Coolant is vanishing without a trace!

[noah]

Hi everyone.

I have a mazda Bongo 1996 WL-T 2.5 diesel with 125K on the clock. It has suffered from intermittent over heating problems since I got it 2 years ago, but this has been few and far between (eg runs fine for 5000-10,000kms then might overheat). After a recent flare up of over heating, I had the radiator replaced with a new one (not genuine mazda, but the recommended copy that plugs straight in) and all rubber cooling hoses replaced. Since this was done, I have NOT had any over heating issues, BUT, the coolant is literally disappearing. There are no coolant leaks onto the road or my driveway. The engine oil is not milky. The cooling system has been pressure tested both while cool, and at idle when the engine is hot by 2 independent mechanics (one of which was the local Mazda dealer) and both have said the system is holding pressure. Tonight I took it for a 100km long drive. I departed with the header tank at the full level when the engine was cold. I drove approximately 30kms mostly at a speed of 100kmph and checked the coolant. It seemed not to have moved. then I drove a further 30kms an the header tank was totally empty. I waited for the engine to cool down and double checked the header tank again - still EMPTY! Can anyone shed some light on what may be going on here?

PS. I'm stuck out here in Australia where Bongo's are still few and far between, so local knowledge is zero.

Thanks in advance for any assistance.

PSS.. Oh...and since the new radiator and hoses went in, there is a noise (sounds like it's coming from the power steering) that happens when I make a tight turn in either direction. I don't think this is related. But nothing surprises me any more with this saga, so thought I'd mention it also. Any ideas on what it might be and how I can fix it? cheers.

[Doone]

There have been a few posts about disappearing coolant; finding a leak can be tricky, have you seen the advice ON THIS LINK? (I don't know if they sell the dye or the coolant mentioned, in Australia.)

[321Away]

I've seen on a couple of occasions bongo's that leak only when they're hot, make sure the connections between rubber/metal pipes are clean as build ups there can lead to seepage. The main engine inlet hose is prone to rubbing n opening a tiny pinhole that only allows fluid escape once the engine/coolant are hot, not always but worth a look

Julian

[haydn callow]

To lose tankful in 30k's is quite a leak...You could try the leak detection fluid and a uv torch....

[noah]

Thanks for all the advice posted! Greatly appreciated!

I will try and get hold of some radiator dye today and test this path out.

If the dye doesn't reveal any leaks, is the next logical step to remove the head?

Thanks in advance.

[haydn callow]

If you hajust been refilling a empty expansion tank without going through the correct "bleeding" process you will at best have loads of air trapped in the system which leads to overheatinf...and at worst damaged your cylinder head.....As you are loseing coolant without trace I would suspect the latter.
Can you get a garage to do a combustion gas test in the header tank.

[noah]

If you hajust been refilling a empty expansion tank without going through the correct "bleeding" process you will at best have loads of air trapped in the system which leads to overheatinf...and at worst damaged your cylinder head.....As you are loseing coolant without trace I would suspect the latter.
Can you get a garage to do a combustion gas test in the header tank.

Good point. When I replaced the radiator and all hoses, the system was properly bled by my mechanic (I made him read the 3 pages of instructions from this site). Since then I have topped up several times from the header tank but was hoping that as long as the fluid level was above the hoses in the header tank that this wouldn't introduce air into the system. I hope I got this right ( but it's likely that damage could have been done prior).

I got Mazda to do a combustion test and they confirmed that gasses were not found in the cooling system!!

So from here. I'm taking the great advice from this thread (thanks to everyone that have commented) and have tracked down the one place in Australia that has UV coolant dye, and see if I can track it this way.

If we don't find a leak, I'll get the head donef, or leave it parked in Corio (our version of the Bronx) unlocked and with the keys in it.

[mister munkey]

Stating the obvious - A Low Coolant Alarm really is a must in this kind of situation. At least you know when it drops, preventing any further damage. I'm guessing Haydn can get one to Oz . . . .

[haydn callow]

I have dye you want...if you want to go to my website below you will see it there....not easy stuff to get in small doses.