Chris Lockhart

'89 S4 engine is out of the car and in a stand, sans heads: What is a safe, effective method to clean the scale off of the coolant passage area around the cylinders?? I've done plenty of searches on RL as well as Google in general, and the only effective processes I've seen are for iron blocks, and are not aluminum safe. TIA.

Mrmerlin

with no heads and the engine in a stand you could position the bock to one bank facing up,
then add some CLR/water mixed, note this is not a full strength mixture.
and let it soak for 24 hours use a brush to agitate the liquid,
use the block drain to empty,
then rinse it with some distilled water,
if your careful you wont get any of this into the cylinders.

Mrmerlin

FWIW its best not to flush the 928 engine with the heads installed,
as you can really clean the head gaskets,
This cleaning can cause a leak after the debris are rinsed away.
If anything flush the block with distilled water then drain,
do the same for the heater core and coolant bottle

Chris Lockhart

Stan, that's kind of what I was planning to do, then I read all kinds of stuff about not getting CLR near aluminum as it will cause damage and discoloration, so I stopped. I looked at the label on the CLR and other similar brands and they all say not to use on aluminum. If you've personally done this and recommend it, I will gladly follow your lead. I just want to be sure first.

I've been using stiff plastic bristle bottle brushes on a cordless drill, and it helps, but just not enough. Thanks.

69gaugeman

Use distilled water. It has no minerals in it at all and will absorb the stuff that is on there more readily.

dr bob

Stan is on the money as usual. If you are concerned about oil or other deposits, try some liquid Tide in solution as a soak-and-rinse. It has a slew of water softeners in it that might help with mineral scale and oil/coolant deposits, but is relatively benign around the aluminum. CLR would be good for some things, but you really want to stay on top of it and rinse thoroughly. It removes the oxide layer on the aluminum, brightening it initially, until a dark hydroxide layer starts to form.

I kept a "cold tank" reconditioning the surface color for aluminum air-cooled cast parts, with Mr Clean and warm water. Forget a piece in there and it would corrode to a dark gray after a short while. There isn't anything that will effectively dissolve calcium and rust without getting into the aluminum too, unfortunately.

Chris Lockhart

Thanks gauge and Dr. Bob. (and of course Stan).