Running Hot (ugh)

[DoctorRobert]

Ok, so I just fixed the a/c on my 1986 300zx 2+2 auto. Since it's been sooo hot down here I have only been driving my car from home to work and back, nowhere else - it was too hot to enjoy! Well, when I got the air running I drove it all over town, just to enjoy it. When I got back home I parked it and heard this odd gurgling sound. I raised the hood and found the water in the reservoir was boiling over and out of the car. However, the temperature gauge in the car did not rise above it's normal position.

I have no idea where to start, to be honest. I have searched some, but come up with nothing of real use. My car has a new radiator and water pump, as installed and documented by the previous owner.

Why would the temp gauge not rise if the water is boiling? Is that faulty?

Where should I start looking to fix the overheating issue? I am about to buy a new thermostat and try that...

Oh, and there was no oil/water mixing. I checked both.

Thanks.

[AZ-ZBum]

Thermostat would be the second thing I'd replace. First would be the rad cap.

[evildky]

if the gauge isn't rising it'd have to be the cap
and to be sure you are cooling efficiently, be sure the electric fan in front of the conderser comes on when the a/c is on

[AZ-ZBum]

be sure the electric fan in front of the conderser comes on when the a/c is on

only found on turbo models.

[DoctorRobert]

Thanks guys,

I replaced the radiator cap and the thermostat.

I haven't driven it as far as I did the other day, but I did drive it today during the hottest part of the day around five miles in stop and go traffic with the a/c on. When I got home it showed no signs of running hot, so I am hoping the problem is fixed - however, I am nervous to drive it too far to really test it since it didn't indicate on the dash the other day that it was running hot. I guess we will just have to see...

[DoctorRobert]

Alright, feeling somewhat secure from driving earlier I took the car out and went to the bank this evening. When I got to the bank (around five miles away) everything was ok. When I got her home - I got out and heard the water gurgling/boiling in the resavoir. I am really crossing my fingers that the heads weren't damaged this time.

And again, the gauge in the car showed the temp being normal.

Where do I start looking now? Or should I just give up having a/c?

[Perrenial Badass]

Weirdness. Still sounds like the rad cap or something. Are you sure that the radiator isn't being blocked by debris, or has been damaged since it was replaced? Have you visually verified that it has been replaced?

The stock temp gauge is crap, it doesn't appear to give an actual temp reading; but more an indication if the motor is cold, at operating temperature, or overheating. It might be worth buying/borrowing another (aftermarket) gauge, even if only for testing. Then you can tell for sure what temp the car is running at.

The cooling system in these cars is actually quite good, it's more then capable of handling the car with AC as long as the system is in good shape. Hell, a friend of mine has a 86 2+2 auto. The headgasket blew and the transmission started slipping, he put headgasket sealer and friction modifier in it and runs around with the AC freezing him out of the car for 2 years now. A week ago the e-fans quit and the car didn't overheat, even in stop and go traffic, provided that the AC was off.

So something is awry in your cooling system. I say put in a cheap mechanical water temp gauge into the unused water port on the LIM, zip tie it to the wiper arm, and test drive it 5 miles and see what it reads if it's boiling.

[evildky]

first thing I'd do is get that temp gauge working or add an aftermarket gauge (this is a pita due to the metric holes in the manifold but I heard some of the racer stores sell the metric adaptor, otherwise you have to tap the hole in the intake which is loads of fun with it in the car

[DoctorRobert]

OK, I went and looked at some aftermarket gauges at the parts store yesterday and some of they came with several different types of adapters, but I guess they are all SAE threaded most likely? I have no real experience with adding gauges or anything... Where is the unused water port? Is it near the distributor behind the #2 spark plug?

Also, where is the sender for the stock gauge located? I had a look around for it (although I haven't had the chance to fully search or look in the FSM) but I couldn't see it. What steps would you suggest in checking/trying to fix the stock gauge?

I also might be able to borrow the stock gauge from my '85 to see if I could get it working on the dash. It confuses me about the gauge in the dash though, because it starts at the bottom or cold and slowly rises to right in the middle - just never goes any higher. I talked to the PO today and he said it always worked for him, because he ran it hot when he had it due to a bad radiator, which is why he replaced the radiator, water pump and had a head job done. There also is one racer store here in Columbus, so I can also check there to see if they have the metric adaptor. Right now I am kind of at a stand still waiting for payday as so far getting the a/c fixed and now trying to fix the overheating has sucked away all my money...

Also I plan on going ahead and buying a fan clutch for it on payday, as the PO said that was the only thing he did not replace when he was working on it.

Thanks a lot guys.

Oh, and yes I flushed the system and checked the radiator. Visually it's still "new." And when I watch it with the cap off the water seems to flow pretty perfect.

[Perrenial Badass]

Stock temp gauge reads off of the lower intake manifold, on the passenger side. On the driver's side, the port you are talking about is the one I was referring to. Though you might have the sensor for the injector cooling fan there already.

The stock gauge's sensor is like $8 at Autozone. If something goes bad with the stock gauge, it's either the sensor or a broke wire. I've never actually seen a faulty temperature gauge (the actual gauge in the dash). I'm talking about the analog gauges here, but if the digital water temp gauge is displaying I will assume that it is just as reliable.

I tapped the bolt that was plugging the hole when I put my aftermarket gauge in. I haven't tried to find an adapter.

And I would ditch the clutch fan if I was you. I seem to do an obscene amount of work on my cars, making the clutch fan go away makes working on it much easier. For $30 you can get a set of Maxima e-fans from a junkyard, they're the right size for the radiator. You can also hook up the Maxima's stock sensor to control the fan if you don't feel like having an aftermarket thermostat.

[AZ-ZBum]

I would replace the rad cap again. Get one from the dealership.

I would also NEVER buy electronic sensors from anywhere but the dealership. When I first started out, I went through 4 different oil pressure sending units from AutoZone before I went with one from the dealership. Every one of the AutoZone sensors read way wrong. It was either way too high, or way too low. The Nissan unit was just right. They generally only cost a couple bucks more, and they work so much better.

Also, check to make sure you've burped the system properly. Any air in the system will cause a false reading.

[DoctorRobert]

Ok, I got an aftermarket temp gauge going. The parts store across the street had the adapter and everything. I drove it up the street for about five - ten minutes with the a/c going and the temperature kept going it, until it reached around 240, then it seemed to even out a bit, but I had it back home by then.

I will try the radiator cap again, the local Nissan Dealership closed down, so I have to go 30 miles out for the nearest one. They are actually building a new one here, but under different owners.

The oil pressure sensor in the car now came from Autozone and doesn't work right at all. That was the previous owner...

I already have the fan clutch on hand, and I am actually about to go down and change it now, but I am seriously interested in replacing it with the Maxima's electic fan. What year Maxima do I need to rob?

By the way, this is kind of late in saying, but the engine in my car is actually out of an '87 300zx... just to say...

[DoctorRobert]

Alright, I am guessing it is something else - maybe the heads... which I really, really hope now.

It still ran hot. It runs around 240, and I never let it get hotter. It also doesn't seem to climb much above that...

However, when I turn the a/c off the temp does appear to start going back down.

[Perrenial Badass]

Possessed b**** (aforementioned troublesome 86 2+2) runs between 190 and 205 with the AC on. I live in Florida, so yours shouldn't run hotter than mine.

89-94 Maxima fans.
http://upload.wikimedia.org/wikipedia/c ... Maxima.jpg

[DoctorRobert]

Thanks for the fan info.

Yeah, I just test drove the Z some more and even with the air off it is running about 220. With the air on it goes to 240 and keeps very slowly climbing.

I am wondering if it has been running warm all the while, but since the dash temp gauge was crap I had no idea until I ran the a/c causing it to boil over...

I don't know, but this is really starting to suck...

[DoctorRobert]

Hey man,

what kind of block sealant did your friend use in his car? I think I am going to try that and see what it does. Then just start saving for a head job... or a turbo motor...

[DoctorRobert]

Not to keep replying to my own post, but I am really stumped. I have been working at it since 2. There is no water-oil mixing at all. I checked and there is no water in the exhaust either. It's not holding pressure though, I tested it and it went from 15 psi to 4 in two minutes or so.

Any thoughts? I am thinking head gasket now... but I don't know. It isn't losing any water, unless it's boiling out. Which I only let it do that once and that was because my temp gauge was screwed....

[evildky]

do not use "block sealant" ever, it's bad stuff, it sticks in all the wrong places, like your radiator, heater coer, overflow canister, valley of the block etc, and it's a real pita to dig it otu of the bblock later on

as yfor holding pressure, you said it bled down form 15 psi, you presurazed the system and it beld down to 4 psi in just a few minutes? it's leaking somewhere, look in the interior for a leak at the heater core, look at the radiator for leaks, look at the little coolant hoses going to the tb, look around the waterpump and thermostat, if oyu can't find it there pull out the spark plugs, and look and listen for signs of leakage into the cylinders

[Perrenial Badass]

I don't remember what brand the stuff was, it's kind of an experiment to see how long it lasts. About 2 years now, surprisingly. And yes, it does stick everywhere, and it also only runs the car up to 205 with all that crap in there.

Are you losing water?

Unless your rad cap is rated for less than that 15lbs of pressure you are pushing...

[DoctorRobert]

I am going to look again for leaks tomorrow, but I cannot find anything.

No, it is not losing water... I take the radiator cap off and it is always the same amount.

I didn't figure the block sealer was good, but I figured I might try it if I find it is the heads, as I really do not have an interest in having a head job done to that motor. I would rather replace it was a turbo or something.

I also thought I might try by passing the heater core and see if that makes any difference. Although I find no signs of leakage in the car... Tomorrow I will just start going over everything again. I have never found any coolant under the car either, I have checked over and over again.

[evildky]

if you are loosing pressure you are loosing coolant, you just havn't found where. the radiator cap and overflow canister alos for coolant and air to escape under pressure, it also allows for the cooling system to draw coolant back in as the system cools

if you do bypass the heatercore put a restrictor inline or you end up recirculatign hot coolant through your heads and thats a bad thing