Carbon build up on Valves? Prevention? Treatment? How often to change oil?

Many yrs ago, Car Talk Radio show said change oil every 4k - then we were using regular oil (not Full Syn).

So since I moved to Full Syn, I started doing it every 5k despite Mobil 1 tells me to do every 7k. Oil gets dark but color of oil should not be the factor. Another guy said that color gets dark because of the oil filter. So I used Wix but I do not think there is a change in color.

  1. How often should I change my Mobil 1 5W30?
  2. Which filter should I use?
  3. Carbon build up - Valves
    M/c tells me that my car has above avg carbon build up.
    What really works to treat Carbon build up - DIY (other than having M/c using his specialized tools)?

It really depends on your engine. If it is DFI or not about the valves. I do not think the oil filter can do much for oil discoloration. Me when it looks dirty change it.

Type of filter: Ford type filters kept the oil looking new. General Motors was always dark. It was said that Ford used a sump type filter. I can’t remember who said it.

The answer is in your owner’s manual.


And, it is very important to note that it will state both an odometer mileage value and an elapsed time value, with the proviso of whichever comes first.

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AcDelco you mean?

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Outdated for this year car. Then Full Syn was not available

It doesn’t matter. Synthetic oil should be changed at the same interval that the mfr specified for conventional oil. Synthetic oil can be a definite advantage when you need to start the engine in sub-freezing weather conditions, it will probably provide better protection in very high temperature conditions, and it is less prone to viscosity breakdown, but it gets “dirty” at the same rate as conventional oil.


I’d be more than happy changing Mobil 1 every 5000 miles or one year, whichever comes first, with a name brand filter.


Normal: Every 7.5k miles or 12 months
Severe: Every 3.75k miles or 6 months

  • On the top, it shows all the way to 120k. Beyond that there is no recommendation
  • With Full Syn, how it translates?

one can endlessly watch for how fire burns and water flows and … how “oil change intervals for SYNTHETIC (!!!) oil should be extended” gets discussed on

Not at all. If the car was spec’d for conventional oil and you use synthetic, it will only protect your engine better if you change at the manufacturer’s recommended mileage or earlier. It can’t hurt and it can only help. You can push longer if you want to, but that’s your decision.

As for filters, as long as it isn’t a cheap “white box” filter, most any of them will do just fine.

BTW, There is NO difference between GM AC Delco filters and Ford Motorcraft filters except size. They are virtually identical inside…

If the engine is not direct injection, no special treatment is required besides using good quality fuel. If it IS direct injection, an intake cleaning treatment every 30K miles may delay the inevitable walnut blasting of the intake valves. CRC and Seafoam both make products for this and they are DIY. Just follow the instructions or watch one of the many YouTube videos that present this.


@Mustangman - thanks for the post:

  • Is Seaform safe to use on cars by way of spraying it to the intake manifold?
  • Will it clean carbon on Valves?

That’s because it requires zero maintenance after 120k.
Seriously, though, when you pass 120k, just revert to the beginning of the maintenance schedule. If the first maintenance interval was… let’s say… 6k miles, then your next service would be 126k miles and should include whatever is listed for 6k miles.

Is this really a complex concept?

Mobil ! didn’t make your car.

Follow the recommendation in the owners manual.

Use the cheapest oil filter.

Oil filters are by-pass oil filters. That means not all the oil passes thru the filter media as the engine is operated.

Oil filters are at best 50% efficient at removing particulate down to 10 microns.

Anything smaller than 10 microns passes thru the filter media.



Yes indeed - on my Mazda, more mileage, manuf recommends shorter interval.

Thanks @Tester
So use cheapest oil filter and change every 3.75k or 6 months.
Presume use regular oil - which brand? Mobil, Valvoline or …?

… and yet you thought that using synthetic oil would allow you to ignore the mfr’s recommendation?

Yes, read the instructions, watch the videos. The most difficult part is finding a vacuum line.

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Why not as I follow the logic - just spoke with Mobil guys. They say change it at 10k or 1yr. I have been changing 5k or 1yr. Half the recommended interval - I am very protective of my car.