Hydro-Locked

[jjubeck619]

99 gt 3800 series II 100,000 miles


I recently had to rebuild the top end due to 1 & 3 cylinders being flooded with coolant. In the process I found the upper intake gasket blown and figured that was my problem. I tore it down to the block and replaced all gaskets, took it to the dealer to check my work and they said everything was fine.
Low and behold I'm Locked up again in the same cylinders. Any recommendations or something else I could have missed? It's a lot of work, and I don't want to have to do this again. Thanks for the help.

[HotZ28]

Did you replace the UIM?
L36 MOTOR PLASTIC INTAKE

[BNaylor]

What brand gaskets were used for the UIM, cylinder heads, LIM and throttle body?

GM revised both the UIM and LIM gaskets due to continuing problems. Revised UIM gasket came out around May 2004 and the revised LIM gaskets this past Spring. The LIM gaskets are now aluminum.

The '99 and up models with L36 SII 3800 have the revised UIM and although we get a few cases of problems like warpage or leakage seen external none are supposed to have the EGR stovepipe and coolant passage problems like the 98 - 97 GP models and very seldom if ever require replacement. However, it should be closely inspected when removed, replaced when in doubt.

[jjubeck619]

Thank you very much for the help!!!

I don't know the name brand of gaskets that were used, only that I bought them at Napa. They only sold one rebuild kit. Is there anything else it could be? I only want to do this one more time.

[BNaylor]

I'm trying to figure out why only the odd bank cylinders #1 and #3 have coolant and causing the hydrolock. You'd figure other cylinders would be affected. I recall on UIM coolant leak problems cylinders #5 and #6 were good indicators.

When you do a top end job whether it involves just replacement of gaskets or more in depth mechanical work like valves, etc. the most overlooked part of the process is checking the cylinder heads and the lower intake manifold for warpage. An automotive machine shop can check this for you. One of our GP members recently did his UIM and LIM gaskets (<--Installed new aluminum framed type) and found the LIM was warped. He had it machined and took off .004" off it to true it up. It was a '99 GT.

On the rebuild gasket set bundles from NAPA, I haven't heard anything bad about them but I am not sure of the overall quality either. The only one I trust is the one ZZP offers. Next choice are the GM gaskets.

For the time being I would pull the UIM and at least perform an inspection of that area. Look for coolant puddling on the top of the LIM and the condition of the aftermarket gasket.