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Update: I went ahead and changed them without penetrating fluid in the end as suggested in the answer, and they came out quite easily, I'd estimate I needed to use 5-6 Nm to loosen them. Engine was cold.

I need to change the glow plugs on a VW BKD engine. The glow plugs in that engine are located under the valve cover as shown in this video.

As I know the glow plugs can sometimes can stuck and are easy to snap, I've been planning to use some penetrating oil on them (this product) before attempting to remove them. But I'm wondering: since they sit under the valve cover, would that contaminate the engine oil, or is it not significant?

I'm also hoping that because the glow plugs are covered in oil, they'll be easier to remove in that engine, without needing the fluid in the first place.

user4520
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According to the MSDS (pdf), the main ingredient in this product is ethanol (ethyl alcohol). While no one wants ethanol in their motor oil, a small amount will quickly evaporate and should cause no harm.

However, I should point out that the glow plugs will almost certainly come loose with very little effort because they are constantly bathed in motor oil and there is no chance for rust or corrosion to form. In the video, the glow plugs loosened with one hand on the wrench and almost no force.

I have a VW ALH TDI which has the glow plugs in the open and exposed to the under-hood environment. Road salt is used in my area. Still, I have changed glow plugs several times since this car was new in 2000 with no trouble whatsoever.

Do yourself a favor and forget the penetrating fluid -- you won't need it.

MTA
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