Not Sure What Engine I have

If you have an '84 Deville, then the engine was replaced with another 4.1 liter. No way someone swapped a Northstar in there...

Here's a picture of the Northstar.

Is this a FWD c-Body car, or a RWD full size coupe? The smaller FWD cars were introduced during the '84 model year, but they were titled as '85s. If it's a full size model, I think the '84 only came with a longitudinal 4100 or a 5.7 diesel. If it has chrome or finned aluminum valve covers, it's probably an OEM (junkyard) replacement. If the covers are plain black, it's an upgraded GM replacement.

Don't to flush the cooling system with any chemical product - and USE THE GM SEALER pellets. If you have a blown headgasket, the oil on the dipstick will look like a lumpy milkshake.

The oil residue under the oil filler cap will show signs of coolant leakage sooner than the dip stick. Monitor the oil fill cap every day. If the color is light chocolate brown then theres a leak. The intake gaskets were more prone to failure than head gaskets. They would corrode away where the coolant crosses over from one head to the other. As prior poster says, install the sealant pellets mentioned on the white decall in front of the radiator, assuming no leak is found. Coolant MUST be change every 24 months without fail and sealant replenished! A Northstar has no distributor whereas a 4100 does!

it's a RWD.the covers are black,but not flat. they have "raised lines". The oil looks fine also.

Sounds like HT4100 with aluminum covers. Usually there is a HT4100 sticker on the air filter cover.

Peteski