Greeting to all,
Ive heard and read different opinions about how often one should change the oil in your car. Well its a 90 C4 L98 with 108k miles on it. I bought it 3 years ago when it had 107k miles on it and changing the oil was one of the first things I did. Mobil One, high mileage full synthetic.
Today it has a little over 108K miles on it. Lack of funds and other life issues caused me to delay getting the repairs needed for it to be an every weekend runner, but now it is. I don't drive it much. So here's my question.

What should be the determining factor in deciding when to change the oil in a 22 year old car that does not get driven a lot? The age of the oil? The miles driven with the oil? Right now the oil is about 3yrs old with just over 1000 miles of usage.

As always thanks for your input and advice.

Not proven but I believe an annual oil change would be sufficient. My cars get between 1000 and 1500 miles per year tops. I wouldn't personally drive with 3 y/o oil. Hell, Firestone does a synthetic blend oil change for less than $30. That's better than doing nothing IMO.

Personal preference. In my DDs I use regular oil and change it around 4500 miles. In the vette, I'm just past my break in period for the motor so I'll be switching to synthetic soon, but I just haven't gotten around to it. Synthetic oils are generally good for 5-10,000 miles depending on how bad you beat on it. Most corvette guys change it once a year since they drive so few miles, and change it for peace of mind more than the fact that it's no longer functional. I think that's ok but not necessary. Oil won't go bad sitting in your car. I think you're fine.

Matthew

I put 3 to 4K miles on my C5 yearly and change once a year. I use Mobil 1 10-30w. Good to see you posting.....

Speaking of oil changes I notice Mobile 1 as being the oil of choice. Question, has anyone heard of the L98 as being more prone to oil leaks with synthetic oils? I've had a running problem with oil leaks and it has been suggested a straight 30W could be better. Not sure I buy this but. . .

Welcome to the forum....here is some info to digest from past threads....


http://www.corvetteguruforum.com/modu ... t_id=38973#forumpost38973

Mobil 1 is the oil of choice - since 1992, technically, and 1993 officially. GM ditched the oil cooler (I call it an oil heater) with the intro of the LT1 in 1992. At the same time, they introduced a synthetic oil to make up for the lack of an oil cooler - synthetics can take a lot more heat.

As for oil changes? Drive it! If you drive it 1000 miles a year, and if each time it is driven long enough to get up to op temp and stay there - meaning 40 to 50 miles - then change the oil every 3000 miles or 3 years. Otherwise, change it annually.

Synthetic oil will not age on the shelf, or, if it does, it is very slow. Dino oil can wax over time, which is why its bad for high temp environments.

@Scott - NEVER EVER use straight 30 weight on modern engines. I don't know who suggested that to you, but they are idiots. Seriously. If the engine was made in 1945, sure, but the tolerances of modern engines are so tight that you must have the multi-viscosity oil. The 10 number refers to how thin it is at start, when cold, the 30 refers to how thick it gets when warm. Neat science, really. Too thick when cold, and no oil will get through to the bearings. Real bad. Remember, the bearings are hydroelastic, they rest on a layer of oil no thicker than a human hair.

However, why do synthetics leak? It's simple, really... Synthetic oil is physically thinner because all of the waxes have been removed from it. It is these waxes in conventional oil that gum up the works and create that thick tar within an engine. Synthetics are also brutally effective at cleaning. They will take off a layer of goo like you won't believe. Essentially, synthetic and conventional oils come from the same dino base stock, unless otherwise noted. I suspect over time we will see more and more non-dino base stocks being used.

If you ever need to clean an engine internally, be sure to run a couple of conventional oil changes thru first to get rid of the heavy deposits, then get fancy, but be ready to swap a few filters! A friend is restoring a 58 Lincoln convertible (Mark 3). The inside of the engine was gnarly, so he used straight non-detergent oil as the first pass. This loosened up the big stuff, then changed the filter, did it again. As the filter became lighter, he then used conventional 30 weight with detergents, ooh boy, that filled up another half dozen filters!!! Real quick too, apparently. Finally, he ran that 30 weight with detergents, with a shot of kerosene, IIRC, to finish the gunk removal. This made sure the lifters were clear and the push rods were clear... a few more filters later and the insides were clean... at least as clean as he could make them without rebuilding. I think now he is running straight 40 weight, with detergents, and is changing the filter frequently.

I have been using Mobil 1 in my 92 Vette ever since I got it. The insides of the oil pan and valve covers are spotless, the top of the heads, where the valves/springs, etc, are located are equally spotless. And you can see the hone marks on the cylinder walls. That was seen 172k miles.

Sorry, of course I was referring to conventional oil verses synthetics. My main interest is about leaking which as you say, it can leak. In my case I'm fairly sure I'll need to do some R&R to correct, just not looking forward to it.

I ran 10W-30 Mobil 1 in my 90 C4 and never had trouble with leaks but it only had 58K on it.

Scott - no need to be sorry!! At all! It's all a learning process. And it's all good!

Chevy Small Blocks leak... And there is little one can do to stop ALL the leaks ALL the time.

There are a few here that have gotten there cars perfect, but they are the few. Top oil leak points:

1. Intake Manifold. Replace and use "The Right Stuff".

2. Front cover

3. Valve cover

4. Oil Pan

5. On L98, Oil cooler

6. Rear main seal

In most cases. Felpro is your solution. NAPA makes a rear main seal that is saturated with teflon that is supposed to be real good.

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Mine don't.

yea, he says now... just you wait...

Well mine does and it's just a real pain in the butt. All the leaking is coming from what looks to be the pan area but as you know you can't see much of it. The top half is very clean but the bottom - not so much.

BTW - Just on the subject I also change oil annually and have been running Mobile 1 since 1991. After rebuilding the Carroll supercharger a couple of times and then having the engine rebuilt after it blew up when the Paxton unit let go for the third time and took out a piston, I switched from the Carroll/Paxton unit to a ProCharger unit. I've been very happy with that change but this oil dripping is my new challenge to correct. Simply put, I don't like leaving spots when I park :-)

I hear that.

Try simply to retorque the oil pan bolts. It could be that simple. Check the front for any signs of a pan gasket blow out.

You can also add dye and look for any leak sources that way.

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How long?

Besides, gaskets are just maintainence items with a longer timeframe.

BTW, the sbc in my Silverado doesn't leak @ 140k.

My Harley doesn't leak...........no really it doesn't.....if you don't put oil in them while in storage it helps...........