Surprising difference with Viscous heater disabled...

dgeist · **Posted:** Wed Mar 23, 2011 4:12 pm

So, I'd held off on the Viscous heater relay pull until yesterday because I thought, "Hey, how bad a thing could it be? It'll shut off when it's warm and I won't need to worry." Well after the 3rd day in a row with temps in the 70s and still noticing it's on, and my milage still hovering around 20 with mixed conservative driving I finally got fed up. Something I hadn't considered heavily is that it's triggered off operating temp, not ambient, so if you are waiting on an aftermarket t-stat system like I am, you're probably hovering around 160 degrees and are ALWAYS having the computer tell the heater to stay on.

Well, after about 20 miles (and half way down on the tank already), my EVIC-reported economy jumped by 3MPG.... again, in 20 miles. That's pretty huge if you factor in that it's an average with 10 gallons of crappy mileage to overcome. I shudder to think what it will be when I hit reset on the way home and start recalculating...but we'll see

Anyway, just thought I'd share. if you haven't done the viscous heater relay pull and you have a bad/going thermostat, you're literally blowing the money out the tailpipe....like I have been for a while.

Viva la aftermarket tinkerers :wink:

Dan

mvoss15 · **Posted:** Wed Mar 23, 2011 4:41 pm

Question - how does one determine if their viscous heater is running or not? I haven't been able to tell, but, would be all for an increase in MPG if mine has been running and I can disable it! My thermostat seems to be showing early signs of failure (running about 2 ticks left of 12:00).

dgeist · **Posted:** Wed Mar 23, 2011 4:50 pm

I imagine some kind of test light across the leads on the relay would tell you if it's on or not, but here's a post from the GDE forums:
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Here are the revised settings for the viscous heater:

Air temp shut off threshold stock = 54 F, new setting is 44 F
Coolant temp shut off threshold stock = 162 F, new setting is 131 F

If either condition is met the viscous heater will not be turn on. There is a 10 F hysteresis for turning the VH back on. With these settings you would only have the heater on for maybe 2 months out of the year and then only for the first 2-3 minutes after a cold start. After the engine is warm it would take several hours to cool down enough in order to meet the on conditions again. These settings have been released with the tune since mid October.

The largest contributer was reducing the coolant temp by 30 F, this prevents the VH from running during the winter months during light load city driving. The engine can run between 140-165 F in the cold winter months. We did not notice much difference in cabin heat, still comfortable inside.
------------------------------------------------------------------

I personally question the "either condition" statement (not its intent, but its accuracy in practice). The temperature was easily over 54 degrees where I live, but unplugging the relay made an immediate perceivable difference in the load on the engine.

Dan

Squeeto · **Posted:** Wed Mar 23, 2011 5:20 pm

mvoss15 wrote:

Question - how does one determine if their viscous heater is running or not? I haven't been able to tell, but, would be all for an increase in MPG if mine has been running and I can disable it! My thermostat seems to be showing early signs of failure (running about 2 ticks left of 12:00).

The viscous heater is at the upper passenger side (U.S.A) of the belt. With cold coolant, the face of the pulley will spin and not spin, repeat.

Now how to find out if it is making heat?

papaindigo · **Posted:** Wed Mar 23, 2011 6:42 pm

X2 dgeist's comment. I don't believe the EVIC mpg reading but with the most recent GDE eco-tune upgrade it's been close for 2 in-town tanks in similar weather. On the current tank after the viscous heater was disabled it has jumped 2mpg or so. I'll be real interested in what I actually get with the next fillup when I hand calculate and correct for odometer error. Will report at that time but since I just retired it may take a few weeks, lack of daily commute has significantly reduced miles driven in town.

LibertyCRD · **Posted:** Wed Mar 23, 2011 6:45 pm

I experimented with pulling my viscous heater relay. I saw no difference in fuel economy, so I plugged it back in. To me, any minute loss in fuel economy you might realistically see is worth having heat in the cabin sooner on a 5 degree day outside.

The ONLY thing I've experimented with that has actually increased my mileage remains to be the GDE TCM tune.

ATXKJ · **Posted:** Wed Mar 23, 2011 7:39 pm

The GDE tunes turn off the heater - fairly quickly - don't remember how long - but within a minute or two - stock stays on for a while

ihavelotsoftoys · **Posted:** Thu Mar 24, 2011 11:30 pm

Using the viscous heater sparingly is one of the tricks the GDE tune does to get better fuel economy. They do a bunch of other things with the timing and removing one of the pre-injection pulses. Any of you guys that still haven't sprung for the money really should. Get the trans tune also. Our jeeps are junk without it. I was ready to dump mine cause it was such a POS. After the GDE tune (trans and engine) it was a totally new car. So much that I bought a second jeep for the wife. Now that we have one with and without the GDE tune it's easy to tell the difference. She is getting hers chipped next month.
My economy jumped from 19-20 to 22-23 with the tune. And that's in cold weather. Can't wait to see what happens when it warms up. As a side note, the tune seems to work fine with biodiesel. It's still too cold to go 100% bio, but it seems to be good with 50% so far. Quiet, smooth, and no noticable loss in power.
GDE, Get it!!!

JL Rockies · **Posted:** Fri Mar 25, 2011 12:28 am

ihavelotsoftoys wrote:

Using the viscous heater sparingly is one of the tricks the GDE tune does to get better fuel economy. They do a bunch of other things with the timing and removing one of the pre-injection pulses. Any of you guys that still haven't sprung for the money really should. Get the trans tune also. Our jeeps are junk without it. I was ready to dump mine cause it was such a POS. After the GDE tune (trans and engine) it was a totally new car. So much that I bought a second jeep for the wife. Now that we have one with and without the GDE tune it's easy to tell the difference. She is getting hers chipped next month.
My economy jumped from 19-20 to 22-23 with the tune. And that's in cold weather. Can't wait to see what happens when it warms up. As a side note, the tune seems to work fine with biodiesel. It's still too cold to go 100% bio, but it seems to be good with 50% so far. Quiet, smooth, and no noticable loss in power.
GDE, Get it!!!

So you're saying that GDE turned your Jeep into a car? Lame.

ihavelotsoftoys · **Posted:** Fri Mar 25, 2011 10:00 am

No, the GDE tune just properly spelled the name from JUNK to JEEP. The bio turns it into a car, makes it quiet and not smoke. The stuff just makes the engine run quieter. Kinda lame, but it cost's me $0.85/gal to make.
Overall I am happy with it now and will keep it running as long as I can. It's still young.

I just helped my friend change the camshaft on his Mark V Jetta tdi. The cam is a known problem, but his has 185K on the clock. A lot of work but nothing to be afraid of.

Surprising difference with Viscous heater disabled...

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