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My son owns a 1998 Toyota Rav4, 5 speed manual AWD. It has 165k miles on it. He bought it in the Pacific North West in April of this year.

He recently had a challenge where his Rav4 would begin overheating at any speed above 70 MPH. In the past week he has had a thermostat replaced, had the radiator cap replaced and has had a pressure test (it passed) and had the radiator flushed three times.

There are no known leaks.

During each radiator flush some particles of rust have been found as well as some other sediment. Other than that and the slight reddish color of the coolant during the flush, there has been any other indication of a blockage.

We flushed the radiator today for the third time and ran water through the whole radiator and engine. Then flushed it of water and filled it with coolant.

We tested by getting onto the highway and noted that everything was normal except when we exceeded 70MPH and as soon as he took his foot off the gas, the temperature gage showed the temperature to climb near the red line. After he put his foot back on the gas the temperature began to drop to normal. He did it again to prove it was something we could repeat and we had the same results.

He has been driving across the country and spent 3 days trying to get through Kansas when he was beginning to have the overheating issues, prior to that, he drove from Seattle south through Oregon, California, Arizona, New Mexico, Colorado, Nebraska, back to Colorado then on to Kansas. Prior to getting to Kansas, he had no issues. After some of the repair work in Kansas, he drove from there to Columbus, Ohio but stopped several times when the car began to overheat when he went faster than 70 MPH.

I'm beginning to think everything is normal except that the temperature gage is faulty. I'm probably wrong but I'm not finding any other posts here that have a similar situation.

Does anyone have any suggestions?

Thanks
 

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Sounds like the water-pump is going.
Toyota replaced the water-pump and the oil-pump when they replaced the my timing belt at 159k. Most recommend changing the water-pump at each timing belt change since they are right there together.

Other than the 3 days in Kansas, it sounds like he is enjoying the Rav4.
 

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Water Pump

Thanks Roundabout. What indication do I have with my description that says I need a new water pump? I'm not opposed to the idea, it is something we considered but I didn't want to spend money needlessly.
 

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I didn't want to spend money needlessly.
Given the mileage, a new water pump and belt can be considered preventative maintenance.
.
 

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Thanks Roundabout. What indication do I have with my description that says I need a new water pump? I'm not opposed to the idea, it is something we considered but I didn't want to spend money needlessly.
Looks like you have checked everything else, but mainly it is the symptoms. At 70 mph it sounds like you are not moving enough water to cool the engine. And the heating up when you let off the throttle tends to point to even less water cooling all the hot metal from a weak pump. This is assuming that you had the same problem before and after replacing the thermostat.

Just a side note: I once saw an old chevy that was missing a spring in the lower radiator hose, hard throttle would suck the hose flat and shut off the water. Idling or cruising about town it was fine.
 

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My guess is a worn out and inefficient radiator. The rust coming out is an indication and it likely has disintegrating fins. I bought one on eBay for an Accord years ago. Price was excellent, fit was perfect.

Water pumps usually fail due to leaking seals not loss of pumping efficiency.

A quick test is to turn the heater on max. If the temperature goes down the little extra engine cooling the heater adds indicates the radiator is bad but the pump is good.
 

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I agree with Dr Dyno - it's likely an inefficient radiator. Overheating at high speed is a classic symptom of a clogged radiator. Flushing is a preventive measure and most times won't cure anything.
 

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Could be the radiator, but seems odd for the radiator to suddenly clog this late in his trip.

But on the subject of changing the radiator, it can be done without removing the AC condenser and Autozone sells one with a lifetime warranty. I changed mine last year.
 

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It probably isn't clogged as in no flow just reduced flow combined with fin degradation showing it's effect in hotter weather.
 
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