Overheating when idle??

[ZEROBREACH]

I think I may have figured out what the problem is, but can't diag it fully without the proper tools. The radiator fan is not coming on (ever), at any temp. I've check the relays and the fan motor is fine, kicks on when I ground it. I'm stumped at the computer. I can't tell if the sensor is not reading the temp properly or if its the $400 computer. The A/C does not work at all either. I hope the problem is linked somehow. Please Help! :frown: -Troy

I've got a tech on it, he's needing to know what the codes or actual temp the computer would read from the sensor before kicking on the fan. I am relaying this from him.. does this sound correct? Is this data within the 91 NSX Service Manual? If so, where?

 

[Doc308]

I'm not an expert at this but, if the fan kicks on when you ground the wiring, it would seem that one clear possibility is that you have a faulty sensor. When you ground the wire, I believe that you are bypassing the sensor. If it kicks on that way, everything in the system is working , except the sensor. Maybe before investing lots of hours in dx work, replace the sensor--or at least test it. Good luck!

 

[Briank]

Check fuses #4 and #31,#36,#37 but with the ccu being down my bet is on #4 15A in the dash fuse box :smile:

Also see Sec. 23 page 112 to 122 in the online manual
http://www.nsxprime.com/FAQ/Reference/1991_svcman/1991servman.pdf
for cooling fan control operation and trouble shooting.

 

[godspeed01]

just keep the fan on all the time till you trouble shoot the problem.

Ground the negative so the fan stays on so you car wont over heat.... anything is worse then over heating your car. Then get a new sensor to replace the old one. Easy fix.

 

[ZEROBREACH]

OK! I've temporarily grounded the fan to be on all the time until I can knock this out. A definate must considering its in the hundreds in Texas now. Thanks everyone, I'm running the check list tonight.

..............................

All fuses were fine relays too!! I'm testing the cooling control unit, coolant temparature sensor and gauge next.

pdf page 1100
pdf page 1104 <--has cooling fan control unit resistor test data, should be .54-.66 ohms.

pdf page 1102 states the cooling fan control unit uses inputs from the coolant temperature sensor and A/C pressure switch (A and B) on the A/C system to determine when the fans should run and at what speed. I'm wondering if it the A/C pressure switch could cause this as well - the A/C is not working.

Cooling Fan Control - Coolant Temperature Sensor Test
pdf page 1108
Temp 183F, 194F, 226F, 230F
Resistance 1.047, 0.872, 0.519, 0489

Coolant Temperature Gauge - Gauge Test and Sending Unit Test
pdf page 1122

Doing some 91 NSX Service manaul homework. The best way I've found to browse this thing is by searching keyword phrases. Going by Section or Page number is a nightmare.

 

[ZEROBREACH]

Using the 91 NSX service manual I was able to test the controller and sensor.. both were fine!! it ended up being the wiring harness... easy cheap fix!!! :smile:

 

[NSX 3.0]

Just curious does the fan have two speeds.

 

[Briank]

Yes and no, it has 2 running speeds, low and high and off.

 

[NSX 3.0]

So how do you know if your high speed is working.

 

[Briank]

On low you can hear the fan but it’s quiet, on high it much louder. At Ginger Man I heard Tom's fan start once in the paddock I think it was between back to back sessions, when he started the fan was on high and then it dropped to low and then off very quickly. I am trying think of a easy way to fool the sensor so you can test run it and see that off, low, and high work.

 

[Briank]

Looking are the manual you could connect a pot across the connector for the cooling temperature sensor. Looks like the fan will be off with a resistance of more than 1.2 K ohm and as you reduce the resistance it will come on at low speed and then at high speed at about 1.0K to .87k ohm

 

[RP-Motorsports]

On low you can hear the fan but it’s quiet, on high it much louder. At Ginger Man I heard Tom's fan start once in the paddock I think it was between back to back sessions, when he started the fan was on high and then it dropped to low and then off very quickly. I am trying think of a easy way to fool the sensor so you can test run it and see that off, low, and high work.

Me run back to back sessions? :biggrin:

My car seemed to be running perfect that day! (knock on aluminum)