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Discussion Starter · #1 ·
77 280Z

My car is running hot and I didn’t drive very far. I don’t see any leaks. So I‘m thinking the thermostat went bad, or the water pump. The thermostat is easy enough and not very expensive, but I don’t want to touch the pump if that’s not it.

Any way to see if it’s working? Thanks,
 

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Maybe try replacing the radiator cap.

I just put a different car back on the road after a light fender bender. It kept over heating and pushing coolant into the reservoir. I thought it might be the thermostat or possibly a leak in the radiator because the core support got pushed into it slightly. Replaced the rad and no luck.

Ordered new cap and have been good to go. I guess it just wasn’t holding the pressure

When the water pump goes bad it leaks out the hole in the bottom of it. Even when the seal or bearing go bad, it’s still “pumping” unless it’s locked up. And if it’s locked up you would probably already know it.

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If its super old and the coolant was not cared for, its possible the impeller has rusted away. They are pretty cheap and they do go bad often enough that I would consider it a wear item, replace it to be sure. Get the cast iron impeller not the stamped steel. Make sure you replace the coolant on a reg schedule, I generally replace it once a year with a 50/50 mix of the green stuff and water.
 

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Discussion Starter · #4 ·
If its super old and the coolant was not cared for, its possible the impeller has rusted away. They are pretty cheap and they do go bad often enough that I would consider it a wear item, replace it to be sure. Get the cast iron impeller not the stamped steel. Make sure you replace the coolant on a reg schedule, I generally replace it once a year with a 50/50 mix of the green stuff and water.
Thanks Dave, the coolant is good. I now think it’s the sending unit that is acting up. When the car is running, the needle is in the dead middle; but when the engine is off and the car is on, the needle swings to the 210* area. When I start the engine, the needle moseys back to the middle. I recently messed with the cooling system, by removing the hard line and replacing it with braided hoses in order for the new fuel rail to fit. The coolant hose rest right up against the temp sensor though I don’t see why that would matter. So now I wonder if the gauge is accurate when the motor is running or when it’s not. sigh
 

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Its not uncommon for the heat to rise after shut off the engine, with the pump not running the engine heat will def heat up the water that is not moving. I did not realize you were looking at it after shut down.
 

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To see if the pump is working, Start with a COLD engine and take the radiator cap off.
When it warms up, after the thermostat opens, you should see the coolant circulating past the radiator cap hole.
You may have to rev the engine a little to get it moving.
 

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You'll know it when your water pump goes, trust me. what's left of your coolant will leak out the bottom and your engine will overheat very quickly. I remember when I had one go bad on my 280z several years ago... I started hearing a noise inside the engine bay a few days prior and I couldn't figure out what it was. It was a loud 'churning' sound. Well, it ended up being the WT well on its way to total failure.

one thing you haven't mentioned is the clutch fan. is your fan running at idle? and have you tried to drive at highway speeds?
something else you can do is look at the front area of the radiator and the AC condenser. Make sure there is no leaves, sticks, plastic bags and other debris blocking the flow.

Bon
 

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Discussion Starter · #8 ·
Thanks guys, I was thinking I did a bad job burping the system, but I’ve let it idle with the cap off quite a while. Meanwhile, I still get no heat from the vents even the the heater hoses are pretty hot. I’ve been having to add coolant to the reservoir after 20 minute drives, but I see no leaks at all. The needle definitely stays to the right a little more than before, but this is my first summer with this car here in Florida, so I’m not sure if that’s normal. I’m going to mess around with it a little more, but I may have to throw in the towel and take it to a mechanic
 

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You don't need to take it in to a mechanic and get charged an armful. You can do all of this yourself.
Follow the FSM troubleshooting steps for the cooling system. And you know what? Depending on how long you've owned the car and what cooling maintenance has or has not already been done, you might just be better off just replacing everything, all at once, with quality parts. This isn't the best way, but may be in your case especially if the parts are old and worn.

(mind you, its better to learn troubleshoot each component and truly see if it has failed or not as this will help you understand how to diagnose and will also save you money in parts)

If you choose to replace everything, and if your budget can handle it, go for the following:

Radiator
Rad cap
Rad hoses (upper and lower)
Water Pump
Belts
Thermostat
Water Temp sensor switch

You don't need to buy a new clutch fan.... you can buy just the clutch assembly. But for this, don't replace it unless you know its bad. and make sure you have a full shroud.

Again, I highly recommend going through the diagnosing process first. But ultimately its up to you.

Bon
 
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where are you in florida? I am in central fl and will take a look at it if you want.
I agree with wat bon said, you may be better off just replacing the listed items, I too typically opt for diagnosis, but some things can be hard to check. The rad is a prime example, you can only get a limited visual inspection looking in the neck. If you see crud built up on the tubes that you can see, you can bet it the same or worse further down the rad.

Once burped you should not see any coolant loss, esp with a 77 that has a overflow tank. No heat thru the vents sounds like something it plugged up. there is a water **** and a heater core. You may want to confirm you are not leaking from those, check the passenger area for dampness.

Maybe I mentioned it already but you should do a exhaust gas in rad test, easy to do with a kit from napa (maybe others have it too), you just pull a sample of air from the rad after its running thru a test fluid that is blue. if it changes color you have a head or block leak.
 

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Take the radiator cap off after the thermostat has opened. If the water pump is working you'll see the coolant moving.
 

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Discussion Starter · #12 ·
where are you in florida? I am in central fl and will take a look at it if you want.
I agree with wat bon said, you may be better off just replacing the listed items, I too typically opt for diagnosis, but some things can be hard to check. The rad is a prime example, you can only get a limited visual inspection looking in the neck. If you see crud built up on the tubes that you can see, you can bet it the same or worse further down the rad.

Once burped you should not see any coolant loss, esp with a 77 that has a overflow tank. No heat thru the vents sounds like something it plugged up. there is a water **** and a heater core. You may want to confirm you are not leaking from those, check the passenger area for dampness.

Maybe I mentioned it already but you should do a exhaust gas in rad test, easy to do with a kit from napa (maybe others have it too), you just pull a sample of air from the rad after its running thru a test fluid that is blue. if it changes color you have a head or block leak.
I would take you up on that, but I might be too far. I’m in east Hillsborough. I’d pay you for your time, but right now, I think I just didn’t burp it good enough. I really hope it’s not under the dash; that’s the last place I haven’t checked. I have low vacuum and I have a smoke machine which has not shown me any leaks, so the quest continues. I’ve almost got it to where I want it to; I just want a solid, reliable daily drivable Z
 

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well if you get to a place where you cant get it worked out, I would be happy to look at it. No charge, its a hobby not a business for me.
 

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Discussion Starter · #14 ·
well if you get to a place where you cant get it worked out, I would be happy to look at it. No charge, its a hobby not a business for me.
Thanks, I just started the car since Elsa came through. Seems to be doing fine, but the needle creeps forward at idle, then goes back as I start driving. Again, I’m not sure how normal that is since this is my first summer with the car. I’m thinking I’m running lean at idle so I’ll be going round and round on that for a while.
 

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I assume the shroud is in place, if it creep a lot while sitting still it maybe the fan clutch. If it has lost its oil it may not be engaging well enough as the car gets hot and there is not airflow over the rad due to sitting still.
 

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I would also recommend you take a look in the rad, if you see crud built up on the inside of the cooling tubes, you can bet its at least that bad everywhere else. I recently replaced the rad with a new one (copper and brass, NOT alum). with that and a new fan clutch the temp is solid even on very hot days with the AC on and in traffic. Examine the plugs if you are concerned about fuel/Air mix, and make sure your timing is set correctly.
 

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Discussion Starter · #17 ·
I would also recommend you take a look in the rad, if you see crud built up on the inside of the cooling tubes, you can bet its at least that bad everywhere else. I recently replaced the rad with a new one (copper and brass, NOT alum). with that and a new fan clutch the temp is solid even on very hot days with the AC on and in traffic. Examine the plugs if you are concerned about fuel/Air mix, and make sure your timing is set correctly.
Where do you get a copper radiator around these parts?
 

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A good radiator shop can take apart, clean our and re-assemble an original Z radiator. I've had mine done twice.

My guess is that you'd need to find an original radiator to get anything but aluminum.
 

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Discussion Starter · #19 ·
Yeah, I’m pretty sure my radiator is perfectly fine. But the thought of a copper radiator seems really sexy. What I really want is a copper intake manifold, but I’ll just have to live with disappointment on that…
 
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