oil in coolant - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 08-02-2007, 12:52 PM   #1
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Default oil in coolant

Durning a oil change/checking to see if anything is out of the ordinary I noticed some oil in the coolant. Now this struck me as odd because I'm guessing its the lim gaskets but the thing is they were replaced with the rest of the engine about 10k miles ago. Could they go that quickly also my dad is convinced its a head gasket but after three years and 8000 members in the club I know its defintly not a head gasket.

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Its a 1993 SE L27
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Old 08-02-2007, 02:17 PM   #2
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Think of where in the engine you have a gasket or seal that flow both coolant and oil.
Since your oil pressure (60 psi) is a lot higher than your coolant pressure (15 psi), oil will leak into your coolant.
When coolant leaks, it is usually directly into the crankcase.

Your heads are one of the only seals that contain both oil and coolant passages.
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Old 08-02-2007, 04:28 PM   #3
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I agree with Paul about thinking where each is located and would like to add.. remember where pressure is located and where it is not located.

The cooling system is 100 percent pressurized once up to temp/etc at ~16psi. The oiled areas aren't necessarily pressurized. The oil pump sends oil to the main/rod/cam and balancer bearings, this is where the majority of back pressure on the pump comes from to yield ~40-70psi. Oil gets pumped by the lifters up the rods to the rockers and them drips/drains back into the crankcase.

For the most part..where the oil and coolant could mix at gaskets..there aren't many places the oil would have a higher pressure than the coolant.

The pcv area may have a leak and could be slightly pressurized near the cooling jacket.. however it should be more air than oil.

Do you have a radiator oil cooler? I know it was not typical on an SE....after all the work you did.. it'* possible.
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Old 08-02-2007, 05:17 PM   #4
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No oil cooler. And I'm going to poke around some more. But after I finish replacing the fuel line which I found to have two kinks in it. If its not one thing its another
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Old 08-02-2007, 11:17 PM   #5
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I have discovered the same problem within the last couple weeks...i had a new radiator put in today, since mine had the oil cooler...hopefully it will fix the problem, most likely an internal leak...my oil was clean, as well as the tranny fluid
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Old 08-02-2007, 11:28 PM   #6
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Speaking of radiator oil coolers, it is possible that coolant and transmission fluid could mix if the radiator coils for the trans are cracked. Not common, but it does happen. That could result in oil contamination of the coolant, too. You might want to look at the trans fluid to make sure it is not emulsified with coolant. The pressure differential should favor the trans fluid going into the oil when the car is running, but when the car is turned off hot, the coolant pressure would remain high while the trans fluid pressure quickly dropped to zero.
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Old 08-03-2007, 12:05 PM   #7
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That seems like a likely scenario to me, but in that case wouldn't you then end up with coolant in your trans fluid also?
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Old 08-03-2007, 07:17 PM   #8
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Quote:
Originally Posted by lash
That seems like a likely scenario to me, but in that case wouldn't you then end up with coolant in your trans fluid also?
You would think so, since the coolant will remain pressurized on a hot shut-down, while the trans fluid pressure should drop to zero. That'* why I suggested above that he check out the trans fluid for emulsification. Probably best to drop the pan, as that is where any coolant would end up.

But maybe it is possible for the trans fluid to go just one way - into the coolant. Consider a crack in the trans fluid cooling coil that can just seep a little into the coolant when the line pressure of the trans is up to open it a bit. When the line pressure drops, the crack closes. That could explain how trans fluid could get into the coolant but not the other way around.

Just thinkin' out loud.
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