Cannot remove 4.0 ltr engine block drain plug. What is the next best alternative?
 

I'm doing a radiator fluid flush on a 2002 TJ and have been successful right up until the engine block drain plug. Have made the correct fitting to go into the plugs square hole but the plug is not going to come out (square hole has now been gnarled into a more circular hole) regardless of force and lubrication.

Is there another point on the engine block I can drain as a second best option instead?

The 97 FSM shows the drain plug under the #5 exhaust port but uses an older picture showing a temp sensor location slightly higher up under the #2 exhaust port. If you are lucky that hole is still machined into the block but has been plugged and could be used.

https://c2.staticflickr.com/6/5533/1...2d82d907_o.gif

Other than that, flushing with distilled water would be your best option, then putting in five quarts of neat coolant and using distilled water to fill to the correct level, including the reservoir which will mix as the engine heats and cools.

Unlucky the proper plug didn't come out. I'd heard they could be stuck fast, but have had no problem removing mine in the past.

Are you suggesting trying to release coolant in the engine block via the temp sensor port?

I've already flushed distilled water through the radiator and heater core. As an alternative to the engine block plug I'm considering just running the vehicle on straight distilled water until it heats up, then dumping it again, and then running it on coolant as a final step.

Seems like you are going a bit overboard.

Unless you have some kind of cooling problem, or heater problem, I really wouldn't feel the need to take plugs out of the block.

Use a coolant flush additive and water, fill it up, drive it around making sure your heater is getting good and hot on both feed and return pipes that run along the rocker cover.

Give all your pipes a good squeeze when they are warning up, they should be flexible not crunchy. Crunchy means lined with rust on the inside from age.

After a hot run with the flush solution, get it out, you really don't want that stuff left in there for more than an hour.

Drain it, and if your being particularly fussy, repeat the full and flush with another flush solution. I did mine twice to get it clear, you will never get it completely clear, but you will get it good enough.

Then fill it with premix Nulon green, if you buy it at the right time from supercheap its about $25 for 6L, fill the rest with distilled, drive it till your next service.

Then at service time just dump the coolant and refill to the correct percentages.

My recommendation is based on keeping the cost down, because I'm almost prepared to bet that after you have flushed it, sometime soon you will find something in the system that forces you to drain and refill anyway.

Radiator, thermostat, thermostat housing leaks, water pump, rubber pipes, hopefully not heater.

Just flush it, fill it cheaply, use it, keep an eye on it.

If you really have to , knock out the Welsh plugs and get the hose in there.
You'll get out left over casting sand and iron scale.

If there's a plug I'd try it. It's possible they stopped machining the hole so there may not be a plug there at all.
I first removed the drain plug on mine when I changed coolant type to Zerex G-05 as used in later TJs, as I figured it was the simplest way to get rid of all the old coolant.

I gave mine a good hit with compressed air.
Sadly the ports are rather small on the head, and it dosent take much build up to restrict flow. Getting the crumbs out is probably more important than getting some distilled water out.
Last flush I did, I refilled it with distilled water, and left the lower radiator hose off , ran it till hot, then gave it 3500rpm till it blew off under pressure.
The blast spat crumbs out everywhere.