As I have most of my engine taken apart pretty much for a head gasket replacement, I noticed it has, over the 8 years and 120+K miles, collected a fair amount of carbon blowby inside the cylinder heads and intake manifold, as well as oil crud on the outside.

Should I clean the blowby inside the cylinder heads, valve covers and intake manifold with Seafoam and what should I use to apply it? Possible options include but are not limited to abrasive wire sponges, wire brushes, rough shop rags and smooth microfiber cloth.

Pictures of the intake manifold are below. Please note that the excessive blowby buildup could be due to the fact that maybe my oil was mixing with the coolant due to the blown head gaskets as well as that maybe PCV was recycling fuel mixed with oil. But that should be outside the scope of this question. I do not have pictures of inside the valve covers, which has more crud than the cylinder heads (almost none) but less than the pictured intake manifold.

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1 Answer 1


First of all, I believe you are misunderstanding what "blowby" is. Blowby is caused when the air/fuel mixture is passing by the compression rings (top rings) in the cylinder. Every vehicle suffers from blowby to some extent (unless they use gapless rings). The extent is usually dictated by how old the engine is and how well maintenance has been done to it. New engines will have less blowby than older engines. Blowby can be detected at the oil filler cap and at the PCV. The gasses that go through your engine due to blowby will have a greater amount of hydrocarbons in them, which is why you have a PCV. The buildup from that is usually in the vicinity of where the PCV is located, though. What you are seeing at the edge of the port is more than likely carbon buildup left behind because this is near where the injectors fire at.

With that said, I'd highly suggest you use carburetor cleaner and a wire (or small bristle) brush (shaped like a tooth brush) to get the carbon deposits cleaned out. If you have access to a parts cleaner, I'd highly suggest you use that. It will get the parts cleaner than any other method. If all you have is Seafoam, use the spray can stuff (I think it's called Deep Creep) instead of the regular Seafoam. It should work better.

  • 1
    What do you mean by parts cleaner? Like Brakleen ? Do you think there are any consequences to leaving scratches from using a wire brush inside cylinder heads or valve covers ?
    – amphibient
    Jun 29, 2015 at 19:00
  • and is it better to use a soft microfiber cloth or just a shop rag ?
    – amphibient
    Jun 29, 2015 at 19:02
  • also, i can't tell if you prefer carburetor cleaner or parts cleaner ?
    – amphibient
    Jun 29, 2015 at 19:03
  • 1
    A "parts cleaner" is generally a device that holds a chemical solvent designed for degreasing and cleaning parts. They typically contain a pump, hand held chemical resistant brush with built in sprayer, and a positionable spigot for rinsing/wetting. More fancy models contain filters to clean the fluid or may draw cleaner from a 55 gal drum below it. These tools are more commonly associated with the brand "Safety-Kleen", however, it does not necessarily have to contain that particular brand of solvent. You can usually use mineral spirits with decent results. May 13, 2016 at 6:44
  • That being said, if you do not have access to a parts cleaner/washer, I would get a chemical safe nylon brush (Gun brushes, particularly those used for cleaning rifles come particularly handy and are quite resilient from my experience with "heavy" solvents) and some heavy duty cleaner. As for what cleaner, Brake parts cleaner is going to be the most aggressive and probably going to give you the most success. The chlorinated stuff works the best, but it's really nasty and should be used in an EXTREMELY well ventilated area. May 13, 2016 at 6:51

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