The Northstar engine was another propaganda tool that GM is famous for. It was advertised as being able to go 50 miles without engine coolant so you could drive to safety or a repair shop. What they didn't tell you was the engine was used up and had serious damage after trying to do that. We had five of these engines that were donated to my technical college program so GM could use that as a tax write-off. They were all replaced under warranty, and they didn't even want them back to try to figure out what had gone wrong or to try to rebuild them. There are a lot of these "experimental" engines in GM's history. Instead of testing them on the proving grounds, they sell them and let the owners find out what shortcomings are common.
What the seller is saying is the coolant is disappearing. He is assuming a cylinder head gasket is leaking but there can be other, less-serious causes too. On other car brands leaking head gaskets are not uncommon, but the repair is more complicated on the Northstar engines. I've also read about the threads pulling out for the head bolts. The tightness, or "torque" on those bolts is critical and is adjusted with a special torque wrench and angle gauge. On older engines you just used that torque wrench like a normal ratchet, and tightened the bolts until it clicked. On many newer engines the bolts will never get to the desired tightness. You'll just keep on turning them until the threads peel out of the block. Instead, you use the torque wrench to adjust the bolts to a relatively low torque, then you turn them another specified amount such as 1/4 turn. Even that is not precise enough for many GM engines. They specify a number of degrees of rotation after reaching the specified torque. Some engines even use a tool that beeps when you turned the bolt far enough.
Getting back to the original story, the Northstar engine has a bad reputation and I wouldn't be in any hurry to want to own one. Before you go to look at the car, stop in at an engine machine shop and get their opinion. Very often dealers' repair shops are limited to factory-approved repair procedures, and they aren't allowed to do anything else. The aftermarket industry is real good at coming up with solutions to all kinds of problems caused by original factory parts. This is true with Ford steering and suspension parts, Chrysler electrical parts, and GM drive train parts. If you learn of a solution to leaking head gaskets on this engine, you can decide if the car is a good value after you add the selling price to the cost of repairing the engine. Also, if the coolant use is real low, you might just want to live with it and keep on buying antifreeze. I had a GM car years ago that used about a quart of coolant per month since the car was new, and I just kept on adding.
You can consider adding a small bottle of dark purple dye to the coolant, then search a few days later with a black light. The dye will show up as a bright yellow stain that you can follow back to the source. If the head gaskets are leaking, you'll typically find the dye inside the tail pipe. Coolant can leak into the engine oil too so check for the dye under the oil fill cap. That is much worse because antifreeze will melt the very soft metal of the first layer of the engine bearings. Failure of the bearings leads to a total rebuild and a lot more expense than just repairing the head gasket issue. Auto parts stores will have the correct dye for coolant, and those that rent or borrow tools will usually have a black light.
You're lucky the seller disclosed the problem. Some people will sell the car and pretend there's nothing wrong with it. Also watch out for anyone who says, "it just needs this little inexpensive thing". If that were true, they would have bought it and made the repair to increase the car's value. In reality, they know what's wrong and they're selling the car because it needs an expensive repair.
Thursday, May 28th, 2015 AT 7:49 PM