i'm about to clean up the block and i noticed that inside the jackets there is a lot of sludge next to the cylinders. im wondering if it would be a good idea to try and loosen up that sludge a bit and flush the coolant later. also if i can do this, it wont be so bad if i get some dirt inside the jackets when i'm cleaning or buffing the deck (a lot of holes to cover up). i'll only have to worry about the ones that go into the oil pan.

 

leave the sludge alone. just make sure you change the oil before you start this thing up. the sludge could end up in the radiator and clog it.

 

If you're talking about sludge in the cooling jackets, I'd clean it up. As long as the heads are off, you should be able to use a long slender tool to reach the bottom of the jackets around the cylinders and break free any deposits. Since the heads are off, you should also be able to remove the knock sensor and drain plug on the opposite side, then flush out most of the debris.

When you refill the system, use only water at first. This will serve several purposes:

• Any leaks will only be water and residual sludge and coolant. If there are leaks into the oil pan, your risk of damaging bearing surfaces with plain water are a lot less than with coolant mixture.
• The water will help dissolve any other coolant sludge, deposits, and contamination.
• You'll want to drain and flush the cooling system to remove any traces of this contamination, gasket chunks, sealants, etc., once you have determined that there are no leaks and everything is working correctly. There's little sense in wasting coolant mixture for that.
• Once the engine is sealed, running right, and ready to go, it's a good excuse to flush, use a cooling system cleaner in water before the final flush, then refill with coolant mixture. That way, your cooling system will be all set to go for the next three years.

 

Yes on the sludge removal. I couldn't beleive the amount that came out of my 305 (+110K miles on may 3 coolant changes). There was almost enough to fill an average size coffee cup. Yeeech.
Vader- I had never thought about using water for first startup- but your points all makes sense to me. Thanks,
S-D