Oil in Coolant

Marksman762

Original poster
Member
Apr 22, 2012
26
Hi everyone,

I'm in need of some help - my Envoy is in the shop right now as I discovered some engine oil in the coolant overflow tank. It was a relatively slow leak, but it's painfully obvious that it's engine oil and it's getting worse. I noticed a slight amount of oil film a number of months ago, now it's a good sludge in the overflow tank. There was a very small amount of oil on the radiator cap, as the upper radiator hose is showing signs of oil contamination. There is no noticeable amount of coolant in the engine oil, nor does it appears as though the transmission cooler is leaking. Pretty clear it's engine oil and no other type. The engine has about 92K miles on it. We have owned it for the last 25K or so.

The big problem is, nobody at the shop can tell me where the leak is. There is very little info out there on this type of issue for the I6. They think it is either a head gasket, some type of seal in the timing chain system, or a cylinder sleeve. They have not done a compression test or a leak down test because they think due to the design of the gasket/engine it would not tell them much. Nor have they done a compression gas test of the coolant.

I'm worried that they will want to just start tearing things down to see what they find. That will get extremely expensive very fast and may not yield good results - especially if it ends up being a cylinder sleeve.

I need help guys - any ideas? Any tests you can think of? Anyone have this situation before?

Thank you everyone.
 
Dec 4, 2011
520
Are you sure it is engine oil. If it is the only place I know where they get close to one another is the head. You could have a leak from the oil galley's to the coolant ones.

If it turns out to be tranny oil then the only place they get close together is in the tranny cooler in the radiator. This would be the easier fix.

Does it have a tinge of red, then it could be transmission fluid.

Good luck with the search.
 

Sparky

Member
Dec 4, 2011
12,927
Definitely not a common problem on these engines...

What year is your truck?
 

Boricua SS

Member
Nov 20, 2011
3,080
Ohio
in all my years experiencing the oil/coolant "chocolate milkshake" look,it has been a head gasket for me... hope thats not the case for you...
 

Marksman762

Original poster
Member
Apr 22, 2012
26
Thank you for the replies so far. Some further info - it's a 2005 Envoy. They are 99% sure it's engine oil and not transmission fluid. Aparently they've seen the radiator failures before. As far as myself and the shop could tell, there is no coolant in the engine oil or in the transmission fluid. That's what has everyone so baffled. They have been trying to figure out where oil could get into the coolant but not vise-versa. Their big concern is that it is possibly a cyliner sleeve failure, which of course would be stupid expensive.

If it's a head gasket, fine. We'll fix it and move on. But it's the unknown part of it that has me so worried. I don't want them to get in there and find the head gasket to be in good shape and that the problem is something else.

The more thoughts you guys have are appreciated, greatly! Thank you.
 

limequat

Member
Dec 8, 2011
520
Marksman762 said:
Thank you for the replies so far. Some further info - it's a 2005 Envoy. They are 99% sure it's engine oil and not transmission fluid. Aparently they've seen the radiator failures before. As far as myself and the shop could tell, there is no coolant in the engine oil or in the transmission fluid. That's what has everyone so baffled. They have been trying to figure out where oil could get into the coolant but not vise-versa. Their big concern is that it is possibly a cyliner sleeve failure, which of course would be stupid expensive.

If it's a head gasket, fine. We'll fix it and move on. But it's the unknown part of it that has me so worried. I don't want them to get in there and find the head gasket to be in good shape and that the problem is something else.

The more thoughts you guys have are appreciated, greatly! Thank you.

I'd have them just go ahead and swap a used 2006/2007 engine in.
 

Marksman762

Original poster
Member
Apr 22, 2012
26
limequat said:
I'd have them just go ahead and swap a used 2006/2007 engine in.

Doing a little google work, it seems there are many places online to order used engines from. autopartsfair.com seems to have quite a selection for around $1000 shipped. If I went this route, anything in particular I need to know?

Thank you!
 

Marksman762

Original poster
Member
Apr 22, 2012
26
limequat said:
I'd have them just go ahead and swap a used 2006/2007 engine in.

Doing a little google work, it seems there are many places online to order used engines from. autopartsfair.com seems to have quite a selection for around $1000 shipped. If I went this route, anything in particular I need to know?

Thank you!
 

Marksman762

Original poster
Member
Apr 22, 2012
26
limequat said:
I'd have them just go ahead and swap a used 2006/2007 engine in.

Doing some google work, it seems autopartsfair.com has a huge selection of used engines for around $1000 shipped. If I went this route, anything special I need to know?

Thank you!
 

Mark20

Member
Dec 6, 2011
1,630
Any chance some place started to put engine oil in the coolant recovery tank?
 

Marksman762

Original poster
Member
Apr 22, 2012
26
Mark20 said:
Any chance some place started to put engine oil in the coolant recovery tank?

It's possible, but I 'think' the amount of oil was increasing... I may just end up flushing and watching the system.
 

Marksman762

Original poster
Member
Apr 22, 2012
26
The final word came in from the shop - engine replacement was going to be the only cost effective option, used or new crate engine. They were leaning towards a cylinder sleeve or a cracked block over a head gasket. As others have said, the labor to do a head gasket would likely be the same as replacing with a used engine. Their recommendation was to get rid of the vehicle over doing any work on it.

Long story short, my wife now drives a different vehicle. I still have my '05 Envoy, I wouldn't be without it!

Thank you everyone for the advice. Of all the diagnostic services the shop had, as well as utilizing GM's network (whatever it is) there was nothing conclusive available. As many have said, there just isn't a history of these engines with this kind of problem.
 

RayVoy

Member
Nov 20, 2011
939
Marksman762 said:
Long story short, my wife now drives a different vehicle. I still have my '05 Envoy, I wouldn't be without it!
I assume, this means you still have the vehicle with the oil in coolant. If so, I have an observation that needs to be tossed out there.

The coolant is under pressure, about 15psi, when the vehicle is hot.

Yes, the oil is under pressure while the engine is running, and this pressure is higher than the coolant pressure, so oil could enter the coolant system; however, when a hot engine is turned off the water pressure is still there, oil pressure is not, water should enter the engine through the same crack.

Why is there no water in engine? Yes the heat could boil it off, but the water level should fall.
 

Denali n DOO

Member
May 22, 2012
5,596
I had this issue last year, coolant reservoir looks like oil in it dark brown, radiator has chocolate milkshake color to it. They put a new raditor on it because tranny fluid was mixing with coolant in the raditor. Tranny coolant line leaking internally into radiator. that was the fix then. NOW TODAY it is back there for the SAME ISSUE. I noticed on the weekend alot of water(?) leaking from underneath after driving, I check the reservoir and it full of what looks like oil again. thats 2 times for me now. your issue must be the same as mine. I'll let you know what they say when they call today.
 

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