Slow drop on coolant level (expansion tank)

[Eugen A]

Hi everyone,  one of our Lexus cars, 2022 RX450H F -sport Takumi pack have a minimal loss of coolant level on each 3000 to 5000 miles. If the expansion tank is filled on full, at 10.000 miles service  , on cold engine, coolant level is around one inches below the max. Car has been checked twice by Lexus dealership, no leaks, no any other issues. I use the car to tow a caravan (Coachman VIP575  - 1700 kg ). The dealership  checked everything and the car seems to be fine. I was wondering if someone else has the same issue? All my other Lexus cars which we own at the moment (Nx300h and UX300e) have not had this coolant dropping symptoms.  Thank you

 

Edited March 7, 2023 by Eugen A

[Spock66]

3 hours ago, Eugen A said:

I was wondering if someone else has the same issue?

Nope, mine never needs topping up, I suspect there must be a small leak somewhere, maybe a hose clamp or something similar.

[Brian26]

I also tow a caravan (Coachman Laser 665 with a plate uprate to 1900kg ) with my RX and have no drop in coolant level. I feel sure you have a leak somewhere, have you checked the coolant filler cap?

Bri

[Eugen A]

The car has been checked twice by Lexus Tunbridge Wells and they haven't spotted anything wrong. The loss is very minimal,  but is there. They have checked everything.  The car has nearly 20.000 miles from new, bought last year. I suppose they have checked the coolant filler indeed, no leaks and nothing wrong with the car. They will recheck everything at the 20000 miles service. The car always stays between minimum and maximum on coolant level , but drops always to middle if topped up to full after 4000 miles to 5000 miles. But,the level of coolant never  dropped further on expansion tank. 

[Greisingel]

Yes, in my RX400H. I suspect that I need a new water pump as the tell tale signs of pink spray can just about be seen behind the shroud.

[Spock66]

2 hours ago, Eugen A said:

The car always stays between minimum and maximum on coolant level , but drops always to middle if topped up to full after 4000 miles to 5000 miles.

So if the fluid level is falling the coolant must be going somewhere....

[Eugen A]

Yes,I agree , but I got a loaner no long time ago, RX450h takumi, 2022, 3000 miles odo only and when I checked by curiosity, tge coolant level was halfway through between min and max on cold engine. 

[Bluemarlin]

2 hours ago, Eugen A said:

Yes,I agree , but I got a loaner no long time ago, RX450h takumi, 2022, 3000 miles odo only and when I checked by curiosity, tge coolant level was halfway through between min and max on cold engine. 

Am I undertstanding this correctly, in that when the coolant is topped up to full the coolant level drops to between min and max. However, once it settles halfway between min and max, then there is no further sign of coolant loss?

If so then it just sounds as if the coolant is heating/expanding sufficiently to be expelled via the oveflow, and once it's got down to beween the min/max point then any expansion doesn't get high enough to get expelled. So, either it seems like the normal function of the expansion tank or, if there is a crack or leak then it will likely be at the top of the tank or filler cap.

In the absence of any visible leaks, and no loss of coolaannt once it's between min and max, it may well be that the midway point is the normal level for the coolant to be.

[JasonH]

You can get very tiny pinhole leaks that eject coolant when the system is under maximum pressure. When this happens the car is usually being driven and the engine hot. The coolant just evaporates.

To find it there are two options:

1) Get the engine very hot and inspect it whist running - if that's even possible with a hybrid.

2) Get the coolant system pressure tested, and because it's a tiny leak over a bit longer than usual, say 1 hour.

Just because the Main Dealer can't see the leak doesn't mean there isn't a leak.

Having said all that, in the original post it's not 100% clear whether the drop is due to the coolant being full during the service (possibly a warm engine) and dropping when cold. I'd expect a drop in this case. The coolant needs to be topped up and checked only when the engine is cold.

[Bluemarlin]

3 hours ago, JasonH said:

1) Get the engine very hot and inspect it whist running - if that's even possible with a hybrid.

 

It's possible, in that there's a maintenance mode that allows you to idle the engine while parked without it cutting out. I can't remember the process to set it, but a cautionary note is that it's only to be used while stationary and it's not be driven like that, so one would need to get the engine hot with a run first.

[Eugen A]

Many thanks for all your replies. I will keep you updated. 

[Eugen A]

On 3/15/2023 at 6:20 PM, Bluemarlin said:

Am I undertstanding this correctly, in that when the coolant is topped up to full the coolant level drops to between min and max. However, once it settles halfway between min and max, then there is no further sign of coolant loss?

If so then it just sounds as if the coolant is heating/expanding sufficiently to be expelled via the oveflow, and once it's got down to beween the min/max point then any expansion doesn't get high enough to get expelled. So, either it seems like the normal function of the expansion tank or, if there is a crack or leak then it will likely be at the top of the tank or filler cap.

In the absence of any visible leaks, and no loss of coolaannt once it's between min and max, it may well be that the midway point is the normal level for the coolant to be.

Yes, you are correct on your presumption. The coolant level always been checked when engine cold, topped up to full and after few thousand miles drops down to between min an max and stays there. Lexus dealership told me that seems that on some trim specs, it's a normal characteristics.  But, I have had many Lexus cars before and I never remembered none of our previous cars to have this kind of coolant behaviour.  I still assume that somewhere is a very tiny and small drop but never needed to top up huge amount of coolant, only around 200 ml...

[Eugen A]

On 3/16/2023 at 8:01 AM, JasonH said:

You can get very tiny pinhole leaks that eject coolant when the system is under maximum pressure. When this happens the car is usually being driven and the engine hot. The coolant just evaporates.

To find it there are two options:

1) Get the engine very hot and inspect it whist running - if that's even possible with a hybrid.

2) Get the coolant system pressure tested, and because it's a tiny leak over a bit longer than usual, say 1 hour.

Just because the Main Dealer can't see the leak doesn't mean there isn't a leak.

Having said all that, in the original post it's not 100% clear whether the drop is due to the coolant being full during the service (possibly a warm engine) and dropping when cold. I'd expect a drop in this case. The coolant needs to be topped up and checked only when the engine is cold.

The technician,  I know him for a very long time and seems a capable technician,  but, maybe you are correct and I will insist again very soon. Thanks again 

[Eugen A]

On 3/12/2023 at 5:36 PM, Brian26 said:

I also tow a caravan (Coachman Laser 665 with a plate uprate to 1900kg ) with my RX and have no drop in coolant level. I feel sure you have a leak somewhere, have you checked the coolant filler cap?

Bri

Will do, thanks