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Discussion Starter · #1 ·
Hi guys,
My first post. I wish I knew about this site in '94 when I bought my Suburban new. I love it, but with 225K+ miles she's getting a little long in the tooth. This car has always used more oil than I'd like ( about 1 qt per 1500 miles). GM says this is normal. In the last 20,000 miles or so I'm seeing Blue smoke in the exhaust. It's always worse if I'm idling, although it's intermittant and seems to go away as I'm driving(no blue cloud trailing). There's also some white vapor mixed in, especially when it's cold out. OK, so I'm thinking the head gasket has finally given up the ghost. I checked compression and all cylinders are 130-145. The plugs for 2, 6 and 8 have a HEAVY, chunky, crusty tan deposit. OK, so I'm thinking that excess oil is burning in those cylinders. Is there an easy way to check if the oil source is valve seals vs. head gasket vs. worn rings. (Obviously, I'm hoping one of you guys will tell me the rings are probably OK based on the compression Numbers). The motor runs great with no trouble codes, although power is down a bit in the midrange. Any help would be appreciated. I'd like to do the work myself.
 

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Discussion Starter · #2 ·
Forgot to add it's a 5.7L. Also, I checked the vacuum and it was rock solid at 20 inhg in idle. When I rev it the vacuum drops to almost 0 and when I snap the throttle off it jumps to 25 momentarily and resettles at 20. No needle vibration or movement at steady throttle. PCV seems normal (rattles) and has good vacuum.
 

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The compression readings are within 10%, which is good. The vacuum indications sound almost perfect to me. I think the tan color of the plugs indicates it is burning OK - I believe excessive oil consumption would cause the plugs to be an oily black, not tan.

You state that 3 cylinders have a heavy deposit on the plug, which to me would indicate something different in those cylinders. Are these 3 the lowest of the 8 in compression? Maybe some head gasket leakage.........? I don't know for sure.

However, it seems to me that the engine is basically sound, and if it was mine, I would keep an eye on the oil and drive it till it pukes.
 

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:sign0016:My mechanic John, loves to say: "Its a hand grenade and the pin has been pulled." So whatever you do don't let go! If you are on a budget, save your dough for a top end or shop around for a good deal on a crate motor. If the smoke bothers you, switch to a full synthetic, it will smoke less.
 

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Head gasket can be checked with a pressure tester on the radiator. If it leaks down most likely you have a bad gasket, head or intake.

Oil burning can be rings or valve seals and can be check by using the old school wet dry test.

Check compression dry, write all the numbers down. Now start all over and put a couple of squirts of oil in each cylinder and test it again.

Here is where my memory fails me.

But I believe if you have a lower number dry than wet you have a ring problem.

If it’s the same you have a valve guide leak.

If I am wrong I’m sure someone will chirp in.
 

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My 1995 used do have a similar problem and it turned out to be the PCV valve. But not the valve itself, it was to vacuum port that it was hooked to the port was clogged with black carbon. I had to remove the throttle body and punch though it with a small screwdriver and then i cleaned it with carbuerator cleaner until it was clear. didn't burn a drop of oil after that. and i agree abiout the full synthetic.......it will give you a lot more life to your motor. i had 236K and my burb when i sold it.....never broke down.....ever.
 

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Discussion Starter · #8 ·
Thanks to everyone. I rechecked compression and it was 175-185 on all cylinders. I pulled the valve covers and found about 1 pint of oil pooled over the "crusty" head. Seems the oil drain ports were blocked, so oil was probably sitting on the valve stem seals. I replaced them and reset the valve lash. The obvious exhaust oil has stopped but HC emissions were just a little higher than NJ inspection will allow. I guess the head gasket may have a small leak. Or the Cat may be going after 225K. Anyway, thanks again for the prompt responses. I'm sure I'll be back, as I just picked up a 1999 K1500 w/88k.
 
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