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Old 02-01-2011, 01:57 PM
BogiesAnnex1 BogiesAnnex1 is offline
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Originally Posted by satdiver1
I have a new motor radiator water pump. The new thermostat is 180 degrees. The temp goes up and down from 110 to 180 and never settles or stays at 180. I replaced the thermostat with another new one; with the same results. Any ideas as to what is causing this? Oh by the way I used a laser remote sensor to verify the temp variations. It's not gauge related.
OK, I'm lost in all this; are the temp swings with gauge like the type that would be installed in or on the dash, or are these numbers you're getting off the laser?

Lasers are sensitive angle of impact and return the beam makes to the part tested. Basically the temp read cannot be trusted on a hand held device because of this.

If you're seeing this on a mechanical or electrical gauge it means there are several things to look for:

- Sender, wiring, bourdon tube, or gauge is faulty.

- Thermostat faulty

- Lack of bypass, Chevy small blocks in particular are sensitive to this. For air-conditioned models there must be a three-way valve in the system that bypasses the heater circuit when the AC is switched on, this has plenty of failure modes of its own resulting from whether the AC controls on the dash are working as well as the bypass valve working as commanded. Lack of bypass causes pump cavitation which puts vapor in the cooling system, tears up the impeller and can result in pump bearing failure as it shakes the daylights out of the impeller shaft.

- The excessive use of RTV rubber sealants, this stuff breaks off and circulates till it cuts a passage off which then makes steam out of what inadequate amounts of coolant get to it.

- Leaking head gasket putting compression and combustion gases into the cooling system that end up insulating the thermostat from the coolant.

- Cooling system not fully filled.

- Water pump faulty
- Wrong rotation pump for type of belt drive. Chevy uses the same casting with a different impeller for Vbelt or Serpentine belt, common to see the packaging ID for the wrong pump inside.
- Impeller not turning with the input shaft.
- Foreign object in the pump blocking flow.

- Inlet hose collapses with pump suction.

- Foreign object or crud in the radiator though this usually results in a constant overheat.

- Pump driven fan has incorrect rotation for belt drive used, like the pump the end user is 100% dependent that the correct part is in the packaging.

- Failure of the pressure cap, loss of system pressure will result in local boiling even though the bulk coolant temps may be in a "normal" range. The resulting steam becomes trapped at the thermostat screwing with its temperature sensing abilities.

- Missing shroud, results in uneven cooling on radiator face.

You get to check all this out.

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