Just an update on my previous post concerning the red flashing coolant light. The quick summary is that in my case, I needed to replace the capacitor in my coolant temperature gauge to fix the constant red flashing LED problem. If you want to be bothered with the details, keep reading...
I did purchase a used cluster and swapped the coolant gauge with mine. That was a fairly stupid thing to do as I neglected to test the used cluster first, and it turned out that its coolant gauge had exactly the same problem as my original. So instead, I decided to do this properly.
"Properly" means testing the coolant gauge outside of the car. This is not hard to do if you have a basic understanding of electricity. If not, you can probably find somewhere to send the gauge for testing and repair. What's needed is a 10 Volt (9.5-10.5V) DC power source and some resistors that give you a few different values between 30 Ohms and 250 Ohms. A multimeter is also needed to confirm your values.
For a 10V power source, I used 6 flashlight batteries in a couple of battery holders chained together. I confirmed the voltage was just about 10V using a meter. I picked up six 10 Ohm resistors and two 100 Ohm resistors (rated for 1W) at the local electronics shop.
The rear of the coolant gauge has 3 screw terminals. One is smaller diameter than the others. This one should be connected to earth. The screw terminal at the top of the gauge (meaning the top one if the gauge was mounted in the cluster), is the terminal which connects to the coolant sensor. For this test we'll connect it to one side of the resistor, and then connect the other side of the resistor to earth. Finally, the last terminal (which is the terminal closest to the fuel gauge when the gauges are in the cluster) is connected to 10V.
If you're curious why 10V and not 12V, it is because the coolant and fuel gauges do not get power directly from the battery, rather via the voltage stabilizing transistor on the rear of the cluster.
According the the manual, the gauge wants to see between 40 Ohms (hot) and 258 Ohms (cold) on the signal line - that is the resistance between the signal terminal and earth. So by changing the resistors, we should be able to get the needle to move to different positions on the gauge. Note: the manual quotes settings on the VW1301 tool. Bentley has a table which shows what the 1301 settings correspond to in terms of actual resistance values here:
http://www.bentleypublishers.com/tech/v ... esting.htm
The red LED should flash for a few seconds when power is first applied to the gauge, or if the coolant is really hot (30 Ohms caused the LED to flash for me). I knew my gauge was bad because whenever I'd apply power, the LED would flash constantly. (Low coolant should also cause the LED to flash, but the coolant level control unit in the fuse panel does this by making it look like an over temp condition, so it's really all the same).
The next step was to replace the 10uF capacitor as described in Vanagon link I posted previously. If you're uncomfortable with your soldering, it shouldn't be too hard to find an electronics tech who can replace the cap for you. I did it myself using a fine tip soldering iron (25W) and desoldering braid. It wasn't as bad as I thought it might be. I used the technique shown in the link of putting the new tantalum cap on the top of the board. The other option is to disassemble the gauge further and replace it on the bottom of the board, but that is more involved.
With the cap replaced, I tested the gauge again, and now the light blinked for 4-5 seconds when power was applied, or if I used a 30 ohm resistor in the signal path, simulating overheating. With the gauge reinstalled in the cluster, all seems fine now (keeping fingers crossed).
A few points worth mentioning:
- if you decide your coolant gauge is bad and want to replace it, don't just swap in another used one. At least test it first. But even if you test it, the capacitor may be on its way out. A better idea would be to just go and replace the capacitor on the gauge so you only need to do the job once.
- when testing the cooling system electrics, you really should not simply short the signal wire directly to earth to see the needle move. This causes a lot of current to flow through the gauge, and while I haven't tried it, I would not find it hard to believe this could ruin the gauge. If you want to test the gauge, grab a 30 or 40 Ohm resistor and short the signal lead to earth via the resistor instead.
- The coolant temp gauges are available from VW Classic (at least the type in my 1984 model), but they are fairly expensive.
Finally, I should mention that I found out about the capacitor issue and how to replace it by reading the very helpful posts David Beierl made on the Samba website, so a big thank you to David!
