Coolant overflows from expansion tank

[Ectell]

Hey guys, I was wondering if anyone could give some advice on an ongoing issue I've been having?

 

I have coolant that was overflowing and bubbling out of my expansion tank following a coolant flush and refill that I did myself. Car is a 2006 GT automatic.

 

The coolant bubbles can be seen after driving for 5-10 miles on a hot day. The level of the expansion tank goes from the low mark when cold, to overflowing after the drive. After shutting the car off, I can usually hear coolant pushing past the filler tank cap, into the expansion line. Ive also noticed that the filler tank always seems to be half empty after the system cools down again, which is odd because the coolant does seem to flow back into the filler tank as the coolant cools off.

 

I did multiple block tests with the car running and bubbles right underneath the tester and its always been negative. I have done a pressure test up the nearly 20 psi and noticed zero pressure decrease after 3 hours. Left the tester on overnight and saw less than a psi of drop. Had a friend turn on the car and watched the exhaust and there was zero smoke after the pressure test.

 

I have replaced both radiator caps, the filler tank, radiator hoses and almost all the filler tank hoses (only one left is the return to the expansion tank). I have also burped the system multiple times using a spill-less funnel both with the front jacked up and also just the passenger side. Both times ran the car until zero bubbles were visible. (including when I grabbed on the radiator hoses.)

 

Im starting to think I'm being paranoid and creating my own problems, and this could be something as simple as the system being over serviced. Do these cars not stay full in their reservoirs by design? I filled the radiator to the point the cap pushed coolant out of it on its way in, and did the same for the filler tank. I usually service the expansion tank to the low mark when it is cold.

 

Any advice or insight would be much appreciated.

[bdcvg]

My guess is 1 of 2 things. 1. It's overfilled and will find it's own level if it's not over heating. 2. There is a head gasket leak between 2 cylinders which will slowly presurize the system and push coolant out.

[Max Capacity]

If you hold a HC hydrocarbon tester over the radiator with the engine running, it will tell if you have HG leak.

[whitetiger]

Head Gasket failure.

[Ectell]

Yeah, I have done multiple hydrocarbon tests and they were always negative. The car only has 10000 miles on it since it got a brand new block, so I'm hoping it's not a head gasket. It doesn't bubble at all at idle if I just let it warm up, and it never overheats.

 

I think it only bubbles when the turbo engages. I know that the car is supposed to flow coolant through the turbo and it gets hot as anything. Maybe it's just mass dumping coolant after getting heated by the turbo. It does seem to level out in the expansion tank sometimes. I just don't like that the filler tank is always half empty when I check it.

[Max Capacity]

Couple things,

 

Why did you flush the system ?

 

"I just don't like that the filler tank is always half empty"

 

The overflow tank is only supposed to be filled to the cold line about 2.5" from the bottom of the bottle. When the engine is cold, as in overnight.

[SubOperator]

^^^ What Max just said.

 

 

 

There are MIN and MAX markers on the expansion tank, if you top it off when cold it WILL overflow, as it has nowhere else to go.

[Infosecdad]

Let’s make sure we are all talking about the same things.

You mention “filler” tank and “expansion” tank.

Which tanks are you referring to?

The tank by the turbo should have an OEM cap with wings and be full.

The semi-transparent tank by the radiator cap (OEM w/o wings) is usually 1/2 full or less when cool.

You should be able to see fill lines in it with a flashlight.

[Ectell]

The tank next to the turbo is called the filler tank in my manual. The clear tank is always called the expansion tank in it too. I service the expansion tank to the low mark when it is cold, and fill the filler tank completely. But the filler tank is always half empty after I drove around, and the expansion tank tries to overflow, or come close to it.

 

I flushed the system because it had been a few years since it had been done and just wanted to be thorough.

[Max Capacity]

Just saying, in the 17 years I've owned the wagon, I have never flushed the cooling system, or in the 1o years I've owned the Spec B.

 

I have topped them off yearly, but other than that, never worried about the system. When the timing belt kit is done, the system is topped off. I do eyeball the tank when checking the oil.

[Ectell]

Thanks for all the advice, I'm still trying to learn more about how these cars work.

 

The car seems to be leveling out now weirdly enough. I've taken it on a few more drives and it doesn't seem to want to overflow anymore. I think it just didn't like being completely full.

[Max Capacity]

Explain, "completely full"

 

The coolant level should only be up to the "full when cold" line on the expansion tank attached to the radiator. In the morning, after the car has sat overnight.

 

You also need to burp the air out of the system in these turbo cars. There are funnels for that, but I just jack up the right front corner as high as I can, remove both caps, run the engine until the fans cycle while watching for air bubbles in the turbo tank and radiator. Do that with the heater on full heat.

You can squeeze the hoses from time to time a little.

[Ectell]

I burped the car several times. I burped it with the turbo tank open, but after that I had the overflow issue. So I burped it again by lifting the front end of the car until the radiator got to be the highest spot on the system, and burped it through the radiator. Still had issues, so I got a no spill funnel and burped it again using that on the turbo tank jacking up just the front passenger side of the car. All those times I had the heat on full blast with the fan on low.

 

What I Meant by levels being completely full is the coolant levels in all the reservoirs. Completely full radiator, completely full turbo tank and the expansion tank at the full mark. When I inserted the caps on the turbo tank and radiator, I literally spilled coolant because it was so full. I was convinced that there was too much air in the system.

 

But the expansion tank would overflow and the levels in the radiator and turbo tank dropped. The turbo tank could be half, to three quarters empty when I checked it after the car cooled completely from a drive. I started thinking something was letting air into the system, so I replaced both radiator caps and most of the hoses attached to the turbo tank, and the turbo tank itself.

[Max Capacity]

Usually when the coolant is overflowing, the expansion tank, that's caused by a HG leak.

 

The system is simple...we just need to understand what is happening.

 

I assume the engine temp gauge reads normal all the time ? That would be just a touch below the halfway on the gauge.

[Ectell]

Yeah, it never goes over the middle of the temp gauge.

 

Thing just overflowed on me again. I got 2 drives out of it and everything was going well, but decided to drive it a bit more aggressively this time. When I stopped, the coolant was overflowing from the expansion tank again. I am thinking the issue only occurs if I engage the turbo for a decent amount of boost.

[Max Capacity]

That leads me to think HG or cracked head.

 

Mat be time to have an expert take a look at it or talk to a machine shop.

[whitetiger]

you have a little flap in the HG that opens under boost and pumps air in to the coolant jacket. Had the exact same thing happen to me. it wont overheat when driving, but if you let it sit running with low coolant the temp gauge will creep up.

 

time for HG replacement.

[Rusty9]

I would check if you have the correct caps in the correct locations. The cap on the radiator is different than the reservoir cap above the turbo.

[Max Capacity]

I thought the caps were different, so that couldn't happen...

Yep, just walked out to the cars.

First one is the 09, others are the 05

 

 

 

Edited August 9, 2021 by Max Capacity

[Max Capacity]

Here's the 09's radiator cap.

 

[SubOperator]

Here's the 09's radiator cap.

 

[ATTACH]292782[/ATTACH]

 

 

05 OEM is the same.

[Ectell]

I bought all new caps when I was having issues, hoping for the easy and cheap fix, but it didn't work. I have the oem ones in the correct positions. I also tested them, and they seem fine. ( One is around 15 psi and the other one is around 20)

[Rusty9]

Ok always worth a shot to check the simple solution first. I have seen people install new radiator and get the caps mixed up and have the same symptoms. As far as I know, one cap is a 2 way, and the other a single way.

 

I know Mishimoto puts this installation note in their instructions as well.

[apexi]

Just bored curiosity, the block tester was stuck in the top of the overflow tank right?

[Ectell]

I did the block test once in the overflow with bubbles directly under the tester, and it was negative. Did it again later on the radiator directly and it was also negative.