Zd30 filling overflow not sucking back

[Bre77p]

Hi there,
I have an 02 patrol with zd30, I have blocked EGR and catch an for crankcase breather. I have EGT gauge and boost gauge. I just came back from WA trip when car started filling overflow bottle and not sucking back. Replaced cap, removed thermostat and replace (old one had some scrape marks) flushed radiator ( only 20% blocked) Still doing same thing, mechanic did to test negative. I don't know what else it could be, engine running perfect. I do notice u can see flow of water circulating in header tank above overflow. Any advice would be great.
Cheers
Brett

[pearcey]

Make sure the hose into the overflow bottle is not sitting upright and touching the bottom of the bottle as it may work like a one way valve.
also check the hose for any soft spots that may collapse in a vacuum situation.

[Bre77p]

Hi pearcy no hose isn't blocked I can blow water back into pressure bottle with cap off. Mechanic did to test came back negative did pressure test on cooling system all good replaced thermostat flushed and serviced radiator but is still purging into overflow and leaving radiator down on coolant. Where do I go next ?? Really need help could it still be head or head gasket runs perfect no oil in water or water in oil. Help!

[the ferret]

Have you done a compression test?.
Cheers, the ferret.

[97_gq_lwb]

I have seen this on a gq that had a pinhole in the inlet to the overflow tank.
And once it was a small leak on the bottom hose where it joined to the radiator.
Even seen it from a leaking water pump.

But the most common cause would have be a compression leak into the cooling system cracked head or gasket .
Have it tested by a specialist and save the guess work and dollars asscociated.

http://natrad.com.au/?storelocate.html

[BusaKaine]

how did ya go?

[aaron]

sounds like you done a head gasket to me mate .

[krogh]

If you have checked for leaks in the overflow hose and replaced the radiator cap and it is still pushing water into the recovery bottle it is likely to be a head gasket or cracked head. To test you can use a old radiator cap and remove the rubber seal that seals in the lower part of the filler neck of the radiator, leave the seal that seals on the top of the filler neck in place. You should also disconnect the fan belt that drives the water pump. Then put the overflow hose into a clear bottle to see if you have bubbles. Rev the engine and watch, if you have constant bubbles then you have combustion gas leaking into the cooling system.