Rep Power: 0

I just bought an '02 Civic Si with about 150k miles last week and it looks like the oil hasnt been changed in quite some time. My mechanic told me I should flush the motor. I'd like to do it myself with an oil flushing agent to save a bit of cash.

What's an additive/product that is most effective but safe? I have no idea where to start. I've read about seals leaking after a flush and would rather not have to deal with that if possible.

 
Rep Power: 518

HI. I'm ezone.
I'm here to be rude and obnoxious this evening.
Let's get this thing started...

Grab a flashlight.
Go to the garage.
Open the hood.
Is there actual sludge built up on the cylinder head that you can see when you take the oil cap off?
I doubt it.
Can you see the valvetrain parts?
Are they covered in tar, or can you still tell they are made of metal?
Gold colored from oil?
I bet they are not covered in tar.
Put the oil cap back on.

Pull out the oil dipstick.
Is the oil color golden?
Brown?
Black?
Coal tar?
(If the oil looks and clings like coal tar, I might worry for a minute. Then I'd change the oil.)

Hell no, don't do any sort of flush.
It's a gimmick, a rip off, and designed to clean cash from your wallet.
And a flush can ruin your engine in the process.

Change the oil and filter.
Use quality oil of the proper viscosity and rating.
Ideally, an oil that meets Hondas specs.

Check the oil level often, every time you fill the gas tank is good.
You don't know how fast it uses oil.
You don't want to run the engine out of oil.

Change your oil regularly.
I'd change oil before it looks black on the dipstick.

Find a competent and trustworthy mechanic for use in the future.
Whoever told you this sounds like a JizzyLube hack.
Maybe it was a JizzyLube you were at.
The JizzyLube business model is upselling you everything they sell.
Almost all of it is unnecessary.
I bet they sold you an air filter that you didn't need too.
Maybe JizzyLube has what you consider to be mechanics.
Mechanics with real talent won't be found there.
If a good one is there, he won't be there for long.

Does your owners manual mention anything about flushing the engine?
Look in the section titled "maintenance".

 
Rep Power: 200

If you do see sludge leave it alone. If you loosen heavy deposits they will clog oil in other areas of the engine. If you don't see any sludge a flush is relatively safe, but spend the money and get a good product to do it with. I have used BG several times. If it says change it in 500 miles do it. That is to get the product and impurities out. They will clog the filter up, so do not under any circumstances run it for a normal change interval. #1 it clogs the filter if it does clean anything out, and #2 most cleaners thin the oil, obviously you don't want to run thin oil for a prolonged interval. I know some that swear by marvel mystery oil and all that jaz, but use at your own risk. BG products have a garantee. They not only garantee the engine with it in there, but also have a mileage garantee to. Ask a rep about it for details. I didn't start turning wrenches yesterday, I have been in this for 15 years. Exp with BG for the last 6. I have yet to see one single problem with any of their products. They have treatments for basically any fluid system in a car or truck. Look them up online.

With all that said, the best treatment for an engine that isn't sludged up is to change the oil, on time. Doesn't matter what oil you use, every one will sludge up if you go long on changes. The better oils will last longer, but they will as well.