rollingjack

I started to study this a little, because was full week with temperatures 86F and up.

First I measured with IR thermometer and ohmmeter, which resistance has NTC sensor (sensor by oil cooler) by 212F (100C).
That was my goal for turn on first speed of oil cooler fan. I got reading about 1009 ohm.

Now I putted in NTC plug rheostat instead NTC sensor. By changing resistance I find points where CCU turn in first and second speed for fan. I got readings 696 ohm for first speed and 591 ohm for second speed of fan.

Then I measured, when fan first kicks in. It was by 230F (110C)

So, how to do, to got from NTC sensor resistance 696 ohm by 212F?

As we know, to add some resistor increases resistance. Not in all time. If we put resistors parallel, then we can reduce resistance sometimes:

1/R1 +1/R2 =1/Rtotal

I wrote in one MS exel worksheet in box A1 "=1/1009+1/x" and in next box B1 "=1/A1". I putted then instead "x" different readings and goal was in B1 to get reading 696. To closest "x" was 2200. OK, this exel is only for example, you can calculate it of coarse in better way.

It means, that I must add resistor 2,2 kohm parallel to NTC sensor, to get resistance 696 ohm by 212F.
I find one 2,2 kohm resistor for 0,6W. It is enough, because current here is very small. And this resistor is small, about 0,24 inch long. I choose metal film resistor, not carbon. Metal film resistor is more durable for vibration.

Good place to put resistor was in plug by NTC sensor. Turned rubber protection by plug back, I got access to wires. Cleaned wires little from isolation, then I soldered my resistor between two wires in plug. Rubber protection back and you see no difference with foregoing.

It works! Fan is turning now on by 212F and out by 196F.

Material cost was only 5 eurocent.

KaiB

Good work!

Steve Weiner-Rennsport Systems

Very well done!!!

This will be quite useful for many people on here since the factory setup turns the fan on too late to properly control oil temps on hot days.

jimq

Did you take any pictures of how you put it in the plug?
That would be a handy mod in the Florida heat.

rollingjack

many thanks - KaiB and Steve.

jimq- here is picture of my setup-little tricky work (resistor is so small) in NTC sensor plug under front right fender, but doable:

Vandit

Do you have a link where I could get the appropriate resistor stateside?

I checked Radioshack's website and it doesn't seem like they have a 6w in 2.2k ohm resistors, unless I'm looking at them wrong (very possible).

http://www.radioshack.com/search/ind...=2.2k+ohm&sr=1

Laker

rolling jack found one that was 0.6 watt, and it's low wattage application, so ...Radio shack's 0.5 watt... should do.

ja78911sc

Nice work !

How did this mod effect your fan high speed setting (second speed) ?

Your new low speed fan starting point is at 212 and ending at 196. If your temps continue to rise above 212, will the low speed setting be the only functioning fan speed ?

Thanks,
Jim

Vandit

Is this plug the same plug visible in this pic?


Between where the oil lines go into the cooler.

rollingjack

Thanks Jim,
High speed for fan turn in, if oil temperature rises to 221F.
This is same setting as before, but turn in points for oil cooler fan are by lower temperature.
CCU get same readings for resistance as before, but temperature by oil cooler is lower.

rollingjack

Vandit-
there is no difference in Watt, you can use 0,5W or 5W resistors. More important are dimensions- if it is big, you have problem to put it between wires in plug.


About pictures- yes, right- this is plug by NTC sensor, located by oil cooler.

ja78911sc

So the change in resistance effected the low & high speed fan--nice work. High is now operating around 221 vs. the factory setting at 240+.

Question on the resistor:

Does it make a difference which wire from the resistor you attach to the sensor wire? (Basically, If you changed the direction of the resistor in your photo, would it still work)

Thanks,
Jim

cjoenck

Resistors are direction independent. Unlike a diode, you can use a resistor either way.

This is a clever mod. You just "fool" the CCU by changing the resistance of the sensor by a fixed amount.

Nice.

rollingjack

+1

Laker

Thanks Rollingjack for the idea, pictures and crunching numbers to come up with the correct resistance!

Did the mod today since I was in there anyway for the low tone horn.
Five resistors for $1.20 The first four people that PM with their mailing address can have one.

Remove front right wheel
Remove front mud guard.

The temperature sensor is at the top of the resistor 5-pack.
with two small flat bladed screwdrivers, carefully peel back the boot over the sensor connector.
Take your time, because it's 20 years old and a little brittle.


Nicked a wire to remove insulation on 3 sides without breaking any of the copper strands.

wrapped a resistor lead around the exposed wire.

Wrapped up the exposed solder and part of the resistor with some tape, then nicked the other lead about 1cm higher as I want the resistor to run parallel to the leads so the boot would fit over two leads and a resistor.
Taped it all up , then rolled back the boot over the leads, resistor and it fit nice and snugly.

It's pouring rain today, so will have to test later and post results.

Edit: having issues with linking photos... here is a direct link to the album
https://rennlist.com/forums/members/...istor-mod.html and adding as attachments