Need help diagnosing loss of coolant
 

Hey guys

So my wifes LSJ has 126k miles. Car is 100% stock minus an Option-B coolant bleed.

A few months ago, she needed a thermostat. So I swapped that and all was fine.
A week or so after she told me it had a "low coolant" light come up on her way home. So I filled it up her coolant overflow with some more dexcool but it wasn't extremely low. just enough to set the light.
Thinking it was the thermostat burping, I thought nothing of it. A week later, I checked the coolant again and it was a bit below the "full" line.

It needed an oil change, so i changed the oil and sent out an oil analysis to blackstone. They told me there is significant coolant in the oil. Thinking a headgasket, I parked it until I had the time to look at it.

So Ecaulk and I looked at it this weekend. Things we did:

1. No evidence of oil in the overflow. I pulled out some coolant it doesn't look milky at all.
2. Pulled valve cover. it looked great for the mileage. Cam wear was fine, no milky substance or anything.
3. Did leakdown test with engine slightly warm. Numbers are as follows:

1. Cylinder 1: 6% leakdown
2. Cylinder 2: 6% leakdown
3. Cylinder 3: 6% leakdown
4. Cylinder 4: 6% leakdown

We both hear no bubbling from the coolant overflow when pressurized up to 90 psi with each cylinder at TDC on compression stroke.
4. With engine cold, we revved it to about 3000 RPMs for ~15 seconds then shut off the car and pulled the overflow cap to see if any bubbles were there. No bubbles
5. I did a block combustion test and it never changed from blue to yellow. I did it multiple times from car cold, to car fully warmed up and no change in color

I am sort of lost with this. I recognize there could be a very minor leak that is not showing up on any tests. I did some googling about the oil cooler, but it seems that if you have oil in your coolant its the oil cooler, but coolant in your oil means head gasket.

Part out.

i would agree with the oil cooler theory, generally you will end up with oil in coolant and coolant in oil. this is because when its running the oil pressure is higher than the cooling system so oil flows into the coolant, but when you shut the car off the cooling system is still pressurised so coolant flows into the oil. that being said, i doubt its the oil cooler.

your head gasket seals 3 things, the cylinders, water passages and oil passages for both feed and return oil. you can have perfect leak down and compression and still have a head gasket problem. there could be a small breech between an oil return passage or between the front of the head into the timing chain area where coolant is leaking through. it wouldnt be leaking into an oil feed passage, same deal here as the oil cooler theory. ecotecs arent really known for this, but its possible.

3rd thing, and i hate to say it but im leaning towards this, a cracked head or block. while we are talking about an lsj that uses a gen 1 block, it sounds an awful lot like the lnf cracked block thing.

i would go after the head gasket and have a real close look at everything, have the head checked out at the machine shop for cracks and flatness, and if you cant find anything definitive you have to decide weather to put it back together and see if its fixed, or pull the engine out and have a deeper look.

If it is a cracked block, that would be unfortunate. I have no problem pulling the head I just didn't want to pull it without a definite reason

I may look at the water pump gasket too

I still say part out or just send it till a rod makes a window

Yeah im not putting another engine in .

What adapter did you pick up for the coolant overflow system? I have a vacuum bleeder for coolant, but none of the rubber adapters will seal because of the overflow hole location.

What percentage of coolant did Blackstone say you had in your oil? I know you said significant but wondered exactly how much that was because I had a very similar small coolant leak with my LSJ block.

My coolant leak was very slow and sporadic. For example I once drove 600 miles round trip and had no noticeable coolant loss. I kept a real close eye on it. It seemed like it would stay at level and then suddenly be a bit low. Not much, about 1/2" to 1" max drop in the coolant reservoir. Another funny thing is my coolant system would hold pressure for weeks on end. I never did a pressure test but I assume it would pass. When I removed the head this time the pistons were steam cleaned and void of carbon buildup around the edges relative to the center of the piston which could indicate a head gasket leak. I do inject water/methanol but I didn't know if it could be enough to do that. I thought surely it wouldn't be getting into all cylinders but Trevor indicated that is possible and said to never use Copper spray on these MLS head gaskets that they work better without the spray. I still never for sure identified the source. I pulled a vacuum on my oil heat exchanger, left it overnight, and it held vacuum the whole time. I'm getting a new head that is going to be decked. I'm also going to replace the water pump. If none of that fixes it I am guessing the block is screwed up.

Be interested to hear back if you discover what the cause of your leak is.

JD, here is the UOA

https://cimg0.ibsrv.net/gimg/www.cob...3d1ac6b33e.png

If I recall correctly it was you and someone else in another thread recommending it which is why I did it. Then he told me that when I sent pictures after taking it back apart. I don't know for sure if it helps or hinders but I have been told both.

That's pretty damn close to how much coolant came up in my oil analysis as well.

I just have a hard time believing a stock LSJ will crack a block but I know it can happen.

its gone

sold it to some guy on craigslist for $1500

gave him the water pump to go with it.

so glad its gone.

I like your style

Lol fixed the issue and got some money out of it nice

yeah I only paid 2000 for it.

I told the dude everything I did and that I thought it was the water pump.

he will be posting on FB pages soon. "hey guys new to cobalts, im loosing coolant, where should i look?"