Resting fan rpms
Thread Starter
|
Elder User
Joined: Sep 2016
Posts: 509
Likes: 0
Resting fan rpms
What's everyone's fan rpms at idle? Mine vary and lately I've experience a strange issue where fan immediately locks up and rages right after cold startup. Today it was running 2900 rpm. It settled to about 480-500 but I know I'm the past it's been like 300 or so at idle.
Mountain Pass
Joined: May 2015
Posts: 128
Likes: 8
From: Cottonwood, California
I have recently had the same thing happen.
Truck sat over the weekend and this morning when I started it the fan went to 2400 rpm for about 10 seconds and then slowly went down to about 600 rpm.
Outside temperature this morning was about 65 degrees.
I have had this occur several times before and always thought it might be related to humidity since where I live it is usually very dry (below 20% humidity) but when I have noticed this happen it has always been after a cold soak overnight and a fairly humid, cool morning.
Would be curious to hear other peoples experience with this issue/occurrence.
Truck sat over the weekend and this morning when I started it the fan went to 2400 rpm for about 10 seconds and then slowly went down to about 600 rpm.
Outside temperature this morning was about 65 degrees.
I have had this occur several times before and always thought it might be related to humidity since where I live it is usually very dry (below 20% humidity) but when I have noticed this happen it has always been after a cold soak overnight and a fairly humid, cool morning.
Would be curious to hear other peoples experience with this issue/occurrence.
Token Redneck
Joined: Jun 2007
Posts: 9,337
Likes: 346
From: Breckenridge, TX
Are you shutting down after idling when it's really hot or with the AC on max? The clutch can stay engaged for the next start up if it's fully locked on shutdown. Depending on how much fluid is still in the clutch reservoir on shut down it might just be throwing what's already in there up on the clutches until it clears out.
I'd say 480-500 is entirely normal for a 0%DC just driving around. The chart I put up in one of the other threads shows that to be a consistent fan speed across the entire engine RPM range.
I'd say 480-500 is entirely normal for a 0%DC just driving around. The chart I put up in one of the other threads shows that to be a consistent fan speed across the entire engine RPM range.
Mountain Pass
Joined: May 2015
Posts: 128
Likes: 8
From: Cottonwood, California
Hi texastech_diesel,
That might be it! It has been 105 degrees during the day and I have been running the air a lot.
I usually am good about shutting the air off before I shut the truck off so I'll bet the fan was just locked up due to the hot temperatures before shutdown.
Thanks for the insight, I really appreciate it.
That might be it! It has been 105 degrees during the day and I have been running the air a lot.
I usually am good about shutting the air off before I shut the truck off so I'll bet the fan was just locked up due to the hot temperatures before shutdown.
Thanks for the insight, I really appreciate it.
Thread Starter
|
Elder User
Joined: Sep 2016
Posts: 509
Likes: 0
also I thought I saw mention of a theory that the fan speed value shown on my torque app screen is the commanded value not the actual rpms but if that's true then the truck is commanding it to run 2900rpm so I don't think it's a commanded value.
Token Redneck
Joined: Jun 2007
Posts: 9,337
Likes: 346
From: Breckenridge, TX
I would disagree with that theory, the logs we've seen show three distinct steps of clutch engagement via the modulated ground signal to the valve in the clutch, and the rpm range of those bands varies by 200+ RPM. I don't think a viscous fan clutch could be calibrate well enough to respond to a specific rotational speed, other than "completely engaged".
5+ minutes is much longer than it should take to disengage on a cold start though. Checked all the other temp sensors to make sure they're in range? I don't recall my fan speed acting up with the TFT sensor went out (the trans sure acted up though), so unless you're still having AC problems this could be the beginning of the clutch failing. The valve leaking and filling the clutch reservoir with fluid when the engine is off, then it takes a couple minutes to spin out all the fluid at basically idle versus high speed engine operation.
5+ minutes is much longer than it should take to disengage on a cold start though. Checked all the other temp sensors to make sure they're in range? I don't recall my fan speed acting up with the TFT sensor went out (the trans sure acted up though), so unless you're still having AC problems this could be the beginning of the clutch failing. The valve leaking and filling the clutch reservoir with fluid when the engine is off, then it takes a couple minutes to spin out all the fluid at basically idle versus high speed engine operation.
Thread
Thread Starter
Forum
Replies
Last Post
dbuck50
1987 - 1996 F150 & Larger F-Series Trucks
11
Dec 4, 2003 03:26 PM
