Cavity wax injection

I’ve had a quick look underneath to size up the job of cavity wax injection on my 1998 308. The main areas appear to be the chassis rails, to which there is obvious and easy access and the cills - to which there is not.

I am thinking of removing the cill plates and drilling a couple of 1/2" holes in the upper surfaces of the cills for the injection lance. I assume the cills contain only one longitudinal cavity each side (between the inner and outer) and there is no foam fill or other obstruction.

Has anyone done this job and have any tips?



On other cars I remove the interior sills.
There are usually some small holes.

I then get a tiny funnel and pour old engine oil in.

This reaches parts and joints other waxes don’t lol

Its necessary to bung up the drain holes under the car with tissue for a few hours to ensure the oil don’t come straight out.

It’s cheap and very effective. And no drill of holes required.

Car may smell for a day or two !

Well, it was a warm sunny day today - so ideal for wax injection. Left the can in the sun for a few hours and then set to. All pretty straightforward really, and I had the luxury of a compressor, air gun and flexible lance. The cill cover plates looked too nice to risk damage so I drilled one x 10mm hole in the bottom horizontal face of each cill just inside the down-stand seam and forward of the B pillar. This is half cill length (3ft 6 inches for the LWB models) and co-incidentally exactly the length of the lance I used. Reassuring to see the wax seeping out of the drain holes and seams remote from the access holes.

The underside of the floor pan and wheel arches had already been done, and in due course I’ll brush apply a further application to the subframes.

It’s a car I intend to keep, so worth the effort.


Greetings All,

I have found this procedure works well well on early cars that had no rust proofing, like my MKII, that was imported by me from the UK back in the 80’s.

Learned a lot about this stuff.

Sort of surprised that WaxOyl or whoever does it now doesn’t spray that area. They were known for drilling, spraying, and then inserting a rubber plug. I’m wondering if they ran afoul of manufacturers warranty with drilling the hole?

I don’t see as many places offering this but again I’m not in the UK and they don’t offer it here.