Clean out cooling system before or after part replacement

[XJSteve]

Hi everyone, I have a fairly basic question (and yes I used the search function). I have a '99 Cherokee with the 4.0 and a leaking water pump. Given the challenges the XJ cooling system has and that all of the parts are original, I thought I would also replace both rad hoses, the rad, thermostat, and the clutch for the mechanical fan. My question is this - obviously I am going to replace the rad coolant. Do I clean the whole system with descaled etc. prior to the new parts going on  so that any mobilized scale doesn't go through the new parts or do I clean out afterward to ensure any dirt in the new parts is also flushed out (even if I run a hose through the rad prior to placement)?

[fug]

Interesting question... Personally I'd probably try to flush things out after you've pulled the old parts and before you install the new ones.  With all you're pulling off you're looking at flushing the water ways in the block and the heater core most everything else will be new. 

[bRIBEGuy]

I did the same replacements (full cooling system) in the spring, and I opted to flush and clean everything before the new parts went on.  Drained the system.  Flushed it.  Added a cleaner.  Flushed it again.  Took a while, but by the time I was done the water was pouring out clean enough to drink.  Not that I tried.......

After that, I did the teardown, flushed the heater core seperately again, added the new parts, and filled with coolant.

[bRIBEGuy]

Edit: accidental double post. 

[birdo]

Yup.....remove all the old parts and start flushing...especially the heater core....amazing how much gunk can collect in there.
The bottom of the rad is likely to have a lot of crap settled at the bottom so make sure you flush it really well too.
This will be a really good time to inspect the radiator. You want to inspect for any seepage where the plastic tanks get
crimped to the radiator fins. If they start to leak it's pretty much game over for the radiator. Mine was leaking and I elected just
to place the entire radiator. You can get a new rad from Napa easily.

[XJSteve]

Thanks for all the input guys! Birdo, I'm replacing the rad regardless so no issues with evaluating it. The problem I face now given the cold weather is that I'm going to create a skating rink on my drive way if I elect to flush the system with a hose. I think I'm going to be lazy; drain, replace parts, fill with water and drive to Mr. Lube and have them flush the system with the new parts.

Steve

[rws]

When you flush the heater core make sure you "back flush" it, meaning flush from both the top and bottom ports.  This is a very effective way to clean all the crud out.

[Dingleberry]

When you flush the heater core make sure you "back flush" it, meaning flush from both the top and bottom ports.  This is a very effective way to clean all the crud out.

+1. And keep doing it until the water comes out clean, may take a couple times.