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Lexus Gs430 loosing coolant out of the overflow tank/tube

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Hey guys, just bought a 2000 Gs430 and noticed a coolant leak coming from the overflow tube (and also a bit from the reservior cap itself). Topped ist off a bit today (around 200-300ml) and as i put the cap back on, i noticed coolant pushing out of the reservior tube (right below the reservior cap)

Added a picture of my engine bay, as i noticed, that there are different versions of the radiator and reservior on the 3uz-fe.

As i dont have the radiator cap, as most US spec 3uzs, could the problem occur due to much pressure in the cooling system? The timing belt and waterpump was replaced 20k kilometers ago, the radiator is approx. 15k Km old (OEM Toyota/Lexus one).



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A head gasket leak can result in coolant expulsion. Many auto repair shops can test your coolant to determine if super-hot combustion gasses have entered the coolant.

Here are other ways to check for a blown head gasket:

How to Find a Blown Head Gasket Problem (2carpros.com)

If excessive air is in the coolant, due to insufficient bleeding after a coolant change, this could also cause coolant expulsion from the reservoir tank.

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I also thought about the head gasket. Ordered a CO test, that should arrive on Friday.

Will keep you updated 

ps: The car is also not geting warm inside it at idle, even if im putting it on the highest temp.

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The coolant system is sealed to such a degree that it builds up pressure when the liquid warms up. That pressure results in the liquid expanding somewhere or the system would pop over time. Hence the over flow tank. As the liquid cools and pressure receeds it should create a vacuum enough to provide suction enough to draw the expanded back into the radiator. 

Another thing is the radiator cap itself 'burps' at a given pressure. When it burps coolant can escape. Over time that can an issue if coolant has clogged the pressure escape area. Or if the cap is rated too high of a pressure that can also cause excess pressure.

There is a high and low point in the resevior tank. When the system is cool like after sitting overnight, the coolant in the tank should be at the minimum mark. When the engine is warm the level will be higher. It may or may not reach the high mark. 

If the system is filling up the resevior past the high point and then the coolant is not vacuuming back into the radiator there is definitely an issue, but I'd start with the radiator cap. An improper working radiator cap can cause weird stuff to occur. If the engine had ever overheated a head gasket could be the culprit. 

It could be the mechanical thermostat in the system is stuck closed. That thing opens and closes based off of heat but as they age they came become inefficient, eventually to the point they fail to work at all. 

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I will order a thermostat and some coolant in the next few days, as i also not getting any heat, when the car warms up to operating temp at stand still, only if im starting to drive it.


Still have the hope, that its a broken thermostat + air in the cooling system.


But my CO2 test should arrive tomorrow and i will check. Had the car on a lift yesterday, found no coolant marks on the block itself, only some oil  from the valve cover gasket.

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The no heat thing sounds like a thermostat. If that thing fails it can cause excess pressure in the coolant system. Years ago I ignored one due to circumstances and one day the excess pressure blew the radiator cap off the radiator. 
Point being if you suspect it's that go ahead and remove it asap. The car will run ok without it for a couple of days. But replace it as it regulates the cooling system, particularly in summer. 

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My Co tester came in today and i dont really, what i do with the result.

I have put the plug on the reservoir tank (didnt fit that well). Let the car warm up for approx. 12 minutes with a few very tiny revs and at like minute 16 (with around 4minutes of constant reving right around 2k rpm) it turned greenish (Posted a video of the last few seconds of my recording, had to zoom in really far, hence the bad quality).


I am not sure how to proceed now. I will try it tomorrow on another car i have, just to be sure, as i still not have any exhaust gas smell in the reservior tank nor at the exhaust pipe. No signs at the oil cap or dip stick too.


Just that damn pressure in the reservior.


Ordered a Thermostat today and will try to change it + burping the coolant System as a last try.


The temperature stayed complety steady the whole time, but i dont think it could start to overheat in this short time?

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As the liquid warms it expands. I watched a video not long ago about a home hot water tank where the guy did a system bypass, added a balloon/overflow tank contraption to his system. The line pressure on his system began rising from the moment heat was added to the water in the tank. Line pressure of 60 psi went to over 155 psi in about 15 minutes. It had reached 80 psi in 5 minutes. That was heating 40 gallons of 70 degree water to 120 degrees. His balloon/overflow contraption was a 2 litre bottle. The expansion increased the volume to the point it filled the bottle. 
If the radiator was cold, say 70 degrees and your engine heated it to 210 that few gallons of coolant will definitely expand. But looking at the way the liquid was surging in the test vessel it appears there are either a lot of air bubbles surging or there is exhaust gases reaching the coolant tank (radiator), which might be why the former owner sold the car in the first place. 
I bought a car from an unscruplous seller with a head gasket leak. He had placed a product in the radiator called silver solder, which did actually seal it for a while. After about 5000 miles it showed up. 

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Yeah is still think there is a big chunk of air in the system, because when im pressing rubbertube from the engine to the radiator (when cold), the level itself is expand (goes from below a few cm’s below empty to in between empty/full).


But the test is a dead giveaway for me that the gasket will fail at some time.

Forgot, that i made a video of the car running to temp. before i did the test. From my perspective that does not even look like alot of steam/smoke (was even less when it got a bit of engine temp). Got a clk320 that is steaming more and doesnt even burn one drop of coolant.

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One way I knew my motor was leaking was all that steam, and when I held the throttle a wet spot would appear. Like a 3 foot circle. When I flushed the radiator a bunch of what looked like glitter glue came out. After that a quart of coolant would just disappear from the radiator in about 30 minutes. I also figured out the hard to start thing was from all of the liquid in my exhaust. Yet nothing showed up in the oil or the coolant.

Oh, and sometimes a bit of yellow goo on your oil filler cap is normal. Heating and cooling causes some condensation in the engine that runs short trips. But if you clean it off and it comes right back, chances are good you have coolant getting into your oil, even though the dipstick may look normal. 

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