I buy 40 amp relays and bases from Del City.

A couple of months ago Coach bought a new fan for his Cobra. I don't remember the brand but it was a high dollar name brand. The tech guy told him he needed a 70 or 80 amp relay and fuse for the new fan.
I have never seen a car fan that pulled that kind of amperage so I called B.S.

When the fan arrived I tested it. 11 amps was the max I could get it to pull.
Coach send the fan back and bought a different brand.

Dwight

I think you are overthinking this. It is pretty simple, more air and/or more water. If the issue is at idle you need to move more air for sure (bigger/more fans) and see what the temp difference is between the rad and the motor. If the rad is 190 and the motor is 220 (as an example) the issue is more water. Rather than change the crank pulley, make a smaller WP pulley and overdrive it. If the rad is not cool enough you need more air through it. your only choice is bigger and badder fans. get the air fixed first, then the water. If you get the air fixed and have a temp sensor and proper water flow the fans will shut off whenever they need to. Let the system do its job. as a general rule, I use 100 degrees over ambient as the max target temp in traffic driving for a BB motor in a confined space. it may go 105 over, but that is the range. ambient has an impact as well as bay circulation but get the proper air flow thru the rad, then look at the water and then let the system work.

My Superformance has two (02) puller fans and come on at about 90`C which is 194`F.
I have never had an over heating problem.

Again thanks to all I will upgrade fan once I figure out the best fit for my 2013 backdraft

Why do some car manufacturers use 70 amp relays, because 30 or 40 amp relays don't have the metal cross sectional area for the high current terminals.

I would always rather over-engineer, than a have a fire.

https://www.ebay.com/itm/12V-4-Pin-7...-/153075476588

Gary

I took a different approach when my cooling fan relay quit. I installed a pair of 40 amp relays in parallel, protected by a circuit breaker. My thinking was the pair of relays will share the load and either of them can handle it, should the other fail.

How will I know if I have a failure of one or the other? As of right now I have no idea, though I could test them periodically by unplugging one at a time. Given their location that seems like a particularly masochistic approach. Regardless, my theory is a relay failure is highly unlikely if each is running at well under 50% load capacity, so hopefully I'll never have to deal with it. I know I won't if I end up installing the PROFORM controller mentioned in my comments a week ago.

Oh, no!

You've just created Schrödinger's relays!

(see Schrödinger's cat...)

Sorry, just couldn't resist.

Something that could make sense from a cost and airflow / cooling standpoint is the old Lincoln Mk VIII fans. They were a 2 speed fan controlled by a resistor in the low speed line. When running w/o the resistor they ran on high speed. They are available for cheap money from the salvage yards or if you want to go new I think I paid $180 for mine new from Ford.

Depending on how you start the fan it can have a moderate to high current draw. A soft start at low speed is easiest on the electrical system. An abrupt start at high speed is predictably the most demanding on the electrical system, Low speed operation is about 15 amps and high speed is around 23 amps. If you just turn on the fan without a soft start on high speed it will draw around 70 to 75 amps. I know, its a lot of power, but the easy fix is to use a soft start and a variable speed, temperature driven fan controller.

The really attractive aspect of the fan is the airflow. On low speed, depending on who you ask and which year fan you buy, it will flow somewhere between 3,000 and 3.500 cfm! On high, again depending on which year fan you buy and who you ask, the flow goes up to 4,500 to 5,000 cfm, some say higher.. The fans from the last two production years had the highest flow ratings. The earlier generation MK VIII fans were at the lower end of the rated flow ranges.

One of several attractive attributes these fans have is their intended lifetimes. These fans are 100,000 mile plus continuous duty OEM fans that we don't have to give a second thought to about durability. They are work horses and move significantly more air than any commercial aftermarket fans and they do it at a lower cost.

If you use a variable speed fan controller they start quietly, work as required (to maintain your target temperature) and definitely do not run out of cooling capacity.

The downside is they can require some effort to adapt to different radiator types and of course you don't want to allow small animals or children in the vicinity of the grill opening when they are on. 😊


Ed

Sorry to revive an old thread, but I have a problem with my fans.

Setup: Dual fans (unknown manufacturer), with an adjustable controller. As I posted above, the controller drives the fans through a pair of 40 amp relays. The fans will run after I shut it off, presumably until it's cooled enough for the radiator probe to tell the controller it's cool enough. Like many of these, I have an override switch on the dash so I can cool it down a bit before getting to my destination and shutting it down. That switch has an light to indicate when the fan is running.

A couple of days ago I went to a Show and Shine and, when I got to my spot, the fans ran a LONG time - MUCH longer than they ever have to my recollection even though I had the fan override switch on as I waited for entry and access to my spot. Other than that, everything was fine. When I drove home, I turned the fan override switch on just over 1/2 mile from home. I didn't notice the fans running while driving, but they certainly ran normally once home.

Today, I ran errands and again, turned on the fan override switch for the last bit before going home, but no fans. After I shut the car off the fan override LED remained on, even with the ignition off. Hmmm.... very interesting. I've disconnected and reconnected the battery, and the LED comes back on when the battery is reconnected.

At first I thought the fans had failed - but they're dual fans and it would be a freaky coincidence if they both failed simultaneously.

Then, my thought turned to the relays but, again, dual relays. Regardless, why would the LED light up if were the relays? Unlikely.

So, my thought now is that the fan controller has failed. I haven't tested it yet, but it has power even when the car is off in order to keep the fans running, and the override switch is connected to it through the relay connections.

Does my logic compute? Are these simple fan controllers subject to failure?

P.S. I just turned the dial on the controller a few times, reconnected the battery, and the override switch LED is no longer lit. Turned on the ignition and the fan override switch and there's no fan operation. I haven't tested for power at the relays or the fans yet, but fully believe the problem is with the controller and I've ordered a replacement.

OK, without seeing a schematic of your setup I'm just shooting from the hip to a certain extent, but "yes" they do fail, and DC motor speed controllers that are PWM can fail more flakily, if that's a word, than say just a plain old big ass resistor. The latter just tends to burn up and not work at all while a PWM is just a big switch that turns on and off really fast. There's also circuitry involved that senses how hard the fans are pushing/drawing because moving hot air when your engine is running hard is completely different from when you just throw your switch on in the garage and proclaim "yep, the fans are working fine." Remember, you only have a couple of components in this little circuit: the fans, the controller, the temperature switch in your radiator hose, the relays and the override switch. Plus the connections everywhere and your little light. I don't think it's the little light.:p Dual fans can draw a good 30 amps and dual relays are good, and connections are important. If I were diagnosing this in the garage I would do a voltage drop test along the circuit to see if there was any unusual resistance and then I would immediately suspect the controller. I would bypass the controller so the fans were controlled by the temperature switch in the radiator hose and the manual switch exclusively -- and they only have one setting when running, "full blast." Then I would drive it a few times and if everything was fine I would just replace the controller. But if the temperature switch in the radiator hose won't trigger properly then check that it has a good ground and good connection to the relays and just replace it. You can always test it with a VOM and a pot of water on the stove if you are so inclined. But your problem is going to be one of those components. I promise.:cool:

While I've thought of going to a switch / sensor in the lower radiator hose (or tank), my controller has an attached probe that goes in the radiator fins, so I can't bypass the controller and use just the "temperature switch in the radiator hose". I'll take your suggestion to test it in a pot of water using a VOM, though.

Thanks.

OK, I would suspect a probe that you stick in to the fins as well. I would think your controller would have some sort of port or plug that let you use a temp sensor in the hose like mine below. They're much more reliable.

https://i.imgur.com/m7BH5hz.jpeg

I've thought about going to that setup. Will have to add it to my to-do list.

I have my radiator covered with four electric fans, with the lowers and the upper fans working in pairs.. I had to do some rework concerning the fan circuit. I have two thermostatic switches controlling two relays. I had to isolate the hot terminals at the circuit breakers so as the plastic holder just organized the breakers and wires but were part of the electrical connection not clamped. It had gotten hot and plastic melted making for even worse connection. I rewired the fans so they were thermostatically controlled and I had a double pole - double throw switch on the dash to override the thermotic switches and turn the fans on before hitting the an expected hot situation. I then used verry small indicator lights. Green lower fans and Red al fans. Ignition and master electric switches are involved. I used to have problem twenty years ago, with not killing master switch and come out to find the battery near dead. Now I use a Flaming River master switch located on dash, twist on and bump off.

More info- Relays are powered with Master and ignition on. Thermostatic switches will turn on it's relay when they sense radiator reaching temperature set with adjustable switches . Dash double pole double throw switch is used to go ahead and turn fans on, lower pair or all. two thermotic sensors located in radiator, connected to two adjustable switches that will turn on the two relays, Dash switch uses the same connections on relay to have fans running with out the thermostatic sensors reaching the adjusted temp points.
I went on a cruise last year, and had problem with the engine getting too warm While crawling through a City Park. I found the plastic circuit breaker holder for the four circuit breakers (on the fire wall) had been mounted using the electrical terminals. The terminals got warm, melting the plastic brackets that then gave way, causing an even worse electrical connections. I had the plastic circuit breaker holder crushed in with the wire terminals. Didn't work out Metal to metal now.

Mine are on a toggle switch, turn them off over 20mph.

Problem solved!
 

I received the new controller, but when I connected it the results were the same. Hmmm...

The next step was to check the relays and the circuit breaker. I had battery voltage going both in and out of the circuit breaker, so that's fine. When I bypassed the controller and put power to the circuit I could hear the relays actuating.

Next was to check power to the fans. There's a single power wire that connects to wiring from each fan, as well as matching ground wires. I checked the connection and there was power to the connector. Is it possible that both fans failed?

So, I removed the fans to test them. Lo and behold they worked individually and together. Well, that's a puzzler - why are they working fine in a bench test but not in the car?

The culprit? A corroded grounding lug (see photo). Battery voltage doesn't matter when there's no ground. I should have checked the power AND GROUND before pulling the fans out. Aaarrgghh.

http://www.clubcobra.com/forums/pict...ictureid=21320

Anyway, now I get to fix and improve not only the ground connection, but also clean up some of the wiring while I'm at it.