why change oil after 3 months?

[Piece-it pete]

I spoke to an old hot rodder a few years back, put a couple thousand a year on his Cutlass. He said he uses full synthetic. Once a month he changes his filter and tops it off, changes all the oil once a year. Just FYI :shrug:

Pete

[gadget73]

Oil oxidizes though. If you've ever seen an old piece of machine equipment with oil cups, or even just an oil squirt can, you'll find that in the bottom, the oil has turned to a waxy solid-ish material. The change recommendation is mostly because of that problem. In extreme cases, you have whats called "coking" which is that black chunky shit inside a motor. Basically thats extreme oxidation plus some heat.


For whatever its worth, my Mark VII has been on a 3k mile oil change interval for 20 years and 236k miles. The inside of that motor, at least where I've seen it, is absolutely clean. There is no sludge, no varnish, or anything else that you typically find inside a motor. It also does not burn oil at all, and it had few leaks when I got it. It had well over 200k on the original cork valve cover gaskets, and they were seeping but not pouring oil out like most 20 year old cars are. The front and rear of the intake also does not leak. The only thing I can attribute that to is the oil being kept clean.

[TxVic88]

Gadget - you are running synthetic, right?

[1990LTD]

Oil oxidizes though. If you've ever seen an old piece of machine equipment with oil cups, or even just an oil squirt can, you'll find that in the bottom, the oil has turned to a waxy solid-ish material. The change recommendation is mostly because of that problem. In extreme cases, you have whats called "coking" which is that black chunky shit inside a motor. Basically thats extreme oxidation plus some heat.


For whatever its worth, my Mark VII has been on a 3k mile oil change interval for 20 years and 236k miles. The inside of that motor, at least where I've seen it, is absolutely clean. There is no sludge, no varnish, or anything else that you typically find inside a motor. It also does not burn oil at all, and it had few leaks when I got it. It had well over 200k on the original cork valve cover gaskets, and they were seeping but not pouring oil out like most 20 year old cars are. The front and rear of the intake also does not leak. The only thing I can attribute that to is the oil being kept clean.

Do you (or anyone really) happen to have any pics of the inside of the motor? valve covers off or anything at all like that

I'd like to know what a clean used 302 looks like for comparison purposes.

[1987cp]

The inside of clean used motor looks precisely like fresh blasted metal with fresh 10W30 poured over it.

[91waggin]

Lots of bad info running around here, so I'll throw my two cents in.
Case number one--7,500 mile changes on conventional oil (per the owner's manual in a 91 Honda Civic. The picture below is under the valve cover at 142k miles.

All the maintenance records came with this car when I bought it, so I know they followed the (non-severe) service schedule. I bought it with a burned valve, however, so I can't speak to its oil consumption. The valve seals appear to be in ok shape though. However, it appears that conventional oil cannot stand up to the kind of abuse that a 7.5k change will put it under.

Case number two--98 Dodge Grand Caravan 3.8 with 250k miles. 7500 mile changes with synthetic oil (Wal-Mart house brand 10w-30 full synthetic) since it was new. I don't have a picture of this one, but there were no deposits when I opened the valve cover to change the gasket. No deposits of any kind, no sludge, nothing but clean oil under there. The valvetrain is a nice bronze color. Burns NO oil between changes. 5 quarts in, 5 quarts out.

Case number three--98 Ford Escort 2.0 SOHC. 3k changes with conventional oil for the last 80k miles (since I've been taking care of it). Now has 208k miles on it. Under the valve cover the valvetrain is the same pretty bronze color with no deposits or sludge of any kind. However, it does burn about half a quart between changes.

For a car that sees infrequent trips that are mostly short, combined with occasional heavy duty use, I would definitely be using a synthetic oil. I wouldn't worry about changing it more than once a year if you're not putting the miles on it.

[rick99601]

an epic thread showing what happens to oil if you were to never change it-

http://forums.bimmerforums.com/forum....php?t=1281659

[gadget73]

Gadget - you are running synthetic, right?

Yes. The Mark has been on synthetic since 180k, the Towncar since about 3k, and the S10 I switched over around 150k. I still do 3k mile oil changes, and yes I know its probably excessive. I don't put a lot of miles on my stuff since I have 3 vehicles that I drive, so its as much a time thing as anything else. 10k on the Mark last year, maybe 4k on the truck, and I don't know what on the Towncar, well under 10k though.

[TxVic88]

For anyone interested you can see the most recent post to my thread entitled Coolant in Exhaust. Today I received my oil analysis from Blackstone labs and the results are not too great. And that oil only had 500 miles (20 days) of driving on it.

[Piece-it pete]

When I got the Metro years ago, I ran synthetic in it, 3K changes. The oil came out clean, like it was never used!, so I started using it another 3K in my other car.

Pete