King0824

I have a 1999 Lexus LS400 with 173k miles. When I turn my car on the coolant temperature goes all the way to the top but the car is not overheating. When I turn it off it goes all the way back down. When I hook up the scanner and Im driving I get an average temperature of 185 - 199. I have been losing coolant very slowly every so often I check it. I fill up to the full line and a day or two later it’s on the low level line. I used a coolant pressure tester and there’s no leaks. I’ve replaced the thermostat and the coolant temperature sensor also. What could it possibly be?

400fanboy

For the instrument cluster, read this thread talks about the same issue:

https://www.clublexus.com/forums/ls-...l#post10257568

As for your coolant level - the coolant isn't just magically disappearing. If it were a internal head gasket failure, I would imagine it would be rather obvious since that's a rapid loss of coolant. But you don't, and, 1uz basically has a bulletproof head gasket (I'm looking at you Subaru).

paulo57509

The temperature that you're reading with the scan tool is what the ECU is seeing; your measurements are within normal range so I would say the cooling system is working as it should,

You changed the coolant temperature sensor; this is what the ECU uses for coolant temperature. You need to check the coolant temperature sender; this is what the gauge is connected to. The temperature sender has a one-wire connector. The sender (and gauge, if needed) inspection procedure is attached.

Did the coolant level start dropping start after the thermostat change? Was the cooling system bled after the thermostat was changed?

King0824

I bought the car with temperature Guage reading about 5/6 high of the way when driving for a while but it would start at the bottom and go up abut the car wasent overheating. The coolant the previous owner used was green coolant. So I did a complete coolant flush and replaced the thermostat with the oem one from Lexus. I followed the instructions on the reservoir and bleed the air out of the system. Idk if the coolant was leaking before hand since I changed it the week I got the car. When I seen that the Guage was still reading high. I replaced the coolant temperature sensor and it also didn’t work. So I thought I could be the cluster itself. The Rpm guage Guage and speedometer were also inaccurate after my car stalled once on the road. So I bought a cluster on eBay and installed it yesterday and the rpm and speedometer are now accurate but when I start the car the coolant temperature Guage goes straight all the way to the top and when I turn the car off it’s goes down. Even when the car is off and I step on the brake or put the key in the ignition (not turning the car) the coolant temperature Guage goes all the way up and if I take my foot off the brake or the key out of the ignition it goes down slowly.

CLLEXUSS

Coolant level fluctuates depending on hot or cold. But if you are constantly losing fluid that is rather curious. Maybe test your coolant for combustion leak detection? That is if you think you are losing fluid. But it seems you have electrical issues as well so its tough to say.

King0824

Isn’t the temperature sender supposed to be next the coolant temperature sensor? It looks like it’s just a bolt and I don’t see no lconnections

paulo57509

I reviewed two part catalogs and one catalog shows both a one and two wire sender - sorry for my confusion but it's still not clear to me what's going on here. I'm assuming that at some time, Toyota must have combined both gauge and ECU functions into a single sender/sensor.

I would still as a minimum, perform Step 15 that's in the attachment in my earlier post. It should tell you whether it's the sender (and it's circuit) or the gauge that's faulty.