An airpocket in the rad will float to the top.
Yes the rad will warm up on the bottom first.

The cold patch on mine was  just like, completely unmistakeable. An
irregular patch in the middle that was stone cold as the rest of the rad
warmed up evenly.  Clogged rad.  Not a super precise dianostic tool. But
worked for me. Took ten minutes, and no cash.

BTW, the cleaned radiator has been running fine since.
Bill M
82 GL
  

-----Original Message-----
From: David Maurio [mailto:maurio11@COMCAST.NET] 
Sent: December 30, 2003 9:35 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: FW: RE: Coolant Overflowing!

Couldn't a blockage in the lines or an air pocket cause the same
symptoms?
> On Tue, 30 Dec 2003, MacLachlan, Bill wrote:
>
> > Start the cold engine.  Let it run. As motor warms up, feel the 
> > radiator surface. If its all stone cold, the thermostat ain't opened

> > yet. Once the thermostat opens and the radiator starts to warm up,  
> > it should warm up evenly all over. Clogged patches in the radiator 
> > will stay cold while everything else warms up. If you've got an 
> > unevenly heating radiator, you've got a clogged one.