Lexus082

I just completed the timing belt service on my 94 Sc400 for the second time. Now the car has 300,000 miles on it and the engine is very smooth and purrs like a kitten. However, I have noticed the temp needle fluctuates ever so slightly from the middle point (normal operating temp) and it slightly increases to the line right above the halfway mark. At first I just figured there was air in the system and that was the cause of the needle moving back and forth ever so slightly. But I've driven the car about a hundred miles and each time it has cooled down I have added a small amount of coolant. I'm pretty sure its just the air escaping and the coolant level drops as the air is displaced. However, I've drained and filled the cooling system many times and at this point I think the temp needle should be staying right where it should be in the middle and not moving slightly above the halfway mark and then it'll drop back and at times it will go back up and then drop back down.

I suppose its still possible there is still air in the system that could be causing this as I said I'm still adding a small amount of coolant after driving it for 30 minute intervals and allowing it to cool back down to cold. But I completely drained the coolant from the block when I performed the t-belt job and water pump replacement. I also changed out the thermostat with a Stant thermostat. I usually use an oem Lexus thermostat, but due to availability I went with an aftermarket thermostat. I also changed out the coolant temp. sensor that supplies the engine temp signal to the temperature needle on the gauge cluster. That also was an aftermarket sensor. I replaced the radiator hoses, water pump, thermostat, and used oem Toyota Red Coolant.

I'm just dumbfounded as what could be causing the engine to run slightly hotter than normal. Like I said the needle will rise up to the line that is right above the halfway mark and then it will drop back to the middle. As far as I know, there are no coolant leaks and the thermostat is operating as it should. Do you guys think there may just be some air trapped in the system? Or did I make a mistake by using an aftermarket thermostat. I think the thermostat I bought is a 180* degree thermostat, should I replace it with an oem Lexus thermostat or a lower temp 170* degree thermostat that Stant makes. I've really never had this problem before and I'm kind of stumped as to what is causing the temperature changes.

TheAzn

iTrader: (2)

It could be simply the thermostat... different wax components/ mixtures from different companies... etc.

I wouldn't worry though as long as it is not overheating. I think mines runs at slightly above halfway as well. I recently had my timing belt and water pump replaced as well. No leaks, Toyota red coolant, etc.

Lexus082

I agree with you, I'm thinking it is the thermostat causing the temp. needle to spike slightly higher than normal. Does anyone off hand know what temperature the oem Lexus thermostat is? Thanks alot I appreciate it!

Mattrob

Could quite possibly be the aftermarket temp sensor. After all your temp gauge takes a direct reading from the Temp sensor. Reinstall your old one if you still have it and you will know. I would put my money ther before the T stat.

Not that the new sensor is bad but not quite to Toyota spec by design.

1WILLY1

iTrader: (9)

my cars normal operating temperature is slightly above the halfway mark, doesnt sound like anything to worry about as long as it doesnt get worse.

Lexus082

Yeah, there's something up with this aftermarket BWD coolant temp sensor. I''ll drive the car for about 30 min. to get to work on the highway so it's completely warm and at normal operating temps. I'll come back about 3 hours later and start it up. It's winter time so its about 30 degrees and then engine is completely cold. I'll start the engine and it will idle for less than five min and that temp needle will already be at the halfway mark without even driving the car. I know its a false reading. This engine takes a few minutes to warm up even while its being driven.

So I don't know if all the sensors they make are all gonna act that way or if I just got a defective sensor.

TheAzn

iTrader: (2)

Holy damn, 5 minutes to normal temps? My SC takes almost 3 min for the needle to move far enough for the automatic climate control to come one. I'll say it is the temp sensor. Aftermarket stuff is usually cheap **** anyways so it's to be expected.

Why not just get a Lexus coolant temp sensor? $26.29 from Sewell Lexus. Register and make sure you add in your ClubLexus username to get the ClubLexus discount. Less than $26.

http://lexus.sewellparts.com/oem-cat...C400-1994.html

Think that's the sensor, right?