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99 GMC Sierra UOA #4610523
12/21/17 06:48 PM
12/21/17 06:48 PM
Joined: Nov 2012
Posts: 41
FL, US
tech230 Offline OP
tech230  Offline OP
Joined: Nov 2012
Posts: 41
FL, US
Truck has been using coolant these past 5-6 months with no obvious exterior leaks. A gallon of coolant will last me 3 months. I just top it off every couple weeks. Truck does not overheat & does not burn oil, but leaks from rear main seal. The oil did not look milky on the dipstick & neither did the oil when I drained it. Intake gasket or head gasket? Truck is a 99 Sierra with the 4.8

Re: 99 GMC Sierra UOA [Re: tech230] #4610527
12/21/17 06:53 PM
12/21/17 06:53 PM
Joined: Nov 2012
Posts: 41
FL, US
tech230 Offline OP
tech230  Offline OP
Joined: Nov 2012
Posts: 41
FL, US
Some gunk on the oil cap & filler neck.


Re: 99 GMC Sierra UOA [Re: tech230] #4610529
12/21/17 06:56 PM
12/21/17 06:56 PM
Joined: May 2012
Posts: 5,890
Fort Lauderdale, FL
DoubleWasp Online content
DoubleWasp  Online Content
Joined: May 2012
Posts: 5,890
Fort Lauderdale, FL
Time for a cooling system pressure test. See if the coolant ends up pooling in your crankcase, or in a cylinder.

Leave all the plugs out while you test. The offending cylinder (if there is one) will begin dumping coolant out of the hole. That will be a head gasket.

If it's only in the crankcase, then try just intake manifold.


07 Lincoln Navigator M1 0w-40/FU
68 Charger R/T / Supercharged 440 VR1/DBL7349
07 Ram 3500 4x4 / Cummins 6.7 /DBL7349
17 Maserati GranTurismo Cabrio
Re: 99 GMC Sierra UOA [Re: tech230] #4610534
12/21/17 07:00 PM
12/21/17 07:00 PM
Joined: Nov 2012
Posts: 41
FL, US
tech230 Offline OP
tech230  Offline OP
Joined: Nov 2012
Posts: 41
FL, US
Every once in awhile Iíll get a check engine light. When I scanned it, it said it was running lean on bank one.

Re: 99 GMC Sierra UOA [Re: tech230] #4610549
12/21/17 07:15 PM
12/21/17 07:15 PM
Joined: May 2009
Posts: 1,083
ohio
caravanmike Offline
caravanmike  Offline
Joined: May 2009
Posts: 1,083
ohio
Could be the castec head failure?


Oils I use: Any 5w-30,5w-20 conventional

Re: 99 GMC Sierra UOA [Re: tech230] #4610583
12/21/17 07:46 PM
12/21/17 07:46 PM
Joined: Oct 2006
Posts: 1,900
Oshawa, Ont. Canada
irv Offline
irv  Offline
Joined: Oct 2006
Posts: 1,900
Oshawa, Ont. Canada
Were the intake gasket issues still around in 99? My 97's 5.7 were replaced under a recall/warranty but that might not have been for a couple/few years after 97, I can't remember?


2017 Chevy Impala 3.6 L.
2013 Ram 5.7 L Hemi Bighorn QC 4x4
2008 Chevy Malibu 2.4 L Ecotec
Pennzoil Platinum and/or Pennzoil Ultra Platinum in all 3.
Re: 99 GMC Sierra UOA [Re: tech230] #4610656
12/21/17 08:57 PM
12/21/17 08:57 PM
Joined: Nov 2012
Posts: 41
FL, US
tech230 Offline OP
tech230  Offline OP
Joined: Nov 2012
Posts: 41
FL, US
Wouldn't the oil be milky if the head gasket was bad? The oil I drained, which was the same oil I sent to Blackstone, was not milky at all. Was black like it always is after 5,000 miles. I've already put 400 miles on the new oil & pulled the dipstick, & it's not milky at all. Just condensation on the oil cap & filler neck. I'm gonna do what Blackstone says though, & change the oil every 2,000 miles or less till I figure it out. Still runs great & doesn't misfire, overheat, or anything. Just the high lead, sodium, & potassium levels worry me.

Re: 99 GMC Sierra UOA [Re: caravanmike] #4610679
12/21/17 09:31 PM
12/21/17 09:31 PM
Joined: Dec 2013
Posts: 2,592
Fort Worth, Texas
clinebarger Offline
clinebarger  Offline
Joined: Dec 2013
Posts: 2,592
Fort Worth, Texas
Originally Posted By: caravanmike
Could be the castec head failure?


1999 was not affected by Castech head casting failures.....But the heads could have been swapped out I guess, If it has "706" casting numbers, They have been swapped as that casting number didn't exist in 1999.


2001 Chevy Camaro L92/4L80E
2006 Chevy 2500HD LBZ/Allison 1000
2010 Toyota Corolla 2ZR-FE/U341E
2000 Toyota Avalon 1MZ-FE/A541E
Re: 99 GMC Sierra UOA [Re: tech230] #4610689
12/21/17 09:44 PM
12/21/17 09:44 PM
Joined: Dec 2013
Posts: 2,592
Fort Worth, Texas
clinebarger Offline
clinebarger  Offline
Joined: Dec 2013
Posts: 2,592
Fort Worth, Texas
Originally Posted By: tech230
Wouldn't the oil be milky if the head gasket was bad? The oil I drained, which was the same oil I sent to Blackstone, was not milky at all. Was black like it always is after 5,000 miles. I've already put 400 miles on the new oil & pulled the dipstick, & it's not milky at all. Just condensation on the oil cap & filler neck. I'm gonna do what Blackstone says though, & change the oil every 2,000 miles or less till I figure it out. Still runs great & doesn't misfire, overheat, or anything. Just the high lead, sodium, & potassium levels worry me.


Not necessarily If the leak is small enough! The intake is "dry" on LS engines so it's not the intake gaskets. No oil cooler on a 4.8L.

That leaves a head gasket leak or a Busted/Cracked cylinder head.


2001 Chevy Camaro L92/4L80E
2006 Chevy 2500HD LBZ/Allison 1000
2010 Toyota Corolla 2ZR-FE/U341E
2000 Toyota Avalon 1MZ-FE/A541E
Re: 99 GMC Sierra UOA [Re: tech230] #4610740
12/21/17 10:49 PM
12/21/17 10:49 PM
Joined: Jun 2003
Posts: 18,044
Deplorable in apple valley, ca
Chris142 Offline
Chris142  Offline
Joined: Jun 2003
Posts: 18,044
Deplorable in apple valley, ca
The 4.8 has a dry intake. A common problem was the heads cracking on the valve spring side


02 Wrangler carlube 5w30
87 F250 traveler 15w40
07 fjcruiser Chevron 10w30
Z400 castrol T 10w40
Can am maveric edge 5w40
57 case tractor 15w40
Re: 99 GMC Sierra UOA [Re: clinebarger] #4610754
12/21/17 11:09 PM
12/21/17 11:09 PM
Joined: Nov 2012
Posts: 41
FL, US
tech230 Offline OP
tech230  Offline OP
Joined: Nov 2012
Posts: 41
FL, US
Originally Posted By: clinebarger
Originally Posted By: tech230
Wouldn't the oil be milky if the head gasket was bad? The oil I drained, which was the same oil I sent to Blackstone, was not milky at all. Was black like it always is after 5,000 miles. I've already put 400 miles on the new oil & pulled the dipstick, & it's not milky at all. Just condensation on the oil cap & filler neck. I'm gonna do what Blackstone says though, & change the oil every 2,000 miles or less till I figure it out. Still runs great & doesn't misfire, overheat, or anything. Just the high lead, sodium, & potassium levels worry me.


Not necessarily If the leak is small enough! The intake is "dry" on LS engines so it's not the intake gaskets. No oil cooler on a 4.8L.

That leaves a head gasket leak or a Busted/Cracked cylinder head.


Worth it to replace head gaskets, or should I just replace the whole engine? Engine runs great but has 223,000 miles on it. Has brand new fuel pump, new a/c compressor, rear end work done, & suspension work. So this is a truck I intended to drive for another 4-5 years as I got a lot of time & money invested in it. Didn't expect the head gaskets to start going, as this truck has never been overheated or abused in the 6 years I've owned it. I've owned older Chevy & GMC trucks they never had engine problems. Only had to replace normal stuff like fuel pumps, u joints, alternators, starters & a/c compressors due to high mileage.

Re: 99 GMC Sierra UOA [Re: tech230] #4610761
12/21/17 11:23 PM
12/21/17 11:23 PM
Joined: Jul 2008
Posts: 753
Maryland USA
rubberchicken Offline
rubberchicken  Offline
Joined: Jul 2008
Posts: 753
Maryland USA
You might consider GM Cooling tabs to slow down the coolant loss. The pictures to me clearly indicate coolant- sort of a reddish hue.

Re: 99 GMC Sierra UOA [Re: tech230] #4610787
12/22/17 12:01 AM
12/22/17 12:01 AM
Joined: Nov 2015
Posts: 24
california
slowrench Offline
slowrench  Offline
Joined: Nov 2015
Posts: 24
california
I have a 1986 k-20 GM 6.2L Diesel 4x4,that has similar problem.Ive been driving it that way for 25yrs.Its a great truck. (270,000 mi.)

Re: 99 GMC Sierra UOA [Re: tech230] #4610845
12/22/17 03:24 AM
12/22/17 03:24 AM
Joined: May 2012
Posts: 5,890
Fort Lauderdale, FL
DoubleWasp Online content
DoubleWasp  Online Content
Joined: May 2012
Posts: 5,890
Fort Lauderdale, FL
Replace the engine. 4.8 motors are cheap as rocks.


07 Lincoln Navigator M1 0w-40/FU
68 Charger R/T / Supercharged 440 VR1/DBL7349
07 Ram 3500 4x4 / Cummins 6.7 /DBL7349
17 Maserati GranTurismo Cabrio
Re: 99 GMC Sierra UOA [Re: tech230] #4611442
12/22/17 03:52 PM
12/22/17 03:52 PM
Joined: Nov 2012
Posts: 41
FL, US
tech230 Offline OP
tech230  Offline OP
Joined: Nov 2012
Posts: 41
FL, US

Once the truck warms up it starts putting out a slight white fog/smoke at idle. Lots of moisture in the exhaust too, & this is after driving it home from work 15 minutes away. My trusted shop Iíve been going to for almost 15 years is gonna do a leak test on it. He said if it is the head gasket, it will be a little over $1,000 but that includes sending the heads to a machine shop. Seems reasonable.

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