Cadillac Repair: oil pan, hi-rev problem, engine oil leaks, engine oil pan

Question
I have a 99 Deville Councours with a 4.6 northstar.  When i got my oil changed, the mechanic discovered a leak on the oil pan gasket.  He told me since he had to pull the engine to change the oil pan gasket, it would cost me $1800.  I just wanted to know if this is true.  Also, when i noticed my oil was low, i accidently put 5w-30 oil in my car, but just one quart.  The rest was filled with 10w-30.  Now, periodically, the engine will high idle.  In park i've seen it get to 3Krpm.  Do you think that the 5w-30 is burning off inside the engine?  Thanks for your help.

Answer
Hi Jesse,

      With the Northstar engine changeing the oil pan gasket isn't an easy job to do. So yes $1800 to replace the gasket isn't out of line.  When I was at the dealer we always removed the engine because it was easier for us being that we liked to work on the engines. Other shops I have talked to their techs and because they are transmission speciallists they like to remove the transmission and then remove the engine oil pan gasket. The problem is that the exhaust crossover pipe is so close to the oil pan and has to be removed before the oil pan can be removed. And the only way to remove it is to eithor remove the engine and trans. together and then separate the two or remove the transmission first.

        This engine is kind of differant in that it has an engine block, an all-in-one main bearing lower section instead of individual bearing caps and then the oil pan that all bolt together to form the outside of the engine. There have been several bulletins published on engine oil leaks because to diagnose the leak propperly all the oil needs to be cleaned from the block and the engine run to see exactly where the leak(s) are. A leaking engine oil pan gasket doesn't happen as often as a leaking block to main bearing saddle joint and it would be a bad situation for the shop to do the repair only to find that they misdiagnosed where the leak was and the engine would need to come out and appart again even further to repair the leak. The other more common oil leak area is the 2 crankshaft sensors in the middle LH side of the block. My recomondition at this point would be that if you don't see any drops/puddles on the ground if the engine were idled in park for 30 minuits in your driveway or the oil level doesn't drop 1-2 quarts between oil changes would be to just drive the car and forget you were even told the oil pan gasket was leaking but continue to monitor the oil level every 2-3 gas fill-ups.

     As for putting 1 qt of 5W30 in the engine that shouldn't matter because your engine holds 7 1/2qts oil and the 1 qt wouldn't delute it much at all. The fact that the engine has now started to idle higher is probably a coincidence too. There could be carbon in the throttlebody that is causeing it to stick open at times or the idle contol motor gears could be starting to bind up or carbon build-up on the pintle will cause a higher idle.  

     Sounds like takeing your Caddy to another shop, preferably a Caddy dealer and getting these problems diagnosed would be in your best interests. I would go into the second shop and say that you had your oil changed at a quick luble place and they said there was an oil leak and you would like them to doublecheck the leak and if there is one show you where the leak is comming from. That way you will know the diagnosis was correct and the propper repair will be made. If it does turn out to be the saddle joint it would require aprox. 25 hours and maybe $400-$500 in parts. So a rough estimate of $2375 plus tax.

     Hope that answers your questions. Bill