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Re: 2002 Nissan Pathfinder, leak cylinder head and above...
Leaks are usually attibuted to torque sequence. You must follow these exactly or you will warp parts and create leaks. Take it back apart and try it again. You may want to have your head tested to make sure it is flat and true. A head shop should be able to do this for not much $$$. Exhausts can leak because of an inferior gasket also.
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The above are valid answers but knowing what is for sure eases the mind. Questions need answers. How quickly do you lose coolant? Offers an idea how big of a leak you have. Is the exhaust white with humidity? Points to cylinder leaks with possiblity of head leaks. Does a simple radiator pressure test reveal a dramatic loss of pressure with cold coolant? With oil pan off and pressure on the coolant, you may be able to spot the source from beneath or elsewhere. A clean engine may help spot the leaks forming. Through elimination & logic thinking I'm sure you can figure which direction to go. Good luck.
Many possible causes. Leak can be when you drive, but not show on your driveway. The heater could be leaking into the passenger area, though you'd likely smell the "maple syrup" smell of anti-freeze.
It's also possible that you have a head gasket leak into the coolant, causing the overheating, and blowing some of your coolant out. Get a compression test on the cooling system, and a compression check on the cylinders.
When your Pathfinder overheated you now have a blown engine head & gasket. When it overheats you run into costly problems that make your vehicle only worth scrape. You do know that using your a/c or heater puts strain on engine and could have leak at freeze plug or plugs and slowly leaking water from radiator or water backing into overflow that has it boiling with steam coming out.
The cylinder head gasket or a cracked cylinde rhead or heads can cause this problem, a new engine is not required to fix these problems, just new gaskets for heads or rebuilt heads. Cost about $1200 worst case.
White exhaust smoke usually comes from coolant in the cylinders, indicating a cracked head or blown head gasket. The best test is to pressurize the cooling system, then remove the sparkplugs and look for moisture in the cylinders. Turning the engine over with the plugs out will spray a mist from any cylinder with coolant in it.
I just purchased a 95 Pathfinder about a month ago from a gentleman that thought he had blown the motor due to the knocking sound that was coming from the right side of the motor. Turns out that it was either some really bad gas or some carbon build up. After purchasing I took it out on the interstate and gave it a good run, thinking it'll either blow or go and the knocking stopped all together! I talked to a Nissan mechanic and he advised me that the V6 does not have lifters as it is an overhead cam engine and that the knock sensor ( which BTW is on the right side) will not cause the knocking sound. What you need to be able to distinguish is the sound of the knock. I know that may not make much sense but it the knock is light and fluctuates with the engine RPM's and does not get worse or sound louder, then it is either the exhaust leak that you know of, or possibly some carbon build up or bad gas. If the sound is hard and gets louder with the engine RPM's then you may be looing at an internal engine malfunction such as a rod or main bearing issue. The V6 engine used in that model is one of the best and most durable engines that Nissan produced, so the likely hood of it being a bearing issue is slim to none if the vehicle has been maintained and regular oil changes were a part of that maintenance. I would recommend getting some Seafoam (which you can find at just about any autoparts store for under 10.00 bucks and putting half in the engine and the other half in the tank and just let it run *( If the knocking sound is not a hard knock) It will not hurt the engine and is compatible with all engine oils including synthetic. I would drive it as well. Now, back to the exhaust leak, if the leak is not that bad and the gasket has not deteriorated then it should get quieter as the engine warms up, but if the gasket is gone or deteriorated then the sound or knocking will pretty much remain the same. I have priced the replacement of the exhaust manifold(s) and it runs about 300.00 per side, the right side being the harder of the two. My Pathfinder has 232,000 and like I said, it worked for me. I hope that it will work for you as well and I hope that this information was useful to you.
This is probably a head gasket problem and not an oil cooler problem.
The oil cooler is fairly easy to test.
Remove the cooler from the engine but do not disconnect cooling lines and then pressurize the cooling system. You can use a radiator test tool to put pressure on the cooling system and look for leaks. If it leaks, replace it.
You may also be able to bypass the oil cooler altogether if it leaks.
The head gasket is another story.
Get a 1/4" pipe to spark plug fitting and put a male air coupling fitting in it.
Then you can charge the cylinders with air from your compressor.
Make sure each cylinder that you test is at top dead center so that the valves are closed.
If air bubbles into your coolant, you found your problem.
If air leaks out your intake you have a bad intake valve
If air leaks out your exhaust you have a bad exhaust valve etc.
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