lstommy

My temp gauge doesn't reach operating temperature.
It says a little over the 1st pin

What was done:
-The previous owner did a timing belt/water pump change 10k miles ago at 70k miles, Im at around 85k miles right now
-I changed the thermostat and temp sensor
-I went for a drive and notice my upper radiator hose is slightly warm but not as hot as the lower hose.
You think that thermostat is still bad? As in, it's staying open.

AlaskanLS

If your car has stuck open thermostat then it would make the engine idle high for longer than normal because the ECU would try to make it reach operating temperature. If the thermostat and the temperature sensor are aftermarket then their is high possibility it's not functioning properly. I believe it is the temperature sensor, not to be confused with ECT sensor. There is another temperature sensor that is close to the ECT sensor that is connected to the instrument panel to show you how hot the engine is running. Check this link https://www.clublexus.com/forums/ls-...the-forum.html
In picture the sensor that is labeled number 1 is I believe faulty in your car.

AlaskanLS

2nd is Engine coolant temperature sensor. If that is aftermarket then I would suggest to replace with OEM.

lstommy

Okay, Im going order an original one. As for number one, i found it to be part# 83420-20040 called GAGE ASSY, WATER TEMPERATURE SENDER, which is the one you recommend replacing?

AlaskanLS

I recommend replacing ECT (engine coolant temperature sensor) with OEM but I am not sure if that will fix your temperature needle but regardless you should always use OEM sensors. If you still have old ECT that u replaced with new non OEM try to install it back and see if that help fix your low temperature problem.
If the problem still exist then change GAGE ASSY, WATER TEMPERATURE SENDER.
The link I gave u, open that and download the pdf file I uploaded there and test Your ECT as explained in the pdf file.

AlaskanLS

Keep one thing in mind. Don't start throwing parts at your car for no apparent reason, I am wondering why you changed your ECT sensor? Those sensors very rarely go bad, before replacing any parts, test your old parts and confirm yourself 100% that the part you are replacing is actually bad. Test every part before replacing it.
Just because if someone has said by replacing so and so part helped fix his car's mpg, might not be the case with your car.

LS400FAN

Did you personally change the thermostat yourself? If so did you replace it with an OEM thermostat?

lstommy

Yes, I did it myself, I put the OEM back in. I plugged in my OBD reader and the temp is around 186F on the scanner but my temp gauge on the dash is showing a little over the first pin.

AlaskanLS

Now change GAGE ASSY, WATER TEMPERATURE SENDER, but before changing it, take it out and clean it with a fine sand paper and put it back in. Many times residue from the coolant make a layer over the sensor that residue won't let it function properly. If that don't work then change it.

AlaskanLS

Do the same for old OEM ECT sensor. Clean the tip that stays inside the coolant with a very fine sand paper. Check the ECT with a multi meter also and make sure it's resistance is within the range as described in the pdf file.

AlaskanLS

And lastly make sure the thermostat jiggle valve position is at 12 O clock.

LS400FAN

AlaskanLS....great advice, I agree 100%.

Banshee365

Hook up a scanner to the car and read the ECT through the ECU to see if it jives with what you're seen in the cluster. As you've probably found out, there are 3 coolant temp sensors on these cars.

lstommy

I replaced the sender unit that connects the dash and the temperature is still the same on the dash. I hooked up my scanner, it reads 180ish when warmed up. Temp gauge still at the first pin.

Edit: FYI, my fan clutch also starts up right away when I start my car.

TaninAuto

Cluster likely needs repair. We see it every day.

https://www.taninautoelectronix.com/...luster-repair/