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  1. #1
    Member B747VET's Avatar
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    Default Need Expert Help With Unusual C5 Oil Issues

    I'm pretty good with most mechanical automotive issues that aren't overly complex. But, I've had a couple of oil related issues with my "new" 2002 C5 that really have me puzzled. It has 21,000 miles and was, superficially at least, always babied and extremely well cared for - the car is virtually immaculate. Maybe these oil issues related below are just anomalies but I would really appreciate a little help.

    I decided to do a new Mobil One oil & filter change. On my previous '94 C4 ZR-1 and '89 C4 Z-51 I always used Mobil One 10-40, 15-30, or 20-40 and never had an oil related problem of any kind. Back then there were numerous warnings from experts that Mobil One 5-30 was prone to sudsing. (Back then, Dick Guldstrand's shop did all the work on my ZR-1.)

    I took the C5 it to a reputable big name Corvette specialty shop (not Guldstrand) for the oil change on top of a few other improvements. They said 5-30 or 10-40 and I went with 10-40 because of my past experience with the other Vettes. Oil filter was the blue GM. On the freeway ride home everything seemed fine.

    Next day I made a few high speed slalom and road course type runs doing 4500 to 5000 RPM's on several segments. Nothing over 90 MPH. I shut it down for a few hours and then got an engine warning light when driving to the airport to pick up the wife. It went away after 10 minutes of easy driving. 30 min later it came back again while driving easy.

    I pulled into a Mobil station to assess things and started with an oil check. (Note: On the previous runs, oil temp never exceeded 220 and mostly was at 190-200 with OAT of 75 deg F. Oil pressure seemed to get a little high a few times at 55-60.)

    Anyway, when I pulled out the dipstick to check it, smoke was wafting out of the dipstick tube and there was no oil on the dipstick. (I got a little worried) After 15 mins, still no oil on the dipstick. I'm thinking, "Boy these engines really do suck oil at high revs." So, still a little worried, I decided to add a full quart of Mobil One 10-40. After 5 mins the level was at the bottom mark on the dipstick so I decided to drive it home easy.

    Next morning, the oil level was about 3/4" ABOVE the max fill line. I started it up and idled awhile, waited 10 minutes and oil was still at the same overfill level. I pulled the oil filter and put in a new one and it still shows 3/4" high. Engine was also running ever so slightly rough. I could feel it straining although RPM's were OK and temps and pressures normal. I decided to do it all over with a new Bosch filter and this time using 5-30. Did some normal runs and then some high rev runs and all seems fine. No sign of a blown seal and the engine is now maintaining an even strain. It just feels much better. The stressed sensations I felt before are gone. Oil pressure seems to be 5 or 6 lbs lower at all RPM's than it was with the 10-40 oil. Pressure only gets to about 50-52 at 3500-4000 and all temps hanging around 190. The dipstick now always shows a normal oil level even after a high rev run and no smoke coming out of the dipstick tube.

    So, does any of this ring a bell? Is it possible that 10-40 Mobil One somehow drives this hi torque hi rev push rod engine a little nuts? Other than that, I and a couple mechanics I know are all shaking our heads. Just thankful everything seems OK.

    Any thoughts or experiences on these issues would be hugely appreciated...

  2. #2
    Moderator catbert's Avatar
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    When all else fails, use the recommended viscosity oil. If you still have a problem, you know it's mechanical. I've run the livin' crap out of C5s and 6s with the recommended 5-30 with no issues - either consumption or obvious wear.
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  3. #3
    Member timfitz63's Avatar
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    Default Geek speak alert...!

    OK. Based on this explanation on oil viscosity ratings (which I can never seem to commit to memory -- probably because, with the advent of the internet, I don't have to... ), a 5W30 oil (which is the recommended oil for the LS1 engine) has a lower viscosity (i.e., is thinner) at operating temperature than a 10W40 oil. Thicker oil doesn't circulate as readily, and under hard operation, may not be providing the proper lubrication; you were essentially running the engine with thicker (SAE 40) oil. Also probably explains the higher oil pressures you were getting with 10W40 oil (mine typically reads in the 35-45 psi range with 5W30, corresponding to idle RPM through 'ordinary driving' RPM's).

    However, I don't have a good explanation for the apparent lack of oil on your dipstick before you added an extra quart yesterday; then why it showed up 3/4-inch 'high' after the engine had cooled off...

    As "catbert" advises: always use the recommended grade of oil in your engine!

    The next obvious question you're likely to be asking: did I do any engine damage? Since you've inspected the engine and find no evidence of leaks, and have now put in the proper 5W30 grade of oil, probably not. I'd recommend keeping a close eye on things for a while, just to be certain. But had you continued to operate the engine with the thicker oil, it may have created problems; probably best not to test the theory, though...

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  4. #4
    Member B747VET's Avatar
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    Thanks for responding & I agree with both of you.

    As background, years ago at a ZR-1 Registry meeting, a Chevy engineer told us that 5-30 was not the optimum oil viscosity for the ZR-1 LT5 engine. He said that 5-30 yielded maximum results in the Federal Gov MPG ratings tests and that was why Chevy had to make 5-30 the official "recommended" oil.

    I was "assuming" the same MPG rating issues probably held true on the C5 LS1 engine 5-30 rating and that an engine with rings that allowed high RPM oil blow-by might benefit from 40 wt oil.

    Apparently, I was quite wrong in those assumptions. Maybe dangerously wrong, so wanted to share my mistakes with others while looking for feedback. Thanks again.

  5. #5
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    Default Might Need to Do A Little Investigating...

    All the C5 Super Stock (SS), A Street Prepared (ASP), and B Prepared (BP) SCCA auto-xers that run locally and/or run Nationally tend to overfill their crankcase by 1/2 quart for high rpm/high g courses. Both the LS1 and LS6 drivers tend to use Mobil 1 10W-30 unless they get something free from their sponsor (usually an AMSOIL dealer). None of them has experienced anything like you described.

    Since the Vette is new (to you), I would do some poking around to see if the previous owner added an aftermarket oil cooler or put screens in the drain back holes in the heads (to preclude metal from broken springs from dropping into the oil pan and chewing up the oil pump). Something was holding at least two quarts of oil out of the oil pan after your high rpm runs to have no oil on the dipstick IMHO. It shouldn't take more than a minute to drain back the oil into the pan from the heads at operating temperature when sitting still. Why this doesn't happen with 10W-30 is a mystery to me.

    You're correct about the fact that Mobil 1 5W-30 was chosen for fuel mileage. I believe that Jerry Watts used to tell that story whenever he addressed C4 owners. BTW, Mobil has addressed the "sudsy" problem in the API SL/SM oils by adding additional silicone additives as anti-foaming agents. (Just enough to freak out the guys on BITOG when they see a Mobil 1 virgin or used oil analysis since they associate silicone with dirt leaking past the air cleaner!).

    I would recommend continued use of Mobil 1 10W-30 in your C5. (I used it in my daily driver/auto-xer C4 with 261K miles on the clock up until the day I sold it. Only burned 1/2 quart of oil every 6K miles which was my oil change interval.)

    Good luck addressing the problem. Take Care!

  6. #6
    Member B747VET's Avatar
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    Default

    Thanks for the great response. I had read that racers are supposed to add 1/2 quart before the race and then drain it out after the race if it is still there. They seem to be saying that at racing RPM it's better to have a 1/2 quart more than get the ring blow by and be racing at 1/2 a quart or more low. Makes sense I guess.

    Just to clarify, none of the problems I experienced have occurred with 5-30 in the engine. All the problems transpired with 10-40 in the engine. Now that 5-30 is back in, everything seems completely normal again. If any of these problems occur with 5-30 on board, I will follow your good advice and investigate further. I have all the paperwork and repair orders on the car and nothing indicates that type of work.

    I would only say that if 10-40 oil can literally lead to a blown engine, Chevy should be prominently posting some serious bold print warnings.

  7. #7
    Member Junkman2008's Avatar
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    The owner's manual AND the service manual (as well as the oil cap) specifically state to use 5W-30. Nowhere in either documentation does it state that you should ever use anything else. The engineers who designed the motor figured this out with countless hours of testing under every type of condition imaginable.

    Now the million dollar question is, "Why would you ever use anything different?"
    "Marines - Making the other guy die for his country for over 200 years."

  8. #8
    Moderator catbert's Avatar
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    Quote Originally Posted by mr.beachcomber View Post
    All the C5 Super Stock (SS), A Street Prepared (ASP), and B Prepared (BP) SCCA auto-xers that run locally and/or run Nationally tend to overfill their crankcase by 1/2 quart for high rpm/high g courses. Both the LS1 and LS6 drivers tend to use Mobil 1 10W-30 unless they get something free from their sponsor (usually an AMSOIL dealer). None of them has experienced anything like you described.

    Since the Vette is new (to you), I would do some poking around to see if the previous owner added an aftermarket oil cooler or put screens in the drain back holes in the heads (to preclude metal from broken springs from dropping into the oil pan and chewing up the oil pump). Something was holding at least two quarts of oil out of the oil pan after your high rpm runs to have no oil on the dipstick IMHO. It shouldn't take more than a minute to drain back the oil into the pan from the heads at operating temperature when sitting still. Why this doesn't happen with 10W-30 is a mystery to me.

    You're correct about the fact that Mobil 1 5W-30 was chosen for fuel mileage. I believe that Jerry Watts used to tell that story whenever he addressed C4 owners. BTW, Mobil has addressed the "sudsy" problem in the API SL/SM oils by adding additional silicone additives as anti-foaming agents. (Just enough to freak out the guys on BITOG when they see a Mobil 1 virgin or used oil analysis since they associate silicone with dirt leaking past the air cleaner!).

    I would recommend continued use of Mobil 1 10W-30 in your C5. (I used it in my daily driver/auto-xer C4 with 261K miles on the clock up until the day I sold it. Only burned 1/2 quart of oil every 6K miles which was my oil change interval.)

    Good luck addressing the problem. Take Care!


    I ran national autocross events for many years in C4s and C5s , and never saw a need for increasing viscosity to 10/30. WOT in autocross lasts for 30-90 seconds, and it's hard to imagine oil thinning out too much. ON THE OTHER HAND, 10/30 will cost horsepower (as well as mileage), another reason why new cars are tested and delivered with 5/30 these days. I witnessed back to back dyno runs with 10/30 versus 5/30 in the same car (a C6). The difference was 2 - 4 horsepower through the band. Not bad for no money!
    There are times for thinking, and times for acting, but the art is in the balance


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  9. #9
    Member B747VET's Avatar
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    Quote Originally Posted by Junkman2008 View Post
    The owner's manual AND the service manual (as well as the oil cap) specifically state to use 5W-30. Nowhere in either documentation does it state that you should ever use anything else. The engineers who designed the motor figured this out with countless hours of testing under every type of condition imaginable.

    Now the million dollar question is, "Why would you ever use anything different?"
    I don't disagree, but would only remind you that because of the Federal mileage tests and their huge impact on the entire Chevrolet line of cars, Chevrolet has a long 20 year+ history of putting 5-30 in owner's manuals and on oil filler caps and then publicly admitting that other oils, like 10-40 or 20-40 were actually preferable for those same Corvettes. Federal performance regs dictated 5-30 long before the engines were specifically designed with tolerances that actually dictated 5-30 from an engineering and performance perspective.

    Blindly following Chevrolets oil recommendations has never been a caveat until recently.

  10. #10
    Member Junkman2008's Avatar
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    Quote Originally Posted by B747VET View Post
    ...Blindly following Chevrolets oil recommendations has never been a caveat until recently.
    Trust me, with as many Corvettes and LS1's that GM pumps out of it's factory, they would never knowingly recommend anything that would cause an engine failure BEFORE the warranty period was up. That would be stupid on their part from a business stand point.

    I'm not saying that GM employs the absolute brightest minds in the engine building business but I will say this. A good engine design is built upon information, as is any solid business model. The amount of testing that is done to a design before it is released to the public cannot be duplicated by Joe engine builder do to the massive cost alone. Joe engine builder cannot blow up aluminum blocks left and right in order to find the sweet spot that will endure a 100,000 mile warranty. Only your automobile manufacturers can do that. Thus, "blindly" following the manufacturer's recommendations may not be the "in" or "cool" thing to do for those who think they know a lot about engine building but it is definitely the "safe" thing to do. It is also required if you want your warranty to be honored.

    Information is king. A lot of information went into the design of the LS1, from the race track to the testing. I'll put my money on that information any day.
    "Marines - Making the other guy die for his country for over 200 years."

  11. #11
    Member B747VET's Avatar
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    I don't think anyone has really addressed or disagreed with the points you are making. It seems to be a given that the LS1 and newer engines are specifically designed for 5-30 oil.

    What some of us were addressing was that during the C4 era Corvette engineers were openly speaking to groups of C4 owners and telling them that the 5-30 recommendations of that era were not driven by engineering considerations so much as by fuel economy tests. Also, it was widely known during the early 90's that Mobil One 5-30 oil was prone to sudsing and no C4 or C4 ZR1 owners that I knew back then ever put 5-30 Mobil One in their C4's.

    That was especially true of the ZR1 owners who knew that a new engine would run them $20 grand or more. So, was GM technically risking liability by saying to use 5-30 back then? Probably so. Hey, the money they might have risked on a few warranty claims was likely far less than the fleetwide EPA mileage penalties on the other side of the risk equation. That is the reality of big business.

  12. #12
    Member Junkman2008's Avatar
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    Well I'm a little confused now. Didn't you put 10W-40 in your C5 (LS1)? That's what I though you were questioning when you started this thread. Maybe I've missed something along the way?
    "Marines - Making the other guy die for his country for over 200 years."

  13. #13
    Member B747VET's Avatar
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    Quote Originally Posted by Junkman2008 View Post
    Well I'm a little confused now. Didn't you put 10W-40 in your C5 (LS1)? That's what I though you were questioning when you started this thread. Maybe I've missed something along the way?
    You are correct. Sorry for any miscommunication on my part. I put 10-40 in the C5 based on my previous C4 ZR-1 experience. I quickly realized that something was probably very wrong. That was why I came on here asking for input.

    It was when you said, "Now the million dollar question is, "Why would you ever use anything different?" that I felt we were miscommunicating. None of us ever said that GM recommended the wrong oil for the C5. Apparently, this C5 engine is indeed very specifically designed for 5-30.

    What some of us were saying, and why I decided to try 10-40 in my C5, was because for 20+ years GM Corvette engineers admitted that their recommendation of 5-30 in the C4 ZR-1 and the base C4 engine was based on maximizing EPA testing scores, not on engineering or performance considerations. Many of us used something different because experimentation confirmed 5-30 was not the optimum oil for those engines.

    When I heard that the C5 engines from 2000 through 2002 have serious potential for oil blow by due to improperly specified rings and maybe pistons in all those C5 engines, it seemed plausible that 10-40 might help to solve that problem. That was a faulty assumption on my part.

    Just keep in mind that the same company that has apparently properly recommended 5-30 for the C5 engines also knowingly and quite improperly put a bad combination of pistons and rings in these engines for at least three years. So maybe, again, the question is why would anyone blindly trust GM or any other major manufacturer who has a long track record of making decisions based on costs to the corporation rather than what is optimum and proper for the end user?

    Again, it is apparent that whereas testing various viscosity levels was very commonplace in the past, C5 and C6 generation engines do not require such experimentation because these newer engines are truly optimized for a specific viscosity.

    This last week I've asked two high end well known Vette shops and two dealers about these C5 oil issues. None of them had the slightest idea what I was talking about regarding the critical nature of viscosity in C5 engines. The actual bad performance of my engine on 10-40 and the much better performance on 5-30 has convinced me that some of the folks on here have their act together and I appreciate that they are basing their input on more than "because GM says so."

  14. #14
    Member Junkman2008's Avatar
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    Quote Originally Posted by B747VET View Post
    ...This last week I've asked two high end well known Vette shops and two dealers about these C5 oil issues. None of them had the slightest idea what I was talking about regarding the critical nature of viscosity in C5 engines. The actual bad performance of my engine on 10-40 and the much better performance on 5-30 has convinced me that some of the folks on here have their act together and I appreciate that they are basing their input on more than "because GM says so."
    Okay, I see now. As for the dealerships and Vette shops, that doesn't surprise me at all. I question so called "Vette shop experts" about common issues concerning the C5 and a lot of them have never heard of some of the things that I have found to be common. I am by no means an expert mechanic but I am real familiar with the C5. As a matter of fact, that's the only car I'm real familiar with. A lot of what I have found has come from reading the experiences of other Vette owners and then experiencing the same issues myself. When I go into research mode, there ain't a document out there that is safe from me. I inhale information about this car.

    You will find a ton of information on these forums that a lot of mechanics won't know about. Don't let that surprise you regardless of the technician you're talking too. At the same time, some of the mechanics you will run into on these forums will knock your socks off with what information they can provide. You just have to sift through a little garbage now and then, which is why I like getting an understanding of the theory behind a man's answer if I can't find it in the service manual. It has to make sense to me before I'll bite on it.

    By the way, get the service manual on DVD if you can. It makes owning this car so much more affordable if you turn the wrenches on your car.
    "Marines - Making the other guy die for his country for over 200 years."

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    I want to agree with Mr. beachcomber-the owners manuel-if you read it,says 5-30 or 10-30 here in HOT florida I switched to 10-30 with no probs.

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