96UCF20

Hello everyone, this question is in regard to my 1996 Lexus LS400. Yesterday, I noticed the vehicle's engine coolant temperature gauge rising and immediately shut off the vehicle to let the vehicle cool down. After allowing ample time for the vehicle to cool down, I inspected my coolant reservoir and found that the coolant level was normal. I also inspected the engine bay and underneath the vehicle for evidence of a coolant leak and did not find anything.

While driving, the engine coolant temperature gauge reads at normal operating temperatures with or without the air conditioning running. If I stop and let the vehicle idle for a few minutes, the engine coolant temperature gauge will start rising with or without the air conditioning running.

Today, I noticed the same issue occurring while the vehicle was idling so I turned the heater on to alleviate the issue. This seemed to be effective in reducing the engine coolant temperature. I arrived home approximately 5 minutes after I had turned on the heater. When I arrived home, I noticed that my heater was not blowing warm air anymore.

What are some possible scenarios I should investigate to resolve this issue of my vehicle overheating? Thank you and have a great day!

RA40

iTrader: (6)

Welcome to Club Lexus.

My suggestions would be the usual for cooling system maintenance, fresh coolant and thermostat. Checking the radiator fins to be clear of any obstructions like leaves, bugs road grime, etc. Checkg vacuum hoses to the heater control valve for any cracks or poor fitment. As supplemental, going through all the vacuum lines to verify fit and replace any that are hard-brittle.

96UCF20

Thank you, RA40! I'm glad to be a part of the forums. My hunch is that the thermostat is the culprit behind my issue. I'll inspect the radiator fins tomorrow to confirm that they are free of obstructions. In regard to the heater not blowing warm air, I feel that there's a correlation between my overheating issue and my heater not blowing warm air.

I was driving my car about an hour ago and the engine coolant temperature was fine and the heater was blowing warm air. I drove home with no issues and did not let the car idle this time when I got home. Regardless, I will inspect the vacuum lines while I am inspecting the radiator fins.

Bercasio

iTrader: (1)

Went through the same issue, turned out to be the radiator cooling fan. The fan motor was replaced, no more overheating since then. Hopefully this is the culprit.

RA40

iTrader: (6)

+1 and check the fan clutch.

YODAONE

Another problem prone area sometimes overlooked is seal leakage from the water control valve at the base of the actuator arm...

Easy enough to diagnose....simply wedge a wad of folded paper towels beneath water control valve and see if evidence of coolant.(red or green)

This valve can be compromised by hasty jacking of the engine such as when replacing motor mounts, without first unfastening valve from the firewall.

1993 LS400 was running slightly hot, but intermittently so...and according to the temperature gauge replacing the leaking water control valve solved the problem.

Not sure if a coolant system pressure gauge would pick this up

Possibly the internal rubber seals were age hardened.

96UCF20

Today, I inspected the radiator fins and found them to be clear of debris. The vacuum hoses leading to the heater control valve were supple and free of cracks. In regard to the engine cooling fan, I attempted to spin the fan by hand and was met with little resistance.

I compared the resistance of the engine cooling fan on my LS400 to the resistance of my other vehicle's fan and it was noticeably easier to spin the fan by hand on my LS400. I can also feel the fan wiggle slightly if I try to move it.

All these signs lead me to believe that the fan clutch needs to be replaced. That being said, I've also been reading about something referred to as the fan clutch bearing bracket as a potential factor to my overheating issue. How should I inspect the fan clutch bearing bracket to rule it out as a variable?

timmy0tool

iTrader: (7)

i've experience this exact same thing down to every little detail and it boils down the air in the coolant system. this is evident with the heater not being hot anymore. if you hold the revs, the heater should become hot again as the air is being pushed out. bleed the coolant properly, and you should be fine!

bleeding involves holding the revs at 1.5k-2k so the water pump can work out all the bubbles. i personally have best experience doing this on an incline, front of the car higher than the rear to move as much air to the top of the cooling system to purge out of the radiator cap (which should be open during the bleeding process).

also remember to check for the color of the coolant, which should be red if factory coolant is used. toyota OEM red long life coolant is highly recommended!

RA40

iTrader: (6)

If there is runout of the bearings that would be an easy spot along with any scraping and visual signs like this YT video:


Enough times we'll have discussions on a failing-failed clutch assembly. If the system has been serviced recently, air in the system will give similar heating symptoms as Timmy mentions.

NotADood

Lexus master tech, I have seen it multiple times now, I would replace both fan motors. Go aftermarket as the OEM ones are outrageous in price, $600+ for both.

96UCF20

After I arrived at school today, I let my car idle for a few seconds and noticed the engine coolant temperature gauge rising again. I turned on the vehicle's heater and followed your advice by shifting the transmission into neutral and holding the revs at ~2,000 rpm for a few seconds.

This resulted in the engine coolant temperature gauge immediately dropping down to the normal operating temperature. The vehicle's heater also started blowing warm air as soon as the engine coolant temperature gauge dropped back down to the normal level.

If the parts arrive on time, I'll be blurping the cooling system as well as replacing the thermostat and fan clutch this weekend. I'll update this thread with my results.

96UCF20

I have good news! I replaced my thermostat, fan clutch and blurped the cooling system and my temperature gauge is not rising anymore! I replaced the thermostat first and blurped the cooling system right after installing my new thermostat.

After blurping the cooling system, I took my vehicle for a test drive and everything seemed to be fine. I replaced the fan clutch as well just for peace of mind. Thank you to those that helped me out!

RA40

iTrader: (6)

Glad that was a easy fix. Good timing with summer weather coming on.

96UCF20

I couldn't agree more! I'm surprised and relieved at how easy it was to work on this car!