Bubbling coolant on the reservoir

[SalvadorP]

So I just bought a 940 turbo wagon with high mileage car (500000km) with an engine rebuilt 24k km ago. Today it was the first time I really drove it. About 100km or so. Well, when I came back home I parked and turned off the car and I popped the hood and opened the coolant reservoir and the level arose and it kept bubbling.
I also think I see a bit of smoke or steam coming out of the reservoir.

Is this a blown headgasket for sure or are there other possibilities?

Here's a video I made. Started filming right after opening the cap. https://www.youtube.com/watch?v=QSk4vw3sk3E

Car doesn't overheat. At least I believe it does not. The temperature gauge needle seats in the middle. Doesn't have temp written on it. Is middle too much for operating temperature?
Also doesn't smoke from the exhaust.

[360beast]

Any particular reason you opened it?

Did you crack it off and allow the pressure to bleed off before removing the cap or did you remove it quickly? If you didn't let the pressure bleed off then yes it will overflow as all the pressure comes out very quickly and it will bubble up.

Normal operating temp is bang on middle of the gauge.

[SalvadorP]

Originally Posted by 360beast

Any particular reason you opened it?

Did you crack it off and allow the pressure to bleed off before removing the cap or did you remove it quickly? If you didn't let the pressure bleed off then yes it will overflow as all the pressure comes out very quickly and it will bubble up.

Normal operating temp is bang on middle of the gauge.

Honestly I opened it because I bought a high mileage car with an engine that has been rebuolt before and I'm super afraid I might find engine issues.
I do recognize I kinda opened it a little too fast.

What about the steam/smoke? It seemed to be coming from the side of the tank that connects to the radiator. Does this symptoms warrant a HG test?

[SalvadorP]

Originally Posted by 360beast

Any particular reason you opened it?

Did you crack it off and allow the pressure to bleed off before removing the cap or did you remove it quickly? If you didn't let the pressure bleed off then yes it will overflow as all the pressure comes out very quickly and it will bubble up.

Normal operating temp is bang on middle of the gauge.

Here is a video: https://www.youtube.com/watch?v=QSk4vw3sk3E
I started filming right after I opened it. Coolant looks dirty too no?

[Laird Scooby]

Looking at the reservoir that cap is leaking every time you drive it. This means it will draw air in when it cools down which will cause airlocks and the resulting bubbles.

I'd suggest a new cap, do a coolant flush and change (i've typed the procedure out many times, when i find it i'll copy and paste it here) and then keep an eye on it. Chances are if it was leaking during the previous ownership, they simply topped up with water, hence the dirt. This can cause other problems such as corrosion inside the block and/or head which can cause blockages, hence the suggestion of a coolant flush (reverse flush) and change.

[SalvadorP]

Originally Posted by Laird Scooby

Looking at the reservoir that cap is leaking every time you drive it. This means it will draw air in when it cools down which will cause airlocks and the resulting bubbles.

I'd suggest a new cap, do a coolant flush and change (i've typed the procedure out many times, when i find it i'll copy and paste it here) and then keep an eye on it. Chances are if it was leaking during the previous ownership, they simply topped up with water, hence the dirt. This can cause other problems such as corrosion inside the block and/or head which can cause blockages, hence the suggestion of a coolant flush (reverse flush) and change.

What you see probably isn't several leaks over a period of time, it's just me having opened it several times in the last few days. I was under the impression that the level shouldn't rise when you open the cap even if the car was hot. I'm starting to learn hiow dumb that is...

What about the steam/smokle coming out? Is that normal?

I was considering doing a flush anyways. But I?m also considering doing a head gasket test. Do you think I'm being too cautious/paranoid? The car doesn't have other symptoms. No smoke. Also the echaust doesn't have any smoke build up. No overheating at all. And today I drove it up the mountain for quite some time...

[Laird Scooby]

Originally Posted by SalvadorP

What you see probably isn't several leaks over a period of time, it's just me having opened it several times in the last few days. I was under the impression that the level shouldn't rise when you open the cap even if the car was hot. I'm starting to learn hiow dumb that is...

What about the steam/smokle coming out? Is that normal?

I was considering doing a flush anyways. But I?m also considering doing a head gasket test. Do you think I'm being too cautious/paranoid? The car doesn't have other symptoms. No smoke. Also the echaust doesn't have any smoke build up. No overheating at all. And today I drove it up the mountain for quite some time...

I saw the recent opening evidence, i also saw the much older, crystalline deposits on the seam where the top and bottom halves of the expansion tank meet.

The level will rise because the system is pressurised which compresses the air in the system - this expands when the lid is removed dropping the pressure in the system.

Given the coolant is going to be in the region of 88-92C, steam is perfectly normal, yes. Also if you took it up in the mountains where the air is at a lower ambient pressure, there is more of a chance of it boiling due to the pressure difference. If it behaved during that then the chances are the HG is ok and so is everything else except maybe the expansion tank cap.

Given the evidence, i would try a new expansion cap first and once fitted, leave it alone unless the engine is cold. Top up to the "MIN" mark when cold, it should go up to about the "MAX" mark when hot and whatever you do, DO NOT OPEN WHEN HOT!!!!!

If my suspicions are correct and the existing cap has gone weak, when you fit the new one and it pressurises correctly to 1.1bar/kPa or 1.5bar/kPa depending what the existing one is rated at, this is either 16psi or 22psi - that's a lot of force behind scalding hot coolant!

Opening the cap with that force behind the coolant would see you getting a hot shower - scaldingly hot!