Skip navigation

Weird colored Coolant sensors

Post

Back to the top

Need help

Hi all,
I have a small(ish) issue with my coolant gauge that is acting weirdly.
Once it works thrice it doesn't…
So, before looking for a replacement, or a donor dash, I was looking to inspect that the sensors are fine.
Problem is, all the information I can get are talking about a blue and a black colored sensors, while mine has a gray and red ones (there is also a black one on the underside of the hose).

Which one should I inspect to find out if the problem is the sensor, the gauge, or else?

A place a pic for better clarify; engine is a 1.6 75hp, 2H code on a '91 Cabriolet.

20211005_173615.jpg

Post

Back to the top
Think they are switches for the warm up squence of the carbs etc. The sender for the gauage will have one wire attached via a spade connector

1983 Mars Red 1.8 Golf GTI
1987 Alpine White 1.8 Clipper Cabriolet

The trouble with doing nothing is that you never know when you are finished.

Post

Back to the top
There are red ones on AUTODOC for about £4
Search on eBay for VW temp sensor red / grey

Plenty to choose from

Post

Back to the top

Early-1800 said

Think they are switches for the warm up squence of the carbs etc. The sender for the gauage will have one wire attached via a spade connector

Like this I have just two sensors, one on the oil filter (I believe it's for the pressure), and one on the side of the head.

Post

Back to the top

jakethepeg007 said

There are red ones on AUTODOC for about £4
Search on eBay for VW temp sensor red / grey

Plenty to choose from

I know, there is also some discount there, but before ordering I'd like to know if they are still in good..

Post

Back to the top
Your coolant sensor is the black one, underneath the the flange.

BC658EF4-48E2-4CDA-9208-A47BDB5E6101.jpeg

Post

Back to the top

Steve1973 said

Your coolant sensor is the black one, underneath the the flange.

So, I can just disconnect that, and short the two plugs?
Or which one should I check?

Regards all

Post

Back to the top
Yea shorting the two pin in the black plug with a paper clip or piece of wire will make the gauge read fully hot. Don't do it for long though as it's not designed to work like that. Ideally you should use a resistor or variable resistor. As for your issues, what exactly is the gauge doing?

Post

Back to the top
The 90's Cabriolets have confusing monikers.  There is the Coolant Temp Sensor that the term CTS is used in two different contexts.  One is the CTS for the engine management, and one for the Coolant temp gauge.

The black sensors are always for Coolant temp gauge in the cluster.

The oil temp sender is black and single pin that is on the oil filter flange if you have center console gauge set.

On the 90's cabriolets, you take the black sender connection off the black sender, key off and out of the car, connect a 9V DC battery to the connector Plus to the colored wire, and ground to the brown, and leave it there for about 3 minutes, the Gauge should be from 3/4 to full hot, and remain there, if it is less than 3/4 or that it goes back to Zero, then your Gauge is at fault.

I have owned 3 Cabriolets that the Water Temp gauge would register low, or be fine for a few minutes sometimes a day or three, then get lower, till it read zero.

What I have found over the years is that the water temp
gauge gets cold solder joints internally and they act up.
Starts out by reading low then goes to 0 turn the car off, wait 20 minutes and it starts working again.

Internally the Gauge has 3 external connections one ground, one power, and the center one is for the over temp flashy light.

If you remove the Cluster disassemble it from the cluster, then file the rivets off the face plate you will find that the thing is basically a Toaster.  A heated wire makes a bi-metallic spring expand or contract to move the needle.  The Posts for the things get hotter than a fire cracker, and melt the solder causing cold solder joints in the gauge.

Screen Shot 2021-10-06 at 8.50.56 AM.png

Cold Solder joints in Yellow that have to be re-heated, de-soldered, cleaned and resoldered
Screen Shot 2021-10-06 at 8.51.10 AM.png

In the archive section I have a How-to on how to repair the gauge set.
 Repairing your Flaky Water Temp Gauge | Volkswagen Owners Club Forum


What do Divorces, Great Coffee, and Car Electrics all have in common?

They all start with GOOD Grounds.

Where are my DIY Links?

Post

Back to the top

Steve1973 said

As for your issues, what exactly is the gauge doing?

Most of the times the needle is not even moving, just once in a while.

Will try a quick short just to see if it works

Post

Back to the top

Briano1234 said

On the 90's cabriolets, you take the black sender connection off the black sender, key off and out of the car, connect a 9V DC battery to the connector Plus to the colored wire, and ground to the brown, and leave it there for about 3 minutes, the Gauge should be from 3/4 to full hot, and remain there, if it is less than 3/4 or that it goes back to Zero, then your Gauge is at fault.

I'll try this check also, regarding the gauge, I won't have that much time fixing it, as it is my DD. I'll look for a donor or full dash.

Post

Back to the top
Sometimes just removing the connector from the instrument panel and giving the contacts a good clean can work miracles. Briano has some good info this.

Post

Back to the top
How long have you had the car? Did it used to work ok?

Does it have a thermostat fitted? Does the top hose get so hot you can't hold it?

1983 Mars Red 1.8 Golf GTI
1987 Alpine White 1.8 Clipper Cabriolet

The trouble with doing nothing is that you never know when you are finished.

Post

Back to the top

Early-1800 said

How long have you had the car? Did it used to work ok?

Does it have a thermostat fitted? Does the top hose get so hot you can't hold it?

I've had the car since 2013/4 but never really used for long trips or more than a couple of days in a row (due to work and all)

Since this Friday I drive it for 100km/day and only once the needle started moving slightly, but it's also been a he'll of a weather (just finished raining since).

It have a thermostat, I believe in the radiator, and as soon as I stopped her, I tried to hold the top hose, and it was warm as I expect it to be.

Steve1973 said

Sometimes just removing the connector from the instrument panel and giving the contacts a good clean can work miracles. Briano has some good info this.

As I said, I have no time to remove half car given my total lack of knowledge on ability on dismantling it…

Post

Back to the top
The Thermostat is on the bottom side of the water pump, if you have power steering then you have to move that out of your way to get to the bolts.

I have a how-do-i-do that in the archive section for water pump replacement, but the first half is the removal of all things including the t-stat.
Get a new o-ring for the t-stat. If you can source a metal cover for it then you are better off.  Why, because plastic parts have a negative air displacement ratio.  (they sux).

How-to-flush-your radiator | Volkswagen Owners Club Forum

to remove the cluster you don't have to remove the steering wheel
Disconnect the Battery, why?  Because if yoou don't then you will short the wire for the flasher, then blow the fuse f19.

It takes me about 40 minutes to remove the bezel, switches and the cluster prior to taking the cluster out.  You will want to remove teh 2 screws on the heater controls and allow that to float so you don't break the tabs getting to the speedo cable.

You can remove the side vent to get to the speedo from the side.
I have a how to on that as well.

What do Divorces, Great Coffee, and Car Electrics all have in common?

They all start with GOOD Grounds.

Where are my DIY Links?

Post

Back to the top
Briano1234 I had in mind to replace the water pump, as the bearing inside is starting to leave me (friend checked with one of those mechanic specific stethoscope).
But right now I'll need to have the thermostat stay where it is.

BTW, what is that used for? Fan?

Post

Back to the top

FatalPuppet said

Briano1234 I had in mind to replace the water pump, as the bearing inside is starting to leave me (friend checked with one of those mechanic specific stethoscope).
But right now I'll need to have the thermostat stay where it is.

BTW, what is that used for? Fan?
Think you are mixing up the radiator fan switch which is screwed into the side of the radiator to turn on the fan when it gets hot and the thermostat which is in the water pump housing.

The thermostat regulates the water flow so the engine warms up qucikly for effeicent running and then maintains a constant high temp.

Thermostats can stick open or people often remove the thermostat to 'cure' problems and that then leads the the car taking ages to warm up and running cold, i.e. the temp gauage never registers a high temp like what you are describing as your probelm.

I'd try the trick of shorting the wires and see if the gauage moves. If so swap the temp sender and if that fails to cure the problem check the thermostat is present and/or working

1983 Mars Red 1.8 Golf GTI
1987 Alpine White 1.8 Clipper Cabriolet

The trouble with doing nothing is that you never know when you are finished.

Post

Back to the top
Smallish update: I could have popped the right cherry!

In the last couple days the weather has gotten slightly warmer in the evening, and I've been keeping the revs higher for a short trip (~4000rpm) and after a short time I see the needle moving and assessing himself between 1/3 and 1/2 of the gauge.

Tomorrow I'll test the cabling with the "short" method, and verify.
0 guests and 0 members have just viewed this: None.