Coolant Leak-Causing Hydro-Lock
 

I am seeking any information on the cause of coolant filling cylinders in my 2003 LB7 causing hydro lock.
First I will tell you that the truck runs and drives great, after clearing the cylinders. There is no smoke from the exhaust while driving, but coolant is consumed while driving at the rate of 1 gallon per 300 miles.

While the engine is running there is not excessive pressure building in the cooling sytem, I would actually say there is a lack of pressure in the system. With the engine running there are not any air bubbles flowing with the water.

When I pressure tested the cooling system, there is a leak somewhere because the 20 psi that applied leaked down to zero in 45 minutes.

When I removed the glow plugs from the cylinder heads, coolant was present in cylinders 5 and 7 (passenger side rear two cylinders).

From there I removed the injector cups and reinstalled them using anaerobic sealer on the tapered seats to rule out that the cups were the cause of the coolant leak.

The leak has persisted with the injector cup replacement, water accumulates in either cylinder 5 or 7, and sometimes both cylinders.

I have done a leakdown test on the engine and those two cylinders leak 5%(#5) and 5.5%(#7). With the oil fill cap off a very slight hissing can be heard (leakage past the rings) from the intake manifold a slight hissing can be heard (leakage past the valve seats) and not a thing can be heard from the coolant reservoir tank with the cap off. Leakdown rates for the engine were from a low of 2% up to 10%, the 10% was on the opposite bank, and the leak was obviously past the rings (perhaps ring gaps lined up). Judging from the low leakdown rates of the affected cylinders I do not suspect a leaking head gasket.

Is there anyone who has experienced these symptoms and not been able to find the obvious leak?

Where is there a potential for coolant to enter the intake runners before the intake valves?

Is there a coolant passage that runs through or is blocked by the intake manifold?

Where does the turbo charger coolant return to the cooling system?

Is there anyone that has access to GM TSBs on hydro locking?

I have scoured over the internet searching for answers or common symptoms and have only found loose ended threads on mysterious coolant leaks, leaving me wondering if those leaks were ever discovered or just forgotten about.

Any help that anyone can offer will be appreciated.

Thanks in advance.

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Does anyone have an LB7 intake setting around that they could look at to see if there is a coolant passage in it anywhere?

Head gasket or cracked head :c:

Thank you for the suggestions. The alternating cylinders filling with coolant is confusing.

5 and 7 are right next to each other right ?

Yes, the rear two cylinders on the right bank.
Where do the LB7 heads crack? With 150 psi during the leakdown test there wasn't any air leaking to the coolant system.

So I broke down and bought a bore scope to send down the intake and there is a crack in the intake port floor of the cylinder head. At this point I have couple options. I can go through the headache of removing the head and weld up the crack or use a quality A-B epoxy, or I can use a sodium silicate sealer which is designed to seal cracks in cylinder heads specifically like the crack my cylinder head has. Thanks everyone for your help!

Or you could fix it once with a new head :c:

Yeah a new head would be great as another option. That will be the next step if the sealer doesn't work. Does anyone cast the LB7 head new without glued in injector sleeves? I've seen the threaded cups but they still rely on O-rings to seal the top...

Update: I used Blue Devil head gasket sealer and so far it has stopped the consumption of coolant. I have only driven it for one week, it should be a permanent repair as it is guaranteed. If it fails I will post it here.

Thanks for the help.

I know this is a old post but I am currently having the same issues. It only hydrolocks after it sits overnight. I have not yet pulled the glow plugs to see which cylinders are getting coolant. I was wondering what was the outcome to the head repair?