Is it possible to change oil seals on an engine with the heads still on the block?

Valve seals allowing oil to run into cylinders when stood and then burning when started.may be possible to change seals with heads still on but im no expert in these engines

The 3.5 is a great engine and in the Concorde pretty efficient for sure over 20 MPG. The 3.5 HO is 1st generation and has a 10.4 to 1 comp ratio. 89 octane is required later engines after 1998 had the compression ration lowered to 9.9 to 1 and 87 might be acceptable. Scheduled spark-plug change is usually 60K miles. If plugs have not been changed than I would certainty start with them. Check tire pressure against the driver door recommended. I expect if all else is well that at 60 MPH just under 2000 RPM in over drive and smooth..

This engine was built in Chrysler's Trenton engine plant in MI and is considered one of the best power planets at the time.

I'm not sure what the problem is specifically, but I can assure you this--you're basically throwing money way (and possibly exacerbating the issue) by using 93 octane fuel. Your car is timed and tuned to run most economically and with best performance with 87 octane fuel. The higher the octane, the slower the fuel burns. Longer burn time can equate to more power, but ONLY if your engine is designed and tuned for this application.
Couple of suggestions..checkto make sure your exhaust is "free". A plugged catalytic converter can really rob mileage. Tire pressure and air filter are worth mentioning as well.

It should be located directly above the oil filter or possibly on the back of the engine block between the heads and behind the intake manifold.

No it will not hurt and there is no reason to switch to a higher octane gasoline with this engine. Certain engines in Corvette, Cadillac, etc with special combustion chambers utilizing different types of metal for performance need higher octane gasoline. Your v6 does not. If you hear knocking, have your valves checked and make sure you oil pressure is good. If you switched for no reason, switch back and save yourself $$$

you should have a factory affixed sticker inside gas compartment cover listing premium fuel only or also listed in your owners manual. Otherwise if you notice that you're vehicle is making a pinging sound while accelerating or climbing a hill for instance then you may want to step up to 89 or 93 octane and try to avoid purchasing fuel with ethanol added it's **** and degrades your fuel quality/octane ratio

REMOVAL & INSTALLATION - Oil Pan

CAUTION The EPA warns that prolonged contact with used engine oil may cause a number of skin disorders, including cancer! You should make every effort to minimize your exposure to used engine oil. Protective gloves should be worn when changing the oil. Wash your hands and any other exposed skin areas as soon as possible after exposure to used engine oil. Soap and water, or waterless hand cleaner should be used. (except 2.5 Premier engine)





Fig. Fig. 1: Exploded view of the lubrication system for all 2.2L and 2.5L except Premier engines



Fig. Fig. 7: Apply sealant to the ends of the new oil pan end seals at the junction of the cylinder block pan rail gasket-1988-95 2.2L and 2.5L except Premier engines



Fig. 8: Clean the gasket mating surface of the oil pan of all old gasket material, dirt, grease or other grime-2.6L engine

1. Apply the parking brake, block the rear wheels, then raise and safely support the front of the vehicle on jackstands.
   
2. Drain the engine oil. This would also be a good time to change the oil filter.
3. Remove the engine-to-transaxle struts, if so equipped. These struts prohibit access to the oil pan mounting bolts.
4. Remove the torque converter or clutch inspection cover.
5. Support the oil pan and remove the mounting bolts.
6. Lower the pan and remove the old gasket, if so equipped.
   

To install:

1. Clean all gasket surfaces thoroughly.
2. For 2.6L engines, position a new gasket on the oil pan using a sealer to hold it in place.
   

1981-87 2.2 and 2.5 Liter engine uses a liquid form-in-place type gasket. Chrysler Part Number 4205918, or equivalent RTV gasket material must be used.

1. For 1981-87 2.2 and 2.5L engines, install new end seals and apply the form-in-place gasket sealant. The RTV gasket material should be applied in a continuous bead approximately 1 / 8 in. (3mm) in diameter. All mounting holes must be circled. Uncured RTV may be removed with a rag. The oil pan should be tightened in place while the RTV is still wet to the touch (within 10 minutes). The usage of a locating dowel is recommended during assembly to prevent smearing of the material off location. Make sure to apply sealer where the end seals meet the block.
   

1988-95 2.2L and 2.5L engines utilize end seals and side gaskets, not liquid gasket as with 1981-87 models.

1. On 1988-95 2.2L and 2.5L engines, install new end seals and side gaskets. Apply RTV sealant to the parting lines between the end and side seals on these engines. If necessary, use a little grease or RTV sealant to hold the side seals in place.
2. Tighten the pan bolts in a crisscross fashion, starting from the center of the oil pan and working toward the ends, to the following torque values:
   2.6L engine-53-61 inch lbs. (5.9-6.8 Nm) 1981-87 2.2L and 2.5L engines-16 ft. lbs. (22 Nm) 1988-95 2.2L and 2.5L engines-M8 bolts, 16 ft. lbs. (22 Nm); M6 bolt, 105 inch lbs. (12 Nm)
3. Allow the oil pan to sit for 15 minutes to ensure that the RTV sealant has completely set.
4. Install the oil drain plug and a new oil filter, if equipped, then lower the vehicle.
5. Refill the engine with oil
   
6. Start the engine and check for oil leaks.

Hope helps (remember rated this).

having over 30 years with general motors and 10 with cadillac the standard 87 octane can be used in your northstar engine
premium is noted on the dash cluster to the owner of course for the price they paid for a 300 horsepowered engine seems they octane should be using the highest made octane to use. it is another bad reflection from general motors in their part. I owned a 96 de ville and always ran 87 octane and took it out west in 98. I cruised at 90 mph through Nevada and received 29 mpg

you need to change the spark plugs and wires to properly burn the gas fully then you can just get agood oil change and you would get better gas mileage

consider a higher octane gas to see if the problem is cured. Many people are having success with cheap HHO kits (do a google search). The hydrogen allows normal 87 octane to hit a peak rating of 120+ octane. I personally use this on my car and have gain 60% mpg (not typical) along with a much smoother and responsive engine.

Good luck.