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Coolant Replacement, minus the big air pockets :-)


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31 replies to this topic

#1 Setright

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Posted 12 September 2004 - 02:02 PM

Hiya everyone, maybe this write-up should be moved to the Ultimate Subaru Repair Manual, but I thought I'd hit a bigger audience here.


Having replaced coolant on my boxers many times, I have been searching for the right way to get all the old fluid out and getting as much new fluid in, without having to burp the system for a week after I'm done. I think I have finally cracked it!

Draining

Drain the radiator as far as possible with the little "faucett", and then detach the lower hose from the radiator. (If you are like me, replace any coolant hoses that you remove, and use stainless steel clamps on the new ones)
Even more fluid will drain from the radiator, and some will drain from the engine block. Detach the upper hose from the radiator, and run clean water through the rad until it comes out of the bottom clear in color.

Now, I do not contest that the best way to flush the engine block is by unscrewing the two drain plugs, but these are often seized and could turn into a source of trouble if you strip the threads or if they won't seal tight when you screw them back in. SO, I jack up the rear of the car until the engine block is tilting slight forward, ie. wheels about 6 inches off the ground, unscrew the thermostat housing, and let the old fluid run out through the thermostat opening. (Needless to say, I replace the thermostat gasket)
Run clean water in through the upper hose until clear water comes out of the thermostat opening. Leave the car in this position until it stops dripping water.

Remove the expansion tank and flush it, there will be plenty of "snot" in the bottom of it! Rinse the hose too. Install the tank again and fill to the FULL mark.


Filling

Close up the bottom end of the cooling system, ie. thermostat and lower hose. If possible, perform the next phase on a slight incline, car pointing upward.
Get a funnel with about 10 inches of half-inch diameter hose on the end of it and slide this down the upper hose in toward the engine block. I do this because bending the upper rad hose causes it to collapse and that makes pouring coolant into it impossible. Pour your preferred coolant directly into the engine block. Pouring slowly, and pausing along the way will help keep air from being trapped inside the block. It should swallow at about two litres before it starts to rise and threaten to come out of the hose. At that point, attach the upper hose to the rad and continue to fill slowly through the rad cap hole. Once it seems full, start the engine, let it run for twenty seconds and shut it off again. This will dislodge the few air pockets that are unavoidable and the fluid level in the radiator should drop a little after the burp, top it off.
Start the engine again, and let it run until the fluid rises and threatens to come out of the rad cap hole - and bleeder hole if you have one - and install the rad cap.
Take the car for a shortish run, just a few miles to get it fully warmed up, and park it on level ground. Check hoses for leaks of course, and let it cool. This will take a number of hours, overnight is good.
In the morning, note the level in the expansion tank, it will probably be a little lower than FULL. Fill to the FULL mark, and you're all set.

Obviously, you should check the level in the expansion tank for a few days afterward, but there shouldn't be any problems. Resist the temptation to open the rad cap, this will only interfere.

#2 cookie

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Posted 12 September 2004 - 04:03 PM

heater is in the full on position. Heaters are famous for trapping air. Otherwise this is very similar to the way many mechanics fill a car with coolant.
Other little tricks are to blast out old coolant from cavities with air if you have it.
Another bleeding trick is to put your pressure tester on the cap, pump it up a few pounds, and crack the highest point in the system.

#3 99obw

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Posted 12 September 2004 - 05:09 PM

Good writeup. Good bleeding advice. Next time I change the coolant (it's due) I will pull up this thread and give your technique a try.

After the flush I like to purge as much of the tap water out of the system as possible using distilled water. Some folks may be able to use their tap water, but for me the minerals would be fatal. Then get as much of the distilled water out of the system as possible by removing the lower hose and opening the drain(s). Close the drain(s), then add half of the system capacity with full strength anti-freeze to result in a 50/50 mix. Then top off with distilled water. Adding premix coolant to a system that still has some water in it will result in a weak mixture. I have run 66/33 mixtures, but the extra anti-freeze just reduces the heat carrying capacity of the coolant, so I have gone back to 50/50. It only got down to -15°F or so here last winter so I am still safe.

#4 cookie

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Posted 12 September 2004 - 06:17 PM

Here in CA the Devil will be looking at snowblowers again before that is necessary. The last time he did that, I believe, was when the Cubs and the Red Sox were in the World Series.

#5 Setright

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Posted 13 September 2004 - 12:49 AM

Cookie, I know that most manuals say you must have the cabin heat on, but why? The coolant circulates through the cabin heat exchanger anyway. The cabin heat is controlled by a plastic flap "mix door".

#6 Setright

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Posted 13 September 2004 - 12:58 AM

99OBW, I hear you on the weak mixture. That's why I decided to see if jacking up the rear would remove more of the old coolant. In fact, it's probably best to pour in the three litres of concentrated glycol first and then start on the demin water, that way you are guaranteed a 50/50 mix.

I just thought it would be easier to concentrate on the actuall filling part, as opposed to starting a religious debate on coolant mixes :-)

#7 cookie

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Posted 13 September 2004 - 12:58 AM

and off for the heater in the on position. The heater controls usually have two parts, one controls water, and one controls air. Otherwise the air can remain in the heater as a bubble. Then when you open the heater control the bubble can make its way to the engine.

#8 Setright

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Posted 13 September 2004 - 04:07 AM

Yes, yes, this is not news to me, I understand the principle. However, I am not convinced that subes are hooked up this way.

When me EJ22 started a head gasket leak, the cabin heater matrix would gurgle in the morning, regardless of the postion of the heater control, meaning that the coolant is free to circulate all the time.

#9 cookie

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Posted 13 September 2004 - 10:26 AM

according to a quick search on the web. Most of them do leak somewhat as they get older.
I have changed this part on my last Mercedes, Fords, Chevys, Toyotas, Datsuns, and some Chrysler products. Since it would be truly stupid to keep running hot water though the heater box on a hot day I assume even Subaru has a heater valve.
All you have to do is open it with the ignition on to make sure that it opens if it is electrical. I think some I have seen were vacum operated, and the old ones were cable. In the last few years all I have seen wre electrical.
If they are leaky it will bleed past them but why take a chance?

#10 Setright

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Posted 14 September 2004 - 01:09 AM

Truth be told, I did have the heater control open when I did this, but I put the fan speed on the lowest setting, 'cause otherwise it's a long time before the engine heats up. I am just not convinced that it makes any difference.

On a hot day, I think the engine would like to circulating hot coolant into the cabin matrix, but maybe not the passengers..

#11 NorthWet

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Posted 14 September 2004 - 01:36 AM

Many cars, especially newer ones, do not bother with heater valves. Fords in particular generally do not have valves. I am pretty sure that the Loyale-type do not have valves, although the '82 EA81 wagon I have does.

There are a couple rationales for not having a valve. It is easier to provide temperature "mixing", and almost essential on automatic climate control systems. It is less likely that the heater core will become plugged with sediment if the coolant keeps moving. Heater valves tend to fail, so why have one if you don't need it? Probably a few others.

(If you want "doesn't make sense" to do something... GMs early, and probably current, climate control had the air conditioner running constantly in order to provide cold air to mix with the heated air to get the right final temp. I suspect that other manufacturers did the same.)

Anyway, all of this effort to remove air seems like a lot of work. What is the drawback to placing a flush/fill "T"-fitting in, for instance, one of the heater hoses? Is there something odd/unique that causes air to remain trapped in the system? I haven't experienced the problem in the EA82 "Loyale"-types.

But I do agree that this is a good documentation of a procedure.

#12 cookie

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Posted 14 September 2004 - 02:10 AM

but if you turn the heater to on anyway it will work on all of them. It is a waste of time if you don't have the valve, but sometimes it is hard to identify the valve.
I agree with you that a bleeder installed on the highest point would be a fine idea. I figure the next time I change my coolent I will install a bleeder valve with a hose running to the expansion tank.
Then I could leave it open until I had done the warm up idle. I often stand in front of a car for five minutes or so watching it run with the cap off and keeping it topped up. I like to be sure the thermostat has opened, and refill it before the test drive.

#13 Setright

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Posted 14 September 2004 - 04:06 AM

NorthWet, maybe it's a EJ engine anomaly. The coolant path was redesigned to provide a more even cooling of the block and heads, and perhaps this is the cause.

Anyway, the important thing is to fill the engine block first, through the upper hose.

The low mounted thermostat is a Subaru quirk, and filling through the radiator means that the coolant has to flow past the closed thermostat via the tiny air hole. Inevitably, the rad fills first and starts "spilling" coolant into the block through the top hose. I think that this coolant meets the other coolant still on it's way up from the thermostat and traps air inside the block. Yes it will come out eventually, but it takes a week of burping/bleeding.

#14 NorthWet

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Posted 14 September 2004 - 12:50 PM

Back in my day... (long ago, in a land far away!)
My first job was working in a radiator shop, clientel was mostly Detroit iron, with thermostats mounted high and proud. But general practice was to do initial fill, replace radiator cap, start and warm up the engine to past the thermostat opening point (as judged by temp of radiator inflow hose and temp of radiator tanks), and THEN opening the radiator cap (carefully!) to do top-off.

The point to leaving the radiator cap on during warm-up was that all cars "burp", kick out an air bubble that is somewhere below the coolant level of the radiaor tank. When they did that, it would push a significant, sometimes hazardous, amount of coolant straight out of the filler neck. If you leave the cap on then the burp is contained, and all you end up with is a radiator ready to top off. Just don't wait until significant pressure builds up before topping off; if this happens, turn off the engine and come back when things have cooled.

Ok, so EJ's (maybe all soobs) are quirky, but it sounds to me like leaving the cap off while waiting for the burp is not a good idea. As a compromise, the cap could be half-on, which should allow any overflow to go the overflow tank instead of out the filler neck.

#15 cookie

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Posted 14 September 2004 - 05:07 PM

Northwets way. Makes sense to me. I learned to do the job the way I did from guys who had trained in the thirties and there are always better ways.
They do go bloop when a thermostat opens for sure, we were taught to stand back for the burp.
The neatest way I've seen though is with a pressure tester and cracking the high spot.
One thing about Subaru that I agree with Setright on is that Subaru engineers must have been given instuructions to use the oddest possible solution to any question.
One of the reasons I bought this car was that the quirky engineering amused me. My BMW is completely conventional in comparison.
I have had about 100 vehicles and nothing is quite like a Subie.

#16 ShawnW

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Posted 14 September 2004 - 06:20 PM

This is one of the best tools for preventing air pockets.

http://www.sjdiscoun.../lis-22150.html

#17 Setright

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Posted 15 September 2004 - 01:21 AM

Subes low mounted thermostat WILL NOT cause the burp to spray coolant geyser style.

Top mounted thermostats will trap all the air bubbles in the housing until it gets warm enough to open and then that cummulative bubble will pump fluid out of the rad cap hole. Yesterday I was draining, flushing, and refilling a 1977 Opel, an believe you me, we left the cap on for burping, and carefully unscrewed it after a short cool.

This simple does not apply to Subes low mounted thermostats. I have bled this way, cap off, tens of times and never had any trouble. There is one major advantage with having the rad open and that is simply that when working with only atmospheric pressure, the air bubbles grow larger more rapidly as the engine heats and this will make them easier to pump out. Under rad cap pressure the bubbles are compressed and more likely to stay stuck in some nook or cranny.

#18 cookie

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Posted 15 September 2004 - 01:08 PM

thermostat would trap less air in the block. I can't help wonder what effect having the thermostat at the top of a Subie engine would have on cooling problems. Since heat rises it seems more logical. Regardless of logic Subies do work. Perhaps Subaru is trying to have the hot water rise through the radiator?

#19 Setright

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Posted 16 September 2004 - 12:46 AM

Uhmmm, what?

The coolant is pumped around the engine, returns to flow across the thermostat. If it's too hot it will open the thermstat and pull in coolant from the lower radiator hose. This mixes cool coolant with the hot stuff and once the balance is right the thermostat closes again.
While the thermostat is open, an amount equal to that drawn in from the bottom is pushed back into the radiator via the top hose.

Although this will mean that the thermostat has to dance between open and closed, it probably gives a more stable engine temperature.

#20 vrg3

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Posted 30 November 2004 - 10:43 AM

This seems like a smart way to do it, Setright.

Interestingly, on turbo models the fill point for the system is the highest point in the system -- a filler tank mounted to the intake manifold. It actually ends up filling the whole system through the water pump and through the passenger side cylinder head (through the turbo). The radiator gets filled through the engine. And when I fill my Legacy Turbo motor with coolant, unless I rush the job, I usually have very little burping to do.

#21 gbianchi

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Posted 30 November 2004 - 04:35 PM

"I usually have very little burping to do."
Just like a good little baby, thats our subbees

#22 WAWalker

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Posted 01 December 2004 - 06:33 AM

ALL Subaru Legacy radiators have a bleeder plug in them. Remove the plug, fill, replace plug, bring to operating temp. so T-stat opens, let cool, top off. Very simple.


ALL Subaru Legacy's circulate water through the heater core all the time. They do NOT have a water control valve.

#23 Gnuman

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Posted 02 December 2004 - 12:17 AM

ALL Subaru Legacy's circulate water through the heater core all the time. They do NOT have a water control valve.


OK, so how do they regulate the cabin heat? Diferential air flow?

#24 vrg3

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Posted 02 December 2004 - 12:45 AM

Yup. The heater control moves a flap that controls how much air bypasses the heater core.

#25 Gnuman

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Posted 02 December 2004 - 12:49 AM

Interesting, so they essentailly replaced a part that is prone to binding and failure with one that is much simpler and less likely to fail. . . Sounds to me like they intended these cars to last a while. . . :brow:




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