Probably kicking a can of worms but I am a new owner of a 1985 Corvette. Previous owner used 10W30 Quaker State conventional oil. I have always ran Mobil 1 in everything I own. Before I read the manual I picked up 10W40 Mobile One high mileage. I now read that the preferred oil is 10W30. Before I change the oil for the first time I thought I would check with other owners. The car has 110K on the ticker and is leaking a small amount from somewhere. I haven't put it on the lift yet to take a look. Eye surgery Friday may delay all my work. I am on Docs orders not to lift anything heavy so that probably means the hood of a C4. Thanks. Bob

 

I went back and read some old posts. Unless someone things I am really doings something wrong I am going to change to synthetic Mobile 1 High Mileage 10W40 for this first oil change and see what happens. I really don't want to stir up the onion pool again but if someone really thinks this is a bad way to go then let me know. I don't plan on driving much in extremely cold weather and the car will be in a unheeded but insulated garage.

 

Driving in under 40 degree weather: Use Mobil 1 full synthetic 5-30w. In Summer use same oil at 10-30w. High mileage is good, but the key here is routinely scheduled oil changes with Full Synthetic Mobil 1.

 

I wouldn't be switching to synthetic in a car that already leaks oil.

 

I have heard that is an issue but I have a MGB that has a small leak and I noticed no change when I switched to synthetic. I plan on resolving the leak this winter if at all possible. Once I get it up on my lift I will know more. Unless it is a rear main seal I think I can handle the leak. I am pretty sure they went to one piece seals at this point so that should be good.

 

Hello There PatzwaldB,

I bought a 1988 C4 that had been neglected and had sludge in it from oil changes that were never done by the previous owner. What I have done in the past is to take a seriously dirty engine and warm it up and let it drain for as long as it wants. Then I fill the engine up to the normal oil levels or slightly above normal with some warm kerosene and let it sit in the engine for a couple hours until I dumped it out.

DO NOT RUN the engine with kerosene as the primary lubricant.

I got a lot of the sludge out but not all. There are products made by reputable companies to assist in the removal of sludge if that would help you. I have not tried them but I would if I needed to.

One important point for you to be aware of is that in 1987 GM changed several key components in the engine including heads and camshaft and they went to the newer style roller rockers and followers. That changes the oil type to allow the cars to run lower levels of Zinc (environmental concerns) like the newer oils made for today's modern cars. This is a problem for any car out there with the older style Camshaft and lifters as they NEED the Zinc or you can wipe a lobe of the cam pretty quickly. Check first, I am not an expert on this but I believe that puts your engine in the same category as my 1968. If this is true then you need to buy oil with Zinc or add Zinc to your oil during the oil change.

On the 1988 C4 after a couple 2000 mile oil changes the oil became clearer and cleaner. Like mentioned to you above, periodic oil changes are the best thing for an older Corvette. I change my oil once a year whether or not I have 5 miles or 500 on all my cars. I don't buy this 15,000 miles oil change schedule, Heck, VW wanted my wife to drive her new 2018 10,000 miles before the First oil change, not... Even the VW Service manager told me every 6 months or 5000 miles. This kind of advice I can handle!

In a earlier post I mentioned taking my Dad's F-150 to a Jiffy lube. There they did an "Engine Flush" using a machine that pumped hot solvent throughout the engine's oil lubrication system and it removed all evidence of any sludge at all. They did it for me to "show" me that it really worked and did not even charge me for the live demonstration. I was very impressed as the engine oil stayed clean after that for many years. The engine was REALLY badly sludged up when my Dad bought it and after this he drove it for years without any problems with dirty engine oil.

I am not a big proponent of Jiffy Lube but what they did for my Dad's engine was amazing. They showed me a filter before and after the procedure, it was amazing that you could have that much sludge and still get oil to circulate inside those tiny passages.

Mobil 1 is the good way to go, I agree that the "High Mileage" type is what you want as it is designed to work better with older engines with some miles on them. On my 1968's Big Block I use the Joe Gibbs Racing "Driven Racing Oil" and is labeled XP4 Conventional 15w-50 Racing Motor oil and it specifically mentions the ZDDP Anti-wear package. I went to a local engine builder and that is what he recommends for the older style performance engines. It is not cheap OIL but is IS cheap INSURANCE. I paid about $8 a quart which is less than the Royal Purple Oils cost around here. I really trust the Royal Purple oil as well for older style engines.

Good Luck with you Corvette! If you take good care of it you should get a lot of "Smiles per Mile" and isn't that what Corvettes are for in the first place?

And Good Luck with your Eye Surgery! You are right about lifting the hood on your 1985 C4 as those things don't weigh much but are bulky. I am supposed to not lift over 15-20 lbs..... hard to do when you love cars, especially Corvettes!

 

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There is a lenghty article on zinc if you need help falling asleep: https://540ratblog.wordpress.com/201...-test-ranking/

I have switched my cars over from mineral to synthetic without massive oil leaks after washing out the sludge holding the motor together.

 

Corvettes didn't get synthetic oil as a factory fill until the LT1 engine was introduced in 1992. Many members here have used a full synthetic in the L98 engines and have not seen any issues. No reason why you can't go to a full synthetic like the Mobil-1 oil or any other good quality synthetic that meets the newer GM Dexos standards. When I had an '87 that I used for autocross and HPDE events, I used Mobil-1 in a 5W30 weight and never say any sort of oil-related problems even with oil temps getting into the 225-230 degree range..

A 5W-30 oil will work fine in your engine as would a 10W-30 weight. Some may not consider 110K miles is "high" given the age of the car. Certainly get a good oil filter such as a WIX, Purolator, or a Mobil-1 filter.

 

Castrol, Quaker State or any name brand 10W30 conventional oil is all I and the original owner have ever used in my 85. I trust it and never had any problems with it. The L98 doesn't require, nor was it designed for the more expensive full synthetic oil. Some guys do use full synthetic for various reasons. I tried it once and it leaked very quickly even with all new gaskets. I dumped it immediately and went right back to conventional. No more leaks. That's my experience regardless of how others like synthetic. Glad synthetic worked for them but it's not worth it for me.

 

any oil, conventional, or synthetic, meeting current API specs, weight as defined by the owners manual will work just fine. change it per the factory maintenance schedule and use a quality filter. if you're running a stock, flat tappet, factory grind, no additives needed. FWIW, I switched from dino to (high mileage) synthetic and did not notice any leaking or other ill-effects. if you plan out your oil changes, mobile 1 has their annual rebate program each spring - $12 off a 5-quart jug. Wal-Mart shopping nets about $2.50/quart - how can you loose? I buy enough to cover my 85's oil changes for the year. filters, i currently run bosch 3510 premium oil filters. these are the same size as the old school delco PF35's. 1985 L98 - 164K miles - 3K changes. tore it down for a valve job a couple years ago - zero sludge. overall she runs like a top.

 

Its allways the valve cover gaskets that leak,change those and you might be good?

 

Always? Have you forgotten the Great Wall of China?

 

Yep same here. Almost 120K

 

Pretty much any 5 or 10w30 will be fine. Actually these thinks will run on just about anything. Again people put too much thought into the simple things and I'll drive you mad.

 

- it's spelled out in black and white in the owner's manual. the factory figured all this out for us. one less thing we need to worry about.

 

You can save lots of money if you choose this environmentally friendly oil:

 

No, the factory figures it out for THEM, not you, not me or anyone else. They are the base standard not the zenith. I exceeded Mercedes standards when they said the 722. 6 trans was a lifetime full till they rescinded it.

 

I get it, but this really isn't as big of a concern as one would think... on a cold start your oil should be pretty clean from the last drive cycle and for the most part would be filtered out in a minute or two anyway. You really shouldn't be generating much if any particles during this period anyway. As long as you're within the recommended temp range for the viscosity you're using it is a moot point. Besides, that, that valve is open a lot more than you think it would be anyway. Actually I'd bet anytime you're over 2500rpms or so it's in bypass somewhat.

I'm not saying you're wrong, but as long as the oil you're using is within your operating conditions it really won't make much difference. Again why you should look at a 5 or 10w30. Unless you've modified the factory clearances you don't need the higher viscosity...

 

not sure where you're going with this, but "for THEM," i'm guessing would only apply during the warranty period - back then, as I recall, 3 years/36K miles. since my owners manual covers maintenance up to, and sometimes exceeding 100K miles, anything outside the warranty period, they are doing for "my benefit" and what's best suited from a maintenance standpoint. not sure how the factory can even define and cover "the zenith." if they could, that would just redefine it as the norm. someone will always push the envelope and that, the manufacturer can't control. not sure i know of any oil related engine failures, outside the warranty period, due to the owner following the manufacturers recommended maintenance and maintenance schedule, so the whole thing is subjective - i really don't care who they figured it out for - them, me, or anyone else. it works for me and one less thing i have to think about. peace.

 

What are your cold & hot oil pressure readings? If your motor is about worn out go up a grade. If it is still making proper oil pressure on the factory recommended grade then stay with it. My car ('86L) has about 125k miles and good oil pressure on 10w30 in Texas heat. It really is up to you, these are JUST small block chevys and are kind of hard to kill unless you beat them really hard.