Hi all, I have an 82 280zx that is overheating, and I'm not sure why, I was wondering if anyone could help me out. I've already replaced the radiator, radiator hoses, thermostat, and water pump, and I'm not sure what else could be wrong... I don't see any visible leaks, and the radiator seems to be holding Coolant fine, but after about 15 minutes the temp gauge will go all the way up to 270 degrees...

Anyone have any ideas what else could be wrong?

Welcome aboard!

Have you replaced or tested the temp sensor? Did you replace the radiator cap? Have you bled all the air out of the cooling system?

Have you measured radiator coolant temp? Measure thermostat opening temp in a pot of water on the stove.

Timing set correctly? Have you tested the temp gauge to make sure it's accurate (via multimeter)?

Once all that's been verified, here's more: www2.zhome.com:81/ZCMnL/tech/280ZXCool.html

Let us know what you find, Alan!

I actually haven't done any of that. I actually have very little knowledge of working on cars short of replacing obvious physical parts. When I bought the car two years ago, it was overheating as I drove it home, and it pretty much just sat there for a good 2 years as I saved up and replaced the water pump, radiator, hoses, and thermostat over time, I just bought new tires and replaced the headlight, and it started up just fine, so I went and registered it yesterday (after 7 and a half hours of waiting >_<) I drove it around for a bit, and it passed smog, and as I was driving it home I noticed the temp rising some on my gauge, so I stopped into a little oil change shop and just asked them to top off my fluids and check the coolant levels, and after that it seemed to be fine for the rest of the day, I drove it to work, and back without any issues.

And then tonight, I started it up, started driving to work and the temp went all the way up to 270 within a couple of minutes.

I will attempt to bleed the air out of the system tomorrow, and replace the radiator cap.

How would I go about checking the temp sensor? And could you go a little more detail into checking the thermostat opening temp?

As far as the timing, I'm not sure, but it was idling fine, and didnt have any misfires/backfires as I was driving it around.

Thanks for the info, and the link, I'll do some more research and try out some of this when I have time and get back to you.

Since it cooled fine once and then overheated quickly on the next cold start, I would suspect a sticking thermostat. Unfortunately, pulling the thermostat may require a new gasket.

I see from your first post that you have already replaced the thermostat. If you want to eliminate it as a potential culprit, remove it. They function to allow a rapid warm-up of the engine and serve no function once the engine is warm. Just remember to re-install one before next winter.

Alright, so I got home those morning to do the testing, I bought a new radiator cap, and popped my hood, pulled the cap and noticed the radiator had no fluid left in it at all. I went and grabbed some water and started to refill it, and noticed a pretty bad leak on the passenger side of my engine block. which wasn't there yesterday.

I'm not sure but could this be something like a gasket? I'm hoping I didn't crack something...

Here's a picture.
http://i.cubeupload.com/8oDmCh.jpg

After doing a little research I realized it was one of my freeze plugs leaking. I'm not sure if it was just a combination of heat and corrosion or if there's an underlying problem (I'm hoping not the headgasket or something, but there's no oil leakage yet, and the car wasn't blowing white smoke from the exhaust)
I've purchased a new freeze plug and some sealant and I'm going to try to replace that probably tomorrow after work. Hopefully then I can do some more of the testing if that holds.

If you find corrosion, put replacing the other freeze plugs on your to do list. When one fails from corrosion, the others are not far behind.

Well, this is proving to be much more difficult than I anticipated. I've been trying all morning to remove that freeze plug using a wide dull flathead screwdriver and a hammer, but it just keeps punching holes through it without the plug budging at all, and due to the angle I can't fit pliers/vice grips/anything really down there to pry it out through the new holes. Anyone have any ideas? I don't have the experience or the tools to pull the engine block out (or the money to have someone else do it)

I've since cut the heater core inlet hose and removed it planning to bypass it altogether, and moved some of the other things away slightly, but it's still an awkward angle and I'm not really gaining any progress.

Thanks for any advice.
http://i.imgur.com/GsFbGxC.jpg

Quoting Tom Monroe from his book, "How to rebuild your Nissan & Datsun OHC Engine" page 41:

"Although core plugs appear difficult to remove, the job is relatively easy. Using a punch and hammer, drive against the edge of the plug, drivingit into the block. This rotates the plug in its bore, making it easy to grab with pliers. Now lever the plug from the block using Channel-lock or Vice-Grip pliers"

In theory yes, however my datsun was sitting for ~20 years and the plug was badly corroded, I watched several videos of people removing freeze plugs using that method before trying it myself, and when I tried using the punch and hammer method, it just punched holes into the plug without it rotating at all, and I actually used very little force. I then tried using a slide hammer and puller that I rented from autozone, but instead of the puller gripping the edges of the hole in the plug, the plug just collapsed, and now there isn't really a plug at all, just the outer ring, that still hasn't budged, I'm at a loss on how to remove it now.

Here's what it looks like currently.
http://i.imgur.com/X2e4ONE.jpg

You were supposed to hammer on the outer ring, not the flat.

I did hammer the outer ring, the flat part didn't end up like that until I tried the slide hammer with the punch/puller. Regardless, I'm going to keep going at it with a dremel as it seems like pretty much the only way to get it out now. Thanks for your help though.

When removing freeze plugs i knock them in then grab the lip with vice grips or similar and pull out. When Installing new ones I find a socket that is the same approximate diameter as the inside cup the the plug then coat with sealant and tap in. I do not try driving against the ring, taping with a large socket in the center allows the sides to flex a bit as it slides in.

I know this may be a little dumb to add in here but just as curiosity is the fan shroud still on the car? I have been informed about those causing issues if they are removed from the z cas. And also if you do replace the thermostat with a Nissan part it is better quality over the aftermarket.