Interesting observation - Temperature differential of my cooling system

[buening 63]

While installing my DCControls PWM fan controller on my Mach with a 19x28" aluminum Northern radiator and Taurus fan, I was having issues with the controller spinning the fan high enough to be effective. My mechanical temp gauge showed 190° with the fan barely spinning, and the instructions state the fan will start up at 160° and will reach 100% speed at 180°. The instructions say to put the radiator probe near the outlet hose of the radiator, which I did. I figured something doesn't seem right, so I get ahold of Brian at DCControls. Upon debugging the issue with Brian, I was told to use a meat thermometer at the inlet and outlet of the radiator after idling awhile and below is what I found:

 

Just below Inlet on crossflow radiator (temp at 190°)

 

Just above outlet on crossflow radiator (temp at 165°):

 

 

That is a 25° temperature difference, meaning the motor is heating up the fluid that much from inlet to outlet. I was expecting more like 10-15° temp differential. Moral of the story, just because your gauge may read 190° doesn't mean the entire motor is running that hot. The average temp of my motor would be 177.5°, just a tick below the 180° thermostat.

 

The fan controller was seeing 165°, which was why it wasn't spinning very fast (@25%). Temps wouldn't go over 190° no matter how long I let it sit, so the fan's low speed was sufficient with the large radiator surface area. Maybe I should go with a smaller radiator so that the fan gets a little more of a workout? :devil:

 

Anyone else every try this test with the meat thermometers??

[Angel 24]

The thermometer probe should be placed close to the radiator inlet, not the outlet. At least that's how my fan thermometer works.

[buening 63]

.....not according to Brian @ DCControls. This controller may be different than others, not sure.

 

A good read by user jscherb: http://www.jeepforum.com/forum/f8/electric-fan-controller-using-oem-temp-sensor-542209/

[Max Power 74]

The thermometer probe should be placed close to the radiator inlet, not the outlet. At least that's how my fan thermometer works.

 

If you place it by the inlet, your fan will be running while you are driving down the highway.

 

Not what you want.

[Angel 24]

Hmm....interesting. All I did was follow directions haha! Thats what the instructions said so thats what i did. Its an adjustable thermometer, I dont know if that makes a difference. I ran it like that for about 3 years with no problems. At highway speeds or on cold days, it would only turn the fan on when I would come to a stop or get stuck in traffic. Max, you're right. I wouldnt want it running when I didnt need it on. But what about when the car is just idling on a hot day? If the car isnt moving and the fan isnt on, would there be such a drastic difference in temperature between inlet and outlet?

[Max Power 74]

Hmm....interesting. All I did was follow directions haha! Thats what the instructions said so thats what i did. Its an adjustable thermometer, I dont know if that makes a difference. I ran it like that for about 3 years with no problems. At highway speeds or on cold days, it would only turn the fan on when I would come to a stop or get stuck in traffic. Max, you're right. I wouldnt want it running when I didnt need it on. But what about when the car is just idling on a hot day? If the car isnt moving and the fan isnt on, would there be such a drastic difference in temperature between inlet and outlet?

 

If you are idling on a hot day with no fan running, yes, it would be hot, both at the inlet and the outlet. You only want the fan on when the outlet of the radiator is not cool to your temp setting. 2 things move air through the radiator to cool the fluid, vehicle movement, or fan movement. You only want the fan to engage when the vehicle isn't moving at an adequate speed to cool it sufficiently. That's why the temp probe needs to be at the radiator outlet, not the inlet.

 

The coolant at the inlet, once the vehicle is at operating temp. The coolant at the outlet depends on the variables you are trying to control.

[LoneWolf2U 136]

Just my point of view here...:001_smile:

But depending on if the probe is adjustable for temps or not is what desides where I would place it.

If it is a fix temp probe that controls the fan, I would place it up 1/4 way from the bottom of the rad.

If it is and adjustable temp probe, then near the outlet is where it would go.

My reasons? Well a fixed probe at the outlet will only turn on the fan when its temp at the bottom of the rad is reached.

Problem with that is now there is less time for the coolant to drop in temp before going back thru the eng. If the probe is up from the bottom when the probe turns on the fan the coolant is given some time to lower its temp while passing thru the rad.

 

An adjustable probe can be set to serve the same purpose, Setting the temp at say 165 so when the temp is reached the fan will start moving air thru rad. This will help keep the coolant temps from creeping while at idle or in traffic.

[Max Power 74]

Just my point of view here...:001_smile:

But depending on if the probe is adjustable for temps or not is what desides where I would place it.

If it is a fix temp probe that controls the fan, I would place it up 1/4 way from the bottom of the rad.

If it is and adjustable temp probe, then near the outlet is where it would go.

My reasons? Well a fixed probe at the outlet will only turn on the fan when its temp at the bottom of the rad is reached.

Problem with that is now there is less time for the coolant to drop in temp before going back thru the eng. If the probe is up from the bottom when the probe turns on the fan the coolant is given some time to lower its temp while passing thru the rad.

 

An adjustable probe can be set to serve the same purpose, Setting the temp at say 165 so when the temp is reached the fan will start moving air thru rad. This will help keep the coolant temps from creeping while at idle or in traffic.

 

Decent philosophy overall, but instead of installing the probe 1/4 way from the bottom of the radiator, you could just run a slightly cooler fixed temp probe and achieve the same results.

[LoneWolf2U 136]

True but that would require that the fixed probe can be replaced.

Many elec fan set ups have a fixed temp probe controller and do not have a choice in temp.

The idea of raising the probes location is to give the coolant a chance to cool down before heading back into the eng.

Ex, If your probe temp is 180* and its placed at the lower hose exit, The fan will not come on till the bottom temp is 180*.

Now no matter how hard the fan is pulling air the coolant temp is already too high to drop the eng temp to allow the stat to control temp.

Now you will temp creeping at stop or in close traffic.

[buening 63]

My probe is fixed but i could use a rheostat to adjust the turn on temp. The easier method would be to move the probe up on the radiator

[LoneWolf2U 136]

Yep, Moving it up is much easier than adding parts that could go out later causing problems.

And the plus side its less clutter under the hood.:001_smile:

[Steve69 0]

Im running the same DC controller, Taurus fan and crossflow radiator in mine. I was getting some radio noise when my fan kicked on and it seemed like when I hit town my fan was on and at idle. Once I hit the hwy it was off. Mine was running at 195 to 205 at idle and the fan light was on red. So a few weeks ago I fired up the 69 and let it idle for 45 minutes to determine how the fan ran and try to get rid of the radio noise. I had a RCA cable that crossed a positive wire from the fan and that was the source of the noise. There was no ryme or reason with the fan running. It would go slow then it would speed up again and I was watching the temp gauge that is wired in the intake manifold and it would go up down and got as high as 205 but then it dropped. But being that the sensor is near the bottom of the radiator it runs the fan from those temps and not from what my gauge is telling me. I figured it was ok since it didn't overheat or have any problems.

Steve69

[buening 63]

Steve69, have you measured the output voltage of your controller? With the above temp of 190 on my gauge, I'm only getting a max of 6v and going down to about 1v (PWM so it goes up and down constantly)

[Steve69 0]

Hey Buening, I haven't measured measured the voltage output. My unit is about 7 years old. I dont think they sell the one I have anymore. Ill have to do that next time I fire it up.

 

Steve69