beasyhomie

hello, i'm new to these forums and would like some help from ppl that know this car well. i purchased a 1999 GS400 with 136k miles and the car is amazing except for my overheating issue. here is what i've replaced on the car. Radiator, Upper and lower coolant hoses, Thermostat (3 times), Timing and Serpentine belt, Waterpump, Upper/lower intake manifold gasket, Coolant temp. sensor, o2 sensors, and the battery. i ordered a new radiator cap this week as well. flushed and bled the system out 3 times over the course of 4 weeks. no smoke from the engine, there are no leaks, no white smoke from exhaust, no rough idle or start up, no coolant mixed with oil, nor oil with water. when i start the car in the morning it can stay idle forever and not overheat. the car starts to overheat when i drive over 15/20 minutes and am idle/at a stop. the gauge starts to creep up at a stop light or stop and go traffic. but once i start going the needle drops to the center just a tad bit below at a perfect operating temp. like it never was overheating. i can even drive highway speeds consistently (60-70mph) and no overheating .. the fan comes on here and there not all the time deff has been off during the overheating. the heat only works when driving then starts to blow cool air when parked or idle too long. the upper hose is super tight and hot. the lower hose is hot and tight as well but not as hot as the top hose. the coolant reservoir boils and steams causing me to refill the coolant every 3-4 days, i can smell coolant when i turn my car off an walk past the front. Infrared Thermometer reads the engine at about 170-190 degrees F. while the hoses are at 190 up to 218F. is this issue common on 2G models? could the fans not turning on cause over pressurization and when are the fans suppose to activate? has anyone dealt with this? and would i need to replace the entire fan or a specific part?


UPDATE: after changing all those parts it lead to my radiator fan not operating. idle an at low speeds i’d overheat gradually and then shoot back down once above 25/30MPH. slow drives sucked while fast drives was the only time i can enjoy the car. my point is please check all the lil **** before trying to tackle the HG. i had 2 mechanics (random ones not my trusted) an a couple ppl online tell me its a BHG for sure. my car is running like a dream now. thank you for those who helped.

lexo98

iTrader: (2)

How did you bleed the system?

beasyhomie

removed the caps, filled car at bleed point, started the vehicle turned the heat on high, let the car idle until at operating temps. added a lil coolant as needed in reservoir.

Saveth

I'm going to take a guess that the heat only blows cool at idle a couple days after filling the coolant reservoir. If that's the case, it's because you have a coolant leak. My guess is the water inlet o ring is leaking because you mentioned doing a timing belt. I've done that job twice and it's leaked on me twice. So now I use rtv on the o ring. If you're using toyota pink coolant, it should be very easy to find the leak.

http://rigs.corequipment.com/Cebby/9...20(Medium).jpg

Tuanville

Yup, might be a coolant leak. There is a water pipe under the intake manifold. I think it's called the water bypass outlet. It has a o ring seal on that pipe and when it leaks from there it's unoticeable. One way is to try and look under the intake manifold to see if its wet. Double check your thermostat installation too.

beasyhomie

i did see this hose when looking up coolant system issues. do you know what its called ? wouldn’t there be signs of a leak? like combustion.

Bykfixer

I wouldn't rule out air bubble just yet but they typically cause the temp guage to rise whether you are setting still or driving at interstate speed.

https://www.clublexus.com/forums/gs-...fan-relay.html
See posts 8 and 18
This may rule out a temp sensor issue.

On one (non Lexus) car I owned the temp sensor on the radiator, the one on the engine and the fan motor switch took turns not working so it took a while to figure out all three were the issue. Luckily the car shared those items with other models and junkyard parts got things going again without costing a whole paycheck.

I'm new to the Lexus ways but see so far that Toyota and Lexus vehicles share a lot of the same parts, which makes sense from a manufacturing cost viewpoint.

You can go to LexusPartsNow and look up part numbers on various models and if they cross match just go to a junkyard and find a Camry or whatever. When I take on a project I'll visit a junkyard to see which models litter the place of the brand I'm fixing up. Then research part numbers as things pop up and often use those. On a Honda Prelude for example a broken inside handle plagued the cars. But junkyards were littered with Civics and Accords that used the same handle. To this day Honda uses a number of parts used in the 90's. Same with Toyota and Mazda.

Best of luck finding the issue. Sheesh, that can be worrysome.

KyleH

iTrader: (1)

If the GS400 is like the GS300 system, there's a thermostat for the fans located in the bottom of the radiator on the driver's side. There will be an electrical plug that goes to it. If this is faulty, it could be causing your fans not to come on consistently. Further, the fan(s) could be a point of failure. As a test/validation, if you unplug this connector on the bottom of the radiator, you should find both fans turn on full power as a failsafe to prevent overheating. If they don't, I would suspect a problem with the fans. If they do, I would suspect a problem with this thermostat.

TrueGS300

Smells like a head gasket issue to me. How long have you had the car? If you purchased it for a "good price" with an overheating issue, it's probably because of a blown head gasket or some major issue the seller knew about and wanted to be rid of. General rule of thumb is, overheating at idle is a fan issue, and at speed is a thermostat issue. But this is with a confirmed full system and no leaks etc. If you have access to a cooing system pressure tester, use it for two things. One: to check for leaks, and two: connect it without adding pressure and start the engine. If the pressure rises quickly, it is because of combustion gasses escaping into the cooling system suggesting a head gasket issue. If you give it gas and the pressure rises quickly, this supports the head gasket issue because more throttle means more pressure into the cooling system. Idling is low pressure, but driving means high pressure and then overheating after driving and no leaks means you have a fan issue or a head gasket pushing combustion gases into the cooling system.

newgsman

iTrader: (4)

I agree with the radiator temperature sensor diagnosis. If the car only overheats at idle or very low speeds the fans are probably not working right. That means either the temperature sensor or wiring to the sensor, or the fans themselves.

beasyhomie

i believe that may be the issue as well. i’m going to replace the fans entirely.

beasyhomie

i’ll test that out tomorrow to see if the fans come on. i ordered a whole new fan assembly. i think the sensor is fine since i just got a new one. hopefully its not faulty. i started up my car today an it was fine per usual cold start, except the fans didn’t come on at all. i know the fans have came on a couple months ago on start up. haven’t been really been able to test it since ive been back an forth at the shop tryna figure out the issue. but i will disconnect that an get back at you. thanks for the reply man.

beasyhomie

my mechanic has done a pressure test an the cylinders are fine. i get not one single sign of a BHG except for overheating at a stop light or below 30mph. it maybe my fans. cause once i start going the temp gauge shoots down as faster than it went up.