Coolant Expansion Tank for Post-Shutdown Turbo Cooling

[qkrthnu2]

Ever since installing my BNRs3 (It was probably happening before, I just never noticed) I'm noticing that after shutting off the engine, even with sufficient low-load cool down driving, a minute or so later I can hear the coolant boiling in the Turbo.

Adding an electric pump sounds like an expensive and headache inducing project, so I'm probably going to rule that out.

As a low tech simple solution I'm thinking of adding a coolant expansion tank w/ cap mounted to the firewall above the turbocharger and connecting it inline with the turbocharger coolant feed (or drain?).

I got the idea after reading this talking about the OEM Subaru setup:
Random fun car fact: Subaru Shutdown Turbo Cooling!

Turbo's deal with this by keeping oil flow high enough to cool things down and very often, and always when reliability is a concern, with water cooling as well. But there's a problem. What happens when you go beat your turbo car like it owes you money, and soon after, when the turbo is still searing hot, you shut the engine off? No oil flow, no water flow, lots of heat = oil coking. Long term this = dead turbo. Dead turbo = sad car. Sad car = sad man (or woman.) Historically this was addressed with the uncivilized and inconvenient practice of running the engine for several minutes at idle before shut down, or utilizing a "turbo timer" to accomplish the same automatically. Subaru, however, seeing the long term importance of turbocharging to it's product line, innovated a simple remedy to this annoying and potentially expensive complication. I can't easily verify this, but I believe they pioneered this technique. As a WRX owner, we're going to operate on that assumption. At any rate, the fix is simple and clever. Look at a Subaru turbo engine bay - something is missing from the radiator...... I'll save you the time: no radiator cap. That's because Subaru has made the highest point in the cooling system a small aluminum reservoir placed directly above the turbocharger who's coolant return is connected directly to it (and this is where the cap now resides.) The reason is simple. Now, when you shut off the engine with a hot turbo, the coolant begins very quickly to boil. Obviously this hot coolant and steam rises quickly to the intelligently located mini-reservoir. This convection draws cool(er) coolant from lower in the system into the turbo and this process continues until the turbocharger cools sufficiently. In this way, even after shutdown with heat soak from the turbine section, the bearings never get much above the boiling temperature of coolant, protecting the oil from coking.

The only disadvantages I can think of are the space it would take up in the engine bay, and that I wouldn't be able to open the Radiator cap without raising the front end high enough to keep the fluid from spilling out. Basically this expansion tank would become the new fill point.

Has anyone else here done something like this.
Even if you haven't, what are you thoughts?

[Nitr0EngiE]

I have experienced the same thing with the coolant boiling, my issue was much bigger than that as when i would cut the car off the coolan would over pressurize and bust open the coolant reservoir cap and spill onto the ground, that issue when away when I replaced my coolant reservoir and thermostat with a new one because I think the cap and threads were screwed from so much molestation or my thermostat was allowing this to happen.

In any even there would be space for a small container as you describe over the alternator.

[Tokay444]

If you can hear it boiling, there is air in the system.
The coolant continues flow when the turbo is clocked properly, syphoning cooler coolant through the bottom as the hot coolant exits the top.

[qkrthnu2]

Originally Posted by Tokay444 If you can hear it boiling, there is air in the system.

I thought so too..... but I just spent $150 buying the tools to do it right, so I hope I'm not still doing it wrong.

I did this today:

1. Turned key to on position.

2. Heat and blower to max (hooked up a battery charger as well)

3. Connected Airlift to radiator Amazon.com: UView 550000 Airlift Cooling System Leak Checker and Airlock Purge Tool Kit: Automotive

4. Set compressor to 100psi and started pulling vacuum



Got a good vacuum, shut the valve and let it sit for 15min or so to make sure it held, which it did.



5. Vacuum filled the system



6. Disconnected the Airlift and put on a spill free funnel Amazon.com: Lisle 24680 Spill-Free Funnel: Automotive in case the system was going to suck any more coolant (it didn't, because it was full).



7. Started the car up and revved it up until it was warm, then let it idle for a while

8. Shut it down, waited for it to cool down, pulled the spill free funnel off, put the radiator cap back on and reconnected the overflow tank (I had put a vacuum cap on it, one thing the Airlift didn't come with which is necessary).

After all that, I still hear coolant boiling on the turbo after shutdown...

[acemanz]

Having Air in the system is not a requirement to boil coolant.

A radiator cap helps increase the systems pressure which RAISES the boiling point of the coolant. Coolant can and WILL still boil in an enclosed system with or without air if the temperature is high enough.

If the entire system was boiling then adding a higher PSI rated radiator cap could help but in this case its just a tiny spot on the turbo so the only way to keep that from happening is to supply it with fresh coolant.

That being said, what Toykay444 said would be true as well if the air bubble became trapped in the coolant passage of the turbo. However, since you have already proven that there is no air in the system we can conclude that it is most likely pure heat causing it to boil.

INC. DIY turbo coolant reservoir?

[Tokay444]

My car doesn't have a radiator cap.
Water can't boil in a sealed system.

[qkrthnu2]

Originally Posted by acemanz However, since you have already proven that there is no air in the system we can conclude that it is most likely pure heat causing it to boil.

Originally Posted by Tokay444 The coolant continues flow when the turbo is clocked properly, syphoning cooler coolant through the bottom as the hot coolant exits the top.

The BNRs3 is using the rigid OEM oil drain tube, so must be clocked the same as the OEM K04, give or take a degree.

The only thing different is that I ended up using some spare silicone tubing I had laying around for the top water connection (Turbo -> EGR delete). It's probably slightly smaller inside diameter than the original hose. Would that be preventing thermosiphoning from working properly? Maybe I'll try swapping that and see if it makes a difference. What size is the OEM hose, 5/16" ID?

Anyone else have boiling sounds coming from the turbo after shutdown?
BTW, it's not super loud. I have to pop the hood and stick my head near the turbo to hear it, and it takes a minute or two after shutdown to start boiling.

[acemanz]

Originally Posted by Tokay444 My car doesn't have a radiator cap. Water can't boil in a sealed system.

how do you think your AC system works?.... the refrigerant BOILS .. and its in a enclosed system.

a pressured system only INCREASES the boiling point.. it doesn't eliminate it.

[Tokay444]

I bet it's boiling oil you're hearing.

[Tokay444]

@silvapain;, does water boil in a seal, pressurized container?

[acemanz]

that is very unlikely given oils boiling point is really high near 575 degrees


coolant on the other hand will boil in a pressurized system much lower then that around 310 or so depending on pressure and altitude

https://www.physicsforums.com/thread...a-tank.283583/


as described in the second post in the linked forum,

"what we are seeing is locally the vapor pressure can be larger than the overall pressure."

Reference https://www.physicsforums.com/thread...a-tank.283583/

[acemanz]

an added point is that the Break system is also enclosed.

Brake fluid will boil when the breaking system is producing a lot of heat, and being hygroscopic, the fluid absorbs moister which Lowers its boiling point over time making it less and less effective.

[Tokay444]

For water to get in the brake fluid, means it isn't a truly sealed system...

[acemanz]

Originally Posted by Tokay444 For water to get in the brake fluid, means it isn't a truly sealed system...

Water gets in when people top off fluid after a break change or bleed. It is only because humans open the master cylinder that water gets in. It doesnt take long for the fluid to absorb moisture after being exposed to air during service.

[Koke382]

Haii

[Cataphract_40]

Bump...

My ATP GTX2867R does this too. Never happened with the stock K04.

Pretty much exactly as OP describes it. Any resolution to this OP?

[KevinK2]

Originally Posted by Cataphract_40 Bump... My ATP GTX2867R does this too. Never happened with the stock K04. ...

This white paper from Garrett turbos may help:

https://www.turbobygarrett.com/turbo...er_Cooling.pdf

They talk about the higher heat load at shut down with both bigger turbines and hot housings. In your case, higher heat loads also occur when at higher hp levels.

Both the MS6 and MS3 have modern pressurized expansion tanks with a cushion of air that keeps the system pressure near the cap relief pressure. One could say there is always air in the coolong system, although it is confined in the plastic tank.

At shutdown, you can have local boiling that sucks away heat from the center section of the turbo, and the thermal siphon moves the local vapor to where the bulk coolant temp is lower, and the vapor disappears. This may cause a gurgling noise that you now hear.


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[qkrthnu2]

The coolant reservoir tank on the MS6 is not pressurized. It's just a typical overflow tank with a siphon tube.

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[Cataphract_40]

After musing on this for a while, here's my hypothesis:

The GTX turbo coolant line that connects to the EGR valve is oriented 180 degrees opposite from the stock turbo's line. Here is a handy picture of the two turbos side by side, GTX on the left, stock on the right:





The stock turbo's coolant line comes out of the turbo UPWARDS - towards the sky as the turbo sits installed - and then curves 90 degrees towards the driver's side and the EGR valve.

The ATP coolant line comes out of the turbo DOWNWARDS - towards the ground - and does this long sweeping 270 degree turn skywards before going into the EGR valve. See my shitty MS Paint pic below.



I wouldn't be surprised at all if the coolant is getting stuck in the turbo by this 180 degree 'trap' and thereby preventing an effective thermal siphon.

Thoughts?

[KevinK2]

Originally Posted by qkrthnu2 The coolant reservoir tank on the MS6 is not pressurized. It's just a typical overflow tank with a siphon tube....

AFAIK, it is pressurized, with the benefits I describe.

I could only find a pic of the MS3 reservoir tank:
MS3 Reservoir Tank Shown

As shown in the enlarged view, the tank has external ribs to allow it to hold pressure, and the cap is not the simple flip variety found on old style vented overflows. You can see the ribs indicating high-low levels, and the coolant correctly in between. Above the coolant is a large volume of air at the same pressure as the coolant.

I assume the MS6 is also pressurized, like the MS3 with same engine. Note my 2004 M6 is also pressurized.


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