2000 Chevy Venture Low Coolant Light

Greetings,
 
New to this site, but unfortunately not new to car problems. Hope someone can help with a question I have about my 2000 Chevy Venture.
 
On a recent trip my Low Coolant Light came on. I added 1/2 gallon or so antifreeze to the fill reservior. Resumed trip and light came back on after a while, temperature stayed good and antifreeze was still in the reservoir. Resumed trip right away and light stayed off for 1/2 hour, then came back on again. Around town for the last week the light has not come on at all and fluid level has been good in the fill reservoir.
 
What could be the cause for the light to come on perodically? It only seems to come on after some time driving at 65-70 miles per hour.
 
Is a new radiator cap in order or perhaps a new fluid level sensor?
 
Is this possibly an indication of something more mechanical (and expensive) that I will have to deal with?
 
PS  I Have to head out on a 3 hour trip tomorrow . . . wish me luck.
 
Thanks in advance for any help and info you may have. 

I've had the same problem but as soon as i had the sensor replaced, the problem was solved.

Dex cool tends to gum up and that's why the lever sticks.  The only really way to fix it is to change that float sensor.

Just a follow up. My worst fears were realized after the van began running rough. Spent good money to have plugs replaced and a tune up. Then discovered the vehicle had a head gasket leak and needed a $2,000 engine replace,emt.
 
 
-reelcharacter

That's unfortunate news but not uncommon.
 
That would explain the coolant loss but not why the low level light being on.