I just bought this 1998 LS400 121,000 miles, I drove about an hour and half home and it was completely fine, I then parked at home went back out to grab food and go grab some stuff from the store when I was at the store I notice it was on H and shut it off immediately. I wasn’t far from home so I let it cool off then parked up. I first thought thermostat, I changed the thermostat still over heating even tried without the thermostat. Next culprit I thought was the coolant temperature sensor as my front a/c fan wouldn’t run, I changed that to see no changes, i then thought maybe there was air in the coolant, so I bled the system still didn’t make any changes. If I was to rev the car at like 2500k rpm the gauge would start to lower so I thought the fan clutch then I was able to stop it while the engine was running so I changed that and really thought that was the issue, the fan ran so much better. I allowed the car to idle for like 15 mins and it didn’t go above what I think is normal temp for this car, I then drove to Wendy’s not even a mile away and when I was in the drive thru it started going up and I shut it off. It has has no leaks from anywhere and the water pump was changed 30k miles ago, this really has me stumped and I’m really stuck at this point. I suppose the last option would be the radiator is clogged as when I bought it didn’t have the red Toyota coolant either. If anyone could help it would be very appreciated.

 

First things first. Pressure test the entire radiator cooling system. I have taken my water jacket apart recently and the previous owner had dumped in the destructive aftermarket CLOG POUR WATERPUMP junk from autoscam stores. Dont use it. Make sure your system is totally free of chemical clog debris. Check your overflow bottle ALL HOSES and entry exits from bottle. My ls 400 had a clogged heater core, Heater control valve ruined, water pump, overflow bottle small lower non visable inlets clogged and a micro leak from a rear water bridge all caused by that JUNK. Next question were you driving hwy speeds all the home for 1 1/2 hours? then in city stop and go it over heats.

 

Mixing coolants can cause many headaches. If it didn't have the correct coolant in it ,then all of whatever was in there needs to be completely purged and then filled with a 50/50 mix of the correct version. Was it green coolant? Did you have the AC on when it started to overheat, if so, was the auxiliary (electric) fan operating?

 

Yeah it was the green stuff, when I bled the coolant system I added water and red Toyota coolant, I’m certain when it intially overheated I had the ac on, now the last time I did as well but I shut it off to see if that changed anything and it didn’t, but I know the ac fan is running as I just changed the sensor for it.. wasn’t running before.

 

And you are sure all the air is purged from the system?

 

Honestly I’m not sure, when the car was off, I filled up the reservoir then I pull the top bolt by the inlet and filled from there with a funnel while holding rpms at 2500k rpm and it was pretty much just shooting coolant out like a volcano afternoon like 2 mins but infially it was letting bubbles just come to the top of the funnel. I’m not sure honestly I don’t know a lot about purging coolant systems.

 

Use the search feature for this forum and you'll find tips on how to do it correctly.I don't want to tell you the wrong way and I haven't had to do mine yet. Try this one: https://www.clublexus.com/forums/ls-...ng-system.html
If an air bubble is trapped in the system it can cause it to overheat.

 

Also, some people raise the front of the vehicle to let trapped air out.

 

You could take thermal readings at various points on cooling system to see if sensor related.

If non-Aisin brand water pump installed could explain overheating

Mine was Autozoned before I purchased it and failure in short order.

See:

https://www.clublexus.com/forums/ls-...-bearings.html

If you do require replacement and purchase an Aisin waterpump/ timing belt kit, lose their timing belt and buy one from the dealer.

See:

https://www.clublexus.com/forums/ls-...eficiency.html

(My opinion)

Also, your radiator could be on way out...

Consider the tow package radiator:

https://www.clublexus.com/forums/ls-...r-options.html

 

Sound horribly close to a similar problem I had on a completely different car where the impeller in the pump was of bad plastic design and came loose on the metal shaft.
Gave a bit strange problems because the impeller was rotating ok:ish when idling and going slow but much too slow when revving. When taken apart the thing had 3 cracks in the plastic hub.
Just lucky it did not desintegrate I was told.
Really feel for you IF you got a crappy water pump...
when I changed cam belt on my 1995 i do not remember any issues with the bleeding.

 

my 99 had a similar problem and after a week of tinkering we replaced the radiator (for no apparent reason) and problem GONE..