temp gauge needle acting up

'94 Aerostar, 140,000 miles :
Cold start in the morning. Warm up seems normal. Heater function seems normal, warms up along with the temp gauge. Once warmed up the needle sits
between the "N" and "O". Here's where it gets strange. After a minute of two the needle starts to creep up to the "L". Heater is normal all this time. About the time I think I'd better pull over the needle goes back down to the "N", pretty quickly.
I drove around for a few minutes with the cap on loosely to get the air out of the coolant, and the level is good. Is this a sign of air in the system ? If so how do I get it out ?
Once it's gone through this warm up scenario the van runs great.
thanks !
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On 8/30/2010 3:31 PM, snipped-for-privacy@yahoo.com wrote:

Sound more like a sticky thermostat to me. Possibly a sending unit going bad...Assuming that coolant level is good....
DaveD
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On Tue, 31 Aug 2010 23:08:46 -0800, Dave Dodson

When was the coolant last changed? Sounds like the thermostat is sticky - and that sometimes happens when coolant is neglected.
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If its when you move I would also check your tranny fluid.
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