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radiator flowing?
06-03-2015, 01:40 PM
Post: #1
radiator flowing?
2000 Jeep Grand Cherokee Laredo /Auto / northeast Washington.
Why is the lower rad. Hose cool with engine up to temp.. Top hose is hot. Replaced radiator clutch fan,
Radiator and thermostat
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06-03-2015, 11:23 PM
Post: #2
RE: radiator flowing?
The lower hose will always be cooler than the top hose because heat rises and the cooler coolant falls even without the water pump moving it around. Also consider that the t-stat cycles open and closed so if you catch it between open periods then whatever is in the radiator has had time to cool off more. When the coolant in the engine reaches 195 degrees it will open again and the cycle repeats. On a hot day the cycles are shorter and on a cold day the period when the t-stat is open becomes shorter. Basically the water pump and the fan are just following along for the ride while the t-stat is what controls the engine temp. The job of the clutch (on the fan) is to slip a little when it's not needed so it creates less drag on the engine. That's more about fuel economy and noise these days.

BTW, did you know an old fashion fan without a clutch can suck up around 10 HP from the engine? Did you know that when driving over 30 MPH there's no need for the fan? The vehicle speed brings in enough air at that point.
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