Turbo 2.5 L Subaru Loosing Coolant, but no visible leaks? Fresh rebuild.

[Ben]

Hey all,

I have a MY09 Subaru Forester XT, and I am about at my wits end.

Long story short;

The car over heated due to a air lock from replacing turbo’s.

Engine was pulled out, heads were sent off to be reco’d

Purchased a brand new shortblock and put on the reco heads

same thing – still loosing coolant and now smoking

Took the engine back out – got the heads checked over again, machine shop found a crack that said was near a oil gallery and exhaust valve (they did not pressure test the heads during the reco), so could be my issue for smoking. but were not confident it would cause coolant loss.

Sourced another set of heads, they were pressure tested, tested ok, then everything was reco’d again.

Fresh gasket kit, used the same shortblock.

Same thing – Still loosing coolant.

Current setup;

2nd set of Reconditioned heads

Brand new STI Shortblock EJ257, would be 2.5 tanks of fuel old now.

Silicone Turbo Inlet

PCV valve Deleted, crankcase and valve covers venting to atmo till can sort this issue.

VF52 Turbo (have put the stock TD04 on as well, same stuff)

ARP Head Studs, toruqed down in three steps to 90 ftlbs as per instructions, in sequence shown.

Genuine head gaskets

Air Pump/TGV Deletes

Throttle body coolant bypass (used little rubber caps on the two lines)

Where do I go from here?

The bottom end is brand new from subaru, the heads have been reconditioned and I have been assured these ones have passed the pressure test.

Is there any other way I could be loosing coolant? I have vacuum filled the system (and manually burped the system) and pressure tested the cooling system to see if i could find a external leak, I can get it up to about 17psi (just before the rad cap opens) and it will drop a psi every two minutes or so (didn’t time it exactly).

I can see some little bubbles in the expansion tank through my spill free funnel when I run the engine when burping the cooling system, but I find I will be burping forever…

Car seems to drive fine, just needs about 100ml in the overflow bottle after almost every drive….not right for basically a brand new motor.

Any idea’s? What could cause air in the cooling system?

Topic

[Richard Kirshy]

A small temperature difference from driver side to passenger side is common enough due to the ducting lengths and routing.
But to have that wide of a range difference indicates something is not right.

[Ben]

Such a strange issue.

What causes the overflow to get sucked back into the system once the car has cool down?

I assume it’s when the coolant cools down the pressure creates a vacuum effect and sucks it from the overflow?

[Richard Kirshy]

Heat = expansion = excess fluid and pressure is driven into the expansion tank
Cold =contraction = fluid drawn back into the radiator.

[Ben]

I have not noticed the overflow actually rising while the engine is at operating temperature…is this normal?

Just seems to suck some in after it has cooled down leaving me topping it up and checking it constantly.

[Richard Kirshy]

It will vary from vehicle to vehicle.
Dependent on temperature and system pressure.
Some may barely change levels.
But considering you found some leaks in your system not unusual for the tank to drop in level to compensate.
FWIW,
If you confirm passing the combustion gas test, I’m still thinking there is a trapped air pocket in your cooling system.
I’ll say it again.
Might try removing the thermostat and drive around and see what results you get.

[Ben]

Thanks nightflyr I appreciate your time and knowledge on the subject.

I will try the block test shortly, following that will try running without a thermostat to see how the temperatures and heat goes.

[Ben]

So last night after I finished driving, I parked the car and topped up the coolant overflow beyond the full mark, in hopes to not allow the system to suck air back in after everything was cooling down.

Sucked out the excess this morning drove the car today, and parked it again – waiting till tomorrow to see if the level drops (fingers crossed I have fixed all the leaks and the level stays solid).

After confirming that, My plan is to either bypass the heater core or remove the thermostat and see how everything goes.

Which do you think would be a better diagnosis to try first?

[Richard Kirshy]

Start with the easiest.
Bypassing the core will have the least possibilities of causing more air in the system.
But removing the T-Stat will allow non restricted flow for the best chance of purging for the system.
Either won’t be effective unless you have done a combustion gas test to see if the air may be getting into the system via the combustion camber(s) though.

[Ben]

I should also mention since I have owned the car – there have been heating issues for the cabin. Specifically it was the drivers side that had minimal heat, but now it’s reversed.

As far as I am aware there is only one blend door on this vehicle – there is no dual climate control.

So perhaps it might be pointing to a heater core issue – the heater core provides the thermostat with the heat required for it to operate (as does the turbo charger outlet) – but I assume the heater core may provide most of the heat for the thermostat.

[Richard Kirshy]

If the heater core becomes blocked or partially blocked here’s what happens.

1.) The thermostat will open under the wrong engine temperature conditions.
2.) The engine will overheat under moderately demanding conditions (i.e. a hill).
3.) The overheating will cause the water in the engine to expand and there will be a big spike in the pressure in the cooling system. This big increase in pressure coupled with the distortion of the cylinder heads will more than likely cause the head gasket to blow.
4.) The increase in pressure will override the spring in the radiator cap and the coolant will flow into the overflow bottle.
5.) When the demand on the engine reduces it will cool down. The reduced volume of water will cause the top radiator hose to suck in.

[Ben]

I have bypassed the thermostat and unfortunately the temperatures seem pretty similar.

Perhaps its just a bad thermostat – I will try running the car without a thermostat and see how the temperatures behave.

Also the car had no cooling missing over night – so happy days (leaks fixed!)

[Ben]

Just another update – I still have the heatercore bypassed, and have replaced the thermostat.

I tested the new and old one side of by side in some warm water watching the temperatures change, the newer one opened a tiny bit sooner but I didn’t think it would make much difference.

Put the new one in and still seeing similar temps.

Will be trying no thermostat next as you have recommended.

I understand these temperatures are still not exactly “overheating” but getting temps of 98c at 100km/h cruising along seems to be pushing it.

[Richard Kirshy]

Two questions.
What temperature are the thermostat rated at.
Do they have a bubblier hole?

If you run without a thermostat and with the system full and still run hot then your looking at a circulation issue.
Make sure you have burped the system as best you can.
Interested in seeing the results, curious to see if perhaps there could be a faulty water pump being the source issue.

[Ben]

Thermostat is rated to start opening at 77c. Just asked some other subaru owners, general consensus seems to be temps around 86c-91c in all conditions.

They both had little jiggle pins at the top of the thermostat to let air through i am assuming.

[Richard Kirshy]

Sounds about right.
Subaru has an odd layout for the way they route their coolant.
Please post the no thermostat results when you get them.

[Author]

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