sup /o/ so my 2007 chevy tahoe has over 300k miles now and my

Switching to synthetic oil on a high mileage vehicle can actually cause it to sprout leaks because it can loosen up sludge that's currently plugging them up. Presumably that's why he says to also add Lucas which is basically super-the-opposite of synthetic oil, very high weight organic oil.

If you're currently not having any trouble with your engine I would keep doing what you've been doing or at most just switch to a quality high-mileage oil.

Source?

>>17500698
>my mechanic told me that i should switch to using synthethic oil
Get the synthetic oil labeled "High Mileage". If you go to walmart, you see the 5 quart jugs for various brands labeled high mileage. These oils have additive to make the seals swell a little bit to reduce oil leaks Full synthetic oil can have both a sludge cleaning effect and a burnt-on-oil cleaning effect. It is that burnt-on-oil (dark brown glaze) that forms on shafts and openings which stops conventional oil leaks. When the synthetic oil cleans out the sludge and glaze, then you can have an oil leak.

So be sure to use the high mileage version. If you change your own oil, then of course it's not a problem. If you go to some independent shop, you'll probably have to buy the oil and bring it in since they don't stock it. Walmart tire and oil service centers will substitute oil at your request as they run into the store and get a 5 quart jug and charge you the difference in price. Just make sure they did get that oil because you might have the bad luck of some lazy turd who says he fetched the high mileage oil (but didn't) doesn't feel like going all the way from the shop to the store, doing the paperwork, and carrying back the jug of oil on foot. After all, it decreases his service metric with walmart of customers served per hour so in one sense you are punishing him.

>>17500698
The lucas stuff probably has the same seal swelling additive the high mileage oils have. But it can take awhile for the addtive in the synth oil to work. I wouldn't add the lucas until after I checked to see if the oil was leaking or not. I guess all you can do is put a piece of cardboard under the Tahoe to wait-and-see.

I wouldn't bother with synthetic anything on a car that old. Put the cheapest stuff in it you can find at Wal-Mart. Only put the oil additives in, if the engine is burning oil.