This is why I pay special attention to the posts of Dennis Haynes and
a few others.  I knew the cooling system was different on the 1.9,
but not exactly how.  I have put considerable effort into
understanding the system on my 2.1 and once I did I stopped
there.  Seems like the heater circuit from one head would lead to
uneven engine temps.  In cold weather with heaters running full blast
that right head would run much cooler and wouldn't that affect the
needed fuel mixture?  I knew about the water pump bearing failure
eating into the crankcase but didn't know that it would have so much
affect on low speed performance.  It makes sense though.

Edward

At 01:36 AM 1/10/2010, you wrote:
>The 1.9 liter cooling systems do make less heat at low speed as the water
>source is only from the right head. On the 2.1 both heads go into a common
>manifold (the infamous one that breaks) and the heaters return almost
>directly to the water pump. However, if the engine has ever experience a
>water pump bearing failure, the back of the impeller immediately gouges into
>the case. This new groove makes an internal bypass behind the pump and
>affects the low speed performance.