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Viscous heater operating test?
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=77577		 Page 1 of 1
Author:  Flingwing [ Sat Nov 30, 2013 6:21 pm ]
Post subject:  Viscous heater operating test?
I'm trying to figure out if my viscous heater is working, it kicks on but the lines don't seem to get very hot. How long does it take for it to generate heat? And how hot do they get? Also, I am aware I need a new thermostat I'm not getting much over 140F.
Author:  thermorex [ Sat Nov 30, 2013 7:56 pm ]
Post subject:  Re: Viscous heater operating test?
It works similar to ac compressor. I think relay #10 is starting it (under the hood fuse box). Bottom line is that if you see the clutch engaging it is working. So if you take the relay out it should not work, once you put it back it should click (both relay and viscous clutch - but try this on a cold engine to make sure it will start). With a bad thermostat it should stay engaged longer. It should decouple once you get at about 1/4 hot on the gauge.

Many people from this forum, especially the southern folks, took the viscous relay out to save some fuel. It really doesn't make a big difference in engine heating, just helps getting the cabin warmer sooner when is cold.
Author:  papaindigo [ Sat Nov 30, 2013 9:00 pm ]
Post subject:  Re: Viscous heater operating test?
The viscous heater relay in the Power Distribution Center (black rectangular box just behind battery) is R36 otherwise thermorex is on point. I pulled that relay a couple of years ago and notice no difference in engine warm up or cabin heat down to 20F with a good tstat. As I recall the viscous will run until coolant temp gets to about 140-145F or a bit lower with a GDE tune and then shut off.

Personally I view it as a rather useless possible failure point especially in warmer climates or if you have access to electric power as using the block heater (ideally on a timer set to ca. 2 hrs before start up) does WAY better kick starting engine and cabin warm up. Translation - absent being able to use the block heater the viscous heater is maybe better than nothing getting a diesel engine to warm up a bit quicker but not much better than nothing.

Rather than being concerned about the viscous heater function you really need to spring for a functional tstat even if it's just the inline option which I personally don't favor much but if $s are real short it's an option for like $15 (tstat and clamp)
Author:  Flingwing [ Sun Dec 01, 2013 12:30 am ]
Post subject:  Re: Viscous heater operating test?
The thermostat will be replaced in the next few days. The heater is turning on (as desired), I was wondering how warm the coolant should be coming out of it from a cold start? I figured if it's suppose to help heat the cabin it would need to come out much warmer than what it is. It's only slightly warmer and it takes a while for it to do that. Does the silicon gel break down? Or would it have leaked out? I'm new to owning a diesel and just love my new liberty! I Just have a few questions about it and kinks to work out. I appreciate all the help!
Author:  papaindigo [ Sun Dec 01, 2013 7:34 am ]
Post subject:  Re: Viscous heater operating test?
I won't swear to be an expert on this but based on past posts the viscous functions as follows:
1. ECU or some such senses coolant temp below viscous heater operational threshold (see my note above) which
2. triggers relay R36 in Power Distribution Center which in turn engages the "clutch" on the viscous heater which
3. causes two or more friction discs inside the viscous to "rub" together which
4. transfers friction generated heat to the fluid (silicone IIRC) inside the viscous heater which
5. transfers heat the the engine coolant flowing thru the viscous heater housing to
6. the cabin heater core and then on to the engine block.
7. when ECU or some such senses coolant heat above the viscous operation threshold relay R36 is triggered to release the "clutch" on the viscous heater and it quits "working".

Important note - there is no "valve" on the cabin heater core so engine coolant is constantly circulating past the viscous, cabin heater core, and back to the block. Cabin heat level is controlled by a "blend" door. The point being that if your cabin heat is not working properly AND you have a good tstat then both cabin heater core hoses should be essentially the same temperature. A colder return line suggests a partially or fully clogged cabin heater core. Equal line temp but poor heater performance suggests malfunction of the blend door system not to be confused with the separate system that activates the doors that direct air flow to the various vent combinations.

As long as the all the above events that need to "happen" for the viscous to work it will work. As far as I know the silicone fluid cannot break down but whether it's possible to leak out I don't know although if it did I suspect there would be issues with the friction discs and then the viscous bearing. As noted the viscous does not produce much heat on it's own and stops producing heat well before engine operating temp. In a really cold situation with a really bad tstat I would not expect cabin heat to be "hot" rather it would be "warmish".

FYI the only viscous failure I've seen on the forum is discussed at viewtopic.php?f=5&t=60567
Author:  flman [ Sun Dec 01, 2013 7:08 pm ]
Post subject:  Re: Viscous heater operating test?
Per GDE

Operates under the following conditions
RPM < 2400
Coolant < 131 Deg
OD Ambient < 44.6 Deg
Pedal < 60%
Author:  DOC4444 [ Sun Dec 01, 2013 11:27 pm ]
Post subject:  Re: Viscous heater operating test?
If you have a "failing" thermostat, you can tell by the fact that the temp gauge never gets close to vertical. Unless you have a GDE ECU with a lowered VH shutoff point, it will never shut off. This lowers your mileage by at least 3 MGP. Pull the VH relay until you get a GDE ECU and get around to replacing the thermostat.

DOC
Author:  flman [ Mon Dec 02, 2013 7:09 pm ]
Post subject:  Re: Viscous heater operating test?
DOC4444 wrote:
If you have a "failing" thermostat, you can tell by the fact that the temp gauge never gets close to vertical. Unless you have a GDE ECU with a lowered VH shutoff point, it will never shut off. This lowers your mileage by at least 3 MGP. Pull the VH relay until you get a GDE ECU and get around to replacing the thermostat.

DOC


I am not sure those parameters are for stock or the GDE tuned CRD? I do not recall his tune modifies VH operation?
Author:  DOC4444 [ Mon Dec 02, 2013 10:43 pm ]
Post subject:  Re: Viscous heater operating test?
GDE used to lower the VH shutoff point. Not sure what they are doing lately. However, they can set it to whatever temp you prefer. I believe mine is set to shut off at 120 deg F, but Keith would probably have a record of the settings.

DOC
Author:  flman [ Tue Dec 03, 2013 8:23 am ]
Post subject:  Re: Viscous heater operating test?
DOC4444 wrote:
GDE used to lower the VH shutoff point. Not sure what they are doing lately. However, they can set it to whatever temp you prefer. I believe mine is set to shut off at 120 deg F, but Keith would probably have a record of the settings.

DOC


Well, thanks for the info. Do you know what stock specs are?
Author:  dirtmover [ Tue Dec 03, 2013 12:50 pm ]
Post subject:  Re: Viscous heater operating test?
It's very noticeable when it cuts out and happens reliably at almost exactly the same spot every morning a few minutes into my commute. It's got to be working because the energy dissipated by that sort of drag must be going somewhere.

Now, my journey home is not so consistent as there are more variables - traffic lights, traffic density, acceleration, deceleration - so the cut out is a lot easier to miss.
Author:  jrsavoie [ Sun Jan 17, 2021 4:17 pm ]
Post subject:  Re: Viscous heater operating test?
Does the viscous heater come on immediately at startup?

I have a chirping sound coming from that area.

The VH clutch did not engage on startup.
Author:  CATCRD [ Thu Jan 21, 2021 1:05 am ]
Post subject:  Re: Viscous heater operating test?
jrsavoie wrote:
Does the viscous heater come on immediately at startup?

I have a chirping sound coming from that area.

The VH clutch did not engage on startup.


If the coolant and ambient temperatures are cold enough it will come on with about a five second delay after engine start.
Author:  jrsavoie [ Thu Jan 21, 2021 7:36 am ]
Post subject:  Re: Viscous heater operating test?
CATCRD wrote:
jrsavoie wrote:
Does the viscous heater come on immediately at startup?

I have a chirping sound coming from that area.

The VH clutch did not engage on startup.


If the coolant and ambient temperatures are cold enough it will come on with about a five second delay after engine start.


Thank you.

I should have noted the temperature is about 30 F and the engine was cold.

We let it run for several minutes and the heater clutch never kicked in.
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