Coolant temp gauge

[hansh]

I've been dealing with a few wonky electrical issues during a long trip of which we are in the middle. This one is regarding the Coolant temp gauge.

The other day the coolant temp gauge began to fluctuate excessively. The needle doesn't show over heating. It reads normal temp for about the first 5-30 minutes of driving and then the needle begins to drop. It'll come back up to normal sometimes but, then drop low again. It seems to have no correlation to revs, speed, air temp, etc. The fuel gauge is operating normally for this van (fluctuates predictably based on uphill, downhill, or flat).

I'm pretty sure that the temp is fine. I replaced the water pump, thermostat, and coolant before we left home. The wire to the sender new, grounded, and well connected. The temp was normal for all conditions before the gauge began malfunctioning.

I have to say that while I am comfortable with the actual performance of the cooling system, the gauge couldn't have picked a worse time to act up. It started just as we dropped into the desert between the North and South Rim of the Grand Canyon. The ambient temp was above 100 degrees, I had the wife and kids so the AC was running, the van was very heavily loaded for a 2 week trip, and a storm was blowing in with sustained 30mph dead-on headwinds and we were struggling to hold 55mph. I really didn't like not knowing how the engine was doing. We are currently just outside of Phoenix until tomorrow afternoon and I'm hoping to figure this out before we hit the road again.

The gauge was working fine until I began having some issues with the dash cluster. The cluster electrical connector has had some issues resulting of a short before I purchased the van. I have it mostly worked out but, it has had its occasional problem. The blinky light stays on sometimes, sometimes shuts off by turning the headlights on and off, and sometimes works normally. I think this is due to the wire connection on the cluster. The differences in the red light behavior seem to be determined by fiddling with the connector.

Also, the cluster lights work fine but, they change slightly in intensity while driving.
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‘85 ej22
'84 Westfalia

[hansh]

Forgot to mention that I can see a small jump in the needle now when I switch the lights on and off.
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‘85 ej22
'84 Westfalia

[hansh]

Voltage stabilizer within specs at 10.14.
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‘85 ej22
'84 Westfalia

[Baxta]

How's your voltage regulator at the alternator? I don't know if the Vanagon's is replaceable, but my Corrado of similar vintage has a replaceable VR - I;d say your symptoms suggest a bad VR...

Good luck!
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Greg
'87 Syncro Westy 'Bastian'
2.2l