Hey everyone, took the SC to hot import night and boy was it amazing. HOWEVER, on the way up, its an hour ride on the highway, the car ran beautiful. On the way back, when the air temp outside was CONSIDERABLY COLDER the heat gauge sky rocketed to the bar right before the red zone. I almost **** myself when I look down and see it so I pull over and turn the heat on and shut it off. The air coming from the vents is cold...on MAX HOT coming from the front vents. We go to open the hood and no steam anywhere, nothing dripping, no coolant smell, and most importantly NO BLAZING HEAT from the engine when you open the hood. So I scratch my head and go back to the car and turn it on and drive away and the heat gauge stayed at normal temp...then right before my house again it rose up to the red again and went back down as I got home...



..?

 

If the engine wasn't really getting hot at all, then it sounds pretty much just like a bad sensor.

 

Stuck thermostat....easy fix...make sure you get all the air bled out when you replace it.

 

My thermostat was replaced last year with a fail safe thermostat. Is that why it suddenly dropped back down to running temp when the thermo sensed overheating? What sensor could this be good2go?

 

bad thermostats lead to blown head gaskets. It could just be your dash coolant temperature sender.

 

Hmm, where is that part located on the car if I were to replace that.

 

Yep, as the other guy already said, the coolant(engine) temp sensor.

A quick search yields quite a few threads on this; here's one:



https://www.clublexus.com/forums/ls4...ange-pics.html



btw, I must say this looks way easier than the SC3's replacement

 

Coolant temp sensor has NOTHING to do with the heat blowing cold out of the vents....so either his cooling system is low, or like I said, the thermostat stuck.

 

I'd also like to interject that if the thermostat is a year old and is the "failsafe" type I would replace it just to be safe after a scare like this. It's a quick easy job and those "failsafe" thermos are dirty lies, I've bought several for several different vehicles before finally finding that not only do they not "failsafe" but they also tend to not work at all straight out of the package. Frustrating.

As for the temp sender, I would have to look to be sure on the sc3 but on most vehicles the temp sender is located right next to or below the coolant temp. sensor.

 

Guys just an update I added a water bottle of poland spring to it this morning before I drove it again to "quench her thirst" and she was fine all day. I sat in post-fireworks traffic for an hour and it remained fine at normal temp and I forgot to test the air from the vents

I went out to the driveway while it was still hot from coming home and it blasted heat. I'm not sure if this is heat from the cars engine bay being pumped in or coolant heat being dispursed the RIGHT way...but none the less the needle stayed the same and I feel like if I had a bad thermo or temp sensor both would have affected the engine temp in one way or another sitting in traffic for an hour.

 

Try a Radiator Flush! Had the same problem less than a week ago with my 93' SC400. Fortunately radiator flush at my local lube spot did the job and stopped my gauge from going up and down! My Lexus mechanic told me to 1.Radiator Flush, if not 2.Temp Gauge Sensor, if not 3.Thermostat