post engine work problems

greetings members,
I have just finished an extensive engine area clean up that started by needing to replace valve cover gaskets and intake manifold gasket, for referance i have a 1989 pontiac 6000 LE with a 2.8 H.O. V6 engine in it.

i begin tear down in the morning to figure out where three left over bolts were supposed to go,,, its odd being that a close friend asisted me with the tear down, and re assembily of the intake manifold, plenum, and valve covers, I did a flushing run cycle with oil and a new fillter to get out any remaining coolant out of the engine that spilled in when the intake was removed and when i pulled the drain plug, i saw something odd, as i slowly unscrewed the bolt the first drop of liquid that came out was what appeared to be very new coolant the exact shade of green that i just put into the radiator as per every bit of old coolant in the intake, heater hoses, pipes, radiator hoses, and radiator were evacuated and brand new was added. prior to post re assembily start up.

i immidiately thought we messed up on the intake gasket some how, but I did not see any oil in the radiator i am a bit confused.

also noticed during the flush run cycle that the engine ran nice and smooth untill it got close to im assuming operating temperature then started shaking with intermittant pauses from shaking, now the plugs and wires are new and i am pretty sure seated properly, I had fixed a cracked vaccume line that went to the map sensor during this overhaul, possibly i didnt mend it correctly.

any advise before i scan for trouble codes and start tear down???

Coolant is heavier than oil. It isn't unusual for it to be at the bottom of the pan when you crack the drain plug.
New" coolant is another matter. If the intake was removed, THAT is where I would look first.

Oil "in the water" can only come when oil pressure leaks into the cooling system. With the 2.8 V6, this can only happen in the block, as there is no "oil pressure" to the heads, except to oil the rockers through the pushrods. No pressurized oil goes through the head gaskets in this design.

The running "rough" on warm-up indicates either a vacuum leak (as you surmise) or a bad sensor somewhere in the electronics. Since it runs okay while "cold", the enrichment side of the injection is working properly ("cold start valve").

Helpful?

Jim

i will check over the engine and vaccume lines again, i may have missed something, thank you for the information and advice.