Black gunk in radiator

babaruka, Jan 14, 3:58pm
Any ideas on what this could be? Has happened three times over past six years. car has started to heat up while towing and once cooled and check water there is gritty black gunk in radiator. Mechanic not sure what it is or why it happens. After first time drove car for another couple years and ended up replacing head as was cracked. About six months later happened again so flushed radiator and replaced thermostat. This time have put in new radiator but still have no idea where crap is coming from causing radiator to block. Any ideas what it is?

jason18, Jan 14, 4:11pm
New radiator needed?

babaruka, Jan 14, 4:29pm
Yep just put in new one :-)

tony9, Jan 14, 4:33pm
Gritty black gunk would likely be carbon. And the source would be combustion leaking through a head gasket or crack in the head or block.

Was the replaced head second hand? Was the block (and the head if not new) resurfaced before putting it back together?

jmma, Jan 14, 4:35pm
Could be rubber water pump impeller failing, what is the vehicle and milage?

skull, Jan 14, 6:15pm
Is there enough rubber on a rubber water pump impeller to block a radiator 3 times and still be pumping water?

panicky, Jan 14, 6:17pm
someone tried the old black pepper trick to fix a leak?

babaruka, Jan 14, 6:17pm
Head was new and actually have no idea if block was resurfaced. Would have to find out. Its a 92 bighorn and done about 220000 km. Cheers.

jmma, Jan 14, 6:31pm
Oh OK, maybe a couple of hoses starting to perish as well :oP

xs1100, Jan 14, 7:21pm
yeh 22 yrs old hoses could need replacing

catwoman1974, Jan 29, 11:30am
Had a Jap import years ago that had black gunk in radiator, car started over heating so flushed it out. Nek minnit, had a leak which turned out to be a hair line crack in the block where the water pump bolts on.