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1994 Lexus ES300 Overheating

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New User

Aug 12, 2014, 3:51 PM

Post #1 of 3 (1879 views)
post icon 1994 Lexus ES300 Overheating Sign In

I have a 94 Lexus Es300 that over heats in about roughly 10 to 20 minutes. I've noticed my hydraulic fan dosen't run at all! I gave it a spin by hand see if it was free well it felt fine. I thought it was the pressure line house which runs from the power steering pump to the radiator. I replaced it nothing still. I replaced the the thermostat nothing either. Although when i took out the thermostat it had like trash on it. I flushed out my coolant truly enough it was dirty. Still nothing. My radiator starts right up when i turn the engine, but slowly comes to a stop and never runs again even if the temperature gets HOT! PLEASE HELP ME IT'S DRIVING ME NUTS

Ultimate Carjunky / Moderator
Discretesignals profile image

Aug 12, 2014, 5:41 PM

Post #2 of 3 (1863 views)
Re: 1994 Lexus ES300 Overheating Sign In

First of all you have to understand the theory of how this system operates, so you can diagnose it properly.

The electronically controlled hydraulic cooling fan system consists of a belt-driven hydraulic pump, a pump solenoid valve, a hydraulic fan motor and an electronic system controller (ECU), Fig. 1. The cooling fan processor (controller) determines hydraulic pressure by monitoring engine and air conditioner operation. A processor-controlled solenoid valve regulates oil flow from the integrated power steering/hydraulic pump to the fan motor. After leaving the fan motor, heated oil is then cooled by an oil cooler before returning to the power steering pump reservoir.

So basically, there is a fan control computer that is taking information in from a few sensors, then processes that information, and uses the results to control a valve that regulates the amount of hydraulic fluid that is used to drive a hydraulic fan motor.

You can separate the system into three parts. Then test each system part to find out which system part the fault lays. The isolate where in the faulty side of the system the culprit is. It doesn't matter which side of the system you diagnose first because you will eventually narrow down the culprit.

I would personally start at the hydraulic control valve and do a bypass test at the valve to see if you can make the fans operate. That would eliminate the hydraulic system and the valve. To do this you would briefly supply power and ground to the valve and see if the fans crank up.

Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Aug 12, 2014, 5:46 PM)

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 12, 2014, 5:45 PM

Post #3 of 3 (1859 views)
Re: 1994 Lexus ES300 Overheating Sign In

Does it still overheat when running 40-50MPH?


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