94 Previa Sc Overheating Only @ Higher Speeds

[ZMANRAMS]

Hi,

I Have A 94 Previa Supercharged Le W/ 185,000 Mi On It... It Runs Great, But At Higher Speeds, And Only @ Higher Speeds It Starts To Get Hot... The Heater Trick Brings It Back Down, But Once It Gets Hot The Heater Will Have To Stay On Intill You Go Back To Lower Speeds For A Small Duration. I Had Flushed The System And Replaced The Thermostat About 100 Mi Ago, And It Didn't Help. I Had Checked The Water Pump, No Problem There; I Had Checked The Fan Clutch, No Problem There; Checked The Radiator, Seems To Flow Fine; Pressure Washed And Blew Out Radiator Fins And Still No Success... It Went In For Smog About 2 Months Ago And Failed Due To A Bad Cat. Replaced The Cat And Passed With Flying Colors. Please Help, I Am Very Mechanically Inclined, But This Is Something That I Just Don't Get... I Had Checked All Of The Most Common Problems With A Cooling System, And I Just Can't Get This Thing From Getting Hot At Higher Speeds. I Had Let It Idle For About 45 Mins To See If It Would Get Hot And It Didn't. Drive It Surface Streets All Day And Still Normal; Get On The Freeway, It Gets Hot. It Is A Cool 70 Degrees Year Round Here, And Have Never Had A Problem; Intill Recently. Does Anyone Have Any Ideas???

Thanks

[dbrick]

I had a similar problem with my 91' it only overheated at slow speeds. normally the fan clutch should regulate the speed of the fan, slow or fast depending upon engine speeds.I think you may have a fan clutch that is working only some of the time. Just becuase the fan is turning does not mean the fan clutch is doing its job properly. I had mine changed easily but with an aftermarket replacement. It cools great but is much noisier than the stock original. alan