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