V1 Check radiator fan circuit

[SwerveMonkey]

I've been trying to find a round about way of checking the radiator fan circuit to ensure that I wired it corrctly. Is there a way to trick the radiator fan to come on without having the engine running?

I thought I could use the 2752 relay in the fuse box, can't confirm that is the circuit to invoke though before i short something that i shouldn't.

 

[Ross]

Remove the temperature sensor #1, and put it in hot water? Guess that only works to 212F.... not 223F.

 

[SwerveMonkey]

Remove the temperature sensor #1, and put it in hot water? Guess that only works to 212F.... not 223F.

Thanks, I think my engine's sensor is rear left side...

I'll try and boil some water and see if the fan comes on that way... will post results here

 

[baustin]

If you have hptuners I think you can turn it on, or at least set the tune to always have it on just to check it and then reset those values.

 

[Torchandregdoc]

I think pretty much any bidirectional scanner. Snap-on Modis definately can.

 

[SwerveMonkey]

I pulled the radiator sensor and tested it as a resistor...

• sitting in the ambient air temp it registered as ~2.29 K Ohm
• sitting it on an ice-pak it registered as ~ 2.9 K Ohm
• holding it in hand it registered between 2.03 and 2.14 K Ohm

I am not familiar with it's normal operating range of readbacks & will try to find some sort of comparable data that can confirm this is normal behavior

I CAN confirm that the Fan Relay can be used just like the fuel pump relay to manually excite that circuit and turn on the fan. I assured myself that the circuit wouldn't explode on me by doing a somewhat inverted test using the fan to produce some current at the fuse box end with the corresponding pins... risky assumption on my part, but I thought that was enough & I had already "jumpered" another circuit in the fuse box.

Also just in case anyone else didn't know what the torque spec on this sensor is after prepping with plumbers tape is listed as 16 ft-lb or 22 N*M.

 

[ctuinstra]

I CAN confirm that the Fan Relay can be used just like the fuel pump relay to manually excite that circuit and turn on the fan. I assured myself that the circuit wouldn't explode on me by doing a somewhat inverted test using the fan to produce some current at the fuse box end with the corresponding pins... risky assumption on my part, but I thought that was enough & I had already "jumpered" another circuit in the fuse box

So you are saying the you did jump the relay and the fan does come on?

I pulled the radiator sensor and tested it as a resistor...

• sitting in the ambient air temp it registered as ~2.29 K Ohm
• sitting it on an ice-pak it registered as ~ 2.9 K Ohm
• holding it in hand it registered between 2.03 and 2.14 K Ohm

What do you get when you put the sensor in boiling water? That would be the range that is designed for and you may get a much lower resistance. You're right, it's best if you can find information on what to expect at a given temp, otherwise it's just checking to see if it's completely dead or not.

 

[SwerveMonkey]

that's correct! I did get the fan to come on using the jumper across the relay pins, so for me that is just something to eliminate as a problem.
Also it is a good sign that I didn't screw up the wiring for that section, Ha Ha!

I really just wanted to make sure that the sensor was not dead, thereby eliminating a possible reason the fan would not come on.
with hindsight on the last time the engine was running and warmed up, I recall that the supply side was not HOT like the return side.
So my next suspect made me suspicious of the thermostat, which honestly for an old engine is a cheap preventative fix worth its weight in gold.

I'll pull the sensor & test in boiling water when I go to replace the thermostat and check what the resistance is then.

 

[ctuinstra]

I doubt the sensor is bad, but if anything, it could be out of range. Typical resistive components are either good or bad, if they are bad, they are usually open, rarely ever shorted. If they were overheated, they may be out of range. My guess is that the sensor is fine.

Not sure where you are at on your build but can you turn on the ignition and read the coolant temp on the dash? If the engine is cold, it should read the same as the ambient temp. If so, you are golden.

 

[SwerveMonkey]

yes! to all of what you just said, ha ha :-D
awesome info! thank you.

can you turn on the ignition and read the coolant temp on the dash?

now that you mention it.... I feel like an idiot.... that was one of the last things I did that prompted me to check the fan circuit in this post
I was able to get temp reading via bluetooth OBD2 reader when the engine was up and running.
before starting up it did read ambient temp, and after running for a while the OBD2 app read at ~ 190 F ?!?!

Right now I am stage 1.5... stage one all done, just waiting on the stage two bits to show up and doing what I can now to optimize the few things that I stumbled with during the initial assembly.