Mystery heat issue – page 4 – nissan murano forum gas and water

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1) I had one garage claim that after running it a long time combustion gasses showed up in the coolant. But these guys were total shysters, and I don’t trust them. Maybe there is combustion gasses in my coolant, maybe not. I like my mechanic but he does not have the ability to test for this. When I took it 2 hours north to a Nissan dealership, they refused to check for combustion gasses because the mechanic claimed he has never seen a bad head/gasket on this model/year car. In a month and a half, I am moving to a city that has Nissan dealerships. Several. Thank god.

3) In it’s current state it never overheats. Ever. I drove it 500 miles yesterday to and from the Twin Cities. It was solid the entire way and has been since the heat issue presented itself last November. No new symptoms. No white exhaust. No loss of coolant. Great gas mileage. No hesitation on starting. Nothing. It is a mystery.

The keys to the riddle are the garage (the shysters) that detected combustion gases in your anti-freeze, the pressurized radiator test and the pressurized radiator after running. Head gasket issue cannot produce these exact symptoms. You more then likely have a small crack (Weak head casting.) in one of your heads that goes from the exhaust valve chamber to the water jacket. That crack will be under constant positive pressure from exhaust gases, so you won’t be pulling anti-freeze back into the cylinder. This scenario fits all the tests that you’ve reported.

When your mechanic pressured the radiator over night, his results were expected because there was no anti-freeze up in the heads to be pushed into the system, and there won’t be until the system is filled and operating correctly. All he was doing was pumping air in the water jacket, which was leaking out into the exhaust passage. While doing that test, if he had used a mechanic’s stethoscope with high air pressure he "might" have been able to locate the issue, hearing air move thru the crack might cause a whistle/hiss. Sometimes there’s just too much noise to hear this.

Your only remedy is to pull both heads. You can have them fluxed, which will reveal any issues, but it would just be cheaper to put a set of rebuilt heads on and be done with it. Rebuilt cyclinder heads are about $400 each and for another $250 installation, total costs could be less then $1,000

The keys to the riddle are the garage (the shysters) that detected combustion gases in your anti-freeze, the pressurized radiator test and the pressurized radiator after running. Head gasket issue cannot produce these exact symptoms. You more then likely have a small crack (Weak head casting.) in one of your heads that goes from the exhaust valve chamber to the water jacket. That crack will be under constant positive pressure from exhaust gases, so you won’t be pulling anti-freeze back into the cylinder. This scenario fits all the tests that you’ve reported.

When your mechanic pressured the radiator over night, his results were expected because there was no anti-freeze up in the heads to be pushed into the system, and there won’t be until the system is filled and operating correctly. All he was doing was pumping air in the water jacket, which was leaking out into the exhaust passage. While doing that test, if he had used a mechanic’s stethoscope with high air pressure he "might" have been able to locate the issue, hearing air move thru the crack might cause a whistle/hiss. Sometimes there’s just too much noise to hear this.

Your only remedy is to pull both heads. You can have them fluxed, which will reveal any issues, but it would just be cheaper to put a set of rebuilt heads on and be done with it. Rebuilt cyclinder heads are about $400 each and for another $250 installation, total costs could be less then $1,000

Paul!! That sounds like the solution!! Thank you, and your son! It makes total sense. I JUST read it, so I haven’t had time to decide what I will do. I will quote a friend of mine here: "Your integrity is all you’ve got". I would never sell a car to someone without revealing "pre-existing conditions".

I forwarded the post from PaulDay to my mechanic. He said he would get back to me and never did. Honestly, I don’t blame him. He has spent countless hours trying to solve the mystery for which he has not charged me. I am fairly certain that head replacement is not the kind of work he would do, so I’m sure he is ready to move on.

I started car shopping and I decided that I would prefer to fix my car rather than buy a new car. So, my problem is, do we have a way to determine without a doubt that it is one of the heads? I’d hate to spend $1000+ for the work only to have the problem persist.

First, another test. Remove the radiator cap. Start the car and go to the exhaust pipe and take a good smell of the exhaust fumes. Different gases give off different odors. Once you have good idea of how your exhaust smells, clear your sinuses. Now go and stick your nose in the top of the radiator and see if the same odor it there. If enough exhaust is pushing thru, you might even be able to see it faintly coming out of the radiator cap opening.

Use the proper wrench to slowly turn the crankshaft a little at time. Using a mechanic’s stethoscope, stick the end into the sparkplug opening of a cylinder. As the engine is rotated by hand, that cylinder’s the exhaust valve will open. If the leak is there you should hear it as the valve opens.

That being said and coming from two families who ran service stations (My father and my wife’s father owned service stations.) it is not good practice to just replace one head on a V engine with a new/rebuilt one. Doing a repair on a head, like replacing a bad valve and seat or something minor is alright, but when you replace just one head (It’s new and tighter running.) the engine is going to run unbalanced power wise. Depending on the firing order, you could end up with rough idle that will be impossible to resolve, at the least a stumble and lack of power when you need it.