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94 Es300 Overheating


doug c
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994 Es300 with 288,000 miles. I have found when buying parts that this was probably a 2003 engine in a 2004 model year, as it was built in november of 2003. Therefore, it has the single hydraulic powered engine fan instead of the twin electric fans later that year.

In the hot (80 + Fahrenheit) weather it starts to run hot. If I keep speed to under 70, and AC off, it will run for an hour or so and then start to creep up. Turning the heat on will bring it back down, at which point heat can go off and all is fine again for another 30 or 40 minutes. Any time the AC is turned on the car will go up towards hot...after about 10 or 15 minutes.

I have recently flushed the system, and replaced the thermostat. The coolant flushed out looked brand new, the thermostat seemed fine, although while out it was replaced.

I find that the upper radiator hose is very hard when the car is warmed up. It returns to normal pressure when it cools off.

I don't see any evidence of a head gasket problem. The oil is not milky, there as been no coolant loss, no smoke from the pipe, etc.

The heat works fine, so I suspect the water pump is functioning.

Any suggestions?

Also, How do you deal with airlock in the cooling system. I see it refered to in several heat related posts.

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with airlock , in my opinion you keep dealing with it untill it is solved. Remove the rad cap first thing in the morning and top up.(50/50 coolantwater) Keep your fingers crossed.Check it whenever its cold (engine) untill there is no need to top up......and then keep on checking checking. Hopefully, problem solved. Worked for me.....or, let a pro do the whole nine yards and hope there s no airlock.

The upper hose is hard because it is pressurized, normal.

The thermostat is working if the bottom hose feels hot.(hot fluid leaving the motor)

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That's about what I thought. I know the radiator is fine, because it is hot as weel as as hard as the top hose, and when I squeeze it with the cap off I can get the coolant to gurgle out of where the cap was.

So if I assume the new thermostat was not defective, and I trust that the mechanic is correct when he said he was sure the spring was facing the right way on the thermostat, then where am I?

How can I determine that the water pump is pumping? I have visually inspected the pump and it seems tight and the shaft is turning, but can the system be flow tested somehow?

And I am doing as you suggest....a half a cup here, quarter of a cup there....

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There is a simple test for the water pump. With the engine running and warmed up, squeeze the upper rad hose. If the pump is working properly, a pressure surge should be felt as the hose is released. (This test is right out of a manuel, and the only one).

You can do other things like get a new rad cap for maintaining proper pressure, check ignition timing for correctness and look for fault in the hydraulic cooling fan system. And, make sure you have no cracked or broken fan blades. Coolant also can find the tiniest escape holes, so look around while your at it. These are all pretty cheap to do and cover a lot of ground, otherwise, welcome to the overheated world of Lexus!

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with airlock , in my opinion you keep dealing with it untill it is solved. Remove the rad cap first thing in the morning and top up.(50/50 coolantwater) Keep your fingers crossed.Check it whenever its cold (engine) untill there is no need to top up......and then keep on checking checking. Hopefully, problem solved. Worked for me.....or, let a pro do the whole nine yards and hope there s no airlock.

The upper hose is hard because it is pressurized, normal.

The thermostat is working if the bottom hose feels hot.(hot fluid leaving the motor)

Water leaving the engine is from/through the upper radiator hose, not the bottom.

IF the upper radiator hose is really tight, you MAY NOT be getting circulation.

The engine/hoses are pressurizing, but, the coolant might not be flowing back to the radiator, to dispurse the heat via air flow/convection.

Here's another test that has worked for many, many years.

Start the car and let it warm up. (Note temperature gauge. When the temp rises, proceed, but, do NOT let the engine overheat!)

Raise the hood.

With the engine running, remove the radiator cap.

You should be able to see the coolant flowing.

If it is. . . the thermostat is working and allowing circulation.

If not. . . the thermostat is most likely stuck or is failing and should be replaced.

Please note: Do NOT turn the engine off while the radiator cap is removed, and do NOT take the radiator cap off with the engine hot and the engine is off.

Mental photograph - Picture "Old Faithful" when she is erupting!

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Yes , heated coolant leaves through the upper hose, gets cooled in the rad and goes back in through the lower hose.. It is still "hot" going back in which is a clue that the thermostat opened(to begin this process) and the pump is pumping and circulation is good and the hoses(and the whole cooling system) are pressurized. Srry for any misunderstanding.

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  • 3 years later...

Hey bud sorry to say but this is very common with these engines I own and run my own workshop and these past 2 years we have had 3 of the ES300 with the exact same problem witch is a blowen head gasket the last one we done was last week and the bill mounted to $2700nz Cheers

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Also to get the air locks out fill a coke bottle up with watter and stand it in the radiator be sur to fill radiator up first and start the engine le it idle and heat up the bottle will take the air locks out and replace it with water cheers

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First, need to know how much it is overheating, is it in the upper third or is it pushing the red zone? Secondly, does the temperature go up while you are driving or when stopped for lights and such? Do NOT remove the radiator cap on a hot engine... running or not. If you want to verify waterpump operation remove the cap while the engine is cold. Start the car and watch, as it warms up it will gurgle a little and might push out a little coolant. When it reaches thermostat temp the water level will drop, when it does look inside the radiator and you should see the water flowing.

Typically if the head gasket is the problem it overheats very quickly and the heater core doesn't help as you are bleeding combustion into the cooling system - combustion occurs at 3000-4000 degrees so that little heater core as no effect. If you want to verify then get a block tester, it will detect combustion products in the coolant.

If the temperature only rises when you are slow moving or stopped then the fans are possibly the cause, if it happens even while traveling at speed then the airflow isn't the problem. In that case I would get an infrared thermometer and look for cold spots in the radiator which would indicated partial blockage. You will still get waterflow just not enough. You might consider getting water wetter and adding it to your coolant - it works.

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