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Problems with a n* leak down test


blk987

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Pep Boys diagnosed the N* with a bad head gasket. The car has set for about a month because Ive been too busy but I was told by someone on this site to perform a leak down test and so i did. I purchased a U.S. General tester, removed the plug for the cylinder I was testing, set the pressure regulator on the tool, connected the hoses and all 8 cylinders were within the proper parameters. I did hear slight leaking out of the oil filler cap which I believe is normal due to ring seals not being 100% sealed but can anyone tell me if this diagnosis of mine is saying the head is good or did I do something wrong.

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yes, I removed the passenger wheel and with a breaker bar i rotated the motor on each test of each cylinder to make sure i was on the compression stroke and all valves closed.

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This is copied from a site on Northstar headgasket diagnostics, it states that your car can pass tests and still have a blown gasket. It maybe fine with the engine cold but as it heats up, things expand and what didn't leak cold is leaking now.

Here are the most common signs of head gasket failure on a Northstar:

- Overheating

- High pressure build-up in the coolant surge (fill) tank, that remains when the engine cools off

- Heavy white smoke from the tail pipes (condensation & water vapor is completely normal for any car)

- Coolant smell from the exhaust

- Engine temperature spikes during acceleration or climbing steep grades

- Coolant in the oil (this will turn the oil a milky white or light brown)

- Sudden severe oil leak coming from rear main seal area

The best test there is, make sure you have adequate coolant, and get the car on the highway and do a few quick acceleration runs. Get the car quickly up to 70 MPH (120km/h) and slow back down to around 30 MPH (50km/h). Only do this where it is legal! Repeat this process, monitoring coolant temperature. If you have the guage, the temperature should never normally run past the 5/8 mark. If you have the digital read-out, the temp should never hit the 240 degree F mark. If the temp keeps climbing to the point where it tells you "A/C off for engine protection" or "Engine hot - idle engine", or your guage passes the 3/4 mark, pull over immediately, let the car idle for a minute and shut it off. Let it cool down a bit, top off your coolant and make your way back home. At this point, keep your foot out of the gas as much as possible. Your head gaskets are blown / head bolts pulled.

Many repair shops are capable of diagnosing a bad head gasket but not all of them know how to deal with the Northstar. Did you know a Northstar can pass all the usual pressure tests, and still have a bad head gasket? This is due to the troublesome head bolts. This is why we recommend the method above for determining the state of your gaskets.

So what to do now? Well, for starters, DON'T use any type of quick-fix in a bottle. I'm sure you've read about miracle sealants that are designed for the Northstar and a bunch of other stuff on the market. All this will do is clog up the coolant passages. The guy who does your head gaskets won't appreciate the mess that will need to be cleaned out once he tears your engine down, and you won't like replacing your radiator and heater core. Of course it is never a bad idea replacing your water pump, checking the belt and tensioner, cooling fan operation (they do fail sometimes) and if in doubt, a new radiator. But a lot of the time, nothing but the head gaskets will need to be done.

If you have coolant in your oil, stop driving, period. Don't run the car at all. This can severely damage your engine. If you must move the car, make sure the oil is at the proper level and not too high.

If you are seeing moderate to heavy white smoke, don't try to start the car again- get to where you need to go and shut the car off. Especially if you have a 2000 or newer model- the engines are not as strong and have been snapping/bending connecting rods when coolant gets in the cyinders.

If you are getting exhaust gasses in the coolant (pressure in the plastic coolant tank), it is OK to drive the car providing you can keep your speed down to about 50MPH (80km/h) and you keep checking/topping off your coolant. No more sudden acceleration or passing, and stay away from long hills. Just don't overheat the engine. Regardless of what the owner's manual says, it's not OK to continue to drive without coolant- these cars have a limp-mode but it is not very effective. If you have overheated your engine, the oil-life-monitor will return to 0%. You should change your oil after overheating the engine

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Wow thank you for the response, I have all of these symptoms except for the white smoke, and strangely the oil is coming from somewhere between the block and the firewall suddenly even without driving the car the oil leak is getting worse. I was not aware of the problem while they were being tested under compression so this could explain why on the leak down test tonight everything is fine.

I think I might purchase the test for the coolant resivoir where the dye changes color when exhaust fumes are present just to confirm my problem before I dive into these heads. Thanks again for the response this was some great info.

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