Temp wiring on 85 IDI question

[JBG3]

I have probably a really simply answered question-

I moved an 85 1.6 into an 86 jetta body, and the 86 has a huge number of wiring problems, so I had to cut and splice most of the harness to make it work, and everything is almost correct. 

Couple of small issues remain related to the temp wiring.  The original 86 body had a fully loaded setup, with all kinds of features, so there was way more wiring, and I spliced in the parts of the simpler harness from the 85 donor car to make up the wrecked sections of the 86.

The issue that I am currently having is extremely low temp reading on the gauge inside.  It does move, but goes just to the bottom of the scale, and stays there.  Also, probably related, the fan runs constantly at all times.  I have installed a new thermostat that I pre-verified in boiling water first, and it is fresh coolant.  Im going through trying to make sure I have everything hooked up correctly.  My Bentley manual shows that a yellow/red wire goes to the temp sender and I have that connected to the sender on the engine side of the upper radiator hose.  Which one of these two temp senders is the one that goes to the gauge? and what is the purpose of the second sender?

I could not find mention in the wiring diagram of a blue and white wire going to any kind of coolant destination, so I might have the one on the end of the head mis installed, or the yellow/red installed at the wrong sender.  Can someone verify for me? 

here is a pic-

[steevz]

Pretty sure the one on the side of the head is coolant temp sensor and the one on the front of the head is for glow plugs temp sensor.

The sensor on the side of the head goes to the gauge in the cluster.

[JBG3]

Pretty sure the one on the side of the head is coolant temp sensor and the one on the front of the head is for glow plugs temp sensor.

The sensor on the side of the head goes to the gauge in the cluster.

You mean in relation to the picture?  Side being the left temp sensor?  If thats the case I have it correctly wired then.  I will check out the glow plug circuit on my wiring diagrams and see if I have that wire hooked up right as well. 

Maybe it is reading correct, but the cooling fan being on all the time is never allowing the temp to come up.  Im going to disconnect that and see what happens with the gauge

Thanks for the info!

[R.O.R-2.0]

Pretty sure the one on the side of the head is coolant temp sensor and the one on the front of the head is for glow plugs temp sensor.

The sensor on the side of the head goes to the gauge in the cluster.

You mean in relation to the picture?  Side being the left temp sensor?  If thats the case I have it correctly wired then.  I will check out the glow plug circuit on my wiring diagrams and see if I have that wire hooked up right as well. 

Maybe it is reading correct, but the cooling fan being on all the time is never allowing the temp to come up.  Im going to disconnect that and see what happens with the gauge

Thanks for the info!

i can put my temp selector on defrost, and make my rad fan run.. and my car still warms up fine..

[8v-of-fury]

Doesnt matter where those temp sensor wires hook up as long as they hook up to one of those flanges.

Both flanges leave the head so will read the same temperature.

[steevz]

You mean in relation to the picture?  Side being the left temp sensor?  If thats the case I have it correctly wired then.  I will check out the glow plug circuit on my wiring diagrams and see if I have that wire hooked up right as well. 

Maybe it is reading correct, but the cooling fan being on all the time is never allowing the temp to come up.  Im going to disconnect that and see what happens with the gauge

Thanks for the info!

No, I mean in relation to standing in front the engine. The glow plug sensor is usually on the head beside the glow plug buss bar.

Doesnt matter where those temp sensor wires hook up as long as they hook up to one of those flanges.

Both flanges leave the head so will read the same temperature.

This makes plenty of sense.


My rad fan never comes on and my car won't overheat. Maybe your gauge is just screwed up.. You should be able to tell if your engine is really hot with the hood up after taking for a spin.

[8v-of-fury]

My rad fan never comes on and my car won't overheat. Maybe your gauge is just screwed up.. You should be able to tell if your engine is really hot with the hood up after taking for a spin.

Well I mean in all reality, if the cooling system were top notch the fan should not have to come on much. Even coasting along in 1st gear (10kmh) with the temp gauge running warm, I can get the temp to drop quickly. I know for a fact my rad fan never comes on, I have it fully manual on relayed circuit of my own .

However, if the thermostat is not opened yet, it would not matter if the fan was on or not. As the coolant from the now cool radiator is not returning to the motor.

[Baron VonZeppelin]

...extremely low temp reading on the gauge inside.  It does move, but goes just to the bottom of the scale, and stays there.  Also, probably related, the fan runs constantly at all times.  I have installed a new thermostat that I pre-verified in boiling water first, and it is fresh coolant

Some of these clusters just have grown old.
One of my 89's gives real low coolant gauge readings (just barely comes off the bottom with 70*C Tstat - and lil over 1/4 with a 87*C Tstat.

And a bit high on fuel gauge.
As soon as it goes below 1/4 its on fumes.

I've adjusted to it.

If you can get the cluster from the 85, it will plug and play.
And maybe be more accurate.
85-87 and maybe part of 88, used same CE1 wiring etc...

You don't want to keep letting the fan run all the time.
Shortens the life span considerably.

Which temp rating Tstat did you use ?
You will also want to get and install the corresponding temp rated fan switch once you get the fan back on auto pilot. Its located in driver side of radiator - yeh you'll have to drain it again.

87*C Tstat takes a 92*C-99*C fan switch
80*C Tstat takes a 85*C-92*C fan switch
70*C Tstat takes a 75*C-82*C fan switch

[Mark(The Miser)UK]

If your rad fan is on all the time, then it is your big sensor on the rad that has fused closed, or in the process of rewiring, you have somehow by-passed it.

[rodpaslow]

I don't know about an 85, but on later cars (I have a 90 gasser with air con) the one on the side of the head at the back of the coolant flange is a shut off or stops the air conditioning from working if the car is too hot.  Years back I had an 86 diesel that had air and had the same thing.  My $.02 - usually the one at the front of the head is the one for the Gauge.  The 90 N/A diesel I currently drive has a newer style connector, but the temp sensor for the gauge is in the front of the head as well.

[Baron VonZeppelin]

Checked the two 85TD Jettas that i have here now -

Yellow w/Red stripe goes to sender at front (by injectors).
Blue w/ White stripe goes to sender on side (by tranny)

[Powjetta]

My 86 has the blue & white on the drivers side of the head and the yellow/brown to the front.  My car has AC and has a second sensor with green wires going to it.

[JBG3]

Ok, thanks everybody!

It seems like I have it wired correctly, although from what everyone is saying, if I had those two leads reversed, it wouldn't make a difference. 

It turns out that now its working properly, or at least better.  I found about 6 inches of corroded wire in the harness on the yellow and red wire over by the transmission plug.  I replaced this and now the temp gauge is coming up to just above the solid white into the normal range.

I'm using an 80c thermostat.

(Some back history on this 86 is that it was in some kind of accident on the driver side, and there was a pretty violent slash in the frame section right above the transmission.  So violent that it cut into some of the wiring, and I don't think the prior engine was the original engine or tranny for this car, looked to be from an mk1 actually.  So basically, the wiring was damaged by an accident, hacked when repaired and replacement engine put in, hacked again when a VO system was sloppily installed, hacked again when someone removed the vo system and tried to make performance upgrades, hacked again when the PO kid starting adding a sound system and leaving wires everywhere before he blew the engine, an finally I come along with a new wiring harness and another engine.   )

I'm surprised it actually runs at all honestly, I haven't moved into the cabin yet following the wiring.  The radiator, fan, relay, and temp switch I moved from my 85 where it was previously working, but that switch could be bad, it did sit for over a year.  I might direct control it with a switch like mentioned above.

[R.O.R-2.0]

i used a mk1 engine in my mk2, and i hooked the yellow/red stripe (wire to temp gauge) to the side of the head, the feed for the heater..