: Northstar Oil Leak

02-13-08, 10:03 PM
Hi, new user here and here is my problem - '99 Deville owned since 20K miles, now has 99K. Sold the car to a friend (after I bought a '05) and he drove it home about 1500 miles. Shortly thereafter, it started smoking and was down on oil. His local mechanic said "it blew the rear main seal" which I didn't buy! He then took it to the local Cad dealer who said (and I discussed with them) that the seal between the bottom half of the engine and the top half had started leaking (or part of the seal was missing, not sure) and it was putting oil on the crossover exhaust pipe. His solution was a Jasper rebuilt engine for $8000. I told the "friend" if he wanted I would take the car back and he had it delivered on a truck. So now - where am I? I let the car set for about two weeks and there was a large oil patch (18" diameter) on the floor. When I drove it, it did have a distinctive burning oil smell and was waffling some smoke when I raised the hood. Dead of winter, so I haven't been under the car as of yet. Cad dealer said they have seen this problem before and often twist off the bolts or strip out the threads during disassembly and so don't recommend tearing the engine down. Car ran great for the whole time I owned it and if I can get it fixed, I may keep it. Local salvage yard quoted $1600 for a Northstar with 109K on it. Is there anything I can try short of pulling the engine out to either fix or replace it assuming this is the problem? Has anyone tried JB Weld or some high temp RTV in the gasket area? Is it possible to see where the oil is coming from? Could it be something else? I read in one of the threads that tightening the bolts helped one person. Thanks for any and all help!

02-13-08, 10:20 PM
It sounds like you're talking about the halfcase gasket or the pan gasket. In either case the engine has to come out to repair it. If it is the pan, you might try pulling one bolt at a time. Spray it and the bolt hole down with Brakleen, then blow it out with compressed air. put some Permatex thread sealer on the threads and reinstall (the ones you can get at). That may slow it down. If it is the halfcase, there is no short cut.

Junk yard engine may have the same problem.

Neither of those two gaskets usually leak oil that bad. They are usually just seepage. Where exactly is the puddle? Check the oil pressure switch on the oil filter adapter as well as the oil filter adapter itself and the oil cooler lines.

02-14-08, 08:26 AM
Thanks, I will be "under" it tomorrow to see what I can see and will try your methods.

02-14-08, 07:18 PM
My rear main seal was shot and leaking a lot of oil on my '97 ETC but I think they had gone to the new design cartridge seal by '99, and I think they are pretty reliable

02-15-08, 07:54 PM
Well, I spent the morning under the car, cleaned the whole area and then couldn't find a leak. Got it out on the road and then it really started. When I went back under, it appears the leak was in the area of the flywheel viewable slot. There were no leaks at the filter adapter area. It leaked enough to put oil back to at least the catylitic converter and drip into a pool of about 3-4 diameter. Appears the oil is mainly concentrated around the crossover pipe - could be the rear seal or the crankcase split. Don't think it is the oil pan. Any suggestions? Are there any knowledgeable Northstar mechanics around the Kansas City area? I hate to be the one to experiment on by most shops. Cost to pull the engine and put in rear seal or crankcase gaskets?

02-18-08, 06:07 PM
i can tell u that before major was bought out by conklin-fangman they had some of the best N* techs in the city but since then i cannot tell you as i haven't used them. i think what gm did to the major family was bs but that is another story. you might try superior chevrolet/cadillac and ask for a fellow by the name of Bill Holland. He's as good as they come. i'll be anxious as i have a leak similar to what you are experiencing on my 95 concours.

02-19-08, 02:24 PM
Sounds the same as my rear main seal leak - do the oil pan at the same time

03-10-08, 06:53 PM
Got it fixed! Found a shop in Claycomo, MO that had done this before, removed the engine and installed the block gasket, new rear seal and pan gasket all for $1200 with a 6 month/6000 mile guarantee. Have about 400 miles on it so far and it's doing fine.

03-10-08, 07:01 PM
$1,200 sounds fair to me... no, wait...that sounds like it's MORE than fair.

If an engine oil leak does come up again, either now or in the future, Ranger is right that the oil filter adapter o-rings, the oil cooler lines, and the oil pressure switch all are also notorious for leaking - maybe also the oil level sensor. These are all pretty easy to fix, with the engine IN the car

03-10-08, 07:26 PM
Claycomo, MO is going to become famous. So is the repair shop.

06-07-08, 08:15 AM
Sorry to bring up this thread , but does anyone have the name of the shop in claycomo ? Would be nice to know for all of Kansas City Cadillac lovers . Been reading the Service Manual an looking at doing it my self (ns300l , head gaskets , oil pan gasket), but if i could get it done that cheap ($1200) , id just pay someone to do it .

09-01-09, 11:38 PM
Has the name of the shop that does the rear seal repair in Claycomo, MO ever been posted?

Jeff linscott
03-15-13, 10:20 PM
Dgkirk im in kc too with a leaking dts. Can you share the info on the shop in claycomo? Did you have a positive experience with them.

03-15-13, 10:48 PM
Don't hold your breath. Dgkirk hasn't been back here since 03-18-08.