How to Remove Silt From a Classic Car

How to Remove Silt From a Classic Car

If the cooling passages of your classic are clogged with silt, it can lead to hot spots in the block and potential catastrophic failure. If you don’t want to remove the engine from the car and strip it completely, it’s often effective to fill the engine with quite a strong solution of kettle or dishwasher descaler, run it up to temperature then let it sit for a week before flushing with a high-pressure hose. Of course, this may have a limited effect on passages that are completely blocked. The descaler can only nibble at the ends of the blockage, rather than softening it along its whole length.

It’s probably a good idea to remove the cylinder head and undertake as much manual cleaning as possible, both of the water jacket around the cylinders and the various passages in and around the cylinder head and water pump. Use a high-pressure air or water jet. Alternatively, obtain a wet-and-dry vacuum cleaner and reduce the suction nozzle down to a length of flattened copper pipe, which will scrape and suck at the same time when used to probe the depths of the block.

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10 Responses to “How to Remove Silt From a Classic Car”

  1. George

    I suggest remove and examine the hoses as well,on more than one occasion I have found the problem to be with a water hose,this would be my first thing to examine,especially heater hoses with being small diameter.

  2. philip birch
    philip birch

    most times the sludge is made up of iron compounds and will stick to a magnet. The small ones on a flexible stick are ideal, bigger magnets tend to pull themselves off coarse.

    • Barry Hack
      Barry Hack

      Also worth removing the thermostat as silt can build up and sometimes clog this area

  3. Larry Ruthenberg
    Larry Ruthenberg

    Caustic soda does a great job but be very careful of caustic burns and flush twice or more times .

  4. Andrew

    Don’t forget to “Back Flush” the heater matrix. You’ll be amazed at how much “Gunge” comes out of this!

  5. Philip Barr
    Philip Barr

    Interesting article but I have found that modern kettle descalers are nowhere as aggressive as they used to be. Caustic soda would be my preference but no mention is made of dilution rates. I’m aware that care needs to be taken with aluminium parts.
    Can anyone give advice on dilution rates

    • Customer Service
      Customer Service

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  6. Philip

    Interesting article. I have found that modern kettle descalers are not as strong as they used to be. My preference would be caustic soda despite having to be carefull with aluminium parts but no mention is made of dilution rates. Can anyone be of assistance with this?

  7. Andy Cole
    Andy Cole

    Kettle descaler contains dilute hydrochloric acid, this is also the main ingredient of brick and patio cleaner but at stronger concentrations.

    • E Dean Butler
      E Dean Butler

      I am surprised no one has mentioned oxalic acid. I have used this for years and years to clean sludge from automotive cooling systems. Commercial grade radiator cleaners are based on oxalic acid. Read the instructions carefully. Leaving the oxalic acid in the system too long can cause a gel to form. I have fixed totally blocked cooling systems by using oxalic acid but some situations require multiple treatments.