Muddy oil...??


Old 09-28-08, 12:39 PM
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Join Date: Aug 2007
Location: Alabama
Posts: 91
Muddy oil...??

I moved this post to where I should have posted it; sorry:

2000 GMC Sierra 5.3 4x4 with 190K; solid truck; no oil burn; no leaks; tediously maintained. About 50K ago, tech talks me into full synthetic Mobil 1. I have synthetic in 1-ton diesel and 07 Tahoe, so I go for it.

All is well....I think....but of late, at 5-7K, I change oil and it's "muddy". Like dark milk chocolate, with some lumps at bottom of stream...just a few, gelatin-like. Oil is not true milky like water in it, though there is a small amount of condensation under oil cap; tech says that's normal. ?? Could it be that the synth oil is cleaning crap outta there? It's not overheating and there's no oil in coolant like a head issue. ?? It has always "used" about a pint of coolant every 3K.


Thank you.
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Old 09-28-08, 01:30 PM
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Join Date: Apr 2008
Location: Oklahoma
Posts: 1,698
that is classic water in oil, your coolant is entering the crankcase, probably by a leak under the intake manifold. you will need to pressure test the system to be for sure but that is pretty common on late model gm's, usually requires either surfacing the sealing areas of the intake or new intake manifold.

if we're not supposed to eat animals why are they made out of meat?
Old 09-28-08, 08:37 PM
Join Date: May 2008
Location: Central, IL.
Posts: 109
Yep sounds like you have coolant in your oil.
Failure to stop this will lead to main bearing failure.

It is pretty common for het rear intake manifold gasket to leak. Typically down the back side of hte engine, however it can just as easliey leak into the engine.

You could do the pressure test, however you already know it is losing coolant.

There is another possibility. This depends entirely how how far you commute every day. If your only driving a couple of miles, then your engine isn't getting hot enough to burn off the condensation in the engine. Over time this will build up and lead to milky brown oil.
Old 09-29-08, 09:05 AM
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Join Date: Apr 2008
Location: Oklahoma
Posts: 1,698
Thank you for your reply. I've read a tech bulletin from GM that talks about the heads. ?? This tech bulletin covers 01 - 06 5.3L engines...mine is a 2000, so I suppose mine is excluded...??

With coolant getting to my engine oil vs. oil getting in my coolant, you're thinking that it's the intake rather than the heads? I'm certainly believing for that, Brother; I'd imagine that intake issue is better than the heads. I can fly the hair of a $15 million UH60 BlackHawk, and can handle some of my own mechanics; but here, I'll find a solid GM mechanic. Below is the tech bulletin, by the way, and thank you again for helping me with this:

Some vehicles may experience a gradual coolant loss over time. A very low percentage of cylinder head(s) manufactured with an embossed Castech logo may develop a porosity crack in a very specific area.

Inspect the cylinder head assembly to determine if the casting was manufactured by Castech. This can be accomplished by inspecting for their casting logo located on top of the intake port, under the rocker arm support rail and in the spring deck cavity portion of the cylinder head.

If the cylinder head(s) is a Castech casting, inspect the area around the five oil drain holes for witness marks indicating coolant seepage over time.

If No evidence of coolant loss is found on inspection of Castech casting cylinder head(s), follow normal diagnostic procedures in SI to determine the cause of the coolant loss.

The crack location can be found in any of the five cylinder head(s) oil drains. This can be seen as a clean or shiny area, on an otherwise stained surface. Pressurizing the cooling system at this time may reveal coolant, air, or a combination, weeping in the described area. If inspection reveals evidence of coolant witness marks, replace the entire cylinder head(s) assembly.

i would not assume your pu doesn't fall under this bulletin, it may mean your's just fell throu the cracks. i would definitely have that checked also.

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