Water Temp gauge or sending unit or thermostat malfunction?

[michaeltag]

About two weeks ago I was cruising on the interstate and I noticed that my temp gauge on my '87 Westy Syncro was not registering at all as far as I could tell.
I pulled over immediately and checked coolant level and it was fine and it seemed that the engine was operating at normal temp. Heat worked.
So, this indicated to me a gauge or sending unit problem.
Also, when I start the car the temp warning light does flash for a second or three.
Then I noticed that there was some movement occasionally in the needle but it just never got to it's former usual position of about halfway between C and H.
After noticing this, I started thinking maybe I had a stuck thermostat.
Is there any way to test the thermostat on the car?
If I park the car headed down hill can i remove and replace the thermostat without losing a ton of coolant?
Does this look more like a gauge or sending unit issue?
Would like a little guidance on troubleshooting this. I am going to drive about 1000 miles next weekend and I would like to feel I can trust the temp gauge!
BTW, I have purchased the GoWesty audible temp warning alarm kit, but it needs a reliable sensor/sending unit, right?

[davideric9]

You can unplug the wire on the sensor and ground this wire and this should make the needle in the gauge go way up. This should only be done momentarily, like have someone watch the gauge and another person ground the wire. If this happens then the gauge and wiring are good and your sensor is bad. If nothing happens you need to figure out if its the wire or the gauge.
_________________
1987 Syncro Westfalia, stock (bought 1994)
1986 Syncro Westfalia SVX, 3 knob (bought 2008)
1987 Westfalia (bought 2010)
1988 Wolfsburg GL (bought 2012)

[michaeltag]

Does it make any difference what temp is when we do this?
I am assuming that ignition has to be on but engine does not have to be running?

[davideric9]

Key needs to be on. Engine temp is not an issue (but hot you may get hurt) as the sensor is negative coefficient resistor the hotter the engine gets the lower the resistance, so shorting this wire to ground is like no resistance and so the gauge will register as very hot. Make sense? Pm me if you need help in Oakland
_________________
1987 Syncro Westfalia, stock (bought 1994)
1986 Syncro Westfalia SVX, 3 knob (bought 2008)
1987 Westfalia (bought 2010)
1988 Wolfsburg GL (bought 2012)

[Ahwahnee]

[davideric9]

If your thermostat is stuck open, good chance you will still get a reading on the gauge if you are on the interstate and your heater works. If it is stuck open both plastic cooing pipes will warm up at the same time, starting from a cold engine within the first few minutes. I suppose if you are in freezing weather you may not get the engine hot enough with an open t-stat, but heck if you are getting heat your coolant is hot and your gauge should show something. I still think the quickest test is to ground the sensor wire to check to see if the gauge works at all.
_________________
1987 Syncro Westfalia, stock (bought 1994)
1986 Syncro Westfalia SVX, 3 knob (bought 2008)
1987 Westfalia (bought 2010)
1988 Wolfsburg GL (bought 2012)

[Tom Powell]

[davideric9]

On 2wd, its a jumper between the two wires, on the syncro (which the original poster has) its only 1 wire, so that one wire goes to ground on this test.

And btw, I thought I had a bad t-stat as the temp gauge reading would drop on freeway to just below the led light, then go up in stop and go traffic. Turns out the bad t-stat was NO t-stat, and the needle on the gauge ALWAYS was above the lower white mark (at least in SF Bay area).
_________________
1987 Syncro Westfalia, stock (bought 1994)
1986 Syncro Westfalia SVX, 3 knob (bought 2008)
1987 Westfalia (bought 2010)
1988 Wolfsburg GL (bought 2012)

[Tom Powell]

[davideric9]

Just to clarify, you need to jumper the contacts in the connector (which are female) not the contacts on the sensor, so a jumper wire works, a screwdriver won't make contact.
_________________
1987 Syncro Westfalia, stock (bought 1994)
1986 Syncro Westfalia SVX, 3 knob (bought 2008)
1987 Westfalia (bought 2010)
1988 Wolfsburg GL (bought 2012)

[Tom Powell]

[hdenter]

If you want to know if your thermostat is stuck open and/or if the gauge system is working, start the car and let it idle. As it idles feel the radiator or use an IR gun to monitor it's temperature. If the thermostat is working right, the rad should stay cool for a good while and then quickly get warmer as the thermostat opens and gets wider open. If the rad begins to warm up shortly after starting the engine and gets warmer at a steady rate, then the thermostat is stuck open. While all this is going on, watch the dash gauge. When the rad gets hot enough to kick in the fan, the needle should be fairly high. If not, go ahead and do the checks to see if it is the gauge/wiring or the sender. Good Luck!

Hans
_________________
'79 triple white convertible bug
'84 sunroof vanagon
'85 weekender

[michaeltag]

I ended up taking it to Karmakanix in Berkeley. Glad I did. It was tricky even for them to diagnose. At first they thought my gauge was bad, because my sending unit was working intermittently, but when they tested it a different way it was my sending unit. New sending unit has got me back in business. They suggested I get a calibration kit from GoWesty because the new sending unit is making the gauge read a bit different. Freaked me out at first.
I have an old set of VDO gauges that they say work well with VW sending units that I may have them install.
I'm going to monitor the ________ out of this engine!
Thanks for all of the replies.
Oh, also, I had them install the GoWesty Audible Temperature Alarm that I had already purchased. So, now I feel safe on the highway again.
They were also able to replace my hi-beam indicator bulb while they were at it.
All in all a worthwhile visit.

_________________
'87 Vanagon GL Westfalia Syncro w/ rear locker
• 1.8T engine conversion from Stephan's AutoHaus
• Schwenk Springs, OME shocks, BFG All Terrains on South African 15-inch steel wheels
• GoWesty Plate Steel Bumpers w/ front skid plate & rear swing-away spare carrier
• Big Shot Shifter
• Transaxle rebuilt with taller heavy-duty 4th gear, GoWesty decoupler and oiler plates by Ken at Porter's Precision
* TruckFridge
• Propex Heater
• Vintage Air in-dash A/C

[chrisfreemanca]

So my 87 is guzzling coolant but the gauge is never coming up to the "normal" halfway point. Coolant light does blink at start up a few times as it should and engine is running good. The gauge does come up to the edge of the thicker white indicator closest to the light but never really goes any higher than that.

I have no leaks anywhere and the exhaust doesn't smell as if coolant is coming out there. Am thinking maybe stat is stuck open and engine is over cooling?

So would easiest attempt to fix be to simply replace the thermostat? If so, where do most folks pick these up as all i'm seeing at GoWesty, VanCafe, etc... are the thermostat housing kits.

Thanks in advance.

[Tom Powell]

[chrisfreemanca]

[Tom Powell]

[Ahwahnee]

[chrisfreemanca]