I've been doing a ton of reading and I think I know how I will be moving forward. Here's what I got. I just got the car last week. Immediately, from a cold start, the temp gauge moves to the exact middle and starts slowly climbing from there. I have found no leaks and have bled the system numerous times. Odd thing is, radiator or engine bay fan never turn on. I directly wired both fans and both work. So my plan is to change the thermostat (mostly for preventative measures) and change all 3 sensors while I'm in there. If that doesn't work, I'll change the radiator fan control module. Last case will be to change the gauge itself. Now, I work the midnight shift, so progress will be slow. Any advise will be greatly appreciated. And yes I did download the service manual and I will try and test the sensors as it indicates. I was just hoping someone has encountered this before. Thanks, the info on here is awesome!
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Temp Issues, Looking for Guidance.
- Thread starter El-Cojonico
- Start date
Your temperature sensor is probably off if its shooting up right when you fire up the car. Normal operating temps should have the needle slightly below the middle point of your gauge.
You need to specify the model year of your car since details do change between model years. In particular, the coolant gauge arrangement changed significantly around 2000 with the gauge being controlled by the ECU. As a result, symptoms and test procedures change. However, you do reference the engine compartment fan, so I am guessing that you have an early model car (or an automatic?).
If you bled the system did you follow the relatively involved procedure in the service manual. It helps to have the back end of the car higher than the front end to get air bubbles out of the system.
- does it do this when you turn the key to run without the engine running? If so, then the gauge and or sensor is almost certainly defective. Assuming a pre 2000 car I would be inclined to first test the resistance of the sensor as per the service manual and see if it is out of spec (and hope that is the problem). If the sensor is in spec, before you remove the cluster test the gauge with a resistor (in place of the sensor) to see if the gauge is working correctly.
If you bled the system did you follow the relatively involved procedure in the service manual. It helps to have the back end of the car higher than the front end to get air bubbles out of the system.
The car is a 94 automatic. Although I did not raise the car to bleed the system, I followed the order specified by the 91 manual I downloaded. I have not checked the gauge with the key on but no engine running. Will do that tomorrow. Thanks for the info.
That kind of temp gauge behavior tells me you still have air in the system. With coolant cold, go through the bleed procedure again with the rear of the car elevated. Get a steady stream of coolant coming out of each bleed locations in the order the manual states. Put a small hose on the heater core bleeder and let it run into a container. It can be then be put back in the expansion tank when done. The upper rad bleeder needs to flow as well.
I have seen cars that owner have never had a cooling issue until they are at the track, then only on that day they have your temp gauge behavior. Air in the system is normally the issue.
I have seen cars that owner have never had a cooling issue until they are at the track, then only on that day they have your temp gauge behavior. Air in the system is normally the issue.
Just got home from work. Put the key and turned it to on, but did not start the engine. The temp gauge immediately went to one tick under halfway, with the engine completely cold. I will do another more intense bleed later today.
That 94 still has the original coolant gauge arrangement. Based upon that test result, I would jump to the sensor / gauge check as the first step.
If you bled a fair amount of coolant out of the system I would recommend that you go through the complete sequence. A vacuum refill tool as discussed here may be useful
http://www.nsxprime.com/forum/showt...se-Project-Accesories?highlight=coolant+flush
Correct coolant flushing is a big issue, particularly on early NSXs. Air trapped in the system can result in head gasket failure and all the related nastiness.
You have electrical issue so fix that first.
You may still have air in the cooling system but that can be dealt with and checked without the assist of gauge info.
Just a reminder. Double check that the water valve is fully opened when dealing with the coolant system.
Same water valvle used between LHD and RHD but operates in 180deg opossite direction.
Probably you already know this but there are 3 x coolant temperature related sensors on our NSX except for the Acura 00+ models.
1. There is the temperature sender unit screwed into the water passage next to the intake manifold.
This is the source signal for the gauge unit.
2. Radiator fan is controlled by the Fan Control Unit (FCU) and the signal source is the rad fan sensor mounted on the thermostat cover.
3. The ECU uses TW sensor for the EFI control and it's mounted at the front bank cyl head under the EGR valve.
Do not turn the IGSW into P2 ON without the temperature sender unit connected unless you can go P0 OFF before the temp gauge needle exceeds the red.
The temperature sender unit:
For the following check, no need powering up the system so keep IGSW in P0.
With the cold engine, measure the resistance of the temperature sender unit.
Should be well over 100ohm but from what you wrote, most likely around 50ohm.
If this is the case, replace the sender unit.
If not and the resistance is well over 100ohm, then you have wiring/gauge/etc issue.
For a quick check, get 50ohm resistor and connect one end to good GND and the other end to the bullet socket of the sender unit connector.
Turn IGSW into P2 ON.
No need stating the engine.
The temp gauge should be around the middle point where the normal operating temperature is.
If the gauge shoots up to the red, turn IGSW back to P0 to protect the gauge unit.
Remove resistor and re-connect the bullet socket to the sender unit.
The rad fan sensor and FCU:
Get 1Kohm resistor and connect it to the 2pin connector of the rad fan sensor at the thermostat cover.
Make sure no obstacle around the rad fan.
Turn IGSW into P2 ON.
No need starting the engine.
The rad fan should be active immediately even with the cold engine.
Depending on the spec of your resistor, it may trigger the eng bay fan as well so be careful not to leave anything around it.
You will need adjusting the emissivity but having infrared thermometer becomes handy.
With fully warmed up engine, you should see around 82 - 85degC at the water passage though remember the effect of emissivity and the spec of your tool.
Mine shows fairly close data even with emissivity kept at 0.95.
With this in mind, start the engine and when it's at around 80degC, measure the resistance of the rad fan sensor at the thermostat cover.
Should be about 1Kohm.
Not easy with the air box in place and eng being hot so prepare the measuring method while it's cold.
This will confirm that at least, the cooling fan control circuit is doing what it should.
Kaz
You may still have air in the cooling system but that can be dealt with and checked without the assist of gauge info.
Just a reminder. Double check that the water valve is fully opened when dealing with the coolant system.
Same water valvle used between LHD and RHD but operates in 180deg opossite direction.
Probably you already know this but there are 3 x coolant temperature related sensors on our NSX except for the Acura 00+ models.
1. There is the temperature sender unit screwed into the water passage next to the intake manifold.
This is the source signal for the gauge unit.
2. Radiator fan is controlled by the Fan Control Unit (FCU) and the signal source is the rad fan sensor mounted on the thermostat cover.
3. The ECU uses TW sensor for the EFI control and it's mounted at the front bank cyl head under the EGR valve.
Do not turn the IGSW into P2 ON without the temperature sender unit connected unless you can go P0 OFF before the temp gauge needle exceeds the red.
The temperature sender unit:
For the following check, no need powering up the system so keep IGSW in P0.
With the cold engine, measure the resistance of the temperature sender unit.
Should be well over 100ohm but from what you wrote, most likely around 50ohm.
If this is the case, replace the sender unit.
If not and the resistance is well over 100ohm, then you have wiring/gauge/etc issue.
For a quick check, get 50ohm resistor and connect one end to good GND and the other end to the bullet socket of the sender unit connector.
Turn IGSW into P2 ON.
No need stating the engine.
The temp gauge should be around the middle point where the normal operating temperature is.
If the gauge shoots up to the red, turn IGSW back to P0 to protect the gauge unit.
Remove resistor and re-connect the bullet socket to the sender unit.
The rad fan sensor and FCU:
Get 1Kohm resistor and connect it to the 2pin connector of the rad fan sensor at the thermostat cover.
Make sure no obstacle around the rad fan.
Turn IGSW into P2 ON.
No need starting the engine.
The rad fan should be active immediately even with the cold engine.
Depending on the spec of your resistor, it may trigger the eng bay fan as well so be careful not to leave anything around it.
You will need adjusting the emissivity but having infrared thermometer becomes handy.
With fully warmed up engine, you should see around 82 - 85degC at the water passage though remember the effect of emissivity and the spec of your tool.
Mine shows fairly close data even with emissivity kept at 0.95.
With this in mind, start the engine and when it's at around 80degC, measure the resistance of the rad fan sensor at the thermostat cover.
Should be about 1Kohm.
Not easy with the air box in place and eng being hot so prepare the measuring method while it's cold.
This will confirm that at least, the cooling fan control circuit is doing what it should.
Kaz
Guys. I ordered all 3 sensors and the thermostat from OEM. The car has 133k miles. At this point I'll just add it to the maintenance I'm doing (Oil, belts, fuel filter.....). The parts will be here next week. I'll fill you in on my results. I'm a capable mechanic so I'm not to worried. I got the car at a good price and it runs really good.
The previous owner sent me the maintenance history and was alarmed by the temp issue. Timing belt was done 30k ago. The crank pulley is still original (will change that soon).
Kaz, you mentioned a water valve? That, I have not seen. Can you describe it and its location.
The previous owner sent me the maintenance history and was alarmed by the temp issue. Timing belt was done 30k ago. The crank pulley is still original (will change that soon).
Kaz, you mentioned a water valve? That, I have not seen. Can you describe it and its location.
While these photos are from RHD model, if you follow the radiator lower hose/pipe, you should be able to find the same black plastic valve mounted at the side of the blower motor fan housing.
Just a reminder, the coolant enters the radiator and heater core from the bottom side, unlike the ordinary production cars.
The water valve is located at the inlet side of the heater core pipe.
On LHD model, the control wire moves towards the radiator when fully opened (hot). With RHD, it's the opposite and it moves towards the cabin.
With the combination of the water valve and the air mix motor at the bottom of the heater unit, they control the amount of the coolant and the air passing through the heater core in order to adjust the blower air temperature.
Kaz
Got it. Thanks!!!
