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Thread: Coolant Flush and Refill Procedure To Avoid Bleeding

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    Devout Follower Of He Who Walks Behind The Rows NightFlyer's Avatar
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    Coolant Flush and Refill Procedure To Avoid Bleeding

    As I've been asked by several people now, I thought that I'd post this here as a reference for owners who don't have and don't want an auto-bleeder on either the radiator or at the waterpump/thermostat housing, but would rather prefer to maintain a stock cooling system and have to mess with bleeding the radiator (or water pump/thermostat housing)



    Instead of pulling the hoses off the radiator, I prefer to pull the hoses (9 and 16) off the pipes (5 and 18 ) in the engine bay. If you still have a stock/OEM radiator with the plastic side tanks and flanges/collars like I do, the less you pull the radiator hoses off and on, the less problems you'll have later on down the road with the radiator - at least that's my take on it. I then proceed to drain and back-flush the radiator (by using a spray nozzle on a garden hose on the opening to pipe 5, and using the nozzle with a rag wrapped around it to build up some moderate water pressure) and heater core / engine (by pushing water through the disconnected top hose of the header bottle) separately. Up to you if you want to pull the block drain plugs - sometimes I do, sometimes I don't.

    If you're trying to collect the old coolant, as opposed to simply discharging it onto the ground, then you'd run compressed air through the system during the catch phase, followed by your back-flush with water. Be careful not to put too much pressure through the system, but a moderate amount is necessary to do a good job and won't hurt anything.

    After the back-flush, I like to blow the system out again with compressed air, using the air to dry the water from the back-flush, as my garden hose water is quite hard and I want as little of it left in the system as possible before refilling. I refill the system only after it's completely devoid of liquid/fluid, or at least as empty as is reasonably possible.

    I then put the drain plugs back in the block and reattach the hoses to their pipes, leaving only the top hose of the header bottle still disconnected. Note that I don't remove any of the hoses near the thermostat / water pump.

    I then prepare my coolant mixture in a clean 5 gallon plastic bucket. 40% distilled water, 60% concentrated Prestone DexCool Antifreeze, and a bottle of Prestone Cooling System Treatment (it's a combination corrosion prohibitor and lubricant). I prefer mixing it myself as opposed to buying the premixed 50/50 stuff (no good reason for this - I just do) and always mix up about a half gallon more than I'll actually need. Yeah, I use DexCool (the orange stuff) and have been doing so successfully for the last 12 years, despite what others on the forum have said about it. DO NOT use any kind of sealant tabs or a liquid sealant product unless you want a mess and a plugged up cooling system.

    I then use an old (previously flushed) fuel pump and prime it with my coolant mixture in the 5 gallon bucket. Once primed (free of air), I hook the fuel pump up to the still disconnected top hose of the header bottle, using a simple barbed coupler and a couple of hose clamps. I then activate the pump and allow the system to fill until the header bottle is practically full (don't worry about overfilling, as the system will purge whatever it doesn't want).

    I then reattach the hose to the top of the header bottle and place whatever mix remains in my 5 gallon bucket into an empty antifreeze jug.

    I then jack the rear of the car about 3 feet into the air and position jack stands in the regular locations. Set the HVAC mode switch to the heater or vent positions. I then start the car with the rear end in the air and allow it to get up to temperature (thermostat opening and cooling fans engaging). But always be sure to watch the temp gauge and immediately shut the engine off if you believe you're on the way to overheating. You'll want a bucket under the purge hose from the header bottle unless you're just discharging onto the ground, although the first warm up should result in most of the excess coolant in the header bottle being sucked into the system. After the fans have run for a minute or two, kill the engine. Check and top off the header bottle if needed. Repeat running the engine up to temp, stopping, and checking/topping off the header bottle until you no longer have to top off the header bottle or the header bottle starts dumping a significant amount of coolant out the purge hose and into your catch bucket / on the ground. You should only need to repeat once. Doing this with the rear end in the air purges all the air from the cooling system via the header bottle without having to mess with any of the bleed valves.

    I don't run any kind of self-bleeder kit on my car - all 100% stock/OEM (with the exception of the heater control valve - original one developed a leak at the pivot).

    Put the rear end back on the ground, top off the header bottle to an over filled level if necessary, and take the car for a good 10-20 minute drive, being mindful of the temperature gauge. At the end of the drive, check the header bottle and top off if needed, leaving it over-filled, but you should be done.

    Note that if you don't refill with some type of purged continuous flow pump as I do, then you'll have to bleed at the waterpump/thermostat housing bleed valve/nipple. Also, if you remove the block plugs during the drain and flush, be sure to teflon tape and anti-seize the threads before re-installing.

    So, that's what I do and it has worked great for me over the years. My car has always run nice and cool, as Steve can confirm (95F ambient temp in bumper-to-bumper slow moving Woodward Dream Cruise traffic for over 90 minutes and my car never breached about 180F).

    As always, best of luck and have fun with your DeLorean!
    "Driving Concours - proving it's possible with every mile!"

    --Josh S.
    #1798

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    This may be a stupid/novice question (or maybe I missed something), but will doing it this way allow you to flush the entire system even though the thermostat would be closed?

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    Quote Originally Posted by Justin51982 View Post
    This may be a stupid/novice question (or maybe I missed something), but will doing it this way allow you to flush the entire system even though the thermostat would be closed?
    First off, there are no stupid questions unless I'm the one asking them

    As to your question, if I'm understanding it correctly, you're wondering about flushing the block/engine, right?

    Quote Originally Posted by NightFlyer
    and heater core / engine (by pushing water through the disconnected top hose of the header bottle) separately. Up to you if you want to pull the block drain plugs - sometimes I do, sometimes I don't.
    My procedure covers that via the forward flush through the heater core, as the return line from the heater core runs directly into the water pump. Pulling the block plugs will result in the engine draining straight down (obviously), thus giving a slightly better flush of the block/engine, while leaving the plugs in place will drain everything out through the #16 hose in the referenced parts diagram above. Note that if you do pull the block plugs, you won't be flushing the water pump at all with my procedure, unless you do a double flush here - once with the plugs out and again with the plugs back in place. Most of the time, I just leave the plugs and don't monkey with them at all, but it's completely up to you.

    Usually, I perform this flush via the factory bleeder hose, which I disconnect at the header bottle, and when I was running the stock/OEM butterfly hot water / heater control valve, it worked just fine. However, I've since changed to using a piston valve when the butterfly valve developed a constant leak around the pivot shaft in the housing. See the following thread for more info on that: http://www.dmctoday.com/showthread.p...-Control-Valve

    In fact, flushing in such a manner probably contributed to the wearing out and eventual leak of the OEM butterfly valve, though, that's pure speculation on my part.

    I don't know how the new piston valve will effect this part of the flush and subsequent fill, as I haven't tried it yet since making the change. The OEM butterfly valve doesn't completely close shut with a perfect seal and was also fairly easy to manipulate in either direction with enough pressure, which is what allowed this to work in the past. As to my new replacement piston valve, I honestly don't know how much it closes or how well it seals, thus I don't know if I can continue to use the factory bleeder hose or not.

    So, if you're running a stock/OEM or even an aftermarket replacement butterfly heater control valve, go ahead and use the factory bleeder hose by disconnecting it from the header bottle. If you're running a piston valve like me, or something else that doesn't work similarly to the stock/OEM butterfly, then I'm afraid that we might have some experimenting to do

    I hope that answers your question - if not, let me know that I'm an idiot and I'll try again
    "Driving Concours - proving it's possible with every mile!"

    --Josh S.
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    Not at all, I appreciate it.

    I'll likely go for the double flush route....The car has been sitting for 15 years and who know's what all is in there or what was done before. I'd rather flush everything and know exactly what I'm working with as opposed to guessing what may (or may not) have been done.

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    Quote Originally Posted by Justin51982 View Post
    Not at all, I appreciate it.

    I'll likely go for the double flush route....The car has been sitting for 15 years and who know's what all is in there or what was done before. I'd rather flush everything and know exactly what I'm working with as opposed to guessing what may (or may not) have been done.
    Exactly! I did the same thing after first purchasing my car for the same reasons - I wanted the assurance of knowing exactly what I was working with. I haven't pulled the plugs since though, as I've been pretty good about doing this regularly.
    "Driving Concours - proving it's possible with every mile!"

    --Josh S.
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    I think once will be enough for another decade or so...hopefully...I have a compressor but not another pump, so I reckon I'm going to just have to bleed it the old fashioned way.

    I did a pressure test up to 17lbs and no leaks, this is why I like your approach...it allows minimal disconnecting and still sounds like it will be pretty thorough.

    That's a question....I rented a pressure tester from autozone...excuse my ignorance, but is there a way to purge the system of air using that?

  7. #7
    PRV block doesn't have traditional coolant passages (heads do, but the engine block itself doesn't). Piston liners sit in big vats of coolant. If you want to flush the block out just take the inlet hoses off and stick a garden hose in there (outlets are the Y pipe).

    After you button everything back up and refill the system, self bleeders at both ends of the car can purge any/all trapped air automatically as soon as you start the engine....

    Bill Robertson
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    Quote Originally Posted by content22207 View Post
    PRV block doesn't have traditional coolant passages (heads do, but the engine block itself doesn't). Piston liners sit in big vats of coolant. If you want to flush the block out just take the inlet hoses off and stick a garden hose in there (outlets are the Y pipe).
    You can definitely do that, but then you're removing and having to replace more hoses than absolutely necessary. I'm lazy, not to mention that I prefer to disturb as few things as possible when working on my car - especially if everything is already working just fine.

    Quote Originally Posted by content22207 View Post
    After you button everything back up and refill the system, self bleeders at both ends of the car can purge any/all trapped air automatically as soon as you start the engine....

    Bill Robertson
    #5939
    Bill's self bleeders have been proven if you don't mind modifying the OEM/stock configuration in a few spots.
    "Driving Concours - proving it's possible with every mile!"

    --Josh S.
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  9. #9
    Devout Follower Of He Who Walks Behind The Rows NightFlyer's Avatar
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    Quote Originally Posted by Justin51982 View Post
    I think once will be enough for another decade or so...hopefully...I have a compressor but not another pump, so I reckon I'm going to just have to bleed it the old fashioned way.
    The pump isn't really that important to air purging, it helps, but it isn't absolutely essential/necessary. What provides a majority of the natural air purging is filling it while you have the rear end jacked in the air, with front/nose of the car buried to the ground.

    If you still have the stock/OEM radiator, I'd definitely do this as opposed to pulling the hose off the plastic barb to burp the radiator, as doing that enough times could lead to a mandatory radiator replacement.

    Quote Originally Posted by Justin51982 View Post
    I did a pressure test up to 17lbs and no leaks, this is why I like your approach...it allows minimal disconnecting and still sounds like it will be pretty thorough.

    That's a question....I rented a pressure tester from autozone...excuse my ignorance, but is there a way to purge the system of air using that?
    Not that I'm aware of.

    I'm actually not a big fan of pressure testing the cooling system, as while the testers do effectively simulate system pressure, they can't simulate system heat, and the system only becomes pressurized during operation as the engine and coolant heat up. As the system warms up, things expand and seals tighten up. If I put a pressure tester on my system right now, I guarantee that it would leak, probably in many locations, even though I don't get a single drop on the ground when parked for multiple weeks.

    Often times, pressure testing causes people to replace more than they otherwise would have to and/or over-tighten hose clamps under the false believe that there are leaks in the system, when the reality is that there aren't any leaks under normal/regular conditions.

    But that's just a personal stance/opinion, and many would disagree with me, and that's OK
    "Driving Concours - proving it's possible with every mile!"

    --Josh S.
    #1798

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    FYI, here's the diagram of the heater system - just thought it would be a handy reference on this thread.

    "Driving Concours - proving it's possible with every mile!"

    --Josh S.
    #1798

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