I don't trust that dealer. A 98 has only one water temp sensor and the signal named THW is directly sent to the ECU as shown in the diagram below. There is no unit called a communication box in our 98.

 

Actually, I am looking at the diagram from the dealer and there is an ECM and a CPU receiving signal from the engine coolant temperature sensor. Like it was explained to me by the 30 year mechanic. The ECM does not send signal to the gauges it goes to a separate box that sends to the gauges.

 

I'm confused. Does the 1998-2000 have one or two temp sensors?

 

A 98 has one temperature sending unit/sensor. Passenger side front intake. Please correct me if I am wrong.

 

Without knowing the fact, some people try to help others kindly. I don't blame them but those kindnesses often mislead others and you have to be careful. I may be one of them and it's you who believe me or not.

A 98-00 only has one ECT sensor for the ECU and the cluster. The ECT sensor sends the analogue signal 4.5V(far below freezing point) - 0.5V(overheating) depending on the coolant temperature to the ECU and the ECU sends the processed signal to the temp gauge in the cluster. There is another sensor at the radiator which is only used for the fan control. I hope I'm not misleading you.

 

This is my understanding.

 

Whatever you do,dont argue with Yamae.

He is THE source for all things electrical,end of story.

 

How often does you engine cooling fan kick in? Not the electric A/C, but on the really hot days under load, when does your main clutch kick in and start cooling the engine at more than passive speed.

 

I just ran down the freeway at 70-80 mph,no engine fan noise.100F outside.Now when driving up mountain from 1500 feet to 5000 feet,in 90 degree weather,if I push it I can get engine fan to roar.Drive sanely,its off.NOW when I reach home,if I stop at post office in 85 degree,and let it idle maybe 5 minutes or so,on my hot engine with A/C on,it will kick in the engine fan.It kicks off again quickly as soon as I start driving again

So in my case,i'd say less than 5%,(even less maybe), of the time do I ever hear the roar of the engine fan kicking in.

 

Sounds like I am installing a fan clutch soon. Mine spins about 2 1/2 times if I spin it with engine off. With engine on and to temp I can stop it with a newspaper. However, never "roars," NEVER. I have been suspecting it.

 

Have you looked into rebuilding it? As I recall (*), they are pretty simple devices, with special fluid in there which has probably leaked out and needs to be replaced. There's also a bimetallic spring in there that changes the valving to make it lock up more as temp rises (which is the opposite of how fluid viscosity usually changes with temperature).

(*) and I'm speaking in general terms for Lexus / Toyota viscous fan clutches. I don't know if this applies at all to any of the specific cars mentioned in this thread.

The clutch on my '91 is still working fine as I'm about to hit 200k miles, and if it ever fails, I plan to try to replace the fluid / rebuild it.