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Discussion Starter #1
I was wondering if anyone has had an issue where the coolant reservoir is always low. I noticed it was almost empty so I filled it, drove it for half an hour, checked coolant again it was back to where it was. I just changed the oil that day and there was no indication of an internal leak. The cruiser is a 2008 TT and has 217k miles on it. I replaced the radiator, water pump, and thermostat 8 months prior in February so I don't think any of those are related because the radiator was completely full. Could it be something as simple as replacing the reservoir itself or maybe a new cap?
 

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I’d check for loose fittings on the recent work you did.
 

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Any residue lingering around the sytems?
 

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If the cap is weak, it could allow coolant to be pushed out of the system, leaving no evidence (the overflow tube drains onto the road), and when cooled the amount pulled back in to refill the rad would leave the reservoir low
 

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Norm356 has touched on an important point. Radiator caps do fail. They are inexpensive and I always replace it along with an new thermostat when performing a coolant flush. If you purchase a new cap from a 3rd party other than Toyota, ensure that it meets the factory pressure specs.
 

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If the cap is weak, it could allow coolant to be pushed out of the system, leaving no evidence (the overflow tube drains onto the road), and when cooled the amount pulled back in to refill the rad would leave the reservoir low
Yes, but enough coolant would have to be forced past the radiator cap to completely fill the reservoir, plus more to actually overflow.

Only severe overheating (generating steam inside the block) or a head gasket leak (allowing combustion gas into the cooling system) would displace enough fluid to cause the reservoir to overflow.

Aside from obvious coolant leaks in the engine bay from hoses, water pump, etc., check the transmission fluid (if an AT model) for water getting in from a corroded transmission cooler in the radiator, and check under the floor mats for coolant leaking from the heater core or its hoses.
 

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I just replaced my thermostat, hoses, serpintine belt and the radiator cap. :)
 

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How full is your radiator? Take the cap off and look in there. It goes without saying, do this when the engine is cold. You'll only be able to see if the radiator is completely full

It sounds to me like your radiator is slightly low and when it cools it's drawing the coolant back into the radiator. One of the hoses runs to the bottom of that reservoir.

I loosened my radiator cap at one point and didn't tighten it down all the way and had it spill over. If it's losing coolant via the cap (or anywhere else) you'll see pink solids running down from the leak point
 

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Expanding on Sparky's post ... the coolant level in the reservoir naturally rises and falls with engine temperature.

Check the level in the reservoir when the engine is dead cold ... if the radiator cap and the connection between radiator and reservoir is not leaking, the coolant should be at the LOW level mark in the reservoir.

Then, check the level in the reservoir when the engine is hot ... the coolant level should now be at the HIGH level mark in the reservoir.

As the engine warms up, obviously the coolant expands and creates pressure in the cooling system, and is pushed out of the radiator past the radiator cap and into the reservoir.

After the engine is shut down, the coolant cools and contracts, creates a negative pressure in the cooling system, and coolant is drawn back into the radiator from the reservoir.

The objective is to never have any air or vapor in the pressurized portion of the cooling system.

(Some folks think that the reservoir is just a 'catch tank' in case the engine overheats, but actually coolant flows in and out of the reservoir every time the engine warms up and cools off.)
 

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G'Day,
did you burp the RAD when you replaced it ?
if not, park your J on a slope, remove the RAD cap, and run the engine for an hour till its good n hot... top up the coolant occasionally till all the air has burped out of the RAD .... seal and top up the over flow container ....
Cheers
Baz
 

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Discussion Starter #13
To answer a number of questions and comments,

All the fittings seem to be tight.

I don't see any residue anywhere.

The radiator is full, I can see coolant at the fill hole for the radiator and squeezing the upper rad hose causes the coolant level to rise even more.

Yes, the reservoir always drops down to the same level of an inch or two under the low line and maintains there. I got the engine to operating temp and filled the reservoir to the high line. I drove it for about half an hour and when I checked it again the coolant was back to under the low line. I checked it again today and the coolant is still under the low line.

Yes I burped the radiator when I replaced it. I used one of those radiator bleed funnels and let it do its thing for maybe an hour.
 

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Not very common, but look for a crack in the coolant reservoir. If coolant is leaking out of the reservoir, glycol should be visible in the engine bay under or behind the reservoir.

Pull the reservoir, clean it thoroughly, and visually inspect it, looking for any tiny cracks, especially near the mounting brackets or other stress points.
 
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