Hello friends,
I’m wondering what process people have found is best to flush the cooling system of a 3.5L motor. I’m sure that people have found better ways over time and through experience of doing this more successfully.
Cheers,
Tim
Hi Tim,
No overheating issues ever on hot Aussie days and peace of mind!
Cheers
Darryl
First, a power flush, using a flush gun. I would do this with the tstat removed, and flush the block separately from the radiator.
Then, if needed, a chemical flush, using a commercially-available flush agent.
As others have noted, all of this is for naught if the radiator is plugged up.
My response was as follows. I am not sure why the first sentences were deleted!
Cheers
Darryl
Hi Tim,
From my experience on my Mk IV - remove radiator and take it to the professional and have it unsoldered and cleaned professionally. It is well worth the effort on your part and worth every cent!
No overheating issues ever on hot Aussie days and peace of mind!
Cheers
Darryl
Hi Tim,
I too had the radiator professionally cleaned years ago, but every three years I drain the cooling fluid and then remove to top and bottom hose (and thermostat) and run water from a hose (heater valve open) until the water is clear.
Before the engine rebuild I also did the 4 hour Bar’s Nural treatment, after which I would drain by opening the bottom hose again to get the crud and deposits to go into the bucket and not the bottom of the radiator.
Cheers!
Ps. I have the ”Ed” mod on my thermostat housing, so before putting in a new (4.2L E-type) thermostat I test it in hot water to see and measure that the “hat” will close the by-pass in the housing.
Thanks, Darryl.
I’ve had the radiator overhauled so it is fine. I suspect that there is some ‘build-up’ in the block so I will run some Thermocure in it for a while then flush it. After that I’ll run it on some Liquid Intelligence coolant with the soluble oil in it. http://liquidintelligence.com.au/product/liquid-intelligence-600-vintage-veteran-super-soluble-oil-radiator-coolant-15-litres
I was just wondering if people had particular techniques for flushing the block out?
Cheers,
Tim
Thanks for the reply. Pekka.
So you remove the thermostat housing then push water through the water-rail then out of the bottom of the block with the hose removed?
Cheers,
Tim
If there’s significant crud in the block, short of removing all the freeze plugs, to clean it out, a cooling system flush gun is indispensable.
Thanks Paul, I’ll try and find one in Australia.
Cheers,
Tim
Hi Tim,
Exactly. And in my case, as I had overheating symptoms in 2012-2016 the problem was really in the head, When I did the head rebuild and removed all the crud form the water channels in the head and got rid of all the air leaks in the inlet manifolds and the blow-by in the valves and deposits out of the combustion chambers it ran well and cool until that piston/exhaust valve/cylinder wall in cylinder nr. 4 broke in June 2019.
I have an infra red camera for the iPhone so I could watch the thermostat operating correctly and how heat is transferred and spread across the cylinder head and radiator. I can post pics if you like. Originally I did the cylinder head rebuild because the one single “Corrujoint” head gasket had failed next to one of the water channels in the LH front corner and was leaking into cylinder nr. 6.
Cheers!
Here’s the bargain basement kit I used. $4.00 at WalMart. Works by the pressure of your garden hose.
The pressure guns do the same thing at higher pressure.
If you think this is not doing the job, there are three core plugs on the exhaust side of the block, which are easy to get at, and you could dig around in there with picking tools to get the deposits at the bottom.
My radiator shop boiled out my radiator without taking it apart, but that was 25 years ago, and those shops that can do that are disappearing. I think it was muriatic acid they used, which cleans copper and brass without hurting it. It is sold for cleaning toilets and swimming pools.
If you use corrosion resistant anti-freeze in a 50% solution with soft water (i.e. no contaminants) and change it every few years, you shouldn’t need to flush it again for many years.
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Thanks for the feedback.
So no one back-flushes their block from the bottom up?
Tim
Well, I flushed mine upside down on an engine stand, if that counts as bottom up. 
Why do you think you need it? Are you not using anti-freeze?
I was primarily asking about the technique people use to flush the motor. It runs fine and holds it’s temperature around 70C when the ambient outside temperature is below 30C. I would’t like to get stuck in traffic at any time though I do have an electric fan fitted. The system was professionally flushed over a year ago and refilled with distilled water and a suitable additive.
However, In time I would like to run some Thermocure through the system to break down any remaining scale deposits. It came highly recommended.
Then refill it with this great product.
Tim
I flush the block in both directions, and the initial flush of the radiator, bottom to top.
Hi,
Instead of 50/50 I use 30-35% of normal green glocol based cooling fluid mixed with 65-70% of soft water.
I believe that this is better, as the more water it has the better it tranfers the heat, and as I replace it (and flush) every 2-3 years I’ve never had any problems with this.
Only on the E-types I also add one bottle of RedLine Water Wetter. Some say it’s snake oil, but IME it gave me an extra 5C degrees in hot weather if we got stuck in traffic (in Germany).
Cheers!
Clearing the cooling system really depends on how and where the car has been used previously. If it has lived in an area of hard water then blockage is very effectively removed by acid. If it has been operated without corrosion inhibitor then the system is likely to be filled will silt and the most effective cure for the radiator is removal of top and bottom and rod it. As to the engine block you really need to take out all the core plugs and scrape it out. You need to be able to invert the block and rock it about to get the silt out through the core holes.
Peter
Hi Peter,
When I first bought the MKV it was inclined to overheat so the radiator was restored (I know that). When I had all the body pad to chassis mounts replaced the cooling system was professionally power flushed with the addition of a chemical cleaning agent for three days (I know that). The temperature only climbs up when the ambient temperature rises above 30C, which is not uncommon in an Australian Summer - it got to 41C today! 
My primary interest was to pick the collective brains of the ‘pushrod’ community as to the best way to flush a cooling system as I’m sure there is a right and a wrong way to do it! 
Tim
It may not be quite so black-and-white, Tim: the wrong way is to just do it with a garden hose. That rarely cleans anything out of the system that is of a solid nature.
If you suspect that you have silt, sand, or build-up in your cooling system, then the only real way to do it is by mechanical means, IE, pulling the core plugs and picking around with wires and using compressed air to blow out as much as you can get.
If that’s the case then very likely your radiator may have some sludge and grit in it too. However you’re saying it stays fairly cool up to 30C ambient, so that shows the cooling system isn’t in too bad of shape.
I’d strongly recommend a power flush, the system cleaner, a good running rinse with clean water, then a 50/50 mix of antifreeze and water.
I posted this somewhere here in the past year. I have a 1949 MK V that would start to overheat going up hills or after driving an hour or so. A friend that is a curator for a private collection of 16 cars, all of which are over $500,000 each, told me what he uses on the cars that he is responsible for. On all of these cars, he drains the antifreeze. Flushes the system twice to get all the antifreeze residue out, then fills the system with EvapoRust. It’s sold most places in 1 gallon jugs but I ordered it from Home Depot for $82 for a 5 gallon pail. Fill the system and run the car everyday for a month. Then drain, flush with clean water twice and refill with antifreeze. I did this and it reduced the engine temp 15-18 degrees. I then used the same EvapoRust on my 1930 Cadillac. I drove it an hour at least three times a week for a month and then drained it. I now use the same EvapoRust to soak rusted parts in.
This stuff is great. It doesn’t effect gaskets or seals. It doesn’t effect aluminum or copper radiators. If you pull a freeze plug after using it, you will see the engine block is as clean as new!
I have used this on all of my antiques and can’t say enough about it. No need to remove or “boil” radiators or any of the components.
I also use magnets on long wire ties placed inside the radiator (hung on the overflow tube) to collect any new scale going through the system.
Try this before taking the system apart. It might (probably will) fix your problem.
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