I've never heard of a L28 block cracking so I ask, where does the L 28 leak water into the oil? My first thought and repair was head gasket but that didn't fix it.

Cracked or Warped cylinder head is one possibility

Another possibility is the timing cover (where the water pump mounts to it). I've seen timing covers get so corroded that there is a hole in the chamber behind the water pump blades, which lets water into the area where the cam and crank gears/timing chain is located.

***are you sure it's not mixed water and oil from the first failure that you are still seeing?

Most likely its the head. Did you change the oil out after you changed the gasket? If you did then did you get it all out?

Carl knows alot about thease things. Knowledge comes with age i gues

Hoe ya get her fixed

Thanks guys. I checked the head and block for straightness. Didn't find any problem there. The corrosion problem remindes me of a similiar problem that occured in the early Pontiac OHC engine. There was a spot inside the thermostat housing that would corrode through and allow water to seep into the engine. I did change the oil and filter after I changed the head gasket. I drove the car for some distance and the water level dropped enough to allow the engine to overheat. That's when I knew that I had a different problem. I don't know Carl's age but I'm looking at 62. Been a motor head most of those years. Still love it,just not that savvy on the Datsun engines yet. I've only been playing with the Z cars for about three years. I'm hooked! Next to the small block Chevy I think they are a terrific engine. My daily driver is a 1981 na coupe that I beat on a regular basis and nothing ever goes wrong with it. The engine with oil in the water is in my 1978. One owner car that has won 1st place in class three years in a row at Z Fest here in Orlando. Go figure, I hardley ever drive it and it has a problem. Thanks again. I've been reading this site for awhile now and I think it's great.

Like Carl mentioned try the timing cover. There is a passage in the cover that allows coolant to go into the block.