Coolant flush?

[76m2002]

Is there a coolant flush that actually works to remove deposits? The M42 engine in our '91 318is was not treated to good maintenance by the PO, and as I get into the cooling system, it was maintained with generic green antifreeze, and I'm finding a fair amount of white precipitate in the fittings. What I can see I can clean off, but it's the internal passages I'm concerned about.

The car does not overheat, but I'd like to try and get rid of as much deposited material before I refill with BMW antifreeze.

Thanks for any suggestions,
Ian

[stillmatick]

green anti here,bmw anti is no different.

[DesktopDave]

I used a Zerex product a while ago.  Seemed to work OK, but I used a garden hose to flush it all out and that seemed to work better.  Perhaps it was just the combination of the two?  That was on an old POS Nissan of mine, so YMMV.

I'm told there's a difference between radiator flush and coolant system flush.  The rad flush shouldn't be used on our cars at all, as it's designed to eat away corrosion in older soldered brass and iron systems.

Just for peace of mind, I'd be replacing the water pump, thermostat and the radiator as well.  The M42 cooling system is only adequate when it's working perfectly IMHO.

[76m2002]

green anti here,bmw anti is no different.

For many years our domestic antifreezes did a poor job of preventing mineral precipitation in BMW cooling systems with aluminum bits, mostly due to the presence of phosphate in the domestic coolants.  This resulted in the small water passages getting clogged with precipitation.  Now that most have removed phosphates, you are right in that you can use most domestic coolants as well.

[kaiser16]

I use the bmw coolant, the green antifreeze has different composition and different properties, my PO had put green anti and I wanted to flush it all out because if you have some green left in your coolant system and put some bmw coolant in it, they will have a chemical reaction and create precipitations. So I did a few water cycles to flush it all out until the water was clear and then put in bmw coolant.

[victor.askew]

I use green and have no problems. As stated above that is a problem of the past.

[DesktopDave]

I like variety, so I've used yellow, pink and even blue.  I also use WaterWetter and a very thin 66/33 mix of 2Gal distilled water & 1Gal coolant.  Distilled water is a bargain at about $1/gal around here.  Those three gallons last long enough to top it off over the two year lifespan of my coolant.  And even better, my mechanic also recycles coolant!  I always have a couple gallons of used coolant around in case I have to flush/refill a new project car or bike.

All decent brands of coolant will work just fine, even intermixed, as long as you blend with distilled water.  If you use tap water, it rapidly eats up the anti-corrosion additives in the coolant and metals will begin to dissolve.  The stub pipe coming out of the head and the profile gasket area are prime candidates.

[iamthatis]

Dave, can you elaborate on the garden hose method?

[DesktopDave]

Sure.  I just pull off the heater hoses, radiator hoses, and the block & rad drain plugs.  I then use a garden hose to flush the old coolant out of the block drain, the heater core and the radiator.  I then re-connect the hoses and flush the heater core & radiator with a bit of the new coolant mix.  Finally, I replace the drains and fill as much of the system with coolant as possible, finally reconnecting the hoses to seal the system up again.

I'm sure it leaves a bit of tap water in the system, but I'm figuring spent coolant is worse for the system than a bit of chlorinated water.  I'd guess you could alternatively do this with distilled water and a short length of hose too.

[iamthatis]

So you actually run water from the garden hose through the engine?

[DesktopDave]

Yep, you should see the crud a hose will blow out of older motor's coolant jackets.  Heater cores are usually pretty clean.

[iamthatis]

got it. will do as soon as i order all the parts.

[bflan2001]

Sure.  I just pull off the heater hoses, radiator hoses, and the block & rad drain plugs.  I then use a garden hose to flush the old coolant out of the block drain, the heater core and the radiator.  I then re-connect the hoses and flush the heater core & radiator with a bit of the new coolant mix.  Finally, I replace the drains and fill as much of the system with coolant as possible, finally reconnecting the hoses to seal the system up again.

I'm sure it leaves a bit of tap water in the system, but I'm figuring spent coolant is worse for the system than a bit of chlorinated water.  I'd guess you could alternatively do this with distilled water and a short length of hose too.

Could you elaborate a little more on this process, Dave? I'm just finishing up a swap with an M42 that's been sitting for several years and I want to make sure I properly flush out the cooling system. I bought a 'flush kit' but after reading the directions they want me to cut a radiator hose and install this fitting inline. I spent way too much trying to make this swap look clean to do something like that. I have a few questions about your flush method.

Where is the drain plug on the block for coolant? Where do you start flushing water through and how do you pressurize the system?

[Nick_318is]

The drain plug is on the passenger side of the engine, kind of behind the header.

[bflan2001]

Found it, thanks Nick!

I could not, however, get any torque on it to remove it with the header & firewall in the way. I ended up pulling a heater core hose and forcing hose water through the engine. I'm hoping I got a pretty good flush without pulling that plug. Time will tell I guess. I'm still having trouble bleeding the system, it runs great but the temp slowly climbs at idle.