Water pump started leaking so I decided to changed it completely. Lots of rusty water so while everything is off I wanted to know the best method to clean/flush the whole cooling system of the rust.

 

Prestone makes a little flush kit for less than $5. It is sold at Walmart, Autozone, etc. It just adapts your garden hose to your radiator, and if you follow the instructions will flush out your cooling system and heater core. The only difficulty I had with it was the running water was keeping the engine cool enough that the thermostat wouldn't stay open. You can take out your thermostat for the flush. I'd put a new one in anyway if the innards are that rusty...and flush again in after a flew weeks.

 

The best way to do it is to take it to a shop that has a radiator flush gun and the skill to use it. Rad flush guns combine water with 120psi air pressure from an air compressor. They not only supply more pressure, but are designed to pulse the water flow which breaks the debris loose.

Low pressure from a garden hose, like the DIY kits, just doesn't do a complete job. (but it's better than nothing if you can't afford to pay a shop to do it, or your local places don't have a flush gun or the experience to use it safely)

Otherwise you can use one of the DIY kits which I would call a "rinse" kit not a "flush" kit

Don't forget to clean the overflow tank.

As Tracy says... always put a thermostat in when you install a new pump or flush the system.
If you can find one, get a "Stant Superstat". If you compare them side by side with the more common el cheapo ones, you will see they are MUCH better quality.

EDIT:
Found a link that shows how a flush is done with a flush gun, along with a comparison to a garden hose type rinse.

 

I agree whole heartedly that the DIY kits are a rinse more than a flush. You kind of have to do it every so often as a routine maintenance thing. There is also the possibility if you have a weakness in your radiator a high pressure flush may expose that and you'll end up replacing the radiator. Depending on what sort of demands you are going to put on this vehicle, replacing an old radiator along with any hoses that carry coolant might be wise anyway.

 

take out the thermostat and pull the bottom hose off the radiator. run water in the thermostat hole until it comes out the bottom hose clear. then with the bottom hose still off run water thru the radiator until clear.

 

I fully agree.


I chatted with my buddy about this last night and he clarified a few things.
1) He uses Stant Superstats when he can't get the oem mopar ones. He says the mopar ones are much superior than anything out there and he keeps some in stock for that reason.
2) Before doing a pressure flush he recommends having the cooling system cleaner additive in the system for 24 hours before flushing.
3) if doing a garden hose flush you need to leave it in longer to help compensate for the lack of using a flush gun.
4) You should use hot water, which cleans better and also is more effective in fully removing any of the cooling system cleaner (He said, coolant cleaner additive can harm the system if any amount is left in there)
5) If you need a new heater core, get a mopar one. The aftermarket ones are crap. (compare them side by side)

(This from a guy who used to exclusively work on cooling systems for a living, back when these trucks were new, and owns a mechanical shop now.)

My own personal thinking on this is it's best to do it right once. Which includes new clamps, coolant, mopar thermostat and using a flush gun.

Cutting corners on the job makes no sense unless you are on a serious budget. Not that it costs much more for a good job by a shop.
Some shops here allow you to supply your own parts so that can save you a bit.

The trick is finding a place with a gun and skill to use it. Many of the local mechanical shops here don't have a clue, unless they specialize in cooling systems. The gun uses air to increase the pressure a bit, but importantly add bubbles to the water (in some cases they automatically pulse the pressure a bit) so that it helps break the debris loose.


Many of these old dakotas have likely never been flushed before and only are getting it now. Hence the flush gun. As you say, the rest of the time a garden hose rinse is a good maintenance thing.

Until I learned this stuff, I thought mopar heater cores were crap. I've learned that they are the best out there. They just need to be maintained correctly.

FWIW, if a pressure flush makes your rad fail it would just fail a bit later anyhow.

In some cases you can get away with re-using the old hoses. The trick is to have enough length so you can trim off the short hose section where the old clamp was and install new clamps if needed.

P.S. Slight off topic but...
In the process of restoring my 90 dak I found a new all metal radiator available from Performance Radiator. It seems they have stores in the USA too.
It costs more but for those intending to keep their trucks for a lot longer. It's a good investment IMO.
Those plastic tank ones are crap. The idea of relying on a gasket and metal tabs to hold the plastic tank (with different expansion characteristics) in place for any serious length of time, is just goofy.