2005 LJR 4.0 Coolant Overhaul - Draining / Flushing Only Engine Block

[KKIBF]

First time posting. I just finished with a coolant overhaul on my recently purchased 2005 LJ Rubicon 4.0 with 100k miles. This included: new radiator, water pump, thermostat, fan clutch, water pump tube, serpentine belt, upper/lower radiator hoses and gaskets...using Mopar parts. Before adding fresh G-05 Zerex coolant I stumbled into threads about draining the old coolant in the engine block...which I did not do. With the effort I did to replace everything I want a complete and clean overhaul and it seems there is a lot of coolant that sits in the engine block. I don't like that I missed old coolant that can get into the new parts. Questions: Do I just drain the engine block through the engine block drain and add new G-05?...or, do I need to flush the engine block with distilled water (somehow)? Was putting on a new bottom radiator hose enough to get all the coolant out of the engine? Thanks in advance for answering!

 

[CodaMan]

When I did mine I just drained it at the radiator, filled it with distilled water, ran it until the thermostat opened and let it all mix up. I then repeated those steps 3 more times. That will dilute anything remaining in the block more than enough to use any coolant you want to use.

 

[Mr. Bills]

^^ This is essentially all I do for a coolant flush. although I typically use a cooling system cleaner like Prestone or Thermocure and do it before I change cooling system parts.

Distilled water is cheap, and filling/cycling/draining the cooling system 2-3 times until the water runs clear may take a couple of minutes longer than pulling a freeze plug or drain plug to drain the residual coolant in the block, but its a lot less hassle in the long run and doesn't introduce the possibility creating a new leak.

 

[MountaineerTom]

I overhauled my entire system back in November and changed every part, hose and sensor with MOPAR parts, except the heater core which was replaced less than two years earlier. I did drain/refill/flush the block a few times with distilled water after running some Prestone engine flush through the system for whatever the bottle recommended. I don't remember off the top of my head right now what it was. It was just something that I wanted to do so that I knew everything that had been done to the system since I became the owner. I didn't necessarily feel it HAD to be done.

If your coolant looks clean, then I don't think I'd worry about it.

If you do it, use some Permatex High Temp Thread Sealant on the outer half of the threads when you put the plug in for the final time if you have concerns of the plug leaking. I also used it on the water pump tube and the temp senor.

 

[eastbloc]

First time posting.
Questions: Do I just drain the engine block through the engine block drain and add new G-05?...or, do I need to flush the engine block with distilled water (somehow)? Was putting on a new bottom radiator hose enough to get all the coolant out of the engine? Thanks in advance for answering!

Welcome!
Yes the drain is from engine block.
Even with plug out, there will be some left In there, which can be blown out by adding water/coolant or some air hose.

Through radiator should work. I think I did mine through heater core. There should be an open system, with only a thermostat serving as a barrier, so any hose that doesn't go directly to thermostat should work.

 

[KKIBF]

Thank you everyone for your quick replies and guidance. I'm off to the store to buy distilled water to flush.

 

[jazz-n-tj]

It might be overkill, but what I did was fill a 5 gallon bucket with distilled water and then flushed the core with the thermostat out and having it drain out the lower radiator hose. I used a submersible pump I have to pump the distilled water out of the 5 gallon bucket? It worked great and the water came out nice and clear by the end. Then I just added 5.4 quarts of coolant and then topped off with distilled water to get my 10.8 coolant capacity. Then I just filled the overflow 50/50.