Nissan 300ZX Engine Overheating – Head Gasket Leak?

Reader Question


I was wondering if maybe you could help me out.  I recently  purchased a 1986 Nissan 300ZX non-turbo for use as a beater/daily driver.  The car has been overheating since I bought it.  So far I  have flushed the system 4 times, replaced the thermostat, radiator,  radiator cap, and a ruptured lower radiator hose.  The car is still  overheating, even after having done all of that!  I’m at wits end with this monster!  What could possibly be causing it??  The previous owner believed the car has a blown head gasket.

However, there is no transfer of fluid between oil and coolant, and no smoke coming out of the tailpipe, and other than getting hot, it runs like a champ.  I don’t know where to look next and it’s driving me nuts!


Hey there Joe,

Get a cooling system pressure test first   Then check the electric cooling fan operation or fan clutch if you have one.

Also make sure you have bled the cooling system and there are no air  bubbles in the system. Turn on the heater so the heater core fills  with coolant just to make sure there are no air pockets in the system.

Austin Davis

Reader Reply


Thank you for your prompt reply.  No wonder so many people ask for your help!  I actually fixed the problem last night.  It was definitely air in the system.  I had to reposition the thermostat with the jiggler valve up (should have read that in the shop manual!) and manually burp the system by squeezing the lower hose to get the air out of the block.  Drove it around for over 20 miles of mixed driving, and even having to stop for the world’s longest freight train and it now sits dead center on the gauge.

Thanks Again!

Posted in: Over Heating

9 Comments on "Nissan 300ZX Engine Overheating – Head Gasket Leak?"

Trackback | Comments RSS Feed

Inbound Links

  1. Bill | February 7, 2012
  1. Jim Horn says:

    My problem with replacing the water pump is that in that car it is a very labor intensive project, I don’t have the time to do it and it will cost nearly $800

    • Austin says:

      $800 seems pretty high to me, but don’t know of any other option except repair or sell it. I would find a mechanic that will let you supply the part (from your local auto parts store) and just pay him the labor. I think its a 4-5 hour repair, at 5 hours and $65 an hour labor rate that would be about $325 in labor

  2. Jim Horn says:

    Just picked up the car and got clarification. According to the mechanic, i have a leaking water pump bearing, which caused me to loose coolant, overheat the engine and burn up the head gasket. This is now allowing the engine pressure to overpower the cooling system pressure and pushing the antifreeze out faster than it was previously leaking from just the pump and I won’t get far once the engine heats up.

    Some background info, the car sat for a year while I was deployed. When I returned I checked all the fluids (except the coolant – dumb) charged the battery and it ran fine for 30mi then overheated. I stopped pretty quick, I thought, let it cool, added water and it kept going and stayed cool as long as I kept the water/antifreeze topped off. I kept this going for about a yr but in the past few months the coolant leak has gotten worse, the engine has lost some power, and i have a little white smoke in the exhaust. But I have not let it overheat again.

    • Austin says:

      If I were you I would replace the leaking water pump first, then re-pressure test the cooling system and test drive the vehicle and see what happens. I don’t see how he can be so sure the headgasket has failed at this stage of the game.

  3. Jim Horn says:

    I have a 1990, 300z (non turbo), 230k. Similar to Chad, I’m not willing to spend the money to replace the head gasket, and unfortunately I did have the pressure test done and it was confirmed to be leaking. The car still runs, but leaks cooling fluid and has lost some power….should I just keep adding fluids and driving it until it dies or should I go ahead and try something like the Steel Seal?

    I think I’m probably at that point, but don’t know anyone that’s ever tried using this (or a similar) product.

    • Austin says:

      So it leaks coolant INSIDE the engine and you have white smoke coming from the exhaust, and the engine is missing and misfiring due to coolant getting on the spark plugs? Are you SURE about that? Before I did anything on this vehicle I would get a second opinion and SECOND pressure test of the cooling system to rule out an external leak like from a water pump or heater hose or something external.

      If you are still certain about an internal coolant leak like a head gasket I highly recommend you try using K&W Engine Block Sealer like I advise on this page (not as can instructs)

      It is my opinion the best product out there for internal coolant leaks

      Keep us posted as to what happens.

  4. chad says:


    I am at a loss. I drive a 1984 300zx.

    I have changed the thermostat, radiator cap, and bypassed the heater core as it was leaking all my coolant onto the passenger side floor board. Now white smoke comes out from the passenger panel, as well as from under the hood (looks like it is coming from the engine). The coolant is leaking but cannot find the leak. There is no oil in the coolant from what i can tell, nor is there coolant in the oil. My only guess is that I have a blown head gasket. For someone who CANNOT afford the 1500-2000 dollar repair job, do you recommend a product like “Steel Seal” to temporarily get my car driving again?


    • admin says:

      Get an inexpensive cooling system pressure test FIRST, this is most likely an external leak not a head gasket leak.

Got Something to Say?