Explain to me how a Prestone flush/fill kit works

[The Critic]

I have a question regarding the Prestone Flush/Fill Kit and its operation.

First of all, I do not understand how a cooling system works, but here’s where I’m confused about the Prestone Flush/Fill “backflush” kit.

From my understanding, the kit is spliced into the inlet heater hose. Garden hose water is attached to the T line, and with the engine running, the water is flushed through the heater core, block, and thermostat, and is ultimately returned through the upper radiator hose. With that said, since the water one is running through will be cool, how does the “backflush” work if the thermostat doesn’t open with cold water?

Thanks.

 

[unDummy]

It'll open with excessive water pressure.
70psi of water pressure will find it way to the low side(open radiator cap or drain)!

I personally don't care for those flush kits. Adds one more point of failure to the cooling system. Plus, I wouldn't want my tap water in my cars cooling system. I only used distilled water. And, most people don't reference their cooling capacity when refilling which will throw off their ratio since the block is now filled with water and not 50:50.

If you truly need a flush, then you are neglecting your cooling system.
A simple radiator drain/refill every year is plenty.

 

[mechtech]

ditto undy

 

[Mr Nice]

In the last 20 years.....I've never used a flush kit for any car.

Just change the coolant every 40,000 miles

 

[MN Driver]

Flush and refill with distilled water until things are clear and then drain the water out and add 50%-60% of your total cooling system capacity of coolant.

I was considering a kit like that until I realized that our 28k grain count of hardness in our water doesn't exactly make a good medium for coolant to work in. Tap water, no way... Distilled water all the way!

I usually like to check my antifreeze concentration with a coolant tester afterwards to make sure I got things right.

 

[Bret Chase]

quote:

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Originally posted by MN Driver:

I was considering a kit like that until I realized that our 28k grain count of hardness in our water doesn't exactly make a good medium for coolant to work in. Tap water, no way... Distilled water all the way!

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I could probably use my tap water.. using my aquarium test kit shows I've got a gH of 0..

I actually needed to "harden up" the water to keep pH at a steady 8.2 (I have Cichlids).

 

[LeeRoy]

So these guys don't use the flush and fill or don't like the flush and fill or only use distilled water or don't like to use hard water or tap water or, or, or...But you had a question about using the flush and fill specifically regards the thermostat.

Well, you should remove the thermostat before using the flush and fill. I wouldn't hit my cooling system with city water pressure (53 psi where I live). System isn't made to take that. the system should be open...water in from garden hose water out from radiator filler neck. I drain as much as I can from the system and discard IAW local laws. I then fill with tap water and run a few minutes and drain again. After doing this three times I got most of the old coolant out.

Now I use the cleaner/flush with distilled water for however long hte directions say. DRain again as above.

After this is done use the flush and fill clear water flush as per directions. I run hose from tap to heater hose fitting, other hose from radiator inlet to sewer (the discharge is water and detergent and whatever rust and scale it picked up--non-hazardous)

Now I go through three or four drain and refill with distilled water and drain again.

The system has been "flushed" and what little remains is almost all distilled water.

Now system is as empty as I can get it. Capacity is 17 quarts. I add 2 gallons of Peak and the rest of the fill is distilled water. My mix is approx 50/50 Peak and distilled

This has been a major hassle and has taken much of a Saturday afternoon, but I won't ever have to do it again because I will be doing the drain routine and refill with fresh Peak and distilled water every two years from now on.

Would have been much easier just to take it to a shop for this service, but I at least know whats in the system and that it has been done "My Way"-- as Frank Sinatra used to say.

My $0.02

 

[The Critic]

Do I have this right now?:

System Flow:

Clean Water travels from the bottom of the rad to the water pump. Pump pushes it through the block passages. Coolant is returned through the upper radiator hose containing a thermostat. Thermostat is closed, so bypass hose takes it to the heater core. Fluid circulates the heater core and is then returned to the radiator via a bypass hose.

So, in fact, there are two upper radiator hoses in a radiator. One that contains the connection between the radiator and the engine and also contains the thermostat unit. The other is a bypass hose that returns coolant from the heater core. And there may also be a third, an upper radiator hose that brings coolant from the radiator to a pressurized surge tank.

Now, for the flush/fill kit, perhaps its spliced into the heater core return line from the bypass hose. The hose water is pushed through the heater core, and back into the block, then through the radiator, where it "exits" through the radiator cap, or through a hose than leads back to a pressurized surge tank, which is why they call it a "back flush?"

 

[olympic]

There is only one upper radiator hose, the large one running from the thermostat housing to the radiator. The heater core circuit is never plumbed directly into the radiator. The fittings for those hoses are generally on the engine in the thermostat housing area. The overflow/surge tank hose will be small(~3/8"ID) and run from the radiator neck to the surge tank.

If your car is FWD, it's likely the heater hoses are inaccessible so installing this kit would be a real nightmare. Also, once the system is flushed, it's now full of pure water. You have to drain the rad and remove the engine drain plugs to get that out before refilling with the coolant mix.

Here's how I do it:
-raise the front of the car(ramps, stands)
-locate and remove the engine block drain plug. 1 on inline engines, 2 on "V" engines. Look in the area of the block between the oil pan and exhaust manifold for a hex headed plug. Consult a repair manual for more help.
-get ready to move quick because coolant is going to splash everywhere when the plug comes out.
-remove rad cap to allow air in the system
-open radiator drain plug
-stick a garden hose in the rad and flush for a couple minutes.
-replace drain plugs, close rad drain.
-refill with coolant mix and purge air from system.

 

[LeeRoy]

 

[LeeRoy]

quote:

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Originally posted by olympic:
There is only one upper radiator hose, the large one running from the thermostat housing to the radiator. The heater core circuit is never plumbed directly into the radiator. The fittings for those hoses are generally on the engine in the thermostat housing area. The overflow/surge tank hose will be small(~3/8"ID) and run from the radiator neck to the surge tank.

If your car is FWD, it's likely the heater hoses are inaccessible so installing this kit would be a real nightmare. Also, once the system is flushed, it's now full of pure water. You have to drain the rad and remove the engine drain plugs to get that out before refilling with the coolant mix.

Here's how I do it:
-raise the front of the car(ramps, stands)
-locate and remove the engine block drain plug. 1 on inline engines, 2 on "V" engines. Look in the area of the block between the oil pan and exhaust manifold for a hex headed plug. Consult a repair manual for more help.
-get ready to move quick because coolant is going to splash everywhere when the plug comes out.
-remove rad cap to allow air in the system
-open radiator drain plug
-stick a garden hose in the rad and flush for a couple minutes.
-replace drain plugs, close rad drain.
-refill with coolant mix and purge air from system.

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That'll work... more like "drain, rinse and fill". But really "flushing" or "backflushing" a radiator at home with just a garden hose doesn't do much anyway. I like to add 50% of the system capacity (which I obtain from my shop manual) coolant rather than premixed coolant/water.

 

[The Critic]

OK. I popped open the hood today and took a closer look.

Here's what I saw.

There is only one location for cooling filling in this system, and that is, the coolant tank surge reservoir.

The reservoir has a hose that is perpendicular to what I believe is, the heater core return line. Anyway, once the reservoir hose meets the heater core return line, the hose becomes larger and goes back into what I believe is the thermostat housing.

There is a lower radiator hose that connects to the same thermostat housing.

And there is also an upper radiator hose, and that connects to the block only.

So from what I understand, this is how the system flows:

Cooled fluid is drawn from the lower radiator hose, through the thermostat housing, by the water pump. The fluid circulates through the block. Somewhere toward the back of the engine, there must be an exit port for the "warmed" fluid to reach the intake manifold. The "warmed" fluid now flows to the heater core. The heater core has the return line, which flows back to the thermostat housing.

However, there is yet another opening in the front of the block. And this would be my upper radiator hose.

I did talk to someone who told me that the thermostat is designed to provide SOME flow even when its closed, which is logical as the water pump would draw the "returned" hot fluid from the heater core back into the block even if the thermostat was closed.

In other words, if I were to "splice" a Prestone T-line "backflush" kit into the inlet side of the heater core (as recommended), the garden hose would push the fluid in the heater core back into the block. Of course, the T-Line will be flowing in both directions, so in the other direction, the water would also be pushing "at" the fluid in the block, causing it to exit into the upper radiator hose and back into the radiator. The radiator would "overflow," and the fluid would exit via a tube connected to thermostat housing, back into the radiator surge tank, which is where it will flow out of the opening.

Did I get this right?

 

[Gary Allan]

I don't think that he's referring to a coolant overflow/recovery tank when he says "surge". Apparenlty this one has a pressurized cap on it (no radiator cap).


There are engines that bypass directly to the radiator. They were GM (Chevy I think).

This is a Saturn.

..and ...

Once warmed ..I've never had a problem with using cold tap water to flush a block. I'd simply start the engine with the cap off. The engine hit the temp to open the thermostate ...the hose was turned on ...viola~. It's no different then having xxx cfm of 60F air travelling across your rad. By the time it hits the thermostat ...it's hot and doesn't cause the thermostat to close ..at least in any ride that I've ever owned

When done ..drain the system via the petcock (which you can have open during this time (the stuff coming out of it will be cool) and once clear ...then allow system to empty (engine off, naturally). If there are any block drains ..open them. When you've got everything out that you can ...close it up and add your coolant of choice with your distilled water and fret not of any minor residuals that may be in the block.

If you insist on an anal aspect to this ..buy 5 extra gallons of distilled water and add them after your drain flow is clear. That should reduce anything left to undetectable.