280Z Temp Gauge Range of Motion

[Indey]

I have a 76' 280Z, and from what I remember, my cars temperature typically used to sit at the E on the Temp gauge. I know it's been hot as of late where I live, however I feel as though it's been running a bit hot as of late. Depending on how I'm driving the gauge will climb to closer to the end of the M on the gauge. For example if I'm driving it somewhat "hard" on the streets it will creep up, and if I'm cruising on the freeway it will go up as well. Being that my gauge used to (again from my recollection) sit relatively steady at the E. I thought my car was overheating. Naturally I started looking for causes, I ended up flushing out the radiator, replacing the thermostat, and replacing the water pump. None of these things had been done since I've owned the car, so it seemed like a better time than not, to replace them. However it's still running within the same range as per the gauge's reading. I was wondering if anyone else had their Z's running within the same temperature range? Or should I genuinely be concerned?

[OldAndyAndTheSea]

Have you confirmed the actual temperature of the engine once warmed up?

 

No need wasting more money on parts if you don't have to.

 

 

Throw a thermometer in the radiator and take the reading. (also while you are there make sure the thermostat is opening and moving coolant)

 

Somewhere in the neighborhood of 180 degrees is what you're looking for.

 

Those gauges are known for giving false readings, especially considering its nearly 40 years old.

[Tony D]

The calculation of needle position and it's "correctness" is a function of actual temperature, & thermostat.

Top reading - bottom reading=spanSpan/100= percentage of relative movement (*PRM)

PRM+Bottom Reading= indicated temperature

Do the math and you will know what your gauge is reading. Nothing near E unless you're in Minot in February warming up...

[Indey]

Have you confirmed the actual temperature of the engine once warmed up?

 

No need wasting more money on parts if you don't have to.

 

 

Throw a thermometer in the radiator and take the reading. (also while you are there make sure the thermostat is opening and moving coolant)

 

Somewhere in the neighborhood of 180 degrees is what you're looking for.

 

Those gauges are known for giving false readings, especially considering its nearly 40 years old.

 

Temperature has not been confirmed at the radiator, however I currently have nothing to check that with, i'll run by my friends shop tomorrow and see what I can get figured out for that. I did make sure the new thermostat is opening and flowing coolant however, so that's good to go.

 

The midway point on the gauge should be around 185 degrees, since the low spectrum is 120 and high is 250. To which I know the thermostat is a 180 degree one currently. (The old one was a 170 apparently). I know that on a 180 degree thermostat it shouldn't be fully open till around 190-ish or so, but the gauge just seems a bit high... regardless once I get the actual temp checked I'll know more along the lines of where it actually is. Thank you!

 

 

The calculation of needle position and it's "correctness" is a function of actual temperature, & thermostat.

Top reading - bottom reading=spanSpan/100= percentage of relative movement (*PRM)

PRM+Bottom Reading= indicated temperature

Do the math and you will know what your gauge is reading. Nothing near E unless you're in Minot in February warming up...

 

I'm not trying to be stupid by any means, and I appreciate the help, this just went over my head though honestly. Though as said I appreciate the help

[NewZed]

I went through a similar period of worry this summer and discovered (I think) a few odd things. It could be an overactive imagination but they seemed real at the time.

 

If you have an aftermarket thermostat with the smaller offset hole, clocking the hole toward the sensors (frontward) seems to drop the reading a small amount. I took the thermostat out to replace it but found that it actually opened farther than the new one I was going to put in. So I put it back but with the hole forward. I would guess that there might have been lower flow past the sensors with it on the back side.

 

I changed my oil pressure sender to one that actually reads correctly, about the same as the mechanical one mounted at the engine, and my temperature reading dropped again, about a quarter letter. They use the same voltage regulator in the gauge, so I would guess that altered current flow on one side affected the reading on the other side. The old one read zero at ~20 psi at idle, the new one reads correctly.

 

I still ended up replacing the radiator with a Murray brand radiator from O'Reilly which made the reading stable and even lower. The other radiator, which looked aftermarket and old, just couldn't keep up on the hot days, I assume that it was clogged. It leaked a little bit anyway so replacing it was an easy decision. For anyone thinking Murray, the radiator core itself seems of good quality, but the shroud mounting holes were too small and misplaced for the shroud to fit right, and only three of the four main mounting holes were in the correct spot. Poor quality but it can be made to work.

 

Just some weird things I saw when I was trying to get my cooling under control. I have a fan shroud on my 76, which probably helps.

 

By the way, Courtesy Nissan has stock made in Japan thermostats available that have the bigger hole. I got one after all of the stuff described above so it's still on the shelf for future use.

Edited September 16, 2012 by NewZed

[Indey]

So just to follow up on this...

I took the car for a drive and it heats up till about the end of the M and then stays there on the gauge. As seen here.

 

I feel that this is still significantly too high, since as said it used to easily run cooler. Regardless when I arrived home to check it, I found this..

It would appear as though something hit the radiator at some point.. I know the leak itself is not massive by any means, however I feel like it's blocked those veins. Which I would guess to be about...1/5 to 1/6th of the radiator.

 

I also ran into very minor seeping under the aux. air regulator.

 

Not only that but I noticed the coolant line that's supposed to go to the heater core, and then back into the block, that's looped, is pinched.

 

I suppose it seems like it's time for a new radiator. As per the aux. air regulator section, I've looked through the EFI bible and my manual for the car and I can't seem to find what these lines are exactly for, I would assume they heat the aux. air regulator to let it know when to close the valve and not let air through? Can someone confirm that possibly?

 

As per the looped line.. I'm going to get a longer line for now and just let the loop not pinch.. I tried to move the inlet since it's threaded, however it's on there quite good, does anyone possibly have some tips for rotating that guy to try and get it to aim towards the coolant lines at the front?

[Tony D]

250-120= 130

130/100= 1.3

 

You're at about 60% of span there, agreed?

 

SO:

 

60X1.3= 78

78+120= 198]

 

SEE HOW IT WORKS NOW?

 

[Xnke]

Looping that heater line is a no-no, there is quite a lot of data on the site to support NOT doing that. Cap those lines off if you are not using them for heating the interior of the car. By looping that line, you are letting hot water bypass the radiator.

 

That's a handy bit of advice there, Tony! Now when I fix my gauges I'll know what they really mean! Thanks to NewZed, I may have to get a new oil pressure sending unit and see if that fixes my temp gauge, too...my oil pressure gauge might as well be an idiot light, and the temp gauge doesn't read at all...but if I short the temp gauge sending unit line to ground it will read full-scale, same with the oil pressure.

[Indey]

250-120= 130

130/100= 1.3

 

You're at about 60% of span there, agreed?

 

SO:

 

60X1.3= 78

78+120= 198]

 

SEE HOW IT WORKS NOW?

 

 

Yes sir, that helped significantly! I'm actually going to write that down for later reference.

 

Looping that heater line is a no-no, there is quite a lot of data on the site to support NOT doing that. Cap those lines off if you are not using them for heating the interior of the car. By looping that line, you are letting hot water bypass the radiator.

 

That's a handy bit of advice there, Tony! Now when I fix my gauges I'll know what they really mean! Thanks to NewZed, I may have to get a new oil pressure sending unit and see if that fixes my temp gauge, too...my oil pressure gauge might as well be an idiot light, and the temp gauge doesn't read at all...but if I short the temp gauge sending unit line to ground it will read full-scale, same with the oil pressure.

 

I've read one particular thread about that right now actually, and interestingly it said, since the line was kinked I got away with a bit of dumb luck. So I'll take the dumb luck that I can get for this exact second. Regardless Tony D also mentioned to not just cap the lines off, as you need some sort of recirculation as well....Though I'm slightly confused by this as it was stated here.

 

You CAN block those passages though, AS LONG AS YOU KEEP A RECIRCULATION LINE IN THE SYSTEM! You need SOME way to recirculate coolant to the inlet of the pump while the enigne is warming up and the thermostat is cold. Otherwise you can cavitate the pump something fierce, and cause all sorts of uneven heating.

 

As said I'm confused by this, as what would "cavitate the pump" mean?

[NewZed]

Thanks to NewZed, I may have to get a new oil pressure sending unit and see if that fixes my temp gauge, too...my oil pressure gauge might as well be an idiot light, and the temp gauge doesn't read at all...but if I short the temp gauge sending unit line to ground it will read full-scale, same with the oil pressure.

 

No guarantees. And my TEMP reading went down with a higher oil pressure reading, not up. If you're not getting a TEMP reading at all, it's probably your temperature sensor, up front. Have you measured resistance through the sensor? It should be between zero and infinity but not either.