A real working temperature gauge

Valhalla · 2 July 2013

Reading through some threads and I came across something that everyone talks about yet I'm not aware of anyone fixing. It's the coolant temprature guage in our cars. Eveyone claims that it doesn't read correctly. If it does start to rise past normal it's probably too late.

So is anyone aware of why are gauges are so poor at reading the real temprature of the coolant? Is it the guage itself or the sending unit? Is there an upgrade or replacement that will make it work like it's supposed to? I've already had the dreaded blown gasket due to the headbolts pulling out of the block. Believe me, it was no fun paying that bill to have the motor pulled, replacing the headbolts with timeserts and then putting it all back together. Could I have caught it earlier if I had a temprature gauge that worked? Who knows but I probably would have stood a better chance.

So, does anyone out there have a fix that they would like to share with the Prime Nation?

SuperSonic · 3 July 2013

I think mine works fine. Just hook your obd up and see what your coolant registers at in relation to the gauge. I think if you have a 91 and it fails, what can you expect after 20 some years. Though if it did fail, it would be the sending unit. They just get worn. ....btw, haven't seen you in a while

bngl3rt · 3 July 2013

The first time I saw it go above normal, it went from normal straight to red. Head gasket = blown.

With a new radiator, aftermarket head gasket and aftermarket head studs, it only moves when I'm driving really really hard in really really hot weather. I'm told under 3/4 is fine, after that the ECU actually starts to reduce power (disable VTEC etc) to keep you from getting it all the way up.

tbnsxt · 3 July 2013

If you really dont like the gauge than just get the aem unit. it places a new sensor directly in the path of the coolant and registers an instantaneous reading instead of being dampened like the factory gauge.

Ric · 3 July 2013

At what temp is it considered too hot?

winreboot · 3 July 2013

What is the recommended location for aftermarket coolant temp sensor?

tbnsxt · 3 July 2013

your coolant temp should be around 190 deg.

Honcho · 3 July 2013

Ric said:
At what temp is it considered too hot?

The ticks on the gauge are:

---- H = 270 F
---- = 253 F
---- = 236 F
---- = 219 F
---- = 202 F
---- = 185 F
---- = 167 F
---- = 150 F
---- C = 133 F

The NSX normally runs at one tick below the middle, which is 185 F. Like Ben said, if the needle suddenly goes straight to "H", then it could be a blown head gasket. It could also be a gauge failure or a hot air bubble in the coolant passing over the sensor. In my case at the track last year, it was the last one, thankfully.

RYU · 3 July 2013

Valhalla - You're on the AEM EMS and NA2 OBD2 3.2L. It's different than my 3.0L OBD1 on an HKS F-Con iS. The EMS should be controlling everything even the fan turn-on temp threshold but I don't know if your OBD2 port still works or not. If it does you can get a Bluetooth OBD2 reader (typically around $20 on ebay) that interfaces with your smart phone thru the Torque App (free for lite version, ~$5 for full). It's enough to be able to see what your OEM ECT sensor is sending to your EMS. I use the [ELM327 Bluetooth Interface OBD2 II Car Diagnostic Auto Scanner] on my pickup when I go off-roading swap into my BRZ for occassional track days. You can probably get an AEM multi-gauge to read from the OEM OBD2 ECU coolant temp sensor as well.

I don't like to run my NSX hotter than 90C or 195F (read from the OEM sensor) because everything else at that point just gets really hot like oil temps but especially IAT (on my car). From a headgasket perspective you should be ok going past 210-220F, normal boiling point is ~212F in an unpressurized system (check your reservoir cap btw) but it's still past my own personal comfort zone. Some water wetter helps too.

Ric - What is considered too hot? Here's my analysis fwiw. Honda designed the OEM radiator fan low relay to turn on when the ECT reaches about 84degC or 183.2degF for the first time and then deactivates the relay once it gets below 78degC or 172.4degF. One can extrapolate that this "normal" operating temperature for our engines (3.0L vs. 3.2L? I don't know..). The high relay for the fan will not turn on until the engine is 90degC or 194degF. This is also when the engine bay cooling fan turned on in the older NSXs. Most never see the engine bay fan turn on because most never experience their cars going over 90C or when they do they don't notice it or it cools down by the time they check it. This is why when my car gets into 90C I start to pull back on my driving... It's a personal threshold i've set for myself which is probably too conservative for some people. There is a lot of hard driving you can do even in hot ambient temps where your car can still stay below 90C if you have a good cooling system. In my own personal experience monitoring via the OEM dash needle gauge is useless because it's too hard to monitor +/- 20C swings with it.

Paul, Just curious, is that scaling documented in the manual somewhere? Reason I ask is perhaps my dash gauge is faulty. I've reached 95C on the OEM sensor and it was still below the halfway mark. A few years ago before I started monitoring temps digitally I've accidently reached past the 3rd mark from the top (i.e. 236F in your scale). This was on the track where I noticed the needle go past halfway and thought it was fine then halfway down the track later it was already 3/4ths of the way up. It goes up very quickly.

Valhalla · 3 July 2013

RYU said:
Valhalla - You're on the AEM EMS and NA2 OBD2 3.2L. It's different than my 3.0L OBD1 on an HKS F-Con iS. The EMS should be controlling everything even the fan turn-on temp threshold but I don't know if your OBD2 port still works or not. If it does you can get a Bluetooth OBD2 reader (typically around $20 on ebay) that interfaces with your smart phone thru the Torque App (free for lite version, ~$5 for full). It's enough to be able to see what your OEM ECT sensor is sending to your EMS. I use the [ELM327 Bluetooth Interface OBD2 II Car Diagnostic Auto Scanner] on my pickup when I go off-roading swap into my BRZ for occassional track days. You can probably get an AEM multi-gauge to read from the OEM OBD2 ECU coolant temp sensor as well.

I don't like to run my NSX hotter than 90C or 195F (read from the OEM sensor) because everything else at that point just gets really hot like oil temps but especially IAT (on my car). From a headgasket perspective you should be ok going past 210-220F, normal boiling point is ~212F in an unpressurized system (check your reservoir cap btw) but it's still past my own personal comfort zone. Some water wetter helps too.

Yes this is my setup and I also have the Torque app with a bluetooth OBD2 reader and I trust that a lot more than the guage on my dash. I purchased a new coolant tank and cap so I am good here.

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Paul, Just curious, is that scaling documented in the manual somewhere? Reason I ask is perhaps my dash gauge is faulty. I've reached 95C on the OEM sensor and it was still below the halfway mark. A few years ago before I started monitoring temps digitally I've accidently reached past the 3rd mark from the top (i.e. 236F in your scale). This was on the track where I noticed the needle go past halfway and thought it was fine then halfway down the track later it was already 3/4ths of the way up. It goes up very quickly.

This is exactly what I'm talking about. The guage is not accurate in it's readings. I want to keep the OEM guage right where it is. I just want it to perform as well as the rest of the car. No one has a better solution to making this guage read correctly? Thaks all for chiming in. Perhaps someone will be able to come up with an adequate fix.

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SuperSonic said:
I think mine works fine. Just hook your obd up and see what your coolant registers at in relation to the gauge. I think if you have a 91 and it fails, what can you expect after 20 some years. Though if it did fail, it would be the sending unit. They just get worn. ....btw, haven't seen you in a while

I'm alive and kicking but working my fool ass off. Looking for a drive soon so I'll keep you posted.

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tbnsxt said:
If you really dont like the gauge than just get the aem unit. it places a new sensor directly in the path of the coolant and registers an instantaneous reading instead of being dampened like the factory gauge.

How do we un-dampen the guage? That is the question. A different sending unit? I want to retain the factory gauge in the dash.

RYU · 3 July 2013

Valhalla, I personally don't think there's anything wrong with the gauge or the sending unit to where one would need to alter it. For most driving purposes a "dampened" gauge probably wards off false alarms and keeps most drivers from getting a heart attack. I get it from a Honda Engineer's perspective. It's just so damn small and the ticks are so close together that it doesn't provide enough detail for some anal owners like ourselves. Your EMS ECT tables are still reading correctly off the OEM sensor so you really don't want to alter that signal. I recommend you get an external sensor for your ZT-2 that can be placed easily in-line one of the coolant hoses or for spirited drives you can use the Torque Bluetooth solution like I suggested?

Valhalla · 3 July 2013

Regan - you calling me anal? That is like the pot calling the kettle "black"!

I understand that the EMS II will take the proper signals and process as to temprature from the OEM sensor but it is dampened, wouldn't that alter what the EMS would really like to know? The EMS can only contol what information it is getting fed. And if there is a lag or bad intel going in.....

RYU · 3 July 2013

haha! I thought I said WE were both anal.

I've noticed the OEM temp sending unit is a little slow. I can't quantify what "slow" means but in the case of the OEM ECU it's expecting the slower data refresh rate. Will you benefit from a faster acting sensor for your AEM EMS? That's a question for someone like Mitch or perhaps DDozier.

I think there are two different issues here though.
1. Your concern with the ability to discern the actual temps via the OEM dash gauge
2. The refresh rate of the OEM ECT sending unit to your EMS

Valhalla · 3 July 2013

This is indeed correct, two seperate but connected issues. Calling Dave Dozier, anybody seen Dave lately?

Ric · 3 July 2013

When I still had my aem ems serie 2 installed last year on a hot Palomar mountain group drive, my temp on the digital display read as high as 230F going up the mountain mostly in third and fourth gear. The oem needle went slightly past 3/4 on the gauge, but never hit the red mark, yet. That was when the group reached the top and took a break before heading down. After that thing went back to normal heading down and driving home.

bngl3rt · 4 July 2013

I think I will try to squeeze in some AEM water temp and oil temp gauges underneath my single-DIN when I pop that in.

E-Nough Logic · 4 July 2013

When I log water temps from my AEM EMS via my digital display the Coolant temps jump +/- 5 degrees 5 to 10 times a second. Oddly enough I think the sensor is fairly responsive but the gauge itself is rather slow to respond to the sensor. Might wire up another sensor and map it against the stock sensor.

Honcho · 4 July 2013

RYU said:
Paul, Just curious, is that scaling documented in the manual somewhere? Reason I ask is perhaps my dash gauge is faulty. I've reached 95C on the OEM sensor and it was still below the halfway mark. A few years ago before I started monitoring temps digitally I've accidently reached past the 3rd mark from the top (i.e. 236F in your scale). This was on the track where I noticed the needle go past halfway and thought it was fine then halfway down the track later it was already 3/4ths of the way up. It goes up very quickly.

It's not laid out anywhere in a chart or anything, but using the values throughout the service manual and a calculator, I was able to figure it out.

greenberet · 4 July 2013

I have a VDO temperature sensor mounted in the big coolant hose in the engine compartment through which the coolant flows out of the engine. I wanted to check how hot the coolant gets with my front undertray mounted and since it never got above like 95°C, if I remember correctly, I unplugged the sensor again years ago.

In my instrument cluster, the normal position of the coolant temperature needle is a bit below the halfway mark. From what I remember, the OEM gauge reaches that level once the VDO gauge shows about 80°C. However, the coolant temperature keeps climbing according the VDO gauge until the normal operating temperature of about 90°C is reached. Flooring the throttle for longer periods can get the coolant a few degrees hotter still. Through all of that, the OEM gauge doesn’t budge.

It seems to me that there is a range of coolant temperatures in which the OEM gauge shows the same reading. So it’s more like an idiot light. If Honda had intended it to show the real temperature, they would have put a scale on the face, I figure, like on the rest of the gauges.

In my BMW it’s the same. I can call up the coolant temperature in a submenu of the onboard computer. The analog gauge in the instrument cluster always shows the same reading as long as the coolant temperature according to the digital gauge is within a certain range.

I wish the OEM coolant temperature gauge in my NSX's instrument cluster showed the actual temperature but based on what I’ve seen, I don’t think it does.

Valhalla · 5 July 2013

OK so everyone seems to agree that the sending unit responds pretty quickly and Honda intended us to feel safe and secure because the gauge isn't really a gauge but an idiot light that goes on when it's too late. Like other projects I've taken on with this car, that just doesn't work for me.

In my Zietronix instrumentation I have a warning buzzer that goes off whenever a certain engine parameter presents itself. I currently have it set for over boost (can anyone ever have too much boost?) and for a shift points. It's audible as well as a red flashing light that I have in the center AC vents. Could a similar device be made/attached/amended that would do the same thing once temperatures reached a certain point? If I'm hotfooting it up a canyon, I don't want to be fixated at staring at my coolant temperature.
View attachment 102812 View attachment 102814
The first picture if of my current gauge setup and the second is of the visual warning light activated. Believe me, you will hear the audio even with a helmet on. Can't we do this Prime? Just adding the pictures so you can see the warning light and placement.

TURBO2GO · 5 July 2013

I think oil temp is much more important than water temp but sure an alarm for either is good. You can always get the water temp version of this. It can go blue before a temp is reached for example, green in operating temp, and flashing red when beyond the set point and the output can trigger a fan, an alarm, whatever you want.

http://www.youtube.com/watch?v=ScpD86Dy5es

E-Nough Logic · 5 July 2013

If you have aem ems and an iPhone you can do this with my digital display. Anything aem ems reads you can log and set up custom warnings for even with multiple conditions. Boost, iat, ect, afr etc... can all all be mapped against each other for customized warnings.

Valhalla · 5 July 2013

TURBO2GO said:
I think oil temp is much more important than water temp but sure an alarm for either is good. You can always get the water temp version of this. It can go blue before a temp is reached for example, green in operating temp, and flashing red when beyond the set point and the output can trigger a fan, an alarm, whatever you want.

http://www.youtube.com/watch?v=ScpD86Dy5es

Dave - very cool stuff but I want to keep my OEM dash.

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E-Nough Logic said:
If you have aem ems and an iPhone you can do this with my digital display. Anything aem ems reads you can log and set up custom warnings for even with multiple conditions. Boost, iat, ect, afr etc... can all all be mapped against each other for customized warnings.

I've looked at your app and commented on it before. But I'm a true blooded Android guy. Now if you wrote a program for Android.....

TURBO2GO · 5 July 2013

E-Nough Logic said:
If you have aem ems and an iPhone you can do this with my digital display. Anything aem ems reads you can log and set up custom warnings for even with multiple conditions. Boost, iat, ect, afr etc... can all all be mapped against each other for customized warnings.

that's cool. Wish I had an AEM lol

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Valhalla said:
Dave - very cool stuff but I want to keep my OEM dash.

Yeah I gave up on that dream. Tokyo by night here I come...

turbolence46 · 5 July 2013

You got a double din? There's the digital setup I'm running from the aem

A real working temperature gauge

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