Water Pump failure questions

[2xtreme]

My mother in laws 88xj recently has a high temp problem (not red, but higher than the 210 norm). It has the newer style system (with a proper radiator cap) a good radiator, new water pump, new oem thermostat, new radiator cap, and does not leak any fluid. A couple of months ago I replaced the water pump (no temp problems, just leaking from the weep hole) and at the same time I replaced the thermostat and completely flushed the system (with water several times and then air) put everything back together and filled with 100% water and had her run it for several weeks to make sure everything was good, before I flushed again and put 50/50 water/anti in it. Everything was great, never got hot even running in hot weather. All of a sudden it has started to get hot when running around town, not when at idle. So I replaced the fan clutch and no change. I have a suspision it is the water pump not pumping properly at rpm? Is this possible? Anyone had this problem? Anything else you can think it could be?

Any ideas appreciated.

Michael

[8Mud]

There really isnīt much to mess up in a water pump. Bearings, seals, impeller. Impeller failure is rare, if the weld breaks and it falls off, it usually makes a racket, radiator flushes (excessive over years) will eat them up some. They usually leak, rarley fail and when they do fail (other than seals)it usually isnīt a progressive problem.
The radiator cap allows excess pressure to escape to the surge tank and when the motor cools, pulls fluid from the surge tank back into the system. Have seen caps gunked up that messed with the recovery process. Removing the cap, usually showed low coolant in the radiator.
Even with the recovery type system in the 88, you may still have some air trapped in there somehwere. Squeezing the top radiator hose, with the motor at operating temp. (thermostat open and motor off). Has helped move stubborn air pockets for me in the past.
On my 88 I can see the thermostat operate at the gauge, the temp. goes up some, then comes down some. Usually between, what Iīd guess to be 185 and 212 at the sender. My aux fan comes on when the temp. at the thermo switch reaches 207 F. What did you do with aux. fan switch (thermo switch) when you changed to the open system?
Rev. up the motor to high RPMīs (above 2000) and look closely at the bottom hose. If the spring has slipped, part of the hose may collapse (usually at one end or the other).

[Matthew Currie]

I'm having a hard time guessing what's the matter, but I think if it were the water pump it would be worse at idle.

Don't forget the obvious: is the gauge lying?