Fan Clutch - Idle questions
10-22-2015, 07:18 PM
#1
Senior Member
Thread Starter
Fan Clutch - Idle questions
I'm somewhat new still to theory and operation. 
I have an issue with my truck where it idles more than "normal". Upon startup, it idles so fast, it actually squeals the serpentine belt. I had some questions about the fan clutch operation.
The truck seems to idle erratically. When standing in front of the open hood today, I noticed it was doing it exactly at the same time the fan sped up. I was having an overheating problem before, so put in a new severe duty fan clutch thinking that would help. (the overheating problem is fixed, it ended up being a bad head gasket). Today I replaced the IAC valve thinking it was the cause of the high idle speed. When disconnecting the valve before the replacement, the truck idled perfectly normal. After the replacement of the IAC, this is when the increasing idle speed in park started happening.
Does the engine idle faster to increase the speed of the fan when the clutch disengages?
I thought when the clutch was engaged, the fan did not spin at all, then when it released, the fan started spinning. My fan has always spun, but at certain times it increases its speed tremendously. Which is correct?
Maybe I just don't understand the sound when the fan starts increasing it's speed, vs higher engine idle. It literally sounds like a jet engine is getting ready to go full thrust.
This is a 1989 5.8l F150 XLT Lariat. If this is normal operation (I don't have a tach) then I'm fine with it, I just wanted to make sure I wasn't laboring the engine too much, or something is stuck and it will continually increase rpm until disaster strikes. The truck runs absolutely wonderfully otherwise, it's just this higher idle issue I'd like to get to the bottom of.
-Pat
I have an issue with my truck where it idles more than "normal". Upon startup, it idles so fast, it actually squeals the serpentine belt. I had some questions about the fan clutch operation.
The truck seems to idle erratically. When standing in front of the open hood today, I noticed it was doing it exactly at the same time the fan sped up. I was having an overheating problem before, so put in a new severe duty fan clutch thinking that would help. (the overheating problem is fixed, it ended up being a bad head gasket). Today I replaced the IAC valve thinking it was the cause of the high idle speed. When disconnecting the valve before the replacement, the truck idled perfectly normal. After the replacement of the IAC, this is when the increasing idle speed in park started happening.
Does the engine idle faster to increase the speed of the fan when the clutch disengages?
I thought when the clutch was engaged, the fan did not spin at all, then when it released, the fan started spinning. My fan has always spun, but at certain times it increases its speed tremendously. Which is correct?
Maybe I just don't understand the sound when the fan starts increasing it's speed, vs higher engine idle. It literally sounds like a jet engine is getting ready to go full thrust.
This is a 1989 5.8l F150 XLT Lariat. If this is normal operation (I don't have a tach) then I'm fine with it, I just wanted to make sure I wasn't laboring the engine too much, or something is stuck and it will continually increase rpm until disaster strikes. The truck runs absolutely wonderfully otherwise, it's just this higher idle issue I'd like to get to the bottom of.
-Pat
10-22-2015, 08:13 PM
#2
When the sensor on the fan is getting hot (sitting still, no airflow) the clutch engages and makes the fan operate at full speed. As it cools (driving, air flow) the clutch disengages and lets the fan freewheel a bit.
Having a clutch in there also lets the engine rev and it'll pull the clutch up to speed in a bit without the fan slowing down the revving up process quite so much.
The idle air control is run by the computer - it's just a solenoid that opens an air valve to bypass the closed throttle plates, which allows the computer to accurately control engine idle speed.
The fan can sound a bit like a jet engine, yes, but your idle speed should be pretty constant - fast idle until the engine warms up then normal idle speed after that.
An erratic idle is more likely connected to the IAC operation, the computer controlling it, or the sensor (engine temp. sensor) (that's sensor, not sender) that tells the computer whether the engine is warmed up or still cold.
Having a clutch in there also lets the engine rev and it'll pull the clutch up to speed in a bit without the fan slowing down the revving up process quite so much.
The idle air control is run by the computer - it's just a solenoid that opens an air valve to bypass the closed throttle plates, which allows the computer to accurately control engine idle speed.
The fan can sound a bit like a jet engine, yes, but your idle speed should be pretty constant - fast idle until the engine warms up then normal idle speed after that.
An erratic idle is more likely connected to the IAC operation, the computer controlling it, or the sensor (engine temp. sensor) (that's sensor, not sender) that tells the computer whether the engine is warmed up or still cold.
10-23-2015, 09:22 AM
#3
1994 F150 XLT 5.8L 2wd
I also replied to your original thread
The fan should spin constantly, to test the clutch you can spin blade by hand, it should move a little then stop, usually less than a 1/4 turn.
From what I've read in both threads this sounds normal, which is one of the key reasons I did the e-fan swap. Now I can barely here the engine running and on one or two occasions, the first week after the swap, I tried to restart the truck thinking it wasn't running and pissed my starter off.
The fan should spin constantly, to test the clutch you can spin blade by hand, it should move a little then stop, usually less than a 1/4 turn.
From what I've read in both threads this sounds normal, which is one of the key reasons I did the e-fan swap. Now I can barely here the engine running and on one or two occasions, the first week after the swap, I tried to restart the truck thinking it wasn't running and pissed my starter off.
10-23-2015, 09:52 AM
#4
Senior Member
Thread Starter
I'm finally going to use the truck for what it's intended for me. Tomorrow going out to Knoxville to a Pinball Auction. It's about 90 miles away (one way). I'm going to see how it runs out there.
I've done a little research on the Temperature Sensor, seems like it's somewhat easy to get to.
-Pat
I've done a little research on the Temperature Sensor, seems like it's somewhat easy to get to.
-Pat
10-23-2015, 05:19 PM
#5
Senior Member
There's no sensor on the fan clutch. There's a temp sensor for the computer and another one for the dash gauge. Nothing controls the fan clutch.
Normally, when the truck is first started (cold start) the engine idle will increase. The fan will also sound like a jet for 5 or 10 seconds then quiet down as the clutch starts to release. It will get loud again when the engine and clutch get warm and it starts to engage the fan. And so on and so forth to keep it at normal running temp. When the fan clutch is completely engaged that heavy fan does put quite the drag on the engine. The IAC will compensate to keep the idle rpm up where it should be. When you rev it up it'll be loud.
Normally, when the truck is first started (cold start) the engine idle will increase. The fan will also sound like a jet for 5 or 10 seconds then quiet down as the clutch starts to release. It will get loud again when the engine and clutch get warm and it starts to engage the fan. And so on and so forth to keep it at normal running temp. When the fan clutch is completely engaged that heavy fan does put quite the drag on the engine. The IAC will compensate to keep the idle rpm up where it should be. When you rev it up it'll be loud.
Last edited by Crownman; 10-23-2015 at 05:25 PM.
10-23-2015, 10:15 PM
#6
Senior Member
Thread Starter
I forgot to add some important information I just realized.
This is all information after the truck has been warmed up and driven for at least 30 mins.
After I drive off of the highway and pull into a parking spot, I will put the truck in park, and the erratic idle starts happening. It's literally like the throttle is actuating without me depressing the gas pedal at all. Shouldn't after the truck has been completely warmed up and driven, the truck doesn't need to do an "idle relearn"?
When I first replaced the IAC, I did disconnect the negative battery cable for about 30 mins, I then started the truck and left it in park to idle for about 20 minutes. During this entire time the idle was erratic, but I just thought it the computer was relearning after the new IAC was put in.
I then drove it, and after putting it in park to idle, the erratic idle continued. I then shut it off, drove home (another 30 mins, some highway speed). When putting it in park at home to shut it off, the erratic idle continued. I then pulled out my code reader, and as I was reading through the book the erratic idle was continuing as well. I then noticed that when the idle would increase after all of this, the fan would engage at the higher speed as well.
I thought maybe the temperature sensor (close to the throttle body, the little wire harness looking piece) is cheap and easy enough to replace.
I don't care how loud the fan is, I just want the truck to idle normally.
-Pat
This is all information after the truck has been warmed up and driven for at least 30 mins.
After I drive off of the highway and pull into a parking spot, I will put the truck in park, and the erratic idle starts happening. It's literally like the throttle is actuating without me depressing the gas pedal at all. Shouldn't after the truck has been completely warmed up and driven, the truck doesn't need to do an "idle relearn"?
When I first replaced the IAC, I did disconnect the negative battery cable for about 30 mins, I then started the truck and left it in park to idle for about 20 minutes. During this entire time the idle was erratic, but I just thought it the computer was relearning after the new IAC was put in.
I then drove it, and after putting it in park to idle, the erratic idle continued. I then shut it off, drove home (another 30 mins, some highway speed). When putting it in park at home to shut it off, the erratic idle continued. I then pulled out my code reader, and as I was reading through the book the erratic idle was continuing as well. I then noticed that when the idle would increase after all of this, the fan would engage at the higher speed as well.
I thought maybe the temperature sensor (close to the throttle body, the little wire harness looking piece) is cheap and easy enough to replace.
I don't care how loud the fan is, I just want the truck to idle normally.
-Pat
10-24-2015, 06:31 AM
#7
1994 F150 XLT 5.8L 2wd
Sounds like you should test the TPS, I had mine do the exact same thing a couple of months ago. Happened to have another TPS just laying around so it was a quick fix.
!!Pull your codes!! You should have something related to the TPS if that is your problem, also chris1 did a great write up on testing it, click on his name, statistics, then threads started by and it should be easy to find.
NOTE:
TPS IS A MOTORCRAFT ONLY PART, anything else will cause you nothing but grief.
!!Pull your codes!! You should have something related to the TPS if that is your problem, also chris1 did a great write up on testing it, click on his name, statistics, then threads started by and it should be easy to find.
NOTE:
TPS IS A MOTORCRAFT ONLY PART, anything else will cause you nothing but grief.
Trending Topics
10-24-2015, 02:55 PM
#8
Salvage Yard Pro
I forgot to add some important information I just realized.
This is all information after the truck has been warmed up and driven for at least 30 mins.
After I drive off of the highway and pull into a parking spot, I will put the truck in park, and the erratic idle starts happening. It's literally like the throttle is actuating without me depressing the gas pedal at all. Shouldn't after the truck has been completely warmed up and driven, the truck doesn't need to do an "idle relearn"?
When I first replaced the IAC, I did disconnect the negative battery cable for about 30 mins, I then started the truck and left it in park to idle for about 20 minutes. During this entire time the idle was erratic, but I just thought it the computer was relearning after the new IAC was put in.
I then drove it, and after putting it in park to idle, the erratic idle continued. I then shut it off, drove home (another 30 mins, some highway speed). When putting it in park at home to shut it off, the erratic idle continued. I then pulled out my code reader, and as I was reading through the book the erratic idle was continuing as well. I then noticed that when the idle would increase after all of this, the fan would engage at the higher speed as well.
I thought maybe the temperature sensor (close to the throttle body, the little wire harness looking piece) is cheap and easy enough to replace.
I don't care how loud the fan is, I just want the truck to idle normally.
-Pat
This is all information after the truck has been warmed up and driven for at least 30 mins.
After I drive off of the highway and pull into a parking spot, I will put the truck in park, and the erratic idle starts happening. It's literally like the throttle is actuating without me depressing the gas pedal at all. Shouldn't after the truck has been completely warmed up and driven, the truck doesn't need to do an "idle relearn"?
When I first replaced the IAC, I did disconnect the negative battery cable for about 30 mins, I then started the truck and left it in park to idle for about 20 minutes. During this entire time the idle was erratic, but I just thought it the computer was relearning after the new IAC was put in.
I then drove it, and after putting it in park to idle, the erratic idle continued. I then shut it off, drove home (another 30 mins, some highway speed). When putting it in park at home to shut it off, the erratic idle continued. I then pulled out my code reader, and as I was reading through the book the erratic idle was continuing as well. I then noticed that when the idle would increase after all of this, the fan would engage at the higher speed as well.
I thought maybe the temperature sensor (close to the throttle body, the little wire harness looking piece) is cheap and easy enough to replace.
I don't care how loud the fan is, I just want the truck to idle normally.
-Pat
Here are some test results I got from an issue of Car Craft (May 2000) All these tests were run on Flex-a-lite brand fans except for the factory 4 blade. To baseline things the first dyno run was no fan at all but did include an alternator.
No fan = 496hp
Electric = 494hp
Thermal clutch = 487hp
Nonthermal clutch = 485hp
HD thermal = 476hp
HP flex fan = 476hp
Stock 4 blade = 473hp
Low-profile flex = 466hp
One piece plastic flex = 460hp
OE replacement 6 blade = 449hp
Here is another Carnut.com link on a GM 350 dyno test for mechanical fan draw.
http://www.carnut.com/ramblin/dyno.html
Last edited by unit505; 10-24-2015 at 03:24 PM.
10-30-2015, 10:53 AM
#9
Senior Member
Thread Starter
What size socket to remove the sensor? Rockauto sells 4 different types for this pickup. I was going to remove mine, and verify the part # before ordering.
-Pat
-Pat
When the sensor on the fan is getting hot (sitting still, no airflow) the clutch engages and makes the fan operate at full speed. As it cools (driving, air flow) the clutch disengages and lets the fan freewheel a bit.
Having a clutch in there also lets the engine rev and it'll pull the clutch up to speed in a bit without the fan slowing down the revving up process quite so much.
The idle air control is run by the computer - it's just a solenoid that opens an air valve to bypass the closed throttle plates, which allows the computer to accurately control engine idle speed.
The fan can sound a bit like a jet engine, yes, but your idle speed should be pretty constant - fast idle until the engine warms up then normal idle speed after that.
An erratic idle is more likely connected to the IAC operation, the computer controlling it, or the sensor (engine temp. sensor) (that's sensor, not sender) that tells the computer whether the engine is warmed up or still cold.
Having a clutch in there also lets the engine rev and it'll pull the clutch up to speed in a bit without the fan slowing down the revving up process quite so much.
The idle air control is run by the computer - it's just a solenoid that opens an air valve to bypass the closed throttle plates, which allows the computer to accurately control engine idle speed.
The fan can sound a bit like a jet engine, yes, but your idle speed should be pretty constant - fast idle until the engine warms up then normal idle speed after that.
An erratic idle is more likely connected to the IAC operation, the computer controlling it, or the sensor (engine temp. sensor) (that's sensor, not sender) that tells the computer whether the engine is warmed up or still cold.
10-30-2015, 12:08 PM
#10
Senior Member
Thread Starter
Actually I think the sensor is ok. It's measuring at 54kohms on an ~50 degree day (F) out here. When warming up the engine it lowered to 3.5k to 5k as I was fumbling around trying to hit the sensor pins.
The voltage being read with the engine on is 4.7volts.
I can see what the difference is with the sensor connected and when it isn't. It seems to idle ok (this is still just by sound, as I do not have a tach yet) when the sensor is connected now compared to when it isn't.
One thing I did notice was as the engine was warming up it idle'd just fine, as smooth as silk (a bit elevated since it was cold, but not erratic at all). As soon as the fan started spinning faster, the engine almost died, then it revved up to a higher ldle, then became erratic as the fan was spinning. After doing my checks, the engine cooled off slightly, so when I turned it back on, it wasn't idling erraticly at all. It really only seems to do it as the fan is spinning faster (clutch).
I know about the electric fans, but my theory is, Ford didn't install electric fans at the factory, and one would have to assume that the new trucks off the assembly line didn't have this problem. There is a fix for this, and I'm going to find it!
I've lost the forum post in which the person describes exactly how to test all the sensors. Does the 4.7 volts sound alright with ignition on/engine running?
-Pat
The voltage being read with the engine on is 4.7volts.
I can see what the difference is with the sensor connected and when it isn't. It seems to idle ok (this is still just by sound, as I do not have a tach yet) when the sensor is connected now compared to when it isn't.
One thing I did notice was as the engine was warming up it idle'd just fine, as smooth as silk (a bit elevated since it was cold, but not erratic at all). As soon as the fan started spinning faster, the engine almost died, then it revved up to a higher ldle, then became erratic as the fan was spinning. After doing my checks, the engine cooled off slightly, so when I turned it back on, it wasn't idling erraticly at all. It really only seems to do it as the fan is spinning faster (clutch).
I know about the electric fans, but my theory is, Ford didn't install electric fans at the factory, and one would have to assume that the new trucks off the assembly line didn't have this problem. There is a fix for this, and I'm going to find it!
I've lost the forum post in which the person describes exactly how to test all the sensors. Does the 4.7 volts sound alright with ignition on/engine running?
-Pat