Well I left the car running for a few minutes with the fans on and the temp sensor unplugged. I shut it off because I could feel and hear the coolant boiling. What could be causing this, the water pump? I'm stumped! What to you think?

 

Does the sensor look similar to this?

 

These are still the answers I NEED!!!!

 

Yes that is exactly what the sensor looks like.

There is no white smoke coming from the tailpipes and the oil is not milky.

 

I hope it's nothing major!

 

So I was thinking a little bit about your problem and perhaps you recieved a defective thermostat??? Which would cause the coolant to bypass the radiator completely and possibly the engine temp sensor that controls that fan.(which would be why the fans wouldnt turn on because its not getting a hot reading)
The coolant would then heat up hit the pressure cap and overflow into the tank at boiling temp.

That or your pressure cap isnt on all the way or is broken therefore decreasing the coolants boiling point.

Those would be two simple and inexpensive fixes.

If it was the waterpump wouldnt it make sense that the coolant wouldnt be super heated because it wouldnt be pumped through the engine?

 

definately not a waterpump.....you need to take it to a mechanic and have them pressure test the system. This will tell you if you have a head gasket leak or any other leak on the coolant system. One of the symptoms of a head gasket leak is boiling coolant in the tank. They shouldn't charge you much at all to do this $20-$30. i would do this before moving to anything else b/c if you do have a blown head gasket then the other repairs are pretty much meaningless. GL and let me know how it turns out!

 

you hear the water bubbling up in the overflow tank right?

sounds like a rad cap

 

in all my years work on cars I have never seen a rad. cap be the source of that! But if it is I really would like to know!

 

Yeah, the radiator/pressure cap usually adds about 15psi to the system which increases the tempature at which the coolant will boil by about 45 F. So that could be one possiblity.

Its defently easier fix than a headgasket, but kevs98gs4 is right. A compression test may not be a bad idea, just to be safe.

 

I'm going to buy a new cap later today. It's worth a shot and I'm hoping the new cap will solve my problem.

Is the temp sensor in the radiator critical to driving the car? Can I replace that later?

 

If it is the pressure cap, then that may solve your problem and your engine temp sensor really isnt bad it was just getting an incorrect reading. But if you replace the cap and the fans still dont kick on after you've had the car running a while then you probably need to replace it before driving the car too much.

 

I had another observation. I noticed that when the coolant reached the boiling point the temperature needle in the dash was in the middle. Does this seem normal? Note that I had the temp sensor on the radiator unplugged.

 

I installed a new cap and the coolant boiling problem is gone. What an easy and cost effective fix. I do need to replace the temp sensor on the radiator. For now I have to leave it unplugged so that the fans will get power. A BIG thanks to everyone who took the time to post thier thoughts and opinions.

 

does anyone know what the part number for this sensor is? the one that goes inside the radiator below the fans? i called lexus but they didnt give me the right info. i bought a coolant temp sensor which is wrong and dont know what is that for