RE: mystery cooling problem
All of the posts here might be correct if the problem has always been there.
If this is a new problem, you have a pin hole blown head gasket.
Everything is great at idle because there's no pressure. Once you get going, it opens up and the pressure goes back to the radiator because the leak is on the inflow side of the engine.
Don't dispair yet. Bars Leak makes a new head gasket repair in a silver bottle for about $10. You'll need two bottles for this treatment. Follow the direction precisely,
NO SHORTCUTS!
You can thank me later. Let's just get you back on the road!
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