Thermostat or ? overheat problem ? running hot ?

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Joined
Jan 12, 2019
Messages
9
Location
Anacortes, WA
While driving on the interstate at 70 mph the other day I noticed the Temp gauge had crept up almost to the 3/4 line. When I slowed down to 55 mph it settled at the mid line (normal?) and when I got off the interstate and slowed to 40 mph it dropped to the 1/4 line. The swings in the gauge were mph (rpm) dependent. Ive only had the 2001 LX470 for a couple of thousand miles. Maybe what I observed is normal but it seemed odd to me. I would appreciate any comments and if this is indicative of an emerging problem any fixes would be appreciated. Thanks much
 
Fan clutch?
 
May be the thermostat is stuck open or not present, because the temp should not drop to 1/4 of the gauge.

If your radiator is old, replace it along with the heater T joints.
 
1. Check coolant level in radiator. Should be filled to the neck. Overflow bottle level is not indicative of coolant level. Cheap & very easy.

2. If problem persists change thermostat & gasket. Cheap & easy-ish.

3. If problem persists look at fan clutch, water pump, etc. Not so cheap or easy.
 
1. Check coolant level in radiator. Should be filled to the neck. Overflow bottle level is not indicative of coolant level. Cheap & very easy.

2. If problem persists change thermostat & gasket. Cheap & easy-ish.

3. If problem persists look at fan clutch, water pump, etc. Not so cheap or easy.


I would add OEM radiator cap to the above as well.
 
Thanks for all your responses.
Radiator is full of coolant, no evidence of fluid loss.
If thermostat were missing or stuck I would expect engine to run "cold". Perhaps I am wrong.
Fan clutch is suspect. I will try to diagnose based on common symptoms.
Could the overheat be due to the cooling system needing a clean and flush?
I will replace the radiator cap although it "looks" good.
Water pump replaced with timing belt 2000 mi ago. (dont know about the thermostat).
Thanks again. If you think of any other probable causes or diagnostics please let me know.
 

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