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Hi just had a code p0128 I think, replaced the thermostat still got the code replaced the water pump again CEL comes on again. The top radiator hose was getting ready hot yet the bottom hose stayed ice cold. I'm my infinite wisdom I just went with the most obvious. So correct me if I'm wrong but the pump pumps coolant from the bottom of the motor to the top, then through the top radiator hose through the radiator then down to the lower radiator hose. Just not sure what way the flow goes. Thanks.
 

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Yes, you're right about the flow directions but if your radiator is plugged it doesn't make any difference which way it doesn't flow.

An easy flow test is to remove the bottom hose and pour water into the filler cap. It should come out as fast as you can pour it in. If not there are low priced replacements on eBay. But if you think you get what you pay for go to the dealer and I'm sure he'll sell you a REALLY good one.
 

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Toyota or after-market thermostat?
Did you test it before installing?
Any chance you put the thermostat in backwards?

Not all new parts are good parts.
 
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Discussion Starter #4
Ya it was an aftermarket thermostat, and no I didn't test the new one. I did test the old one and it opened up pretty good in boiling water. The pump looked good to, I think I just spend a lot of money needlessly. It was around -15 C when I first experienced the problem and I think it was just to cold for it to heat up enough to open the thermostat. Does anyone know where the sencer is for the temperature? I know there's at least 2 it looks like there's some kind of sencer at the bottom of the radio.
 

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Could be a plugged radiator also make sure when you installed your thermostat you place the jiggle valve in the correct position.
 

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Minus 15C is not too cold for a Rav4, I am often out in conditions much colder than that.
Could you tell a little more about P0128 code, my 99 does not use that code so I don't know what it is complaining about.
My 99 model has 3 temperature sensors, 2 are used by the ECU and the third one is for the gauge on the dash, other models could be different.

If you are looking at the temperature sensor for the next part to try, I would guess the one on top of the engine instead of the one in the radiator, but always check the wires and connectors first. Much of this guess is from what you have done so far, and may not be based on facts.

The main problem I have with aftermarket thermostats, is that you don't know if they are exactly like stock, or just close enough to not be a problem for most applications. I am usually lucky enough to have one of the few, where the minor changes cause problems.
 

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P0128 Causes and related Questions

I was cruising down the road the other day when I noticed the RAV wasn't warming up like it should. Later that same day when the ambient air temperature was warmer the RAV hiccuped, the 3 dash lights came on and the cruise control went off while the cruise light started flashing. It did affect my performance as well - felt like the vehicle was dragging a weight suddenly. I checked with my code reader at home and found the P0128 code.

Everything I've read here points to thermostat, but I've also seen on other sites that it could be the temperature sensor, or other things as listed in this forum. Any thoughts? If it is the thermostat should I stick with a stock Toyota thermostat? Do they come in different degrees of warmth like other vehicle aftermarket thermostats do? Living in a cold climate here in Canada I've noticed that it doesn't heat up as quickly as some vehicles I've had until I start driving, or have cardboard in front of the rad and I'd like to get more heat out of it.
 

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Discussion Starter #8
Hi can beamer, the jury's still out on my 1998 rav 4. I had a similar problem with the bottom of the rad tube not heating up and the top one getting really hot and the CEL coming on I replaced the thermostat ( aftermarket) and wate pump and the CEL didn't come on for awhile until i went for a long drive and the CEL came on again :/
So I'm going to get a new rad cap , flush the rad , try a new temperature sencer. Then a new rad after that I guess lol.
 
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