Temperature Gage Red Light Flashing

[fewil]

Hello,
I replaced the blue temp sensor on my 2.1L Vanagon with a new sensor, but I clumsily lost a fair amount of radiator fluid in the process.
When I started the engine after the new sensor install, the red warning light on the instrument panel temperature gauge was flashing.
I only let the engine run for a couple minutes.
The radiator fluid overflow reservoir behind the rear license plate has plenty of reserve fluid.
The electrical connector to the temperature sensor is secure.
Please advise what you recommend that I do. I don't want to ruin my engine.
Many thanks.

[?Waldo?]

That is warning of a low coolant level. Assuming the engine has not heated up significantly, open the engine compartment lid, open the coolant pressure tank and fill it completely full of coolant.

You did the right thing in shutting it down. You should never drive a 2.1 when the coolant light is flashing regardless of what the temperature gauge says the temperature is. On the 2.1, if you have a catastrophic loss of coolant, the led will flash and the engine can completely melt down without the gauge ever reading excessively hot due to the sensor being mounted in plastic.

[Ahwahnee]

The tank on the left is the one you'll want to fill (the cap on yours is probably blue). You may have to do this more than once but best to let the engine cool down each time before opening.

[fewil]

Thank you very much.
Will I need to bleed the radiator?
Thanks.

[SCM]

[?Waldo?]

[SCM]

[E1]

We may be underestimating exactly how much coolant was lost, the stock, cubicle Temp II sensor can be tricky to swap without losing lotsa coolant the first time one attempts this job — according to a friend.

It’s the OP’s use of “clumsily” that makes me think a fair bit of coolant drained out, particularly if the o-ring gets stuck in the housing, one swaps in a new one with o-ring on it, it doesn’t go in for having two o-rings, four letter words abound, etc.

Regardless, I recently changed a Temp II on a metal thermostat housing that’s a screw-in sensor like used on the 1.9s, a much easier swap, but still lost a fair bit of coolant.

I did my usual fill method:
— ON COLD ENGINE, remove the blue cap on the large coolant tank
— Start van
— Swing heater levers to hot, run both fans on high to purge air from cores
— Bring to full-temp, key here is full circulation and radiator fan coming on
— Have someone hold revs at 3,000 rpm, note that coolant level drops
— This allows you to get more coolant in, meaning less air to bleed later
— DO NOT reduce rpm until you cap is back on or coolant may burn you
— Fill coolant to overflowing point, screw blue cap on fully and attach its hose
— Fill overflow tank to between Max and Min, if any air exists level will drop

In my experience anyway, there will always be a little air left atop the radiator. It should self-bleed over a few dozen or more miles, especially on a long downhill, but personally I tap the radiator just the same (13mm open-end wrench), and there’s always a moment of air hissing out.

Just be very careful to tighten the bolt carefully and never very tight — just snug. Many never do this and the bolt locks itself on over time, not good!

Check if bolt is leaking from being too loose, though I’ve never seen that. Again, be careful to not crank on too hard!
_________________
1984 Westfailure/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans

"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere." — Colin Chapman

Jonathan Weisheit, Race in Peace:
https://www.youtube.com/watch?v=z3dS7xiFn7I&t=500s

[?Waldo?]

Assuming that the radiator does not leak and the temp switch that was swapped was at the engine, then if the radiator bleed screw was not opened, I don't see how the radiator would get air into it. If the van was nose up on a steep incline and you drained the engine completely you might be able to get air to flow up into the radiator to displace the coolant, maybe.

[E1]

What I described is just a lesser version of your last sentence.

When coolant drains out, the overall capacity is still approximately four gallons. Since the system can’t contract, what takes the place of the coolant loss?

I’ve never lost even a small amount of coolant without needing to add more to displace air. Perhaps the OP lost enough coolant to empty the overflow and introduce air under vacuum when cooling, and didn’t look at it when cold.

I understand your thinking and it’s interesting, but regardless the overall system “space” doesn’t change except for nominal hose shrinkage when less than full.

Origins aside, what else other than air could occupy the space of, say, a lost gallon of coolant? Perhaps a side effect of that is whenever I open the cap on an underfilled and cold system, it immediately draws in air to fill the void — still being under some vacuum.

Otherwise, where the air “comes from” on an underfilled, sealed system is a worthy and curious topic indeed… best guess is as coolant leaks from an open port (like the Temp II), it’s also sucking in air and especially when cold.

Thanks.
_________________
1984 Westfailure/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans

"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere." — Colin Chapman

Jonathan Weisheit, Race in Peace:
https://www.youtube.com/watch?v=z3dS7xiFn7I&t=500s