I've been told by a mechanic friend of mine that AFTER I've used engine flush I can put in vegetable oil, run engine for a short while then drain. He says that as the veg oil is sticky, it'll help remove more of the gunk that hasn't come out during draining. My car is a T reg Volvo S40 2.0l with 130,000 miles. Any thoughts? Thank you.

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    Is there a reason you want to flush the engine? Personally, I wouldn't risk this on a car I plan to keep, and a 130k engine still has plenty of life left in it. Jun 24, 2017 at 16:33
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    I'd use diesel fuel before I'd use a biodegradable oil ... but that's just me. I'm like Moose, wondering why you are flushing the engine in the first place. Jun 24, 2017 at 16:41
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    I've never hear of or done this, but surely if the vegetable oil is sticky, it will tend to stay in the engine?
    – PeteCon
    Jun 24, 2017 at 16:46
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    The main problem is, you are exchanging one gunk for another gunk. When the biologicals in the vegetable oil start breaking down, it will be more gunky than with what you started with. I'd tell him he can do whatever he wants with his cars, but to me it makes absolutely no sense at all. Jun 24, 2017 at 17:02
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    Engine flush in general is a bad Idea, personally I would rather leave any gunk where its at than dissolve it and run it through my oil pump and oiling system causing more wear and tear on engine bearings.
    – Moab
    Jun 24, 2017 at 17:40

2 Answers 2


I cannot conceive of any benefit that putting vegetable oil in your engine would give you and many drawbacks:

  • The viscosity is wrong, you would not get the right lubricating properties for your engine, which could lead to damage
  • Vegetable oils do not have the heat tolerance that engine oils do, the smoke point for refined almond oil, which is the highest heat tolerance cooking oil I can think of is 270C, your average vegetable oil is going to be far less than that, closer to 210-220C, both are lower than the temperatures they will face in the engine
  • Vegetable oils are organic, so will break down into organic compounds which will then be left in your engine, these may interact with the engine oil you use later and create undesirable byproducts
  • Engine oils have detergents and other additives to make it work in your engine, vegetable has none of those

You are talking about flushing your engine, then pouring fat into it. It may get some gunk out but what it will leave behind isn't likely to be any better for your engine.

  • Thanks, just gonna normal flush. No veg oil will be harmed in this process 😁 Jun 25, 2017 at 10:37
  • Looking at the comments to your question there are a lot of very knowledgeable people who think that a flush is a bad idea unless you have a compelling reason to do it, it might be worth re-considering.
    – GdD
    Jun 25, 2017 at 18:00

Cooking oil think again... If you use a flushing fluid on your first flush I suggest you then use a cheap oil and filter, on your second flush run that for 30 min low revs / tick over. Then drain. Then replace with New oil and filter PLUS An ENGINE OIL ADDERTIVE putting the addertive in first. For the older cars remove the sump give it a clean check for sludge swaf etc. New gasket replace. I don’t use a flashing fluid just the 2 oil and filter change

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