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Found strange balls in radiator


NAXJA Forum User
I found these small, dark brown, soft and mushy balls in my radiator when I did a fluid check yesterday. I'm in Lithuania about 1,500 miles from home and only halfway to North Cape, Norway on this road trip.

I installed a new radiator last February 2021 and haven't driven the xj much due to some additional maintenance. I suspect that there were some styrofoam packing material left in the new radiator when I installed it. I didn't flush the thing, just blew some compressed air in it.

If these are indeed small pieces of styrofoam in my radiator, how likely is it to cause a catastrophic overheating due to clogged passages? I've driven 1,500 miles already and my temp gauge stays at around 195F. Not that it matters to the coolant, but my oil pressure stays around 60 psi at 65 mph.

If these little things are some sort of insect eggs that got trapped during packaging at the factory, then that's not too much of a problem.

What else could it be, and should I worry too much?

Thanks for your opinions.
1994 xj, 2.5l, ax5, 4x4, new radiator, 208,580 miles odometer
How small is small?
First thing that popped into my head was Bar's Stop Leak Tablets.


They softened up and just did not dissolve completely.
Just a guess though.
Did you flush the system when you put in the new radiator?
IMO using stuff like that is never a good thing.
Don't get me wrong I have used that stuff before.
But only on a vehicle that I was trying to keep alive a little longer before I called the boneyard to come and get it. LOL.

Now don't get all nervous. This is just a guess.
Your Styrofoam theory carries a little weight maybe.
They usually put caps over open ports on radiators in the box.
But there is usually Styrofoam in there so...
You say it operates as it should.
Does the heater also?

If were me I would just flush the system best I could.
Hi Ralph77. Thanks for your thoughts. These little mushy balls are about 2mm in diameter, so very small. That's why I think they're the styrofoam packing pieces. I flushed the radiator with water, drained the block as best as I could from one freeze plug that I then replaced. Then refilled with glycol based coolant on an incline until the bubbles went away. Then I filled the overflow bottle to the full line with the coolant. I haven't used the heater yet since it's been soo bloody hot up here lately. I'll try that later with the windows open 👍🏼.

It's been running great at just below 3,000 rpm at 100 kph (about 65mph) and at 60 psi so I havent seen anything weird yet. There are no additives in the coolant. Never has been. Only the green stuff, and now the blue stuff. I look for just the normal glycol coolant for cast iron engines.

I think I'm going to just keep my eye on the temp gauge all the way up to the Arctic and back home to the Netherlands. Unless there are other thoughts about what these things are.
About the flushing, it was the old radiator that was flushed along with the block. When I found the leak in the radiator, I ordered a new one. The new one was not flushed anymore. I just blew compressed air in it.
If its not over heating now then it's not likely to cause a problem, my first thought too was stop leak, but the Styrofoam seems more likely, surely there can't be that many in there.
Thanks, unclewolverine. I'm farther in my journey and haven't overheated yet so I guess I'll be ok. It just couldn't be stop leak since I've never used it. So I'll put my mind to rest. Thanks.
If your radiator was shipped with styrofoam packaging, then that seems to be the likely answer. Styrofoam is a thermoplastic so it will melt before it decomposes. It begins to soften at around 180F and melts above 400F. It is water compatible in the sense that it does not dissolve in water. The presence of antifreeze shouldn't change that. I imagine that its accumulating at the inlet side of the radiator. Assuming there isn't a bunch of it in the radiator, it should be fine.
Yes, it came in a box with styrofoam packing, just like your flat screen tv would come in the box.

I found the small balls stuck to the side of the fill hole when I pulled the cap off the radiator. I think one of them was actually lodged in the cap, but I was able to pull it out with a knife. So, yes, I believe they floated to the top of the water line.

I did have to add some more coolant, so I'll check again tonight at when I make camp.

I hope they will all find their way to the filler cap. If some are lodge in a small passageway, the engine doesn't seem to be hot enough to melt styrofoam. So that could cause problems later. I'll keep my eyes on the thermostat once in a while.

Thanks for all your responses.

Be safe!