HOWTO: manually engage coolant GPs MK4 VE TDI

robnitro

Veteran Member
Joined
Jan 19, 2004
Location
NYC area, NY
TDI
2001 Jetta TDI GLS silver
Hi,
The coolant GP's are a mystery, they only seem to come on when it is freezing cold, below 20F in my past experience.

I decided to write up the basics on how I was able to manually control the coolant GPs (only on manual trans mk4) after being asked by a member. Here is a crude photo writeup of how it works for those electrically handy, it is not a hard procedure. If you aren't sure of how to set this up, please don't try it. I'm surprised no tuners have found how to shift the coolant GP's to come on at 40F for example. It's supposedly based on coolant temp AND IAT temp. Confusing right?!

I have this setup on my car for about a year and a half, IIRC.

Summary:
-Relay 100 does 2 of the 3 GPs, 53 does the other. I measured about 15-20 amps PER coolant GP in the past. So you can figure 200-250 watts approx PER coolant GP.
They are fed 12v steady when Ignition is on. However, the ecu controls them by switching GND to the other side of the coil.
I recommend not putting both relays on, I think the load may be too much. (I ended up switching the 3rd GP on/off with a NC relay energized by tapping off the GP harness- so if the GPs are on, the 3rd coolant GP will not have power.)

The optional goodies:
-You can tap off the output pin to have an indicator light inside the car. Be sure to run a 1 or 1/2 amp fuse inline.

-You can wire up a simple thermostat (put it somewhere to sense heat of engine) in series with the switch to GND in order to automatically switch off the coolant GP's when warmed up.

An idea that I never got to play with:
Use an extra defroster switch (that has the timer inside it) to turn the coolant GP's on, instead of rely on external thermostat switch.



 
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dremd

Veteran Member
Joined
May 31, 2007
Location
South Louisiana
TDI
06 sprinter. 03 jetta wagon premium with 6 speed ALH swap, 14 JSW
Awesome, thanks, I think I will be adding some control to my coolant glo plugs on my new dub.
 

robnitro

Veteran Member
Joined
Jan 19, 2004
Location
NYC area, NY
TDI
2001 Jetta TDI GLS silver
Your welcome! It does really help speed up heat in the cabin, the coolant GP's are right where the heater core gets its coolant flow from.

Let me know if you come up with a better way to do it. The thermostat thing is kind of a pain. When it is really cold out and I am driving highway, it sometimes takes forever to switch off even if the engine is almost fully hot.

I don't like the variability of it, as it is not really measuring the exact coolant temperature, but it's better than nothing, Lol.
 

dremd

Veteran Member
Joined
May 31, 2007
Location
South Louisiana
TDI
06 sprinter. 03 jetta wagon premium with 6 speed ALH swap, 14 JSW
I think I'll switch mine with FIS control, but then again, a defroster switch seems great and easy.
 

robnitro

Veteran Member
Joined
Jan 19, 2004
Location
NYC area, NY
TDI
2001 Jetta TDI GLS silver
Thanks, I didnt see that thread. I knew IAT had something to do with it when I modded my IAT to read low the cgps would come on.

How can Fis do this? Can it switch relays on/off?
 

robnitro

Veteran Member
Joined
Jan 19, 2004
Location
NYC area, NY
TDI
2001 Jetta TDI GLS silver
Cool, fis requires a display in cluster though? I have the stock basic one, no display just icons.

Here's the schematic/wiring diagram of the defroster switch.
We can use it to switch ground to the relay(s) but it may be difficult because the relay contacts also power the indicator light, as the ground for the defrosters are connected to the heaters. So a simple relay would work too.. energize that relay, which contacts pull in ground onto the coolant GP's.

With a relay energized by this, to feed gnd to coolant gp 100/53 relays.
T7/2 connects to ground.
T7/6 is 12v feed to the relay we would use, other side of relay to GND.
12v feed T7/1 and T7/5, one is for the switch itself, one is feed that runs to the output.
T7/1 also can use the dimmer illumination line.



If I can find one cheap, I would do it and get rid of the crappy thermostat.



 
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TDIJetta99

Top Post Dawg
Joined
May 17, 2005
Location
Port Jervis, New York, USA
TDI
03... Faster than yours =]
Lol, I took mine out along with both relays and some wiring.. Mine gets up to 170 degrees on my short drive to work even when it's 10 degrees out..

If it takes more than 5-8 miles of highway driving to reach operating temperature, you have something wrong with your car..
 

sailor15015

Member
Joined
Jul 1, 2008
Location
Norman, OK
TDI
None yet.
So I tried this mod last night. I hooked up my vagcom and set it to group 16 so I could monitor the alternator load. I put my hand on top of relay 100 and I could feel the relay click and engage when I grounded the wire. The only problem is that I saw no corresponding drop in voltage or any rise in alternator load. It stayed at 29% before and after the relay was engaged. Could this be an indicator that my coolant gp's are burned out? Is there a fuse somewhere I need to check? Any help is greatly appreciated. I want to reduce warmup times before the cooler weather is here, for the girlfiend's sake. :)
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2005 BEW Wagon
Yup, there's a fuse for the coolant plugs... it's one of the big "strip of metal" ones in the fuse block that's on top of the battery (owners manual or a quick search will help you track down which one, although it will be very very obvious if it's blown).

If your fuse is fine next step is to pull the connector off the tops of the three plugs and check 'em with a test lamp or (better yet) ohmmeter.... they should be a fraction of an ohm.
 
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