Electric Fan Controller using OEM Temp Sensor - JeepForum.com
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post #1 of 98 Old 04-05-2008, 07:51 AM Thread Starter
jfwireless
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Electric Fan Controller using OEM Temp Sensor

After reading bdmonst recent electric fan thread, I was wondering what the thought was on using a fan controller that utilizes the engines OEM temp sensor rather than a temp probe inserted into the radiator. It just seems it would be better to monitor the engine coolant rather than the radiator coolant temperature. I guess in a Jeep I also worry about the temp sesnor being dislodged from the radiator and not providing the proper temp reading to the controller. Does a temp probe inserted into a radiator actually have the proper coupling to efficiently monitor the radiator temperature in a consistent fashion?

Isn't the radiator temp about 20 degrees cooler than the engine, what about if it is raining hard, wouldn't the temperature differential between the engine and radiator now be much higher ?? I would think you would get different readings depending on where in the radiator you inserted the probe??

Here is a link to a fan controller that using the OEM temp sensor for monitoring the engine coolant temperature. As it is a high impedance pick up it does not affect the existing temp gauge or ECM temp input.

http://www.spal-usa.com/fans/automat...ts/FAN-PWM.pdf

Any thoughts or knowledge/experience here ?

Jim

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post #2 of 98 Old 04-05-2008, 09:39 AM
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no experience here using this particular controller, but this does look like it would be a better setup than the radiator probe. I have used the radiator probe type before and they work good but as you said in a jeep how well is the probe going to stay in place.

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post #3 of 98 Old 04-05-2008, 11:11 AM
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I've got a controller that uses a radiator probe and IMHO it is a better option than one that uses the engine temp sensor. I'll explain why I believe this...

The goal of the engine thermostat is to keep the engine at the proper operating temperature. Note I didn't say cool, because the thermostat is also supposed to keep the engine warm enough as well. The engine temp sensor in a properly operating engine will show a pretty consistent temperature, usually about 10 degrees above the thermostat temp.

The goal of the radiator is to keep the coolant cool enough so that the thermostat can do its job. As long as the radiator is sending cool enough coolant back into the engine, the thermostat will have no problem keeping the engine at the proper temp.

If it is cold out, the radiator can very often cool the coolant enough without the help of a fan, expecially if the vehicle is moving. In other words, you don't need a fan very often on cold days.

If you run your electric fan based on the temp in the engine, you will be running the fan when it isn't necessary and especially on cold days, send coolant back into the engine that is colder than necessary. This can cause temp cycling, and not uncommon to see the engine temp swing up and down as the thermostat opens to let overly cold coolant in.

If you put your radiator temp probe at near the outlet of the radiator, you are monitoring the temp of the coolant flowing back into the engine. Typically you would set the fan controller to come on at some temp lower than the engine thermostat temp so you can be sure you're sending cooler coolant back into the engine. My CJ has a 195 degree thermostat and my radiator probe is set at 180 degrees.

So in my Jeep, the electric fan rarely runs on cold winter days. On warm days, the fan rarely runs when I'm on the highway. My engine temp, as reported by my temp gauge and my EFI computer, stays rock solid at about 205 degrees in all weather. If I was using the engine temp sensor to run my fan, it would pretty much run all the time when the engine was at operating temperature.

IMHO the radiator probe placed near the outlet of the radiator is the best way to optimize the capabilities of an electric fan. The fan runs only when the coolant needs to be colder than it would be by the radiator alone, and there is no temperature cycling in the engine at all due to overly cold coolant.

In addition, I have a variable speed fan controller, so on cold days it often only runs very slowly (and very quietly!) because if the coolant in the radiator is only a little too warm, the fans don't need to spin at high speed.

On the other point, the fit of the probe in the radiator is very secure, I have no worries about it ever coming loose.

I know there will be a million other opinions on this and there are many other configurations that can be used to keep the engine at the proper temp, but this is how mine is set up and my results are excellent.

Jeff
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post #4 of 98 Old 04-05-2008, 01:43 PM Thread Starter
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Jeff:

The thermostat will determine the temperature of the engine, so I really do not think using the OEM temp sensor for the electric fan is going to cause temp swings in the engine.

If your engine is running a constant 205 with a 195 degree thermostat while setting your radiator temp turn on at 180 degrees, your fan will come on about the same time as your thermostat opens. So if you use the OEM engine temperature sensor and set your controller at 195 degrees wouldn't you have the same result? I do not see how this would cause the fan to run longer than using the radiator temp probe. In cold weather your fan is still going to turn on when your thermostat opens up.

The engine cooling control loop is interesting, the engine thermostat controls the engine temperature, and the electric fan controller helps control the radiator temperature, so the fan controller is loosely coupled to the engine temperature and delayed in responding waiting for the radiator temperature to rise up to the engine temperature. I just think it would be better to tightly couple the electric fan controller to the engine temperature to prevent any possible delay in cooling the engine when needed.

Jeff, I do apppreciate your post and wonder what you think about my response.

Jim
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post #5 of 98 Old 04-05-2008, 03:38 PM
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Jim,

Quote:
Originally Posted by jfwireless View Post

In cold weather your fan is still going to turn on when your thermostat opens up.
Actually no, that's not how it works, because the temp probe is at the outlet of the radiator, not the inlet. By the time the coolant has traveled through the radiator and gets to the outlet, in cold weather it has cooled off enough so the fan doesn't have to run.

Quote:
Originally Posted by jfwireless View Post

The engine cooling control loop is interesting, the engine thermostat controls the engine temperature, and the electric fan controller helps control the radiator temperature, so the fan controller is loosely coupled to the engine temperature and delayed in responding waiting for the radiator temperature to rise up to the engine temperature. I just think it would be better to tightly couple the electric fan controller to the engine temperature to prevent any possible delay in cooling the engine when needed.
In my experience with mine set up as I described, any delay that may exist isn't a concern. Doing it the way you suggest certainly would be a fine way to do it, the difference would be that the fan would run more your way than the way mine is set up, at least in cold and cooler weather. In warm weather the fan will probably run about the same with either setup because a trip through the radiator without the fan probably won't cool the coolant enough.

Either way is a fine way to do it. Where I live there are only about four months of the year when it definitely won't snow, so I'm happy with the way I've done it. If I were in Naples maybe I'd do something different :-)

Jeff
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post #6 of 98 Old 04-05-2008, 06:34 PM
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i bought a painless kit, from jegs for $55, i came with a thread in sensor that went into the intake manifold. i felt the same way with the probe, might fall out doing 60mph and not find it until it way to late....

jegs also has different kits for what temp you want your fan to come on and shut off at.
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post #7 of 98 Old 04-05-2008, 06:35 PM
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I have changed the location of my radiator probe based on Jscherbs explanation above (we had discussed in another thread) - And my engine stays between 195-200 and my fans runs less often. I initially had it wired where the probe was at the radiator inlet, which meant the fans came on basically when the thermostat opened - In fact turning the fans on when they didnt' need to be.

I think if you go with the notion that the thermostat controls the engine temp and the fans control the radiator fluid temp (Yes I know they are very much related), then, to me, it makes more sense to tell your fans when to run based on radiator temp, not engine temp.

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post #8 of 98 Old 04-06-2008, 06:58 AM Thread Starter
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Quote:
Originally Posted by jscherb View Post
Jim,


Either way is a fine way to do it. Where I live there are only about four months of the year when it definitely won't snow, so I'm happy with the way I've done it. If I were in Naples maybe I'd do something different :-)

Jeff
Jeff:

You are corect, I am concerned with heat as it is always hot down here in South Florida. That is why I would like to do all I can to make the cooling system react to heat as fast as possible. I can see you have a totally different design criteria.

Thanks for the replies

Jim
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post #9 of 98 Old 04-07-2008, 06:05 AM
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I wondered how much it would cost to get a threaded hole put into the radiator to mount a probe. Or if there is some radiator that will fit the CJ that already has a bong (?) in the radiator. Would the top tank or the bittom tank be better?

I agree with jscherb and monitoring my engine will be to late. It's suppose to be in a steady state and should not vary much.


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post #10 of 98 Old 04-07-2008, 06:30 AM Thread Starter
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I would think on the copper alloy radiator installing a threaded mount of some kind in the top tank near the return outlet would be a simple task for any radiator shop or skilled mechanic, just silver solder in the threaded mount. Maybe adding a small copper or brass plate overlay to strengthen the area of the mount.

John, don't many of the factory late model cars use the ECM or other smart device to control the fan via the OEM sensor?

I was thinking in Florida where it is just hot all the time to just turn on the fan anytime the thermostat is open, I really am more concerned with heat damage to my engine that the time the fan is running. In July, August we are near 100 degrees every day, sitting at a stop light or stuck in Traffic creates lots of heat during this time. I would like to be ahead of the heat not reacting to it.

Jim
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post #11 of 98 Old 04-07-2008, 08:00 AM Thread Starter
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After driving to work and thinking about my last post I realize there is an error in my thinking about turning on the electric fan when the thermostat is open, Obviously at some vehicle speed more air is flowing through the radiator than the fan produces so turning it on at this point is useless.

So maybe putting a fixed mount sensor like John suggest in the radiator tank near the the outlet port is the best way. I will try the OEM engine mounted Thermostat first, and see what happens. If that has any issues I wil try John's approach.

Jim
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post #12 of 98 Old 04-07-2008, 08:54 AM
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Quote:
Originally Posted by jfwireless View Post
After reading bdmonst recent electric fan thread, I was wondering what the thought was on using a fan controller that utilizes the engines OEM temp sensor rather than a temp probe inserted into the radiator. It just seems it would be better to monitor the engine coolant rather than the radiator coolant temperature. I guess in a Jeep I also worry about the temp sesnor being dislodged from the radiator and not providing the proper temp reading to the controller. Does a temp probe inserted into a radiator actually have the proper coupling to efficiently monitor the radiator temperature in a consistent fashion?

Isn't the radiator temp about 20 degrees cooler than the engine, what about if it is raining hard, wouldn't the temperature differential between the engine and radiator now be much higher ?? I would think you would get different readings depending on where in the radiator you inserted the probe??

Here is a link to a fan controller that using the OEM temp sensor for monitoring the engine coolant temperature. As it is a high impedance pick up it does not affect the existing temp gauge or ECM temp input.

http://www.spal-usa.com/fans/automat...ts/FAN-PWM.pdf

Any thoughts or knowledge/experience here ?

Jim
Factory temp gauge sending unit won't readily adapt to use as a thermostat switch...

The factory sending unit is designed to add to remove resistance in the gauge circuit as the temp goes up and down...
Since there is a 'Sliding Scale' there, you have no set 'Open' or 'Close' point to start and stop a fan relay.

If you want to use that sender, you will have to use a set point voltage switch to power the fan relay, and that is a lot more complicated and failure prone than a thermostat/temp triggered switch you can buy for about $20...

The factory 'Idiot Light' switch IS an 'On/Off' type of temp controlled switch, but it's 'On' point is WAY too high for a common fan switch application...
The idiot light switches are normally set to close at 200 to 230 F., and you would want your fans to start at about 160 F.

If you do come up with something, I'd sure like to see it!
This is a pretty common issue, and if someone comes up with a simple solution, I'll be the first to recommend it!

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post #13 of 98 Old 04-07-2008, 08:59 AM
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Quote:
Originally Posted by John Strenk View Post
I wondered how much it would cost to get a threaded hole put into the radiator to mount a probe. Or if there is some radiator that will fit the CJ that already has a bong (?) in the radiator. Would the top tank or the bittom tank be better?

I agree with jscherb and monitoring my engine will be to late. It's suppose to be in a steady state and should not vary much.
Hey don't knock the radiator probes unless you've tried them. They are a very tight fit between the fins, I really don't think you have to worry about them coming loose. If you are paranoid, put a zip-tie through the radiator to secure the probe.

I was skeptical about the probes until I tried one, I really don't think this is something to worry about.

Jeff
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post #14 of 98 Old 04-07-2008, 09:27 AM
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This would probably be expensive but SAMCO, who make silicone hoses, will machine your hoses to your requirements. They might be able to put threaded hole in the hose going to the radiator.
http://www.sporthoses.com/about/manufacturing.html

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post #15 of 98 Old 04-07-2008, 10:25 AM Thread Starter
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Quote:
Originally Posted by JeepHammer View Post
Factory temp gauge sending unit won't readily adapt to use as a thermostat switch...

The factory sending unit is designed to add to remove resistance in the gauge circuit as the temp goes up and down...
Since there is a 'Sliding Scale' there, you have no set 'Open' or 'Close' point to start and stop a fan relay.

If you want to use that sender, you will have to use a set point voltage switch to power the fan relay, and that is a lot more complicated and failure prone than a thermostat/temp triggered switch you can buy for about $20...

The factory 'Idiot Light' switch IS an 'On/Off' type of temp controlled switch, but it's 'On' point is WAY too high for a common fan switch application...
The idiot light switches are normally set to close at 200 to 230 F., and you would want your fans to start at about 160 F.

If you do come up with something, I'd sure like to see it!
This is a pretty common issue, and if someone comes up with a simple solution, I'll be the first to recommend it!

Jeephammer:

The link I provided is a electric fan controller built to use the factory sending unit, it just attaches in parallel to the sending unit and uses the resistance to calculate the coolant temperature just as my TBI ECM uses the sending unit to calculate engine temperature.

It is made for late model fuel injected type senders, and as I have a junkyard GM TBI setup on my 304 with a GM sending unit installed where the CTO used to be that is what I was planning on using.

I guess the best possible way to control the fan is to add input from the VSS to the controller so you have a way of enabling the fan controller below a certain vehicle speed. I think I may be making this more complicated than it needs to be, but a discussion certainly does not hurt and maybe we will come up with something simple and practical.

Jim
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