KC98LS

Hi all.

I figure it's time I contribute something.

I've had my 1998 LS400 for about 3.5 years now. This winter my thermostat finally gave up. I always felt that this car took FOREVER to warm up, like 20+ minutes to reach the first bar on the temp gauge. Turns out my thermostat/thermostat gasket was bad!

I replaced thermostat + gasket using part numbers: 90916-03100 + 16346-50010. Chances are you can get away with just replacing gasket (16346-50010), as mine was broken in pieces, and stuck in the spring of thermostat, causing it to be stuck open.



Here are some symptoms I experienced which allowed me to diagnose the stuck open thermostat.

Poor gas mileage.
Poor heat performance/luke warm heat.
Dropping temp gauge on highway.
Temp gauge never passed first bar.
Fast idle, even after 1 hour of driving.




Job is super easy, this video is very helpful, LS400 has 3 bolts instead of 2 for thermostat housing. Make sure to refill using Toyota Red Coolant & Distilled water (if you're not using premixed)
Too cold, fast idle.
Normal operating temp.

RA40

iTrader: (6)

Glad that was an easy fix! Thanks for posting.

valex

dicer

In hot weather it would run too hot. In cold weather it would like you say run too cold.

saleenssc

how much coolant is lost during the thermostat change ? I imagine the best time to do it is after the car has been sitting overnight.

Superfast1

KC98LS- Considered yourself lucky that it stuck open otherwise your engine could overheated if it's the other way around & yes, it's very easy to change on the LS400 unlike some other Toyota cars i.e. the Corolla. My son's 03 Corolla's thermostat also stuck open recently & had all of the symptoms you've described. Had to remove the alternator in order to get to it.

Saleenssc- Yep, the best time to replace the thermostat is when car has been sitting overnight or when the engine is cold. Just open the wingnut at the bottom of the radiator to drain some of the coolant out so the coolant level is below the thermostat before you remove/replace it. You can re-used your coolant if it was recently replaced and/or clean.

sha4000

iTrader: (1)

How long did you drive with this issue?

KC98LS

Probably less than half a quart.

Honestly about 3.5 years.. it just got really bad this winter.