Frustrating Intermittent Coolant Leak

[brw0513]

Just when I think I've finished working on the 6G74, I get an oddball coolant leak.

The leak comes and goes. I can drive the car for 40km and not see a hint of coolant leak (parking over a flattened cardboard box to check).

I can then drive 2 mins down the road and stop to check and see a leak that is a drop every 2 seconds or so. Things are too hot to do too much exploring at that time.

There is another odd thing happening. Sometimes when the engine is up to temperature the top radiator hose is very bulged and is very firm to squeeze. At this time, the lower hose is very "squeazy". The exact opposite can happen too. The top hose is squeazy, but the bottom hose is very buldged and firm.

I suspect I have air trapped in the cooling system, a faulty thermostat, or maybe I installed the thermostat upside down so the little joggler is at the bottom.

Any suggestions?

I'm waiting for the enginee to cool down now before taking the thermostat out.

[christopher]

Check the heater hose connection behind the motor (drivers side), seriously hard to see, took me 6 months to find out it was the cause with my 93 Paj

[motorazr]

There may be a leak in the hose that runs between the valleys of the heads. Usually leaks where it goes into the back of the water pump. The fluid can sit there then drip when the level of the car changes. Hard to see also and a bugger to fix.

[brw0513]

Thanks for the replies.

The leak is not any of the usual water pump related culprits. All good there.

The leak is coming from the top radiator hose where it joins the aluminium casting.

I've just done the fill up process in accordance with the manual. I did see quite a few bubbles burp out of the top of the radiator and perhaps I had too much coolant in the system. Time will tell.

[aussieintas]

I remember on my NJ some years ago that aluminium housing you mention had corroded a bit causing a leak. May be woryh taking off the hose and having a good look.

[brw0513]

I remember on my NJ some years ago that aluminium housing you mention had corroded a bit causing a leak. May be woryh taking off the hose and having a good look.

I agree. I'll check on a price from MM and ring around a few wreckers.

[brw0513]

Is it possible the 6G74/coolant system could have an air pocket somewhere? I'm curious if the there is an air pocket in the heater box.

The reason I ask is that I have been idling the engine with the radiator cap off over a number of sessions now. I cycle between heater and A/C inside the car. Most times there is nothing really to see when looking down the radiator opening, but every now and again, the coolant rises in the radiator fill neck then there is a burp that I presume is a bubble of air escaping.

I've tried to capture it on video, but mostly the footage shows nothing, then a burp comes and goes very quickly.

[motorazr]

Had a similar thing which turned out to be air in the heater core......but then it could be a host of other things as well.

[brw0513]

Had a similar thing which turned out to be air in the heater core......but then it could be a host of other things as well.

And how did you bleed the air out of the heater core? Just idling with radiator cap off?

[motorazr]

No unfortunately it was a bugger to get rid of as the hoses had to be removed and the core back flushed for over half an hour. It still not completely right as it was partially blocked.
Will necessitate a removal of the heater core. You can test if the core is the problem by by passing the core and joining the hoses together.

[brw0513]

No unfortunately it was a bugger to get rid of as the hoses had to be removed and the core back flushed for over half an hour. It still not completely right as it was partially blocked.
Will necessitate a removal of the heater core. You can test if the core is the problem by by passing the core and joining the hoses together.

So what symptoms do you have now?

[motorazr]

No air bubbling through the radiator but the heater still only gets Luke warm. Good enough for now but eventually will probably need the heater sorted properly.