IS300 F Sport 2018 Overheating Problem
Lexus Test Driver
Joined: Feb 2017
Posts: 6,260
Likes: 1,752
From: Richmond Hill, Ontario, Canada
Well, aside from the block thermostat, everything you've checked would suggest the cooling system is fine and the vehicle should not be overheating.
Just to recap:
When replacing the block thermostat, as you will have the system open, I would suggest flushing the coolant system with water...from a hose is fine. This will confirm there are no blockages in the rad or throughout the system.
At the very least flush the rad...it may be new, but you never know if you didn't install it.
When the car is idling warming up, is the idle normal? Meaning it's not rough or surging.
If the block thermostat fixes it I'd be very surprised...but it's the only left if everything else is good.
Just to recap:
- There is flow observed when the main thermostat is removed...this confirms the mechanical waterpump is working
- There is also heat in the cabin with the main thermostat removed...this confirms there is no blockage between the engine and heater core
- The main thermostat was put in hot water and opened at 82C...it is also a new OEM cap
- The rad fans both come on and the speed varies...confirming the ECU sees that the engine is heating up and turning the fans on...although one fan wasn't working previously and now is
- No external leaks
- Pressure test held for 3 min...so no internal leaks (while this is a good sign, it doesn't rule out a head gasket/internal engine issue completely)
- compression test...this will confirm the engine is ok internally (if good, added to the pressure test, the engine should be fine)
- hose routing...as there is a known good 200t available, confirm all coolant hoses are routed the same
- check for codes...just in case there is a code that my give any clue as to why it's overheating...the check engine light doesn't necessary need to be on, it could be stored in History
When replacing the block thermostat, as you will have the system open, I would suggest flushing the coolant system with water...from a hose is fine. This will confirm there are no blockages in the rad or throughout the system.
At the very least flush the rad...it may be new, but you never know if you didn't install it.
When the car is idling warming up, is the idle normal? Meaning it's not rough or surging.
If the block thermostat fixes it I'd be very surprised...but it's the only left if everything else is good.
Driver School Candidate
Joined: Jul 2005
Posts: 49
Likes: 1
From: CA
Normal idle throughout. No codes, even in history.
I’ll check the hoses again but I’ve already checked and they look good.
How do I do a compression test?
Where would I place the hose if I wanted to check the flow in the engine?
I’ll check the hoses again but I’ve already checked and they look good.
How do I do a compression test?
Where would I place the hose if I wanted to check the flow in the engine?
Lexus Test Driver
Joined: Feb 2017
Posts: 6,260
Likes: 1,752
From: Richmond Hill, Ontario, Canada
I've owned 9 Toyotas all driven to over 100,000kms each, and you know how many I've changed the thermostat because it had an issue...zero. And most of those were 5-10 years old (closer to 10 in most cases) of their life before I traded them on something newer.
The 200t you're working on is 5-6 years old and probably has less than 60,000 Miles...hence my surprise if it was the thermostat.
And true, a thermostat doesn't need a reason to fail, they just go...but since you changed the main thermostat and it made no difference, I can't see the block thermostat fixing it.
And when you flush the system when you have both thermostats out, that will tell you if you have a blockage in the engine.
Lexus Test Driver
Joined: Feb 2017
Posts: 6,260
Likes: 1,752
From: Richmond Hill, Ontario, Canada
Driver School Candidate
Joined: Nov 2021
Posts: 1
Likes: 0
From: Oman
Hi can u please update what happen for your car, please. Did u solved your issue?
I had my 2018 Lexus IS300 F Sport Turbo overheat problem. I imported the car from USA to the middle east.
The overheating started after 2 months of normal driving. The car overheated when I was driving so I had to pull out of the road, parked, let it cool down and continue driving slowly to the garage. We found out one of the cooling fans not working due to cable puled out a bit. So, we put it back and the fan worked fine. The overheating was still there so I thought of faulty water pump and thermostat due to the overheat occurred before. I replaced both thermostat and water pump (yes the water pump was leaking). After that, I bleed the system to take all air out and everything was working fine.
After around 6 weeks, I was driving for about an hour, I reached home with no problem, while the car parked and engine switched off, suddenly I heard a huge amount of water dripping, opened the hood, I saw the bottom hose of the radiator tank has pilled off, I thought because it wasn't tight enough. So, I put it back, tight it, fill the radiator with water and bleed the system to get the air our.
Guess what !!
The car is overheating again. I went to the workshop. They blamed the temperature sensor, cooler fan and the radiator. I changed them all.
BUT STILL THE CAR IS OVERHEATING but this time only when I switch the AC on. Without AC the car is not overheating.
We found out the top pipe of the radiator is hot and the pipe at the bottom was too much cold. So we blamed the thermostat.
We took the thermostat out, took the car for a test drive and it was working fine without overheating.
We placed the same new thermostat back and the overheating issue occurs again.
I don't want to drive the car without the thermostat.
The installed thermostat been tested in a hot water outside the car and it was opening smoothly.
The temperature rating written on booth thermostat (old and new) is 82 C.
The average weather temperature here in the city is 27 C in winter (now) and 42 C in summer (March to September)
Can any body give a suggestion please !!
The overheating started after 2 months of normal driving. The car overheated when I was driving so I had to pull out of the road, parked, let it cool down and continue driving slowly to the garage. We found out one of the cooling fans not working due to cable puled out a bit. So, we put it back and the fan worked fine. The overheating was still there so I thought of faulty water pump and thermostat due to the overheat occurred before. I replaced both thermostat and water pump (yes the water pump was leaking). After that, I bleed the system to take all air out and everything was working fine.
After around 6 weeks, I was driving for about an hour, I reached home with no problem, while the car parked and engine switched off, suddenly I heard a huge amount of water dripping, opened the hood, I saw the bottom hose of the radiator tank has pilled off, I thought because it wasn't tight enough. So, I put it back, tight it, fill the radiator with water and bleed the system to get the air our.
Guess what !!
The car is overheating again. I went to the workshop. They blamed the temperature sensor, cooler fan and the radiator. I changed them all.
BUT STILL THE CAR IS OVERHEATING but this time only when I switch the AC on. Without AC the car is not overheating.
We found out the top pipe of the radiator is hot and the pipe at the bottom was too much cold. So we blamed the thermostat.
We took the thermostat out, took the car for a test drive and it was working fine without overheating.
We placed the same new thermostat back and the overheating issue occurs again.
I don't want to drive the car without the thermostat.
The installed thermostat been tested in a hot water outside the car and it was opening smoothly.
The temperature rating written on booth thermostat (old and new) is 82 C.
The average weather temperature here in the city is 27 C in winter (now) and 42 C in summer (March to September)
Can any body give a suggestion please !!
Driver School Candidate
Joined: Jul 2005
Posts: 49
Likes: 1
From: CA
So I should be able to disconnect the fuel injection harnesses to prevent the vehicle from starting? Does anyone have a diagram of how the spark plugs come out? Does the vehicle really have to be warmed up first?
Lexus Test Driver
Joined: Feb 2017
Posts: 6,260
Likes: 1,752
From: Richmond Hill, Ontario, Canada
Not sure what you mean by the spark plug question.
Ideally at operating temp as all the engine metals will be expanded to provide the most accurate reading...the reading will be as high as possible.
With a cold engine the readings could be low, but at the same time they should still be relatively equally low.
Lexus Test Driver
Joined: Feb 2017
Posts: 6,260
Likes: 1,752
From: Richmond Hill, Ontario, Canada
Compression should be 131 - 174PSI with no more of a 15PSI difference from lowest to highest...so it's good at 150PSI.
Engine thermostat is the only thing left.
If it fixes it I'd be surprised, but everything else checks out, so it's the only thing left.
Engine thermostat is the only thing left.
If it fixes it I'd be surprised, but everything else checks out, so it's the only thing left.