We have a late 2006 Jaguar XJ diesel and there is evidence of corrosion on the front sub frame. We intend to treat the car with this:
ACF-50 and Corrosion Block total Corrosion Control
The first recommended step is to pressure wash to get rid of dirt and salt.
Are we likely to do any damage to the underside o the car by using a pressure washer?
Is there any delicate electrics that could get soaked?
Do we need to remove any covers?
Any help gratefully received.

 

I have had good success with stock muriatic acid (HCl) 35%? with a splash of dish washing liquid to act as a surfactant/penetrant.
It is available at the hardware store.
It converts the iron oxide to an inert form.
Wear gloves and eye protection.

 

Did the vehicle have an MOT failure due to the corrosion?

Pressure washing the vehicle underside should only be undertaken by someone who is trained on how to operate the equipment. Any under trays or covers should be removed and care taken to not subject the alternator, starter motor and gearbox electrical connectors to high-pressure water flow. All wiring looms and connectors should either be covered with cling film or avoided.

 

I am a chemist by training and think using conc. HCL on the metal work is perhaps too risky. I know others use Phosphoric acid to tackle rust.

 

Hoping to keep the vehicle for a good few years so corrosion mild currently, just want to keep it that way. Many thanks for your tips for keeping water out of the electrics.

 

https://sciencing.com/clean-rusty-st...d-8319296.html
Phosphoric acid appears to work too.
http://www.kleanstrip.com/product/phosphoric-prep-etch

I have used phosphoric acid to stop rust on my Ranger frame. Used a spray bottle, safety glasses and gloves.

 

If I understand rt29781, the desire is to treat the rust without removing the subframes from the vehicle. Since HCl/muriatic acid is commonly used to remove paint from concrete and wood, wouldn't its use be incredibly risky around the painted surfaces of the Jaguar?

For items that will be painted, I've had excellent results using some of the commercial rust converters. Typically, you clean any loose rust with a wire brush, but leave a light layer of rust with which the converter will react. 3M, Permatex, Rust-Oleum and Ospho are just a few of the companies that offer these products. I think most of them work the same way: tannic acid reacts with the iron oxide to form iron tannate, which is stable. A second ingredient, an organic polymer, leaves a protective primer layer ready for paint.

Regarding pressure-washing the underside of the engine bay, I would personally recommend that it be avoided entirely if possible due to the risk of wetting electrical connectors and sensors or damaging plastic parts that have become brittle with age. Instead, try cleaning the corroded areas with a small cleaning brush and a mild solvent like naptha or mineral spirits or something like Chemical Guys Waterless Wash. If you need to get into crevices or other difficult-to-reach areas, try the judicious use of brake cleaner spray. After the solvent dries, follow up with a small wire brush to remove any loose rust, then use the rust converter.

Cheers,

Don

 

For others that read this thread.
HCl reacts with rust to produce Ferric Chloride which is water soluble. So from the perspective of removing rust HCl is good. However any halogen salt like NaCl or FeCl3 is also highly corrosive so needs to be removed to prevent further corrosion. Phosphoric acid converts rust to a stable non corrosive product hence why it is used commercially over HCl. Using any acid dissolves the good metal as well as the rust.

I chose the oil product as it covers the metal and keeps out the oxygen and so no further rust can occur. It has to be redone every year.

I am going off using a pressure washer, too much collateral damage.....will gently scrub off most dirt then wash off with low pressure water keeping away from electrical stuff.

Many thanks for all your suggestions.

 

A relatively inexpensive source of moderate-strength phosphoric acid for rust mediation is Lysol Toilet Bowl Cleaner, which has the extra benefit of also including detergent agents. You do need a small brush or brushes to make sure everything is covered and scrubbed, and then rinse well afterwards. But I wouldn't use anything like this in a pressure washer.