Electric fan issues

[GrahamFountain]

This isn't necessarily a much of a problem, but with a thermostat fitted, the electric fan does not go off once the car's warmed up. Well, I think it goes off after a bit at 60 ish, but I've not been able to test that since I fitted an indicator in the cabin. The fan comes on at the guage reading 1/2 and seems to hold temerature at about 3/4 max, and it goes back down to about 1/2, dirving at 30. But the fan stays on. The full rad seems to be getting hot, a bit cooler at the bottom, but far from cold, and there's loads of hot air blowing out of it. The rad core's only about 12 months old, and I've just done the pump.

It's only a problem because, with the halogen headlights, cab heater fan, and wipers all on, the voltage drops below 12, and the engine occasionalle chuffs under load, and that's with a higher output metro alternator. So fitting a higher wattage fan isn't necessarily a solution.

Without the stat, it will go off and on if warmed up from cold on tickover, but if I stop after a run, and leave it on tickover for 20 mins, it still doesn't go off. I didn't have the indicator in the cab when I tried running without a stat, so I'm not sure what speeds it goes off at when driveing.

I'm thinking of taking the termostat out again, as it's no bother in the summer. But I tried that on a TR7 Sprint, and it took too long to warm up in the cold, unless I let it run for a while without moving.

Anyway, I was wondering what others with an electic fan are seening on the guage and with the fan going off, etc.

Graham

[GrahamFountain]

Just been out in it, and it's running even hotter with the replacement pump. Mind you, while this pump doesn't leak, the impeller is a bit scored - looks like it was damaged when the old engine ran backwards on switch off. Don't know what caused that, because the current engine never has unless I set tickover about 1800 rpm.

I think the mistake is I put the spare pump and its impeller under a different, unscored cover - because I broke the good one that came out -, and I should perhaps have used the one it was under before. I'll have to get another set of gaskets and swap next weekend.

Soon, the inlet manifold will come out of the car when I whistle.

Graham

[marko]

Silly question but is the fan pushing/pulling the air the correct way? Some fans are designed to both push and pull but most are one way and if you switch direction then they hardly work.

[GrahamFountain]

Valid question, but it is a straight bladed fan, and was advertised as push or pull, so it has to be bi-directional.

It's only an 80 Watt motor, and I'm thinking I should try a 120 Watt one. But that's going to make the voltage drop worse when it rains, and it does that rather a lot in this part of Lancs.

Graham

[Carledo]

A straight bladed fan can either push or pull, but this is dependent on the polarity of the motor. Get it wrong (as I have seen, more than once) and instead of a nice cooling draft, you get a forced area of dead air, right where the rad is when driving and hot air from the engine bay pushed (or pulled) through the rad when stationary!
From your description of symptoms, it sounds eminently possible that this is what is wrong!

Examine the fan carefully and determine which way it needs to rotate to draw air in from outside the car then test to make sure it is turning the right way! If not, simply reverse the wires to the motor!

Steve

[GrahamFountain]

Mount a fan so it blew air forward through the radiator? I'm not sure I'd even admit to knowing anyone that dumb.

And as to reversing the polarity, that's nearly as dangerous as beaming down in a red vest. As marko correctly points out, you can't necessarily just run a fan backwards and expect it to blow air in the opposite direction at the same speed. Some of them have plain flat blades, and they will blow or suck just the same, in either direction. But it's a little better if the blades have a curved cross section. If they do, and if you're drawing air through the rad, you want the edge with the least pitch at the front and the edge with the greater pitch at the back so it sort of "scoops" the air off the back of the radiator. That way it accelerates the air through the impeller more smoothly, and imparts the maximum energy with minimum drag.

It won't make all that much difference. It's like an aircraft flying upside down. The wing will still give lift from the angle of attack, but it gives more drag that way up, so the aircraft flies slower for the same engine power. So it's definitely better to have the impeller blade curve the right way around or an airfoil section wing the right way up.

Graham

[Carledo]

The first time I met this dumb person he was the owner of a Burlington arrow kit car, a sort of 1930s sports car on GT6 underpinnings similar to the Moss/Spartan/JC Midge/VincentMPH genre but much prettier.
This car boiled in traffic and got hotter the faster you went. Binning the thermostat only slowed the process and a replacement radiator made no difference. I was on the verge of pulling the head off when the fan caught my eye. Now the GT6 has an engine driven fan, directly mounted on the crank pulley. This car, which had allegedly been built by a retired aero engineer, had, probably for space/clearance reasons, been fitted with an "Aerofan" an accessory that used to be popular on Minis back in the days before viscous fans, the blades changed pitch with revs.
What the numpty hadn't realized was that a Mini fan pushes air OUT through it's side mounted rad so this had the opposite pitch for the Burlington. Simply removing the fan cured the problem whilst driving and a Kenlowe fitted later finished the job. Incidentally, Kenlowes are reversed by swapping the motor wires, it's in the instructions, what's so dangerous about that? almost any electric motor like that will run either way by swapping polarity. And a flat blade fan will push or pull with equal alacrity, but pitch is critical, if its turning the wrong way and pushing when it should be pulling (or vice versa) then you have a problem!

Steve

Actually, I shouldn't blame the owner of the Burlington for the problem, he bought it like that from the builder, who undoubtedly should have known better! I later found a couple of other engineering faux pas on the car which made me glad he had retired, so I wouldn't have to worry about flying in something he'd fixed!

[Graham.Fountain]

It's not the motor that's the problem, its the shape of the cross section of the blade. If it's curved, it will not work as well if the air hits the high pitched side first, as that will try to give it a massive initial acceleration, and then slow it down with the low pitched part of the blade. Whereas, if it first hits the low pitched side, it will be accelerated smothly to the maximum velocity.

As to the Burlington, it wouldn't suprise me if whoever installed the fan had turned it over and expected it to blow the other way - I've seen that one on the telly.

Graham

[79Inca]

I've had a Kenlowe on my Sprint since 1983 and its been no trouble. Hardly ever comes on in winter and only when stopped or in very slow traffic in summer. I don't like the viscous fans as I saw two of them in the late 70's come adrift and plough into the radiator.

[GrahamFountain]

I've had a Kenlowe on my Sprint since 1983 and its been no trouble. Hardly ever comes on in winter and only when stopped or in very slow traffic in summer. I don't like the viscous fans as I saw two of them in the late 70's come adrift and plough into the radiator.

I've also had a viscous coupling come a part and the fan destroy the rad. Not nice. But most of the ones that have failed on me have squeeled too bad to live with before that.

On the subject of the electric fan the things I'd like to know are, once it's come on with the car idling, how long before it goes off on it's own - still at idle -, how long is it off for, and what values does the guage go up and down between?

Graham

[red&black]

On the subject of the electric fan the things I'd like to know are, once it's come on with the car idling, how long before it goes off on it's own - still at idle -, how long is it off for, and what values does the guage go up and down between?

Graham

When started from cold and left to idle my fan comes on after 19 minutes here



The fan runs for about 4 minutes and switches off here



It then takes about another 5 minutes until the cycle is repeated.

Measured with the bonnet shut and an outside temperature of 17.5 degrees.

James

[GrahamFountain]

James, do you know what wattage your fan is?

Graham

[red&black]

James, do you know what wattage your fan is?

Graham

Sorry Graham- I don't know how many watts it is but I put a clamp meter on the cable to it and it draws 5 amps without the engine running.
It is a 12 inch Pacet Clubfan.

http://www.pacet.co.uk/clubfanpacets.php

James

[GrahamFountain]

Looks like it's about 80-85 watts.

I don't think I remember measuring the time from start-up to fan on, which aught to be a measure of coolant flow and rad efficeincy. I'll give that a go tomorrow.

Graham

[GrahamFountain]

Ran it from cold on Saturday when it was about 19C. However, this is with no thermostat, so it may change when I re-do it with one in.

It took 10 minutes for the fan to come on at about mid gauge when the thermo-switch should have been, and measured, 90C. However, it still wasn't happy with the choke in when the fan came on, and I needed a bit of the cam to keep the tickover up. I ran it for near half an hour and it went up to just under 3/4 gauge and stayed there, with no suggestion the fan would ever turn off.

I got the IR thermometer on the engine and rad and got these readings when it was stabilized after warming up from cold: The sender for the gauge, the thermo-switch for the fan, and the inlet to the rad were all at about 98-99C. The bottom of the rad where the return comes out was about 96C, and the head down between the carbs was about 102C.

When I drove the car at 30, straight after this, the fan went off after 2 miles and didn't come on again till I stopped at some lights.

I think the radiator is probably the limiting factor in all that. The fact that there's little drop across the rad, and the head's not much hotter than the sender, suggests there's plenty of coolant flow, so the pump's not the main cause (that's because I've got all the parts and gaskets to do the pump again, isn't it?). That the fan comes on early means there's a problem other than the fan. The switch is coming on at the right temperature, and it goes off driving at 30, so that's probably okay. So it has to be the rad. Anybody know what's the specification for a Sprint radiator core?

Meantime, I'm going to give the system a dose of flush as soon as possible, and see if that helps. I'll also put the thermostat in and get some data for how it goes like that. Anyone got recommendations for flushing agent.

Graham