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diagnosing a cracked block/head or head gasket issue.

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i have a recently rebuilt 3sgte, it was rebuilt due to failed ring lands (relatively common on stock pistons)

since the rebuild the engine consumes coolant, not massive amounts but maybe 200ml in 1000klms.

now the engine leaked down fine and compression tested fine and makes good power. (240awkw at 17psi on E85 from a gtx2867)

its just a worry coolant is being drawn back in from the overflow consistently.

have pressure tested the coolant system and no leaks, no white smoke and had an oil analysis test completed and water content was acceptable.

so what tests can i run to rule out a cracked head and block or failing head gasket (cometic on freshly milled head and block)?

Hi,

You could do what you already did, leak down test, but this time remove the radiator cap, and see if there is any air pockets, if you see any air bubbles then there there is something wrong, if not, you may start looking else where,

Normal shop air supply of 100-120 psi often won't be enough to show up a leaking head gasket or a cracked block. You can connect your leak down adaptor to a nitrogen bottle regulated to something like 1000-1500 psi. This is going to be more realistic in showing a problem. If I've got a car on the dyno with a leaking head gasket this will normally show up by water pushing out into the overflow during a ramp run.

Ok so if it is never pushing coolant out it’s unlikely to be a crack or head gasket issues. So apart from a leak. What can cause consumption/loss of coolant?

How many km have you run the car since the rebuild? If you didn't get out all the air while filling it up with coolant, this will slowly suck out water from the overflow tank during heat cycling. But that should stop at some point. Maybe after 10 times of having the engine been heating up and cooling down.

about 1600klms, must admit the cooling system is overly efficient (EWP) so it generally doesnt get over 70'c....

i am PWM the water pump at 10% and its to effective, looking to add a thermostat back in.

There are test kits available, Repco carry them for example, that will check for carbon monoxide in the coolant, which can only get there from combustion gases - depending on the vehicle, it is possible the oil may not be getting contaminated although, IIRC, they look for trace chemicals usually found in coolants, rather than just 'water'.

Do the hoses feel unusually hard when you squeeze them - that is often a sign of pressurisation?

Depending what state you're in, if you don't use the heater, it might still be bleeding through if it uses a water mixing rather than air mixing control method?

Some coolants are flourescent, you could try looking for a leak with a UV light?

@Gordon, the TK testing kits are really not useful in a turbocharged engine that's only lifting the head under high boost. They rely on combustion gas being released into the cooling system while the TK test is being performed and most often the head gasket won't leak at idle or even cruise.

Are we thinking of the same test? A 'sniffer' test for disolved carbon monoxide gas in the coolant that can only come from combustion gases leaking into the coolant?

Ah, see why there may be some confusion, as there are different tests available. However, the gas type should still work perfectly well as once they get into the coolant/airspace, they will remain there and can be tested for - no need for them to be leaking into the coolant at the time, although that would be the classic test*.

Either way, while a negative test may be inconclusive, a positive test will show further investigation must be done and remove any doubt.

Remember one instance of a truck that would puke litres out when when rev'd - surprised it even ran, TBH.

Hi Guys

just to clarify the engine is not pushing coolant, hot cold high boost or low boost the coolant level in the overflow doesn't change.

coolant and oil are clean, pressure test is good.

just uses some coolant over time..

weird

@Gordon, no, we're talking about the same test. I've used them several times on engines that only lifted the head at high load/high boost and the test comes back negative at idle. This situation usually shows up though by the engine pushing coolant into the overflow during a run on the dyno which is pretty conclusive.

@Joshua, that's a weird situation you've got yourself there! Surely there must be a minor leak somewhere in the system?