My coolant change is due so I've been checking tips for doing it.

One procedure (Wally Plumley's, www.nichols.nu/tip154.htm) removes the radiator bottom hose rather than the rad drain plug or the block drain plugs so no risk of stripping threads/breaking off any of the plugs which looks like a good idea.

But it involves running the engine up to temp to open the thermostat, then repeatedly flushing.

My question is why is it OK to fill and drain with cold distilled water at one stage. I thought there was a risk of cracking the radiator or block by adding cold fluid when the engine's hot?

Maybe I should start by trying to loosen the block plugs cautiously at first with a socket (use penetrating oil first) to completely drain the system. I haven't looked at the drain plugs yet but I thought I saw one post saying one plug is not accessible because of the air pump?

Grateful for any advice on either approach before I start meddling!

Thanks,

Adrian

 

When my oil cooler ruptured in the radiator i got oil in coolent and had to flush the system out many many times after I replaced all the rad hoses. I ran motor until the thermostat opened and drained it hot by using the rad drain plug. I turned the hot waterheater up in my house to 190 degrees before I started this,,,I then refilled the radiator with hot water from the tap and dishwasher machine dishwashing detergent (no foaming), burped the system, ran motor for awhile, then drain, and repeated many times. On the last several times with just water (to get all the detergent out) is when I undid the block plugs as well. I think the catch is not put "cold water immediately into the cooling system directly after you drain it. You could wait an hour and be fine, or just put in hot like I did.

 

Another alternative is to start with a cold engine: drain the rad of antifreeze, remove its hoses and flush until clean with a garden hose.
Then, remove the thermostat pellet. Wrap the end of the hose with a big rag to seal it as you stuff it into the pump suction opening ( hoses still off). Flow until the majority of the coolant is displaced and captured - you environmentally conscious devil you ... then the piece de resistance ....
Start the engine with the hose held in place and blasting at full tilt - the water pump will clear everything else out the discharge side, and will be flowing crystal clear in a moment or two.

As much as I enjoy the rifle shot crack of a block drain plug snapping free, this approach is faster, effective, and keeps the stream of antifreeze off ones face.

 

This sounds great Garth but have some dumb questions:

By thermostat pellet do you mean the thermostat?

If you seal and stuff hose into the pump suction opening (presumably the orifice from which you've removed the thermostat) then where is the discharge for the displaced coolant?

When you run water through with the engine running, again where is the discharge if the block plugs are left in? Same as above I guess, but where is that? Do you then turn off hose once it's running clear at the discharge, otherwise you'd be leaving tapwater in the block and I assume that's corrosive compared with distilled water/antifreeze mix?

Thanks,

Adrian

 

Pull the engine.

Seriously, the 928 cooling system poses a problem with those block plugs. Ordinarily I'd drain it, then fill with water and maybe some cleaner, drain that and fill with fresh coolant. More work with the plugs.

The other part of the problem is how do you get the right concentration if the block is water filled? This would be the result if you did a continuous flush approach. That creates a mess and not many are set up to catch the gunk that comes out.

My advice is to drain the radiator and the block then re-fill with a fresh mixture. If you're set on a flush step then do it as an extra fill/drain step.

Never put cold water into a hot system. Yes, it can crack the block and, yes, I know people who've done it.( But no 928s)

 

The radiator plug is plastic and I've had no problems removing them. The block plugs can be a pain, but they may come out easily enough. I would try that first.

 

Thanks for good advice from you and other posters. I'm going to try the block plug route first, and maybe change the thermostat and seal/gasket while I'm at it.

Adrian

 

This is probably a dumb question, but here goes: Why not drain from the radiator plug only, measure and replace with proper mixture. If this is only half the coolant, just change twice as often. Not perfect but you'll always be within working range of additives and cleanliness.

 

an easier way to do a flush, if you really want to do one, is with the engine fairly cold, peg the thermostat. (ask me how) reinstall. then, disconnect the lower radiator hose at the block intake area. get a second hose of the same size and connect it to the block . this will be the hose where your garden hose is stuffed into it.. Now, the lower hose that is disconnected up top, has another tube stuffed into it and point it over the fender. this is the exit water tube. start car, turn on hose, flush. done! there is no way to get the water out of the engine as if the temp of the water is cool, and the termostat is closed, there is is no circuit. the block and pump are essentially sealed via the thermostat.

the other option is to drain the block, reseal, then flush out the radiator with a garden hose by opening both top and bottom hoses.

mk

 

There are no dumb questions ...
Yes, the thermostat itself,sometimes referred to as a pellet, etc. When the thermostat is cold, it is closed causing a complete internal recirculation within the block by the pump - a unique 928 feature ... ergo, remove the thermostat, and force water into the pump suction - otherwise the block will be 'blocked' off .

The 'exit' is the hose that feeds the top of the rad. .... ie. discharge from the block.

By following this method, you do indeed leave clean tap water in the block: there are slightly less than 8l remaining ( ~7l), which is conveintly less than half of the 16l system capacity.
If one carefully reads the directions on several of the long life coolants, they recommend a 50/50 mix in most climates ..... with tap water - not distilled/deionized/demineralized/ .... If one of these products is selected, blissfully dump in two of the standard 4l jugs after reinstalling all hoses and thermostat ... and top off with tap water as the engine warms up.

BTW - do all of this flushing procedure with the heater control open - somewhat academic, as the heater control valve fail safe position is open anyway: just a stickler for details.

I've done this numerous times - hasn't failed yet.

 

Thanks Garth - all very clear and I've learnt a few things,

Adrian