Coolant pressurising

[Brutal]

Hi Everybody
I have a 2.4 d hilux on a 91, I have had it for 5 years, it was fine for 3 years then of course the head cracked so i replaced it.
It was then fine for another 12 months then it started overheating when it was put underload - which it still does.
I have changed the thermostat and cap, I have pressure tested the water system, - all fine, the test kit takes 2 hours to depressurise. I have tested the water for oil contamination.
It doesnt lose any oil other than usual burn and there is no water in the oil.
Now I am completley stuck.
It pressurises and releases in to the expansion tank, so needs toping up every 3 days.
Any Ideas
Thanks

[charvell]

Hi Everybody
I have a 2.4 d hilux on a 91, I have had it for 5 years, it was fine for 3 years then of course the head cracked so i replaced it.
It was then fine for another 12 months then it started overheating when it was put underload - which it still does.
I have changed the thermostat and cap, I have pressure tested the water system, - all fine, the test kit takes 2 hours to depressurise. I have tested the water for oil contamination.
It doesnt lose any oil other than usual burn and there is no water in the oil.
Now I am completley stuck.
It pressurises and releases in to the expansion tank, so needs toping up every 3 days.
Any Ideas
Thanks

Air lock? turn the heaters on full and burp the system

[tintin]

One of the resident surf experts will be along to tell you later, but i'm sure if it expands into the plastic bottle it should also suck back into the system when cool so definately shouldn't need topping up every 3 days.
Check the hose leading away from the bottle(drain) isn't blocked!
Good luck.
Alan

[Diezel Weazel]

Check ya don't have Pinhole in ya Rad or a hose as mine did the same, pin head o solder..... cured it
Good Luck

There's always a Payback .... Ya just never see it Comin !!!!

[Koi]

was going to say change the rad cap as if it is letting by to quickly then expansion bottle could be filling up overflowing. Once overflowed it cant suck back in the system whats been lost hence you need to keep topping it up.
Another possible is the rubber to the expansion bottle is split/perished etc , will allow coolant in to expansion bottle but cant suck as if it is split etc it will only suck air. So next time cap releases it over fills expansion bottle and so on. Low coolant wont sometimes show overheating until engine put under a hard load, then temp rises as not tenough cooling, bit like a blocked rad.
Have you been off roading, rad blocked with mud etc, try flushing rad through with hose etc