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Help with over heating. Is it electric fans or water pump?

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My 1991 LS400 is having a cooling issue.put new radiator on two months ago. All was good after that.

Now when car has engine on and I'm not moving like when parked or in traffic the engine temp slowly starts to climb up.

ehen I give it gas and start to move, at fist there is another small jump in temp but in a short distance the temp goes down to where it should be. Until I'm at a stop. Then it start going up again.

No loss of coolant. Mechanical engine fan is working.

I'm thinking either water pump is acting up or it is the electric fans.

I'm leaning to it being the fans. How can I see if they are on and how do I check them?

Where is the fuse for the fans? Where is the temperature sensor switch?

How do I go about figuring if it is the fans and why they are not coming on (if in fact I find they are not coming on)?

As always I thank all of you!


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I have a 1999 lexus sc300.  Major Overheating, the antifreeze/water is evaporating out. No drainage, no puddle, no visible leak. It runs75% further without a radiator cap (okd one new one and just to be sure a third cap).  I have replaced the radiator, radiator cap, red toyota antifreeze, thermostat, and the fan clutch. Thinking it must be water pump. Any ideas woukd be appreciated

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6 hours ago, StacyB said:

I have a 1999 lexus sc300.  Major Overheating, the antifreeze/water is evaporating out. No drainage, no puddle, no visible leak. It runs75% further without a radiator cap (okd one new one and just to be sure a third cap).  I have replaced the radiator, radiator cap, red toyota antifreeze, thermostat, and the fan clutch. Thinking it must be water pump. Any ideas woukd be appreciated

You should check to see if the radiator fans are working first. Try this: turn the ignition switch ON and check if the radiator fan stops? If it does not stop, then check the fan relay.

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