My 308 has been sitting for a couple months

I would agree. If it's been sitting for months, every drop of old oil that can drain downward has already entered the pan. Why would you want to pump OLD oil back into every passageway of the engine where much of it would remain and then mix with your new oil?

 

One technique I have read (possibly in a Ferrari document) is to drain all the oil and refill. Run up to temperature and drain. Refill with fresh oil. I guess that's just using an oil change as a flush. Sounds okay to me as (most) oil is cheap.

Rick / '79 308GTB running Mobil1 5W30 for 9 years now

 

Is the Mobile 1 5W30 Synthetic? Do you get ok oil pressure with that weight oil?

 

Yes.
6 bar cold idle
8 bar cold 3000rpm
3 bar hot idle after a good sprint

Remember, my car is a dry dump car and it takes some doing to get the oil temp up.

(1 bar = 14.7psi)

rick

 

What I like to do is run the car up to temp. and get all dirt and metal particles in suspension. When still warm I drain the oil and leave the drain plug out for several days or even longer. If the car has been setting for a long time I would think the dirt and metal will have settled to the bottom of the pan and oil cooler as sludge. When new oil is added and the car started the sludge goes back in suspension and contaminates the new oil. My 2 c.

 

If I remember correctly, "detergent" oil is merely oil that contains parafin wax particles. As the wax particles melt, they eventually end up floating downward to the lowest point: the bottom of the oil pan. There, the parafin causes metalic particles that break loose from the engine to stick to the parafin and NOT continue to be pumped through then engine with the oil. If a car has been setting for months, chances are that the metallic particles are already stuck to the bottom of the oil pan sludge. The only true way to REALLY clean the engine is to remove the oil pan and clean it out as well. (Easier said than done on many cars.) I know of a 1967 Corvette with the 427 engine that was pretty much trashed after a total rebuild. The engine was rebuilt, but the small metal pan that is riveted to the underside of the intake manifold was never cleaned out. The pan contained a ton of trapped metalic particles that floated throughout the freshley rebuilt engine and caused problems with the new rings and bearings. I have a 1967 3X2 BBL intake for a 427 engine and the metal pan was removed by cutting the rivets. I had no idea why this was done until a friend told me that they are very hard to totally clean out without removing them completely. (The pan is used to prevent hot oil from splashing up against the underside of the intake manifold.)

 

A little trick that I use when changing oil, is after warming the engine with a brisk drive, I remove the drain plug and after 30 minutes or so, when just a few drops are coming out , I add a new quart of oil to wash out any remaining crud in the bottom of the pan. You'll never get every drop of old oil out any other way.

 

You have to warm the car to ge the dirt and debris back in suspension. Draining it after sitting for months will only waste your time and leave the oil dirty when the sludge liquifies into the new oil. Take the car for a ride and change the oil you'll be glad you did. In fact you should at least start the car every couple of weeks if you cant drive it to flash off any moisture that creeps in to the motor and to spread the lubricant around