86 Golf Temp Sensors and thermostat

[One W/the truckers]

I have an 86 Golf 1.6 diesel NA that has been running great and recently my temp gauge maxed out and the red LED went on. No anti-freeze leaks and it only took 1/2 quart to fill it. I let it sit for several hours and then ran it at an idle and in a couple of minutes, the gauge maxed out and red LED came on. When the red LED comes on, the fan don't. Fan does work when A/C is turned on.

I am thinking a sensor problem. I've found at least 6 (what seem to be) temp sensors. One on the driver side of radiator (#1) -- 2 on the transmission end of block (a bigger one right into block (#2), a smaller one in heater outlet? (#3) -- 2 on the side of block right near the FI pump (a bigger one w/2 wires (#4) and a smaller one with one wire (#5) -- 1 on top of reservoir (#6). Can someone tell what all of these do?

Also, trying to remove the thermostat, I removed the lower bracket for the A/C compressor, took out the 2 10mm bolts for the thermostat housing, but can't get the housing off as it hits against the block where one of the A/C brackets bolts screw in. Has anyone else run into this problem and know what to do?

Little extra info -- new water pump and antifreeze (May 2012) Had car 7 years, same thermostat. All hoses replaced last year.

[steevz]

If I remember correctly there are 2 sensors. One on the coolant flange on the front on the head, should be going to your gauge. Another on the coolant flange on the side of the head, should be going to fan relay? Or maybe vice-vera.

[82vdub]

If you have an infrared thermometer, that can give indication of what actual coolant temps are, not just what a gauge reads.

Stevez, I believe you are incorrect

The sensor on the drivers side of the radiator is the radiator fan switch

The sensors on the drivers side flange on the head are what runs the dash gauge (I believe it's both sensors).

The sensors in the outlet flange of the upper radiator hose are the AC cutout switch.

The sensor in the coolant jug is to detect low level. If your gauge red light flashes, I believe that's low coolant.

I would check the connections of the wires on the drivers side coolant flange on the head. If you disconnect one of these wires, the gauge should go to cold. If the red light in the temp gauge is flashing, it should be low coolant. There is, of course, another possible issue. Your temperature gauge controller circuit relay box thingy (forget the actual name of it) could be going bad and causing the red light to flash, or bad connections at the fuse panel or at sensors, or sensors going bad.

[TylerDurden]

There seems to be some variation on location.

If you can post the colors of the wires, that might help.

[air-cooled or diesel]

sensor on bottom of radiator by trans controls fan. best to test w/a voltmeter first. although the level is the first thing i'd cover, is the wires/sensor at top of resevoir. low coolant/sensor reading will cause that/light to go on and full hot on dash.
i like new thermostats every few years, not the cheap kind ($5 no,nos) about $15.
i dont find a/c bracket in the way of water pump/thermostat opening, its power steering that is right there. i wouldnt remove an a/c bracket yet. do you have a picture of the area? if you dont have power steering remove 10mm bolts (really 6mmX1, 10mm bolt head.) if needed push thermostat housing up some (hand pressure) and angle out some to clear power steering mount on block. have a pan to get coolant which will come out right then. thermo needs to be taken out by hand too. maybe thermostat is blocking housing from coming down. push it up by hand and angle towards front and it should come apart. you'll need a new o-ring too. i also like new bolts and use some extra anti-seize on re-assembly which can be a pain to get thermo and o-ring lined up, kind of slides together clearing p/s mount on block. put some water in (measured for at least 50/50 mix so about a gallon i prefer distilled/and not the real cheap distilled kind like you can find at walmart use a better kind) so put some water in like at least 1/2 gal to make sure thermo housing is sealed.

[air-cooled or diesel]

1 thing is if you run a/c and fan kicks on does temp guage go down? although i wouldnt recommend as your overheating engine it can show you problem. temp guage will come down pretty quickly w/fan on. so run engine as it heats up run a/c if it still goes hot/light flashes on dash, first thing to check is sensor/connections on top of resevoir. bad connections to dash sensors can cause this too, 1 is on side of head should be 1 wire/1 is on front of head also 1 wire. you also have another bigger sensor on front of head (both are on the flange coolant connection) this sounds ok if a/c works and fan kicks on when a/c is turned on. check connections too. and the wire connections to sensor at bottom trans side of radiator too.
sounds like a bad sensor/wire connection to dash sensor(s) or sensor at top of jug(resevoir).

[One W/the truckers]

I have posted some pics at http://s1276.photobucket.com/albums/y477/3500Golf/

I believe the following to be true. (refer to pics) Please feel free to correct me.
#1 sensor (3 wires, red, gray w/black, brown w/white) on radiator controls the fan
#2 sensor (1 wire, light blue w/dark blue) bigger sensor on end of block is ??? Oil sensor
#3 sensor (1 wire, blue w/white) smaller sensor on end of block is temp gaugethis is not the temp gauge, had car at running temp, disconnected this and it had no effect on temp gauge
#4 sensor (2 wires, both brown w/blue) bigger sensor on side of block, shuts off A/C in case of overheating
#5 sensor (1 wire, dark blue w/yellow) smaller sensor on side of block is ???this is temp gauge, had car at running temp, disconnected it and it went to zero
#6 sensor (2 wires, brown, brown w/green) on reservoir is fluid level. Fluid level was ok. see later post

Where does glow plug circuit sense from? Are sensors #3 and #5 interchangeable?

As far as thermostat housing, the car does not have power steering and I had to remove the bracket to get to the (2) 6mm bolts, but still can't get housing off. Feels like plastic and am afraid of breaking it. The bracket bolts to engine block and bottom of a/c compresor.

Does anyone have a manual they want to sell?

[air-cooled or diesel]

#2 is oil sensor to head
3and 5 are dash water temp sensors glow plugs come from reading at #3 i think 3/5 should be same sensors.
looks like bracket you took off (pic#1) is a power steering bracket check belts there should be 2 belts coming off crank 1 bigger one to a/c compressor and water pump, 1 smaller belt on outside going to water pump and running over to power steering unit.
once you remove bracket jiggle thermo housing (or angle a little to clear unit)and should come free of mounting point on block(move toward front should move fairly easily and clear mount point).
water is going to come shooting down!

[air-cooled or diesel]

probably is thermo blocking housing from coming apart, a little jiggling and angle it some (not too hard) and it will all work it self out at once.
or find some way to push thermo up in like w/a small screwdriver. hope water is cold!

[One W/the truckers]

looks like bracket you took off (pic#1) is a power steering bracket check belts there should be 2 belts coming off crank 1 bigger one to a/c compressor and water pump, 1 smaller belt on outside going to water pump and running over to power steering unit.

Thank you for the information, it was very helpful. Is it possible that #3 sensor could be for glowplug and #5 for gauge or vice versa? I am going to swap them out and see if the problem changes.

added another pic of belts http://s1276.photobucket.com/albums/y477/3500Golf/

When the gauge maxed out and the red LED came on, there was very little pressure released from reservoir when I opened it. This makes me believe it is a sensor problem.

[air-cooled or diesel]

i still have original sensors, from 86 the correct ones are hard to find, gas ones i can find not the diesel ones. new sensors may help, also your engine ground can affect this. i like to run ground wires and check ground wires (around batt.)

[One W/the truckers]

My problem has been solved. I ohmed out the reservoir sensor and it was showing open. I connected it back, started the car and couple of minutes later, the gauge maxed out and the red LED came on. I disconnected and jumpered the two wires with a paper clip and the gauge settled back down and the red LED went out. Thank you very much for your help "air-cooled or diesel". Sorry, I mean everybody Will try to get a new reservoir sensor ASAP. replaced sensor and all is OK

See blue writing on earlier post for further info. I did swap out #3 and #5 sensors, will post results, but initial thoughts are they are the same. Will investigate further to see if #3 is for glow plugs. First thing I did was swap sensors and there was a slight difference (less than needle width) in temp gauge reading. Then leaving sensors swapped, I swapped the wires and the temp gauge went back to its original reading. The glow plugs have been working fine. So, I believe the sensors are interchangeable

Still haven't been able to get thermostat housing off.

Thanks again

[air-cooled or diesel]

glad to help, good luck.
you could buy a whole new resevoir, i dont think its too expensive, comes w/sensor.
the bracket you removed im sure isnt for a/c on mine its for power steering pump support. and the power steering is a pain in the a**. as you have to remove bracket to change oil and change belts.

[Fatmobile]

A low coolant situation wouldn't cause the gauge to peg.
Edit: It shouldn't cause the gauge to peg because it is connected to one leg of an op amp,.. and the temp sensor is connected to the other input leg. The gauge doesn't peg on any of my cars when the coolant is low.

Is there a steady stream of coolant entering the coolant resevoir?

A candy thermometer in the resevoir will give you something to compare the gauge too.

[TylerDurden]

I have posted some pics at http://s1276.photobucket.com/albums/y477/3500Golf/

I believe the following to be true. (refer to pics) Please feel free to correct me.
#1 sensor (3 wires, red, gray w/black, brown w/white) on radiator controls the fan
#2 sensor (1 wire, light blue w/dark blue) bigger sensor on end of block is ??? Oil sensor
#3 sensor (1 wire, blue w/white) smaller sensor on end of block is temp gaugethis is not the temp gauge, had car at running temp, disconnected this and it had no effect on temp gauge
#4 sensor (2 wires, both brown w/blue) bigger sensor on side of block, shuts off A/C in case of overheating
#5 sensor (1 wire, dark blue w/yellow) smaller sensor on side of block is ???this is temp gauge, had car at running temp, disconnected it and it went to zero
#6 sensor (2 wires, brown, brown w/green) on reservoir is fluid level. Fluid level was ok. see later post

Where does glow plug circuit sense from? Are sensors #3 and #5 interchangeable?

As far as thermostat housing, the car does not have power steering and I had to remove the bracket to get to the (2) 6mm bolts, but still can't get housing off. Feels like plastic and am afraid of breaking it. The bracket bolts to engine block and bottom of a/c compresor.

Does anyone have a manual they want to sell?

#3 is sensor for GP relay (Bentley, Current Diags., p. 40). I'd try attaching the gauge wire to that sensor (or a DMM), to see if it has the same resistive value.