Replacing a Head Gasket

[cabinlake26]

I have a 1998 Deville Concours. My rear head gasket is leaking. Do I need to pull the engine to relplace the gasket?

[BodybyFisher]

While it is much easier to do with the engine out, some have done it with the engine in place.

You will need to time-sert the block, do no attempt to replace the head gaskets without doing so. Also you will need to do both banks, not just the rear.

There is plenty of info here on time-serting and many members have done the job.

How did you confirm that you had a head gasket leak

[JimD]

The recommended procedure is to drop the entire cradle with engine, transmission, and front suspension.

And do yourself a favor by replacing both head gaskets after Timeserting all the head bolt holes.

[cabinlake26]

While it is much easier to do with the engine out, some have done it with the engine in place.

You will need to time-sert the block, do no attempt to replace the head gaskets without doing so. Also you will need to do both banks, not just the rear.

There is plenty of info here on time-serting and many members have done the job.

How did you confirm that you had a head gasket leak

My mechanic said that there was oil seeping out around the rear gasket. He instructed me to buy a new car, so I trusted his advice.

[BodybyFisher]

While it is much easier to do with the engine out, some have done it with the engine in place.

You will need to time-sert the block, do no attempt to replace the head gaskets without doing so. Also you will need to do both banks, not just the rear.

There is plenty of info here on time-serting and many members have done the job.

How did you confirm that you had a head gasket leak

My mechanic said that there was oil seeping out around the rear gasket. He instructed me to buy a new car, so I trusted his advice.

That is NOT a head gasket problem, that sounds like a case half oil leak. You could also be leaking oil down from the CAM cover seals.

Is your car overheating? Find a mechanic who knows the Northstar platform and one who is honest, leaks are only a nuisense. What are your symptoms?

[Cadillac Jim]

Perhaps your mechanic was talking about the half-case gasket. The Northstar has a lower case half that incorporates the main bearing caps, and it has a big O-ring gasket that seals to the block. The oil pan bolts to that. It's why your engine is so strong that it is Cadillac-smooth at 6200 rpm, and there exist supercharged 500 hp versions of it with basically the same bottom end. Changing that O-ring is a big job, but some seepage is normal because oil pressure lines run through the seal. It's not a problem unless oil squirts out while the engine is idling and you have to add oil all the time. Usually those O-rings last well over 100,000 miles and often much longer.

The head gaskets don't leak oil. A known issue with Northstars is pulling of the head bolts, resulting in head gasket compression leakage. Nearly always this is caused by letting the antifreeze go stale (over two years for green, over 5 years for red) after which minute normal seepage results in a corrosive situation at the threads of the head bolts; after about two more years, the head bolts start pulling out. Thus you see a spike of head gasket problems in 7-year-old cars because most people never change the coolant.

The Northstar head bolts are torque-and-twist types (as in all modern aluminum head or block engines) and are treated with sealant and threadlock at the factory. They can't be removed without some possibility of weakening the threads, although early FSMs said that a clean "crack" as the head bolt broke loose meant that everything was OK with that one. Good practice is to use Timeserts on all head bolts, because it is so expensive to do the whole job twice.

But, don't go there. Almost certainly, you don't have head gasket problems. If in doubt, have your coolant checked for combustion products at any good radiator shop or really good general mechanic.

[cabinlake26]

That is NOT a head gasket problem, that sounds like a case half oil leak. You could also be leaking oil down from the CAM cover seals.

Is your car overheating? Find a mechanic who knows the Northstar platform and one who is honest, leaks are only a nuisense. What are your symptoms?

Thank you. I will go to a mechanic who knows the northstar platform. My symptoms are that i need to add 1-2 quarts of oil every 3000 miles, there is a rough idle, and every once in a while the car will die while i am in traffic (a result of the rough idle).

[jking220]

You definitely do not have a blown headgasket.

Have you tried to check the codes? Your problems may be very easy to solve.

Do you have oil puddling where you park? If not, do a search on this site for the "WOT procedure" and "oil consumption". You will find alot of information that may help slow down your oil use to a level that you can live with. Its alot cheaper and easier to add oil every once in a while rather than pull the engine to do case seals.

I dont know very much about the idle problem as I havent had to deal with that, but I'm sure others who have had issues will chime in. If you check your codes, it may point you to the exact problem. If you cant find the instructions to check the codes on this site, I will post a link when I get home, my work computer wont let me post links.

[SPreston2001]

Your rough idle could be due to alot of things. Could be a dirty MAF sensor, dirty clogged EGR valve, plugs, wires, dirty Idle Air Control (IAC) module, throttle body needs cleaning, or as simple as a dirty air filter. But rest assured your head gaskets are not blown. Your mechanic doesnt seem like he knows exactly what he's talking about when it comes to the Northstar motor. These motors have been known to leak at the half seals and thats probably what your experiencing. If your half way decent with a wrench you can clean and or replace any of the above parts to solve your rough idle. Get you a Haynes repair manual and it will walk you through everything. Go from there and let us know how you come out.

[Cadillac Jim]

Yeah, you need a tune-up and a lead foot or a 500-mile road trip on the Interstate, whichever suits your fancy.

[cabinlake26]

Thanks a lot. I will check the codes and clean or change the sensor, valve and module. There is no oil puddle left behind where I park, but I will have the coolant checked to find out if there are any combustibles. Could the leaky half case gasket be the reason that my mechanic found oil on the rear side of my block?

[SPreston2001]

Yep the back of your motor will have oil on it from a leaking half seal or even a leaking valve cover.

[BodybyFisher]

Thanks a lot. I will check the codes and clean or change the sensor, valve and module. There is no oil puddle left behind where I park, but I will have the coolant checked to find out if there are any combustibles. Could the leaky half case gasket be the reason that my mechanic found oil on the rear side of my block?

You are not overheating, I would not bother having that test done, your issue is with oil leaking, don't waste your money, your mechanic jumped the guy and is not experienced on the NS

[cabinlake26]

Where is the half seal located?

[BodybyFisher]

Its a big job, it is located between the top and bottom halfs of the engine. The engine is split down the middle at the crankshaft centerline. You might be able to improve your leaking by using a high mileage oil, high mileage oils have seal conditioner that might improve your seals.

[lothos]

1 - 2 quarts of oil every 3,000 miles isn't excessive. If the car has been babied, try the WOT procedure.

Another new member from the twin cities, welcome!

[jking220]

Where is the half seal located?

If you dont have any oil on the ground where you park, dont worry about the seal. These motors get dirty, every motor does. If its not leaking fast enough to drip, then thats not why you're using oil. You likely have carbon buildup because the car has been babied around its whole life.

It needs to be driven like you were 16 again.

[rek]

While you're at it, check the FPR...Fuel Pressure Regulator. Check all vacuum lines for leaks.

Check/Clean fuses and relays. Monitor the voltage.