans cut in and out, but my Toyota temp gauge is noticeably stable both during warm-up and stuck in traffic. Personally I would rather see evidence from the temp gauge that both are doing something. It depends on the journey type but if I make the 1 mile or so trip onto the motorway then maintain 70 the gauge cycles a lot higher, sometimes just into the red, than if I am pottering around local roads during warm-up. The curious thing is that during warm-up even if the temp gauge goes way above the normal fan cut-in point the fans do not start, even though the two sensors are only an inch or two apart. Ditto when the steam pipe has been blocked and the gauge is still cycling many miles into the journey. |
| Paul Hunt |
| Chris, You might want to try the large, 16", Kenlowe fan. I've fitted one to my Tr*umph Stag. This is one real mean fan - it normally draws 20 amps and needs a 50 amp fuse to protect it when starting. This is not the 1/10 HP fan that David from NJ suggests - this one has an input power of nearly 3HP - say, 2 HP output power! You might have some difficulty fitting such a large fan but, perhaps, you could try some imaginitave ducting along the lines that Rog Parker suggests. Good luck Peter |
| Peter Hills |
| Chris, Do you have a new guage as well as thermostat? On motorways with all that air flow my guage sits on N in Summer and slightly below N in winter. Paul |
| Paul |
| Paul Yes my temp guage was not reading correctly, so I had that replaced along with the stat. I noticed when driving today that after reaching normal (about the time when I reached the A3 and started driving around 50mph, the temp worryingly shot straight up to almost H before falling rapidly back down again to just below N. Could the delay in water cooling be really that much when the stat opens or is the stat faulty? Chris |
| Chris Holmes |
| Peter, No offense, but a 20 amp fan only has an input of 0.39 HP. 20 amps times 14.6 volts equals 292 watts. One HP is equal to 745 watts. 292 divided by 745 equals 0.39. A 3HP fan would draw 153 amps from a 14.6 volt alternator. Would only draw about 10 amps from 220V mains. |
| Dan Masters |
| Wildy fluctuating temp readings *after* normal warm up (will happen during warm-up too) is a symptom that the steam-pipe on factory V8s is blocked. Many conversions do not have this steam pipe (between the stat cover and the inlet manifold on the LHS slightly further back) and unless they have a similar heater bypass pipe experience fluctuations unless the heater valve is open a little. |
| Paul Hunt |
| Dan, You are absolutely correct - mathematical error! Sorry. 150 amps from an MGB alternator would indeed be lots of power! Nevertheless, the fan is like a small hovercraft, complete with side skirt and shroud. Peter |
| Peter Hills |
| Peter, It sounds like you no longer need bother with a gear boxs, diff' etc, just switch on the fan and Taxi out of the driveway (after clearing with the tower of course). Seriously though, it sounds just the thing I'm looking for , how much room does it take up behing the radiator? |
| Peter |
| It actually takes up the entire engine bay! |
| Peter Hills |
| Marc...sorry for not getting back to you... ....I took my Rover water pump & my TR-7 fan down to my local machine shop & asked them to make an aluminum billet spacer plate about 1/4" thick to mount the fan to the water pump....also asked them to move the fan back so it sits behind the front edge of the water pump...they did so & the fan sits about 1'4" away from the belt pulley & about 3/4" away from the radiator when the engine is installed...the aluminum spacer plate is about 5" in diameter....oh, I'm also gonna build a fan cowling around the upper half of the fan... ...contrary to others, I'll continue to use the 2 stock electric fans out front of the radiator but am building some additional metalwork to force the air coming through the oil cooler holes in the valance to flow upwards to the radiator... ...I beleive the overheating problem isn't one of getting air through the radiator; I think its one of getting hot air out of the engine compartment...&, to that end, I'm making some vent modifdications to my inner & outer fenders...I've also 'smoothed' my inner fenders in front of my RV8 headers to allow air to more easily flow over them & out my header holes...&, what hot air doesn't leave via those holes can vent out the holes I've made in the tops of my inner fenders & through the vents I'm installing in my fiberglass front fenders. ...my web site also describes my thoughts along that line: http://www.theautoist.com/poorb.htm# 14 October 2002 ...its #3 on that date's posting... (again, I hope the URL works & apologize if it doesn't) |
| anthony barnhill |
| Fair game folks, I missed a nought on the power sum! However, if anybody is interested in the fan - wheter to fill their engine bay or to cool it, details can be found at www.kenlowe.com look for the Series 2000 16" fan. This site gives its power ar 225watts, not 2250watts! Regards Peter |
| Peter Hills |
This thread was discussed between 12/10/2002 and 21/10/2002
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