1997 Es 300 Overheating

[Highwater]

Hi all,

I have a 97 ES300 (238K miles) that just started overheating. First thing I checked was coolant, and the reservoir was empty. I filled it up and topped off the radiator. It took about a cup, I guess. Since then (six days) it has not leaked any coolant, but it still runs hot. It takes about 20 minutes for the gauge to get to the 50% mark. It holds near the 50% mark on the highway, but climbs over it in stop-and-go traffic. I suspect it might climb over the 50% at full speed if I drove it long enough.

I checked the radiator fans when the gauge was reading > 50% and they were not turning. However, they run just fine when I turn on the A.C.

I replaced the coolant temperature sensor. There appear to be two sensors, but the computer at my auto parts store only listed one, and that's the one I replaced. Both are near the radiator fill. Also, the Haynes manual only mentions one sensor.

I checked the No 1 fan, No 2 fan, No 3 fan, and main relays for continuity exactly as described in the Haynes manual and they all passed. Can't say that I understand the check because Haynes says there should be continuity across the switch with no voltage across the coil, and continuity when voltage is applied across the coil. That seems backwards to me because the normal operating condition of the fan is off. But they are all that way.

Any ideas would be greatly appreciated.

Thanks.

[tony64peter]

Hi all,

I have a 97 ES300 (238K miles) that just started overheating. First thing I checked was coolant, and the reservoir was empty. I filled it up and topped off the radiator. It took about a cup, I guess. Since then (six days) it has not leaked any coolant, but it still runs hot. It takes about 20 minutes for the gauge to get to the 50% mark. It holds near the 50% mark on the highway, but climbs over it in stop-and-go traffic. I suspect it might climb over the 50% at full speed if I drove it long enough.

I checked the radiator fans when the gauge was reading > 50% and they were not turning. However, they run just fine when I turn on the A.C.

I replaced the coolant temperature sensor. There appear to be two sensors, but the computer at my auto parts store only listed one, and that's the one I replaced. Both are near the radiator fill. Also, the Haynes manual only mentions one sensor.

I checked the No 1 fan, No 2 fan, No 3 fan, and main relays for continuity exactly as described in the Haynes manual and they all passed. Can't say that I understand the check because Haynes says there should be continuity across the switch with no voltage across the coil, and continuity when voltage is applied across the coil. That seems backwards to me because the normal operating condition of the fan is off. But they are all that way.

Any ideas would be greatly appreciated.

Thanks.

[djspawn00]

any signs of coolant in your motor oil? Also... could be a water pump on its way out...

[Highwater]

Thanks for your replies. I didn't see anything except a quoted version of mine in tony64peter's response. Can anybody tell me if they could see something in their view of his reply? I am wondering where the fault lies.

It turned out to be the no 1 coolant temperature switch, located at the bottom of the rad, and described in the Haynes manual. Apparently the coolant temperature sending unit sends a signal to the relay, which sends current to a switch, which turns on the fan. Turning on the A.C. bypasses this switch.

I would be grateful for an explanation of how the relays work, though. Why should the switch be closed when there is no load on the coil? Not important; just curious.

[josempv77]

Hi I'm also having the same problem I replaced all the sensors (4) including the  one for the temperature gauge inside car but I did change the one from the radiator went to junk yard to get one and still doing the same think I put the heat on the one fan comes I put the ac on both fans are on I turn off the ac one fan turns off then the other fan stays on for a while then the temp goes back to normal until the gauge goes back then I turn the ac on to turn the fans on so you think if I get a new radiator sensor it would work I just hope I don't want to do a water pump