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ZBUM's 1984 Nissan 300ZX Overheating Page
In a car that is as old as the Z31 is, it isn't very uncommon to hear about overheating. If you follow these simple steps, you should fix the overheating problems with minimal time and money spent. For the last two steps, you will want to have a manual. My personal preference is the Nissan Factory Service Manual first, Haynes second, and Chiltons third.
Fill with water
Make sure you have water/antifreeze in the system and it is full.
This should be the first thing you check.
If you don't have coolant, of course you are going to have problems with overheating, DUH.
Flush the system
This isn't all that difficult. If you haven't changed coolant for a while, you really should do it.
Even a basic flush and fill is only going to set you back around $20.
If this is all that is needed, wouldn't you be a little happier having tried it first rather than replacing parts?
Check belts and hoses
Inspect the belt and hoses.
There should be no signs of leaking around any of the hoses and the belts should be okay.
If the hoses are leaking, you will want to replace them.
And while you are replacing them, I'd recommend replacing the clamps with the flat screw type clamps.
I've had the original wire clamps actually cut the hoses, because they were tightened down too tight, and/or the hoses were too old.
The water pump belt is also connected to the alternator, so if the car isn't charging, you may have also lost your waterpump.
Replace the radiator fill cap
Can you call it a radiator cap since it's not really on the radiator?
Well, either way, it's cheap and easy to replace.
What generally happens in a pressurized system with a cap that is too old is, the system heats up and the coolant expands.
The coolant flows out of the system and into the overflow container. This is normal.
The problem comes when the system cools down and contracts.
Now, the cap is supposed to bring the water back into the system from the overflow bottle.
But, if the cap is bad, there is no coolant going back into the system.
Now, if the coolant that left isn't replaced, there is less coolant and the water pump may start pumping air.
And this is bad.
Replace the thermostat
Cheaper than replacing the radiator cap, but not nearly as easy.
In order to replace this component, you have to drain the system.
You'll also have to pull the little connector hose off the thermostat housing.
Not too difficult.
Just remove the two clamps and remove the one screw holding the metal coolant tube to the block.
It's a whole lot easier if you pull the power steering belt off. It's also easier if you remove the fan.
Only have to remove 4 small nuts to get it off.
Best way to get to most of this is from under the car.
Replace the fan clutch
This is another high dollar item. I'm choosing this over the radiator because it is very simple to change.
It retails for $185.80 from Nissan. Check the links menu for cheaper places to buy it online.
Basically, the fan is supposed to be able to slip a little either way. If it doesn't slip, you have too much drag placed on the engine and that robs power.
If it slips too much, the fan will never reach the appropriate speed with the engine, and you'll never have enough fan power.
I've been told that once the car reaches operating temp, if you spin the fan (with car off), and the fan spins more than a full rotation, you probably need a new fan clutch.
Give more or less room for error depending on how hard you can spin it.
Replace/Recore the radiator
It's a toss-up between this and replacing the water pump.
Only reason I put this first is because you are less likely to break something important.
This step requires the removal of the front bumper cover.
There are 3 nuts on each side holding it to the fenders, as well as numerous screws and bolts on the top and bottom.
To get to the nuts in the fender, it's easier if the front of the car is off the ground or up on ramps.
You will need to remove at least the front of the wheel well covers to get to the nuts holding the bumper to the fenders.
The top two are hard to get to unless you have a really long extension for your socket wrench.
Once you get the bumper cover off, there are only two bolts and two hoses holding the radiator in.
But you will want to remove the raditor shroud first, and that means removing the air filter box (not hard).
Once you pull the radiator out, you have to decide if you want to recore or replace it.
That's easy. If you plan on keeping the car for a while, replace it.
If you plan on selling it within the next few years, have it recored.
Even a good recore isn't going to last nearly as long as a new one.
And replace it with a dual core if you have a single core.
Call some local radiator shops and ask for prices.
I only paid $130 for mine.
You'll be a lot happier with it.
Replace the water pump
This is going to be my last recommendation just because of the complexity of doing it.
New water pump is only about $50 from any auto parts store.
This requires removal of a lot of parts to get to it.
Basically, if you need to replace your timing belt any time soon (supposed to be done every 60k miles), might as well do it at this time.
Have to remove fan, fan shroud, belts, timing belt covers (top and bottom), harmonic balancer (go rent the removal tool from AutoZone or Checker for free), and then you can get to the water pump.
It's not very fun, and it can take you all weekend if you have never done this before.