Flushing the cooling system

[JayArr]

Hi All

I'm flushing the cooling system today in prep for a new radiator, water pump and fan clutch. I've dumped all the old coolant and have hooked a submersible pump in a bucket to the radiator. I undid the top hose and I'm pumping from the bucket into the top of the rad and the engine is outputting back into the bucket. I pulled the thermostat pipe assembly and replaced it with an older one that I removed the innards from.

So far so good. I ran it for about 45 minutes with just hot water, changing the bucket out out four or five times as it got discolored. (unplug pump, move it and return hose to a fresh bucket of clean water then plug it back in. Dump the old bucket.) After 45 minutes the water was running clear.

I'm now running fresh water with some dishwasher detergent in it, it's getting dark again so the detergent must be cleaning and freeing up deposits that the water alone couldn't get.

I'll do two more stages after this, I've got some Oxalic Acid that I'll run through after the dishwasher detergent and then I'll rinse with Arm & Hammer baking soda to neutralize it all.

Here's a question: How do I make sure the valve to the heater core is open? I tried looking through the menus on my Tech 2 to see if I could command it open but I couldn't find anything. Does the Envoy use an old fashioned valve to control coolant to the heater core? I would hate to go to all this trouble and then find out the heater core didn't get cleaned.

JayArr

 

[mrrsm]

This is arguably the Best "How To Flush the Heater Core" Video around (and the Content Creator is ALSO a GMT Nation Member... which IS Pretty Damned Cool...":

One thing worth researching is the possibility of creating unexpected conditions by experimenting with Chemical Cleaners that may have long term negative impacts on the inner "Lost Foam" Cast Aluminum Jacket Surfaces covered with what looks like the imprinting of "Styrofoam Beads" from a Coffee Cup .

That textured surface inside that may encourage Aluminum Oxides to leech out like tiny Stalagmites growing out from those oddly conditioned surfaces inside of the Engine Block. Aluminum can become Very Chemically Active ... Just ask anyone who works for Morton-Thiokol, where they use it in making their Solid Rocket Booster Fuel.

So besides trying to establish the Neutral Ph liquid environment as you have done so far... As Soon As Possible... Run some Dexcool through the Radiator as the LAST Flush Mix that should go through the Engine Block before re-attaching the Heater Core after it gets properly Reverse Flushed.

This action will Re-Coat and protect the Inner surfaces of the Engine Block Coolant Jackets and Channels and protect the Engine from any residual cleaning agents getting left behind.

This is the reason that using Regular, Ionized Tap Water when NOT using Pre-Mixed 50/50 Dexcool Fluid and instead, mixing your own WITHOUT using Distilled, De-Ionized Water ...is a Very Bad Idea.

Anyone who doubts that this will occur in the presence of regular Dish Detergent Soap has never accidentally left a Stainless Steel Pot with a thick Aluminum Heat Plate attached while soaking in Dawn Laced Dishwater for more than a Day or so... only to find Streams of Aluminum Oxide emanating from the bottom of the Pan.... or maybe that's just happened to ME?

One last mention about the "Black Coloring..." mixed in with the Flush Drain Water in your Bucket This is probably coming off from the Rubber surfaces on the insides of the Black Rubber Heater and Radiator Hoses... and so replacing all of them ...all at the same time...would NOT be a Bad Idea ...either.

 

[JayArr]

I've done flushes like that on older cars I've had but the Envoy has those special pinch lock, clampless hoses on the firewall for the heater so I don't see it as viable to just hook hoses up the way the video suggests. Next time out at the wreckers I'll try to remember to grab a spare set of hoses that I could cut up and attach to my pump and I'll be able to direct flush in the future.

For now I have to figure out how to open the valve from the engine to the heater core so my flush goes through. Forward flushing will have to do today.

I'm also not going to use DexCool anymore. The reading I've done says that it isn't any more effective in cooling the engine than the old glycol and it's prone to some problems that the old glycol isn't. like oxidation if the cooling system leaks a little and has air in it. GM engineers it's products for the warranty period and the car probably won't have a leaky water pump shaft seal the first five years so this won't be a big problem but older cars but as the car ages the DexCool becomes a liability.

There is also the problem of availability, traveling this summer there were lots of small gas stations that only had green coolant forcing me to mix, then I have to flush it all out later. That's expensive, if I stick with green I can buy it anywhere and I don't have to worry about mixing ever again.

The big redeeming quality of DexCool is that it lasts longer but on an old car owned by a DIYr that's not enough of a benefit.

 

[Reprise]

I wish I'd seen this and done some more reading ( Link ) before putting new Dexcool in my totally drained 6.0L a few weeks ago; I might've taken the opportunity to switch.

At this point, I'll leave it as-is, but will consider 'going green' in a couple of years or if there's a catastrophic failure.

In any event, good info on the part of the OP, and I learned something. Appreciate.

PS: Some may find the info at the link I posted above old (it's from 2004).

 

[Mooseman]

For now I have to figure out how to open the valve from the engine to the heater core so my flush goes through. Forward flushing will have to do today.

IFAIK, there is no valve for the front core however, there is one to the rear core. I think it's opened when heat is requested to the rear. It's electrically and vacuum actuated.

 

[JayArr]

Thanks Mooseman.

I find it curious that there is no way to shut off the coolant to the forward heater core in the summer but I guess it's not necessary.

I found the valve that controls the flow to the rear core, it's on the firewall under the reservoir tank. You need to pull the air box, wiper reservoir and coolant reservoir off the right side wheel well to get to it.

I found something interesting that may help others, the rubber hose that runs from the solenoid to the valve was rotten! I wonder if being under the coolant reservoir meant it was exposed to antifreeze that shortened it's life. It fell apart in my hand. This not only affects the operation of the heater core but it could also make the engine run rough since it's hooked to a vac port on the intake and once it fails it would represent a vacuum leak every time the PCM commanded that solenoid to turn on.

I also had a hell of a fight to get the quick connect fittings off so that I could remove the valve. In the end I found that on the larger diameter fittings the Lisle tool I was using simply wasn't long enough to disengage the tabs. After fighting with it for an hour I used a dremmel tool to cut notches in the side of the tool so that tabs molded into the locking ring could be accommodated and the tool then went all the way in and the hoses popped right off. Pics attached, I hope that helps someone too!

JayArr

 

[Mektek]

I think that the heater core has constant flow. How much air goes by it is regulated by the blend actuators. I'm in a hot climate and only need the heater for a month each year. I was thinking of installing a bypass valve in front of the firewall so that the hot coolant wouldn't needlessly circulate in the cabin.

There is a Prestone reverse flushing kit which has a tee and garden hose fitting installed on the heater hose. It can be left installed after the job and just capped off. It works well.

 

[JayArr]

In older cars it was literally a valve with a cable that went into the dash and attached to the hot/cold lever on your "Climate Center" LOL

It should be easy to add one onto the right side of the engine that feeds the heater core(s).

JayArr

 

[Mooseman]

I have never seen a GM vehicle with a shutoff valve to the front heater core. They use dampers to move the air around the core when heat is not requested. I do remember imports having such a shutoff valve. Maybe they don't have air dampers for controlling air temps and use a valve instead. I also remember those valves leaking and seizing.

I think you're over thinking this. If it works, I wouldn't try to fix it.

 

[JayArr]

Thanks Mooseman

If that's the way it is then I'm fine with it, I was more concerned that I was missing something, like there was another valve somewhere else that I didn't know about.

My Cadillacs and Oldsmobiles all have the shutoff, the Oldsmobiles used a wire cable in a sheath, the Cadillacs had climate control so they could open or close it it in varying degrees using vacuum and sintered plugs to act as restrictions. The Blazers and Jimmys used vacuum but only for on-off and even my little Nissan 240SX has one. The Envoy is the first car I've owned that doesn't have that valve so I guess I mistakenly thought all cars had them and it was the exception.

 

[Mooseman]

I don't ever remembering a valve on my 82 S10, 83 S10 Blazer, 93 Blazer or 00 Jimmy but then I'm getting old and my memory is failing.

 

[christo829]

My 88 and 92 S10 Blazers didn't have valves either, just blend doors, and I swapped heater cores and hoses on both of those. I don't recall if my 78 Camaro did or not....that was way too long ago
for my memory cells...

 

[JayArr]

I guess it's my memory that's going. LOL

The ones I'm thinking of look like this: