I've seen great variablility in the quality of the impeller on
waterpumps, with noticable difference in cooling efficiency.  Especially
if the cooling system is having other problems (in my case, a radiator
that was corroded inside).  Stay away from the $50 FLAPS cheapos and
get a good quality OEM. (My $0.02)

Have the flow rate thru the radiator checked as well.  Does the fan cycle on 
and off?  If the fan doesn't come on soon enuf, this may indicate not a bad
fan thermo, but that the radiator isn't getting enuf flow.  Turn on the
heat lever.  If you get a drop - and it STAYS lower, I'd suspect flow.

You can trigger the radiator fan manually as well (by pushing down on the
relay contact).  It's easy to identify, and take the cover off the fan relay.

- Frank

 >My suggestion if you have no visable leaks, but are experiencing cooling
 >problems is to have  a pressure check done.
 >
 >
 >The problem occurs because the waterpump impeller will not create enough
 >flow velocity, with a cooling system that does not have a good pressure
 >build up.  The most recent thread I saw, and a very good one I might add,
 >put the system pressures at 7lbs to 10lbs.  You should double check these
 >values.
 >

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Frank Terhaar-Yonkers
Cisco Systems, Inc.
Engineering Services, W2 F3 5
7025 Kit Creek Road  PO Box 14987
Research Triangle Park,  North Carolina  27709
fty@cisco.com   voice (919)472-2101   FAX (919)472-2940
pager (800)796-7363 pin 1008366 -or- fty@airnote.net