Bad thermostat or water pump ??

[gte901m]

I noticed the J20 was running about 10-20 degrees warmer than normal on the way home today.

I have a BJ's aluminum radiator and electric fan w/ temperature controller.

I pulled over to check things out:

1.) The fan was running

2.) The belts we tight

3.) Normal level of coolant in the overflow bottle

4.) The upper radiator hose was not fully pressured up like it should be.

Do you think the thermostat is partially stuck? The t-stat is about 2 years old.

Or do you think the water pump is not pumping at full capacity?

I've only replaced water pumps due to bearing noise and leaks - I've never had a pumping issue before.

Your thoughts?

[drlocke]

I had a rotor come loose and "freewheel" on the driving shaft on a pump that otherwise seemed perfectly fine. Intermittant overheat was the chief symptom. A telltale sign of a failed rotor in a water pump is to feel the heater hoses. If there is a marked difference in the heat felt on the hoses then flow is restricted. If in concert with an overheating engine suspect the rotor. If the stat fails to open then the heater hoses both will be piping hot, while the upper radiator hose may be only warm, and the radiator cooler still. In my case when the pump failed with a slipping rotor one heater hose was too hot to handle over most of its length while the return hose was nearly stone cold!

[Tripwire]

it would seem to me if the stat was stuck 1/2 way or full open the upper hose would still presurize fully....

DRLocke has a great tip....as well... I have never had one fail on me but i can certanly see how it would cause a overheat condition and have read many posts about this same issue. i suppose you could take off the radiator hose and push a screwdriver against the impeller to see if its still welded to the shaft?

perhaps the rad cap has a defective gasket or is itself defective, what about hose clamps not tight? maybe there is a small leak you cant see?

with the engine coldish...open the rad cap and start engine - if you see flow after the temp comes up the water pump is probably ok IMHO

perhaps the fan clutch is bad, sometimes they still seem to spin ( but are actually freewhelling) but if one ( of course i have never done this and its hazardous:rolleyes: :rolleyes: ) has the engine at idle and pushes a stick against the backside of the blades ( think of the direction of rotation before you do this) i have had the fan stop completely with very light pressure. I replaced the clutch and all was well. Just keep in mind that a termal clutch will engage/disengage depending on engine temp

[Skeeter74]

If the engine is hot, and you have no pressure on the system, you definitely need to replace the rad cap. Unless, of course, your coolant is escaping someplace else. ;)

[jeepjseries]

Also for piece of mind go buy a fail safe thermostat, you cant go wrong with them. Only about 10 bucks or so.

[drlocke]

In re "welded to the shaft" as far as checking rotor status...the replacement pump I got had a metal rotor welded very securely to the shaft, but the "original" pump had a rotor made of bakelite or another fiber material. Such was pressed over splines on the driving shaft. The splining on the inside of the rotor as it fits to the shaft began to wear, causing slippage.

I dunno if there are still water pumps being made this way, but it is perhaps something that should be considered when buying replacements.

[gte901m]

Yesterday I left work around 8pm, it was running a little warm. Pulled into the McParts store and bought a new thermostat and gasket. On the rest of the way home it ran 195 the entire way....

The new stat sitting in the cab must have scared it.

[Blinkinlights]

Had some overheating issues this summer. When it's warmed up, check the lower rad hose for it collapsing. I had heard about this but thought it was a myth. When the engine is warm and the thermostat is open, look at the lower rad hose when you rev up the motor. Mine would collapse, restricting the flow of coolant, and then go back to normal when the engine went back to idle.

Since the OEM lower rad hoses with the anti-collapsing coil aren't made any more the only replacements don't have the coils. Went to a universal flex hose that fit perfectly and all my overheating issue went away. Worth a look.

Greg