ibarje

Hello,

My 97 Lexus LS400 overheats. New Fan Clutch and new thermostat... Recently flushed to get all the air bubbles out. No water leaks. The water doesnt seem to be circulating correctly, however, a lot of pressure builds up. My dad has to always release the build up pressure by lifting the latch located from the water reserve. When driving on the freeway at 65mph, it starts to overheat, but when I go slower, it seems to cool down. So the faster I go the faster it heats up, the slower I go, it seems to cool down. I left the car running with the A/C on and it doesnt heat up, but it only heats up when I start to run it. HELP dont know what the hell is wrong with my car....

LScowboyLS

1. was the thermostat a real Toyota one and is it correctly oriented with the jiggler hole in the 12'oclock position so the system can self-bleed?

2. was the correct procedure used when filling the coolant? - the final top off should be done at the FILL BOLT, a large bolt that points down at the ground near the thermostat housing

3. how many miles on this car? - radiators do not last forever, especially if the car has not had Toyota red coolant for its entire life.

4. when was the water pump replaced, was it a real Aisin water pump like the original?

5. how do you know it is overheating? - the temperature gauge on the cluster is not definitive evidence of overheating, they go bad too, as does the sending unit.

6. the correct Toyota radiator cap has no "latch" you can lift - put the correct one on it from the dealership ASAP

ibarje

I bought an aftermarket thermostat, and it doesnt seem that the water is circulating because the water from the reservoir, stays at the same level. When I see the temp gauge going up, my brother will lift the latch from the reservoir, which releases pressure and when this is done, the temp gauge goes back to normal.

Miles: 214k
No new water pump.

LScowboyLS

replace the following very low cost items:

1. radiator cap with the genuine Toyota part
2. thermostat with the genuine Toyota part
3. guage sensor with the genuine Toyota part

orient new thermostat with jiggler hole at 12'oclock position and then drain and refill with a 50/50 mix of genuine Toyota red coolant and distilled water - use the FILL BOLT to do the final top-off - keep a watch on the reservoir for a few days and top off reservoir up to max line as system continues to self-bleed

these simple inexpensive steps stand a good chance of solving the problem

if they don't, then put an exhaust gas sniffer in the reservoir and if it finds exhaust fumes you likely have a head gasket issue

otherwise, my vote then becomes that a radiator replacement is in order

ibarje

Great. Thank You!

LScowboyLS

the other possibilities are:

1. engine running issue resulting in high temperatures at high rpm which are overwhelming the cooling system capacity

2. worn or broken water pump vanes