My 1999 LS400 had its original thermostat...

Recently noticed warm up times had increased considerably so extracted the thermostat for inspection and found the internal seal inside the thermostat assembly had split and was holding the thermostat valve open...

Gas mileage was down...

Lucky this did not get sucked into engine...

The rest of the thermostat internals were fine but the rubber had degraded with age and use.

If you have an original thermostat, replace it with an OEM part...they are reasonably priced. So no excuse for aftermarket...
DO NOT USE AFTERMARKET crap. About a 3/4" piece of internal rubber seal (not the housing to thermostat seal) had split and wedged between thermostat valve preventing engine warm up.


Parts required..thermostat, thermostat housing seal and crush washer for throtlle body coolant filling cap (1998-2000 LS400)
Coolant filling port is atop throtlle body assembly.Replace cap crush washer.

 

thanks for the tip! sometimes it's the little things that matter.

 

Good reminder! We'll tend to feel the thermostat is good because the coolant has such a long lifespan. Mechanically they may still function but the rubber gaskets do age and will be an issue if left unchecked.

 

mine went around 180K miles on my 1999 LS, I noticed the gas mileage got bad, changed it with OEM, simple job, easier than an oil change.
I now have 238K, all is well

 

Thanks for the great post and pictures of the part numbers needed for this job.. I have been considering changing mine on my 98 which has 180k on it. Your post has inpired me to change mine as well.

quick question. How much coolant did you lose or need to re-fill ? also where did you get the crush washer (part number 90430-20017) ? Lexuspartsnow.com has it for $1.64 but they want $12+ for shipping (ouch). do i just go to my local dealer for this part?

thanks

 

First I drained radiator (but not engine block-doing so will prevent any loss) so as the plumbing sits you will lose about a half quart to a quart of coolant pours out when removing thernostat.from thermostat housing so have a catchment cup or tray at the ready.

Order parts from your Lexus dealer..not much savings online with these parts

 

Great tip! I'm glad I had mine done with the timing belt and water pump. My school of thought is whenever a larger service like that is done, then I best replace the smaller items. Also whenever there is a potential for the thermostat to be exposed to air, I always replace them. That is of course after they have been in service for a while.

 

I was able to buy mine at a Toyota dealer, they were the same part number but saved about $10 over a Lexus boxed one.

 

Did you purchase and replace the rubber gasket as well?

 

Yes, It was the same time I was doing a Timing Belt/WP as I had just bought the car. So I also bought a Crank seal from Toyota as well. Here's my receipt with part numbers

 

21 to 31 year old thermostats are well past their sell by date.

The thermostat employs an internal rubber seal.

Either by mileage or age, it is prone to failure.

Inexpensive preventative maintenance.

 

Nice of ya to bump this thread cuz some people wont remember this as preventive, only usually when they do the T-belt/WP job. I changed mine when I bought my 94 about 4 yrs ago. It still had the original T-stat in it, which failed. At the time I needed the part right then. There was an Autozone around the corner so I pulled in, bought the "Failsafe" T-stat and Fel-Pro gasket ($20 total) and installed it in the parking lot. Now, 30K miles and 4 yrs later it's still doing its job, no problems. But, if ya have time to wait for delivery then spending the extra money for OEM is a good idea. It aint that much more.

 

I've done them each 60K. Also if you drain from the petcok, that is a good time to buy a fresh one.