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98 C1500 5.7 Vortec using oil

This is a discussion on 98 C1500 5.7 Vortec using oil within the Technical / Maintenance forums, part of the General Discussion category; Hey fellas, new member here. Here's my problem: Girlfriends truck (98 C1500 5.7 Vortec) has been an excellent truck. It ...

  1. #1
    Registered User
    Join Date
    Feb 2013

    98 C1500 5.7 Vortec using oil

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    Hey fellas, new member here.

    Here's my problem:

    Girlfriends truck (98 C1500 5.7 Vortec) has been an excellent truck. It now has 220,000 miles, mostly highway. The truck developed a small coolant leak about a year ago, it is from the intake manifold gasket (pretty sure it's original). Found it was leaking externally, to the front of the engine. No leakage to the oil, the oil stays very clean, no sign of contamination. I have been putting off the intake gasket replacement but now I think I need to...

    The truck until recently used about a quart of oil in a thousand miles. Totally acceptable by my standards for something with this many miles. The last few months, the oil consumption has gone way up, probably a quart in 300 miles. It has also developed a misfire and I get a PO300 code (Cylinder 3 misfire). When I checked the spark plug in cylinder 3, it showed ashy deposits consistent with oil burning. I put in a hotter plug (one step up) and it didn't help much. Recently tried a spark plug non-fouler, it also didn't help much, still throws the code. The truck runs fine other than throwing the code and the occasional misfire.

    It does not smoke on startup. If it did it would make me think a valve seal on cylinder 3. My question is...could the intake manifold gasket have gotten so bad that it is the cause of the oil consumption? I have read where the original gaskets are so awful that they basically fall to pieces. I know I am going to have to replace the gasket but am hoping that I won't have to pull the heads also. Money is tight right now. Any thoughts or experiences with the intake causing oil consumption? Really not wanting to swap the cylinder heads out if I can avoid it.

  2. #2
    I love chrome SoSoFLY's Avatar
    Join Date
    Feb 2012
    Edmonton AB Canada

    Re: 98 C1500 5.7 Vortec using oil

    I doubt it. And you don't need to pull the heads to do valve seals.
    DD -07 Illverado, 5.3, Airaid, 2" Procomp level, HID projectors, LED in/out, colormatched ext/int, chrome 20s on 275/55, 15% over factory, rollpan, RST spoiler, lots of mods
    GONE - 05 Yukon XL - ex took me for it
    Project - 94 S10 Blazer 4x4, 3+3, 33s on 17s, 880watt system, tint, HID, mods+

  3. #3
    Registered User ToyHauler's Avatar
    Join Date
    Jun 2006
    Western NY state

    Re: 98 C1500 5.7 Vortec using oil

    i would pull the valve cover on that side so you can inspect things. you can do a compression check. 9 times out of ten its just intake. when mine went the oil didnt get milky just changed viscosity a bit. but the rockers were totally white
    99 GMC Yukon SLE 4dr
    KYB monomax, air lift, tekonosha, reese dual cam, bfg at/ko
    87 Firebird, 07 Monte Carlo lt, 98 Bonneville SSE
    previous;04 F550, 2-03 2500hds, 06 2500hd 11 ram 2500,
    current; 13 e350




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