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Hello! My name is Jake and I have an 04 RX330 with 230,000 miles on it. Not certain on the history of it but I have gotten it with no heat and an overheating problem(EDIT: previous owners said it has overheated on them). I immediately knocked out the easy stuff, checked coolant levels, verified fans were working. So I end up doing serious work that it needed: waterpump, timing belt, power steering pump, upper/lower intake gaskets, thermostat(THM 117-$11.32 at napa), valve cover gaskets, spark plugs. I end up finding smoke swirling out of a crack in the radiator while the car was idling for an hour during a fuel injector decarbonizing process. I end up replacing the radiator as well as the fan motors with the relay because the fans wouldn't turn on. I ended up using a power probe straight to the old fan motors and only fan #2 worked. I end up putting it all together-bled all of the air out of the cooling system with an airlift evacuation tool-and this thing is still overheating! Today I pulled it in and put the scantool on it-temp reads 244 degrees, so it's up there. I take a laser thermometer gun and the passenger-side (or upper hose) of the radiator read 183 degrees give or take and the part of the intake that the sensor screws into was around the same. So I thought it's only a $20 sensor, and replaced it-also considering it had a previous P0117 code(engine coolant temperature circuit low input). I know when the DTC is aiming at the input part of a circuit, it's talking about something with the sensor. I thought this would do it, BUT the car still overheats via gauge. Good news was I had heat, so I'd blast it when it starts climbing up and it'd slowly go down. I'm really stumped now, because I know the heater core acts as a mini radiator, but it doesn't make sense that the heatercore cools the engine down but not the fans and radiator being fully functional. The upper heater hose is piping hot with pressure but the lower hose is room temperature with pressure, I verified by squeezing the hoses. Is the thermostat defective? I installed it with the wobbler pin positioned at the top via installation instructions. I feel like I might run a compression test tomorrow to check the head gaskets, but I feel like I'm missing another sensor or something-I'm a freshman in college so anyone with experience I'd greatly appreciate it! 

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sounds like the heater core is plugged with the temp differences between the 2 hoses.

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A coolant check should reveal whether a head gasket is leaking and subsequently superheating the coolant.

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On 2/13/2018 at 11:34 PM, 04lexusrx33O said:

Hello! My name is Jake and I have an 04 RX330 with 230,000 miles on it. Not certain on the history of it but I have gotten it with no heat and an overheating problem(EDIT: previous owners said it has overheated on them). I immediately knocked out the easy stuff, checked coolant levels, verified fans were working. So I end up doing serious work that it needed: waterpump, timing belt, power steering pump, upper/lower intake gaskets, thermostat(THM 117-$11.32 at napa), valve cover gaskets, spark plugs. I end up finding smoke swirling out of a crack in the radiator while the car was idling for an hour during a fuel injector decarbonizing process. I end up replacing the radiator as well as the fan motors with the relay because the fans wouldn't turn on. I ended up using a power probe straight to the old fan motors and only fan #2 worked. I end up putting it all together-bled all of the air out of the cooling system with an airlift evacuation tool-and this thing is still overheating! Today I pulled it in and put the scantool on it-temp reads 244 degrees, so it's up there. I take a laser thermometer gun and the passenger-side (or upper hose) of the radiator read 183 degrees give or take and the part of the intake that the sensor screws into was around the same. So I thought it's only a $20 sensor, and replaced it-also considering it had a previous P0117 code(engine coolant temperature circuit low input). I know when the DTC is aiming at the input part of a circuit, it's talking about something with the sensor. I thought this would do it, BUT the car still overheats via gauge. Good news was I had heat, so I'd blast it when it starts climbing up and it'd slowly go down. I'm really stumped now, because I know the heater core acts as a mini radiator, but it doesn't make sense that the heatercore cools the engine down but not the fans and radiator being fully functional. The upper heater hose is piping hot with pressure but the lower hose is room temperature with pressure, I verified by squeezing the hoses. Is the thermostat defective? I installed it with the wobbler pin positioned at the top via installation instructions. I feel like I might run a compression test tomorrow to check the head gaskets, but I feel like I'm missing another sensor or something-I'm a freshman in college so anyone with experience I'd greatly appreciate it! 

You could still have an air bubble in the system.

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Wife's car (RX400H) has the same issue.  I don't understand how blasting the heat has a significant effect on the coolant temperature.  Does a head gasket leak itself cause a car to overheat or is it due to loss of coolant?  Coolant levels (radiator and overflow) are fine so how would a head gasket cause overheating in this case?

By the way, the car's first issues were shaking at 40mph and a check engine light related to cylinder mis-fire.  Blue Devil treatments were done but not effective.

 

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Blasting the heat removes heat from the coolant. A head gasket leak injects super-heated air directly into the coolant. 

A bad radiator cap can also cause an overheating condition if the cap cannot maintain sufficient cooling system pressure.

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 my RX 400H has no heat. There is no obvious leak from radiator or coolant as Ive had pressure tested at 3 different garages. However Im topping up very frequently but only on occassion because sometimes coolant reservoir is steady which is confusing. My car overheats sudden high speeds and cools down at constant fast speed on motorways. In the city on constant mid speed it overheats despite having coolant. uphill on a motorway it cools down. no garage i have approached including the main dealer have an answer other than to throw money at it to investigate the cause. my car is 2008 and drives great but is not worth throwing money at. Any answers or solutions?

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A stuck thermostat could reduce interior heat (stuck open) or cause overheating (stuck closed or partially closed).

Has anyone checked it?

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