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 !!

 

Here's a couple questions that may help us to help you:

1. With the thermostat removed and the AC on, does it still overheat?
2. When you turn the AC on does the rad fans come one?
3. Since the cooling system has had many repairs and the coolant drained and filled many times, what coolant is in it now?
4. When you replaced the thermostat, which one did you replace? The turbo engine has 2 thermostats...one is easy to get to, one is not.

 

Thanks for your reply.
Answers to the questions;
1. No. It doesn’t overheat when thermostat removed and AC is ON.

2. Yes the fans comes on when I switch the AC ON.

3. The engineer in the workshop drained the radiator water into a container and after each repair he put it back again. So we having the same water back.

4. We replaced the bigger size one. The one easy to find.

Hope this is clear.


Update:
It worth to mention that the night before the second overheating problem, I did the routine car service by changing the engine oil and filter.
The engine oil was in the car is 0W20 and the new one I put recently is 5W40 as advised by showroom spare parts salesman.

 

I realize it may just be a translation issue, but are you using water in the cooling system, or actual coolant (the Toyota/Lexus neon pink Super Long Life coolant)?

The larger thermostat is rated at 82C and will open 10-12mm at approx. 95C.
The smaller thermostat is rated at 78C and will open 8mm or more at 91C.
So the smaller thermostat needs to open before the larger one can.
Also, the jiggle valve has to be installed in the top position when the thermostat is installed in the housing.

I know you checked the opening of the large thermostat, but it's important to know how hot the water was it was in to make sure it opened completely...and also how far it opened.
Also I'm not sure if the fans or Fan ECU has different specs for middle east destination IS's versus USA destination IS's...I wouldn't think so, but I have no way to confirm either.

Assuming you are using coolant and not water, and the system is full and bled properly, based on everything you've mentioned so far it would seem to be either the large thermostat is faulty, even though it's new, or the small thermostat is faulty, which is still original to the vehicle.

 

Yeah it looks I understand you in another way. However, you are right I’m using actual coolant liquid the pink one.

I need to check the installation of the jiggle valve it might be upside down. But not sure. I’ll check and come back to you.

We check the thermostat opening at boiling temperature level (more than 100 C). I need to buy thermometer to check at which temperature it starts opening. Will come back to you on this too.

The fans specifications according to the manufacturer it’s the same.


So what I’m planning to do now is;
1. Check the big thermostat at which temperature it opens.
2. Check the installation of the thermostat with the jiggle valve at the top.

if problems still occurs I will replace the smaller thermostat.

Thanks for your support and I’ll update you once I’m done.

 

Update:
The jiggle valve currently positioned downwards. But it was positioned to the top and the overheating was still occurring. However, I asked the mechanic to reinstall it with the jiggle valve to the top.

Tried to locate the small thermostat but no luck. Can you please guide me to locate it? any photos or videos?

This is a photo of the way we are bleeding the car, using air compressor. Any idea if this method works with the IS300 F Sport or shall we use another method?
- Does it matter if we bleed the car with hot engine or shall we wait for it to cool down ?




I have some questions in my mind;
1. Can the cause be that I've changed the engine oil type from 0W20 to 5W40 ?
2. Can the problem be with the engine head gasket ? (I don't want to reach to this stage)
3. Is there is a link between the turbo radiator and the engine radiator ?
4. I noticed there is jiggle valve in the big thermostat only, but there isn't one in the small thermostat (the new one I bought). Is that normal ?

 

It's important that the jiggle valve is installed so it is at the top...this allows air to bypass the thermostat when it is closed so that is doesn't get trapped and cause overheating.
The small thermostat does not have a jiggle valve...that is normal...only the large has it.
The small thermostat is located behind the housing that holds the big thermostat and waterpump. A lot of parts have to come off in order to get the water inlet housing off to access the small thermostat.
Given the amount of work to access the small thermostat, you may want to wait and change it as a last resort.

See pic below...i circled in red the small thermostat, the water inlet housing, and the spot on the engine where the small thermostat is located:


For the bleeding method, I would use something more traditional:

1. Remove the Reservoir Tank cap and fill the coolant to the "B" line (leave the cap off until step 11 below)
2. Remove the Water Fill cap...this is the other cap located near the engine just above the waterpump area
3. Fill coolant into the Water Fill cap opening until it's full...squeeze the larger radiator houses to see if any air bubbles up to the Water Fill cap opening...once full, install the Water Fill cap.
4. Start vehicle and set HVAC to Max Hot, blowing on the Face, and Fan speed Low.
5. Monitor coolant level in Reservoir and add coolant as necessary to keep the level between Full and Low...ideally close to Full
6. Let engine warm up until you can feel hot air coming out the vents...depending on the ambient temperature this could take maybe 10 minutes (or longer or shorter)
7. Monitor coolant level in Reservoir and add coolant as necessary to keep the level between Full and Low...ideally close to Full
8. Once you feel hot air coming out of the vents, set the HVAC to Max Cold...leave on the Face and Fan speed Low.
9. Monitor coolant level in Reservoir and add coolant as necessary to keep the level between Full and Low...ideally close to Full
10. Let the vehicle run for 10 more minutes
11. Install Reservoir Tank cap and drive vehicle for 10 minutes
12. Park vehicle with engine off for 1 hour (or until you feel the engine has completely cooled down)
13. Check coolant level in Reservoir and add as necessary so coolant is at the Full line

Changing the oil grade should not have had that much of an effect to cause the overheating.
I've also considered that from the first overheating if it may have damaged the head gasket...but leave that as an absolute last resort to fix.

 

Thanks for the clarifications.

We tried with the jiggle valve at the top still no luck.

Another mechanic told me it might be the water pump.
Is there is a way to check the water pump without removing it?

I checked in the YouTube. Someone says to test your water pump; switch on the heater. If you getting heat then your water pump is fine. If no heats come then it will be faulty water pump.

Guess what !! I tried it and switched on the heater. Very cold air comes out. Heater didn’t work.
only seat heater works.

Is that true? Faulty water pump will give you cold air when you switch on the heater ?

Thanks again for your support.
I will try the traditional way of air bleeding. It looks cool and can do it at home.

 

Make sure the jiggle valve stays at the top, because anywhere else and you'll never get the system bled properly.

With regards to the waterpump, you mentioned it was replaced already, so likely it's fine as I can't see a new waterpump failing that quickly.
I'm assuming you either got the part from Lexus or Aisin, which should be the manufacturer of the waterpump.
If the waterpump has failed then the vehicle would overheated within 20 minutes (or less) of running since there would be nothing circulating the coolant throughout the engine.

The comment about the waterpump causing no heat inside the car is very broad...it could cause that symptom, but also an entire list of other things could cause that.

No heat inside the car could be caused by:

• Faulty waterpump
• Thermostat stuck closed
• air in system
• low coolant
• no coolant
• plugged heater core
• stuck blend doors in the HVAC box
• etc.
• etc.
• etc.

So, you can see while a waterpump could cause the issue, it's just one of many things.
Now that you mentioned there is no heat inside the car, it could be as simple as there is air trapped in the system.
Based on the air compressor equipment they were using to bleed it, I'm not very confident that all the air was purged.
Based on the 13 steps I provided for bleeding the cooling system, you will have cold air blowing out the vents until step 8, because the air has to work itself out of the system so the coolant can properly and evenly warm up.
Air trapped in the system can also cause overheating, so it's crucial that all the air is bled out.

 

HELP HELP MF'r HELP..

I'm having the a similar problem.. My 2016 Lexus IS200T is overheating, it was bought from Copart auctions with some light front end damage. After installing the radiators, hoses, etc.. I tried refilling it and it's overheating within 15 minutes or so..
I have no heat either, so I disconnected the heater hoses and found NO fluid flow either, no matter what temperature the vehicle is at. I did change the outside large thermostat but it did not work either.
Here's a question for you, if the inside small block thermostat was stuck why would that prevent water flowing into the heater core?

I thought the system was largely self bleeding, I did follow the bleeding steps as noticed in the Lexus service manual.

I need help right away, thanks.

 

Do you have fluid flow to the radiator? I.e. is your water pump working?

 

I've been trying to check, I would say yes but I'm not totally sure.. I checked by getting the vehicle up to normal operating temp then removing the top radiator hose cap and I do see some minor movement in the fluid but the fluid is not jumping out or anything. As it happens I have another identical 2016 Lexus IS200T and I've been going back and forth trying to see any difference in the flow, heat from the hoses, etc.. but I don't see much difference, EXCEPT on the good Lexus IS I can't even leave open the top radiator cap because the fluid is completely filled and jumps out the top of the hose pipe, is that an indication that the water pump is circulating the coolant on the good IS200T and the on the bad Lexus IS200T it's not? If so, how on earth could that water pump not be circulating fluid when the vehicle has only 60k miles on it and it's being driven by a pulley?? No physical damage I can see either.

To top it off, this vehicle was an insurance total loss, so it had to be running good prior to the accident else they would never be able to drive the vehicle far and overheat it in the first place!? This is the biggest mystery in Lexus history!

 

There have been a handful of reports of the water pump failing on the 200T specifically on the forums. Are the coolant reservoir levels similar when not operating (of course some fluid will be trapped internally)?

EDIT: I don’t recall anyone having detailed information except that their water pump was replaced, so it’s hard to say if the pump actually failed or not.

Does the internal thermostat control flow to the reservoir? If it does and it failed, it would explain why the reservoir isn’t flowing as much

 

I noticed a build up of fluid in the engine radiator reservoir when operating, then it all spills out when I release the top reservoir cap. Perhaps that's an indication that it's not circulating? That happened a few times already but I thought it was because I just added too much fluid to the system, maybe that's the problem??

 

I can't find any information on which thermostat controls what, the two thermostats made this engine incredibly hard to trouble shoot.