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Old 03-28-2018, 09:38 PM   #1
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Overheating Problems

Driving in my coach I noticed that every time a drove over a small hill I'd see a rise in my cooling Temperature by maybe 15 to 20 degrees. I thought that was odd because my Tacoma's Temperature stays pretty steady unless I start climbing steep hills and then I only see a slight rise.
I had the cooling system flushed and a new thermostat installed. Issue was still noted. So I took it to Freightliner to have the Fan Clutch checked out. Wouldn't you know they discovered there was no high-speed mode when diagnosed and the fan was leaking fluid (I didn't know fan clutches had fluid). They also noted there was dust and debris on 30% of the radiator (I have a rear radiator). So, $2000 later and I will take it for a short trip to see if the problem is cured.
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Old 03-29-2018, 12:04 AM   #2
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Quote:
Originally Posted by krudawg View Post
Driving in my coach I noticed that every time a drove over a small hill I'd see a rise in my cooling Temperature by maybe 15 to 20 degrees. I thought that was odd because my Tacoma's Temperature stays pretty steady unless I start climbing steep hills and then I only see a slight rise.
I had the cooling system flushed and a new thermostat installed. Issue was still noted. So I took it to Freightliner to have the Fan Clutch checked out. Wouldn't you know they discovered there was no high-speed mode when diagnosed and the fan was leaking fluid (I didn't know fan clutches had fluid). They also noted there was dust and debris on 30% of the radiator (I have a rear radiator). So, $2000 later and I will take it for a short trip to see if the problem is cured.
Krudawg,
Well, I have a question or two. First, about 98% of the rear radiator diesel coaches out there, don't have a fan clutch. I'm by far, no expert on all motor homes but, this is to my understanding that they don't have one. Now, side radiator coaches, that's a whole different story. As for fan clutches "leaking", well yes, they have what's called a "viscous" fluid in them. It's like a silicone.

Regular automotive fan clutches kind-a work in this manor. On many of them, you'll see a sort of small, about 1" or so in diameter, clock-wound spring. That spring is a temperature controlled spring. That spring is connected on the inside of the fan clutch, to a valve. The valve controls this "viscous" fluid. And the fluid is between a set of veins, much like a torque converter in a auto transmission.

When the spring heats up, as in being influenced by higher temps emitted from the air flowing through a radiator as the radiator heats up, that spring begins to actually coil up, in a tighter formation. When it does that, it moves the valve inside and, that controls the fluid which, makes the two sides of the internal veins, start to spin together and sort of lock up. Now, when that happens, the fan is now flowing way more air than normal. That intern, cools the radiator fins more, which cools the coolant more.

When the radiator is cooled down to a point, the spring on the fan clutch starts to unwind and, that relaxes the valve which, allows the fluid inside the fan clutch, to move freely and, that allows the fan to coast. When things heat back up, the whole process starts all over again. It's actually a bit more technical than that but, I don't know if you care or not, on how it works.

Sorry for the long drawn out explanation but, not sure you understood how things work. But, it still kind of amazes me that you have one in the first place. Again, no expert here. As for debris in the radiator fins, yep, radiators are calculated for 100% flow, both internally for fluid and, externally for air flow through the fins, for a given amount of cooling, for a given engine size. When either mode of cooling is impeded, be it the interior fluid flow, or the air flow through the fins, the cooling capacity get's reduced pretty quickly.

For us rear radiator diesel drivers, it's imperative that we keep those fins as clog-free as possible. A rear radiator coach, is by far, NOT THE BEST cooling system designed in the world. They do get the job done but, when things are not top notch, i.e. clogged fins or, clogged internal tubing, they suffer immensely.
Scott
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Old 03-29-2018, 08:32 AM   #3
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Quote:
Originally Posted by FIRE UP View Post
Krudawg,
Well, I have a question or two. First, about 98% of the rear radiator diesel coaches out there, don't have a fan clutch. I'm by far, no expert on all motor homes but, this is to my understanding that they don't have one. Now, side radiator coaches, that's a whole different story. As for fan clutches "leaking", well yes, they have what's called a "viscous" fluid in them. It's like a silicone.

Regular automotive fan clutches kind-a work in this manor. On many of them, you'll see a sort of small, about 1" or so in diameter, clock-wound spring. That spring is a temperature controlled spring. That spring is connected on the inside of the fan clutch, to a valve. The valve controls this "viscous" fluid. And the fluid is between a set of veins, much like a torque converter in a auto transmission.

When the spring heats up, as in being influenced by higher temps emitted from the air flowing through a radiator as the radiator heats up, that spring begins to actually coil up, in a tighter formation. When it does that, it moves the valve inside and, that controls the fluid which, makes the two sides of the internal veins, start to spin together and sort of lock up. Now, when that happens, the fan is now flowing way more air than normal. That intern, cools the radiator fins more, which cools the coolant more.

When the radiator is cooled down to a point, the spring on the fan clutch starts to unwind and, that relaxes the valve which, allows the fluid inside the fan clutch, to move freely and, that allows the fan to coast. When things heat back up, the whole process starts all over again. It's actually a bit more technical than that but, I don't know if you care or not, on how it works.

Sorry for the long drawn out explanation but, not sure you understood how things work. But, it still kind of amazes me that you have one in the first place. Again, no expert here. As for debris in the radiator fins, yep, radiators are calculated for 100% flow, both internally for fluid and, externally for air flow through the fins, for a given amount of cooling, for a given engine size. When either mode of cooling is impeded, be it the interior fluid flow, or the air flow through the fins, the cooling capacity get's reduced pretty quickly.

For us rear radiator diesel drivers, it's imperative that we keep those fins as clog-free as possible. A rear radiator coach, is by far, NOT THE BEST cooling system designed in the world. They do get the job done but, when things are not top notch, i.e. clogged fins or, clogged internal tubing, they suffer immensely.
Scott
Fireup
Thanks for the excellent description of the clutching mechanism on these fans!
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Old 03-29-2018, 08:58 AM   #4
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Just a refinement on your usual excellent post, FireUp. A fan clutch is definitely fitted on the very common Cummins 6.7 ISB motor and Freightliner chassis combination with rear radiator. I am the proud owner of this combo and a past victim of fan clutch failure. From what I've read the fan clutch is one of the more common expensive failures on this combination, marring an otherwise very good reliable service. Freightliner specs and buys the fan clutch from Hudson. It has a control unit that gets several electronic bits of information and decides how fast it should be turning. I don't know the exact failure mode, but what happens is it simply stops turning. It will happen, and then come back and run normally on a re-start sometimes, but not always. Mine gave it up around 45,000 miles. It has behaved perfectly for another 10k, but I remain watchful and now keep my engine temperature displayed on the dash. A few poor souls have suffered a 2nd failure within 10-15k. Of course, there must be literally thousands of people with high mileage who have never had this problem. The internet is a 'problem amplifier' as we know. Two other points of interest for our OP, apparently a knowledgeable shop can fit something called a 'Guard Dog' which will run the fan at high speed if the control system fails. This will cost mileage but will get you home. I've also read that there is a 'side of the road' wiring change that accomplishes the same thing. I want to learn more about both of these short term fixes, so I hope someone more knowledgeable and experienced chimes in.
I have no idea whether other engine-frame combinations have a fan clutch, and whether they might have this same Hudson unit. The only failures I've read about are invariably the Cummins ISB-Freightliner combo.

Hoping this is of some help!
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Old 03-29-2018, 09:09 AM   #5
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Quote:
Originally Posted by FIRE UP View Post
Krudawg,
Well, I have a question or two. First, about 98% of the rear radiator diesel coaches out there, don't have a fan clutch. I'm by far, no expert on all motor homes but, this is to my understanding that they don't have one. Now, side radiator coaches, that's a whole different story. As for fan clutches "leaking", well yes, they have what's called a "viscous" fluid in them. It's like a silicone.

Regular automotive fan clutches kind-a work in this manor. On many of them, you'll see a sort of small, about 1" or so in diameter, clock-wound spring. That spring is a temperature controlled spring. That spring is connected on the inside of the fan clutch, to a valve. The valve controls this "viscous" fluid. And the fluid is between a set of veins, much like a torque converter in a auto transmission.

When the spring heats up, as in being influenced by higher temps emitted from the air flowing through a radiator as the radiator heats up, that spring begins to actually coil up, in a tighter formation. When it does that, it moves the valve inside and, that controls the fluid which, makes the two sides of the internal veins, start to spin together and sort of lock up. Now, when that happens, the fan is now flowing way more air than normal. That intern, cools the radiator fins more, which cools the coolant more.

When the radiator is cooled down to a point, the spring on the fan clutch starts to unwind and, that relaxes the valve which, allows the fluid inside the fan clutch, to move freely and, that allows the fan to coast. When things heat back up, the whole process starts all over again. It's actually a bit more technical than that but, I don't know if you care or not, on how it works.

Sorry for the long drawn out explanation but, not sure you understood how things work. But, it still kind of amazes me that you have one in the first place. Again, no expert here. As for debris in the radiator fins, yep, radiators are calculated for 100% flow, both internally for fluid and, externally for air flow through the fins, for a given amount of cooling, for a given engine size. When either mode of cooling is impeded, be it the interior fluid flow, or the air flow through the fins, the cooling capacity get's reduced pretty quickly.

For us rear radiator diesel drivers, it's imperative that we keep those fins as clog-free as possible. A rear radiator coach, is by far, NOT THE BEST cooling system designed in the world. They do get the job done but, when things are not top notch, i.e. clogged fins or, clogged internal tubing, they suffer immensely.
Scott
Hmm. That doesn't seem to jive with what Freightliner told me. I do appreciate your very technical response. I'm going to look into that.
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Old 03-29-2018, 11:24 AM   #6
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Originally Posted by Dark Sky View Post
Just a refinement on your usual excellent post, FireUp. A fan clutch is definitely fitted on the very common Cummins 6.7 ISB motor and Freightliner chassis combination with rear radiator. I am the proud owner of this combo and a past victim of fan clutch failure. From what I've read the fan clutch is one of the more common expensive failures on this combination, marring an otherwise very good reliable service. Freightliner specs and buys the fan clutch from Hudson. It has a control unit that gets several electronic bits of information and decides how fast it should be turning. I don't know the exact failure mode, but what happens is it simply stops turning. It will happen, and then come back and run normally on a re-start sometimes, but not always. Mine gave it up around 45,000 miles. It has behaved perfectly for another 10k, but I remain watchful and now keep my engine temperature displayed on the dash. A few poor souls have suffered a 2nd failure within 10-15k. Of course, there must be literally thousands of people with high mileage who have never had this problem. The internet is a 'problem amplifier' as we know. Two other points of interest for our OP, apparently a knowledgeable shop can fit something called a 'Guard Dog' which will run the fan at high speed if the control system fails. This will cost mileage but will get you home. I've also read that there is a 'side of the road' wiring change that accomplishes the same thing. I want to learn more about both of these short term fixes, so I hope someone more knowledgeable and experienced chimes in.
I have no idea whether other engine-frame combinations have a fan clutch, and whether they might have this same Hudson unit. The only failures I've read about are invariably the Cummins ISB-Freightliner combo.

Hoping this is of some help!
Quote:
Originally Posted by krudawg View Post
Hmm. That doesn't seem to jive with what Freightliner told me. I do appreciate your very technical response. I'm going to look into that.

To both of you,
Well, as I stated, I'm surely no expert on this. I'm primarily used to dealing with or, seeing CAT equipped coaches with either versions of the 3126 or, the C-7 and C-9. None of those have fan clutches. So, for Freightliner and or Cummins to spec out a fan clutch, is just news to me, especially on a rear radiator. And, I'm wondering, are your Cummins/Freightliner equipped coaches setup the same way ours are with the CAC in front of the Radiator?

If so, and a fan clutch is used, then the CAC is not getting as much air as what we are getting with a constant drive fan. I thought many times of installing a fan clutch on ours. It's possible with the right components, it's been done and documented. But, as some pointed out back then, the gains in what little horse power and less noise levels, might surely compromise the less cooling effects for the CAC and radiator by not having the constant air flow.

All of this I'm just surmising here. I'm not an engineer, just trying to logically think things out.
Scott
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Old 03-29-2018, 08:49 PM   #7
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I am not an engineer but I thought the use of clutch fans was for use in a front facing motor where the speed of the vehicle forces air in to and through the radiator thus eliminating the need of the fan. I also have a rear rad and a direct drive fan. They must have some thinking behind the clutch.
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