I am looking for help as I prepare to remove and repair my Northstar engine. I have removed, repaired and installed engines including GM, Ford, Toyota, Mazda, Subaru, VW, etc, so, I think (I hope) I have the tools and the basic skills to attempt the Northstar. I want to do the best possible repair so I can look forward to many years of happy motoring with this really nice car.
I purchased a very clean '98 Deville in January of this year with a leaking water pump, and oil seeping from the crankcase somewhere. The odometer is at 122,000 mi. The owner said the car had never overheated, but had displayed a low coolant light when the water pump began to fail. Before purchase, I ran a block test following the directions (idle with cap off to operating temp). The fluid did not change color and the bulb pulled and held a vacuum on the surge tank. I bought the special tool and replaced the water pump. In a couple months of driving, the highest temperature I have seen (pulling a hill) is 212F. (I keep the digital temperature display up when I drive.) I initially overfilled the surge tank, which resulted in the coolant loss from the overflow, then read here that I should have only filled to the seam. The car has had regular maintenance at the dealer and is filled with clean Dex.
With no evidence of an external coolant leak, and with one episode of a miss on a cold start that cleared after a couple of minutes, about 800 miles after replacing the water pump, I got a low coolant message, and suspected the worst - that the head bolts had started to pull out and that I had an internal coolant leak.
To confirm my suspicions, I purchased an inspection camera from Harbor-Freight, pulled the plugs and found evidence of a coolant seep on the right (rear) bank. Here is what cylinders 1,3,5,7, and 2,4,6,8 look like:
The clean, shiny areas where coolant would collect when the engine sits would seem a pretty good indicator that coolant is seeping into all four rear cylinders. I consider this damning evidence and am looking for help in choosing the best methods and products to make this engine right.
First, is it easier to remove the engine from top or bottom? I know the FSM says from the bottom is preferred, but I'm thinking I would have to jack and block pretty high to provide the necessary clearance. I have an engine hoist but do not have a lift.
Second - Which product for thread repair? I have been researching the various fixes for the head bolts and am considering either the N*performance studs or the Huhn inserts. I like the idea of studs (works for Porsche) but am wondering about the availability of the kits. It seems a lot of folks have had to wait a long time for delivery. Another fix I came across, but have not seen discussed here, is a product called full-torque that claims a patented insert design that contracts rather than expands the surrounding aluminum as it is tightened. Costs $940 (!) for the kit, and $144 for a second set of 20 inserts. Not horrible if you are doing three or four N* jobs, but pretty pricey for one.
Third - As I want to fix the oil seep, I plan to split the crankcase. So, I am thinking I will need to replace the main bearings, and the distributor plate. Haven't decided whether or not to replace the rod bearings. Seems like maybe I might not have to do so? I will probably purchase most parts from Rockauto.com. I have had good service from them in the past. I would like to find the least expensive source for the distributor plate and for new rod bolts if I have to do the rod bearings.
If you have read this far, thanks for your patience, and thanks for any suggestions or help.