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My 1981 280ZX has been running rough intermittently. No rhyme or reason. Sometimes it does it when cold, and some times it does it when warm. Periodically it tries to overheat. I now have a fuel smell in the coolant surge tank. Ideas?? Head gasket perhaps? Or intake/exhaust gasket? I did a combustion test and it tested to be good. Coolant pressure test also was good. Compression test is good as well. Ran a boroscope down the spark plug holes and all looked well. I am lost.
 

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There is a sensor/component on the intake manifold called a "choke stove" under the Auxiliary Air Regulator, that is warmed by coolant. I think it's the only part of the manifold that would have coolant. But I don't know how you would get fuel in the coolant tank, though. If you had a head gasket problem, you would see a piston that has been steam cleaned. Maybe it's just a very small head gasket leak, which is why you can't see anything definitive when using the boroscope/endoscope.

Aux Air Regulator;


I found this 20 part YouTube series on the Z/ZX fuel injection along with details about the components, and common issues and things to look for. It was originally filmed in VHS probably in the early 90s.

Edit: the more I think about it, the rough running sounds like the intake/exhaust gasket. But that still doesn't explain the gas smell in the coolant. They have to be separate issues.
 

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Thank you so very much! I will look into this. My gut tells me head gasket issues but I am a Nissan parts guy and in no way a tech! I appreciate your assistance.
 

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Might be helpful to have a shop do a leakdown test on the coolant system overnight. If there's a head gasket leak, that ought to find it.
 

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I will do that. Thank you for the suggestion. We should have a tester here at the shop....
 

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Tokuzumi, to start off with that block under the AAR is a thermal heater, not a choke/stove. It's not connected directly to fuel so it can't put fuel into the coolant. The only years a choke/stove was used on a z was 1971-1974. It had a metal shroud bolted to the exhaust manifold, with an accordion tube connecting that to the air cleaner.
ElmoZzz, how do you know your car is trying to overheat? Are you going by what the gauge says? Are you sure that the gauge is accurate during these periods? When it seems to be overheating, try running a temperature check at the radiator with a thermometer or even a laser thermometer. If you have access to a CO machine, stick the probe into the bottle part way and see if it registers any CO. Is your coolant fairly new? I've seen coolant get very stinky if it's old and can sometimes smell like gas. The only way that coolant and gas can get together is via a head gasket breech, and that is rare for that mix. Check your oil and see if it shows any signs of fuel contamination. Z man of Washington
 

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Discussion Starter #7
Tokuzumi, to start off with that block under the AAR is a thermal heater, not a choke/stove. It's not connected directly to fuel so it can't put fuel into the coolant. The only years a choke/stove was used on a z was 1971-1974. It had a metal shroud bolted to the exhaust manifold, with an accordion tube connecting that to the air cleaner.
ElmoZzz, how do you know your car is trying to overheat? Are you going by what the gauge says? Are you sure that the gauge is accurate during these periods? When it seems to be overheating, try running a temperature check at the radiator with a thermometer or even a laser thermometer. If you have access to a CO machine, stick the probe into the bottle part way and see if it registers any CO. Is your coolant fairly new? I've seen coolant get very stinky if it's old and can sometimes smell like gas. The only way that coolant and gas can get together is via a head gasket breech, and that is rare for that mix. Check your oil and see if it shows any signs of fuel contamination. Z man of Washington
My Coolant is brand new and clean. I have a new radiator as well. There is no longer a "fuel" smell in my coolant. But it is losing coolant internally. It is not overheating. We have checked with a laser thermometer and it reflects what the gauge shows so at least gauge is accurate.
It doesn't overheat unless heater is off and coolant level drops too low. I am afraid I need a new head gasket.I thank you all for your assistance. I am open to any and all advice. I know Mercedes Benz inside out....learning Nissan.
 

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Elmo, have you ever heard the long-standing story that Nissan developed the 240Z engine by analyzing the 6-cylinder that Mercedes used through the 50's and 60's, and creating their own version? Having had both in the family, I believe that to be true, although I'm not aware that it has ever been proven.

In any event, there are many similarities between the Mercedes 6 and the Z engine. Much of what you know will transfer, if you have ever worked on straight six Mercedes engines of that era. (But the exhaust valves aren't hollow-stemmed and filled with liquid Sodium...)
 

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Elmo, have you ever heard the long-standing story that Nissan developed the 240Z engine by analyzing the 6-cylinder that Mercedes used through the 50's and 60's, and creating their own version? Having had both in the family, I believe that to be true, although I'm not aware that it has ever been proven.

In any event, there are many similarities between the Mercedes 6 and the Z engine. Much of what you know will transfer, if you have ever worked on straight six Mercedes engines of that era. (But the exhaust valves aren't hollow-stemmed and filled with liquid Sodium...)
I did not know that! Interesting. I have worked on my Inline 6s numerous times. Double overhead cams and the intake was on the opposite side of the exhaust manifold lol. I have had everything from J Jet tronic to direct injection.
But I see similarities in the "slant"
 
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