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Discussion Starter · #1 ·
So I finally got my engine back together, but when it's running, the fan never comes on and the temp gauge proceeds to max out. When I turn the A/C on, the passenger fan comes on no problem. When I disconnect the water pump temp sensor both fans go into default and come on. So, I know it's not a problem with my fans. My thought is that it is the one wire temp sensor on the passenger side head. Does it have to ground through the threads? I used teflon tape for the installation. Perhaps this is the reason why my fan is not coming on?
 

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So I finally got my engine back together, but when it's running, the fan never comes on and the temp gauge proceeds to max out. When I turn the A/C on, the passenger fan comes on no problem. When I disconnect the water pump temp sensor both fans go into default and come on. So, I know it's not a problem with my fans. My thought is that it is the one wire temp sensor on the passenger side head. Does it have to ground through the threads? I used teflon tape for the installation. Perhaps this is the reason why my fan is not coming on?
This was the first problem I had with my SS....if you unplug the temp sensor on the water pump and they come on then it's that sensor. I replaced mine and my fans have worked fine ever since...give that a try....the sensor is pretty cheap...
 

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Discussion Starter · #3 ·
After doing some research I have found out that the one in the head only controls the gauge. So, it can't be that since my gauge reads fine. So, it must be the one in the water pump. I'll replace that and see if that fixes it. Should the fans also come on by using a jumper between the two pins in the connector?
 

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After doing some research I have found out that the one in the head only controls the gauge. So, it can't be that since my gauge reads fine. So, it must be the one in the water pump. I'll replace that and see if that fixes it. Should the fans also come on by using a jumper between the two pins in the connector?
I'm not sure... But it really sounds like the sensor in the water pump has gone bad...
 

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Discussion Starter · #5 ·
12 bucks from Advance Auto. I'll pick one up on the way home. Thanks.
 

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12 bucks from Advance Auto. I'll pick one up on the way home. Thanks.
10-4...let me know if it works... And I don't know what thermostat you have but it may take a while for them to come on. My temp needle get's almost to the red before mine come on...
 

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I had this concern too as I was on the highway and had to make a few phone calls in a row and pulled off the highway into a parking lot.

Was on the phone and looked down and freaked out to see the temp gauge about 3/4. I turned on the ac to the "max" setting and that kicks on one of the fans and watched it cool down almost instantly.

I unplugged the temp sensor and both fans came on but neither fan will come on unless things are REALLY hot. You can program the temp they kick lower if you feel like it (I will be doing this)

If you ever get worried about it sitting in traffic just click the AC on for a few seconds and turn off. The fan will stay on until it is back to 1/2 way. (You can check this yourself in your driveway)

Here is a thread on this http://www.impalassforum.com/vBulletin/showthread.php?t=248863&highlight=overheating&page=2
 

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http://www.theherd.com/articles/lt1_cool.html said:
B/D-car coolant fans operate under PCM control at the following engine temperatures and A/C system pressures:

Fan Mode ... Temp ... Pressure

Primary (RH) Fan ON ... 109°C / 229°F ... 189 psi
Primary (RH) Fan OFF ... 105°C / 221°F ... 150 psi

Secondary (LH) Fan ON ... 112°C / 234°F ... 240 psi
Secondary (LH) Fan OFF ... 108°C / 227°F ... 210 psi

Additionally, the PCM will turn off the fans at higher vehicle speeds (above 48 MPH I believe) since running fans can actually impede airflow through the radiator at high speed. Each fan also has a minimum running time. Once activated, the primary fan will run for a minimum of 50 seconds, and the secondary fan for a minimum of 26 seconds. Finally, certain Diagnostic Trouble Codes (DTCs) may cause the PCM to turn on one or both fans.
The stock fan turn on temps are too hot.

When the fans come on that late/hot, you get needlessly high underhood temps, meaning:
a) diminished transmission life without extra transmission cooling upgrades
b) less protection against ping/knock due in part to higher intake air temps
c) rubber and plastic under the hood will get brittle and generally age much more quickly

Reflash your PCM so that the primary fan comes on twenty to twenty-five degrees [Fahrenheit] above your thermostat's specified temp.
Or, if you prefer, five to ten degrees [Fahrenheit] after your thermostat is fully open.
(160°F thermostats fully open @ 175°F, 180°F tstats @ 195°F, & 195°F tstats @ 210°F, give or take one degree Fahrenheit.)

That way, your primary fan will be on often, but not CONSTANTLY - unless the AC is on, of course.
 

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Discussion Starter · #10 · (Edited)
Well, I put the sensor in and let it idle till the gauge was almost pegged and the fan never came on. It usually comes on at 3/4 or so, but the needle was well past that and nothing happened. Any ideas?
 

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Discussion Starter · #12 · (Edited)
Yup. I even have one of those nifty bleeder valves that I bought from a member here. The WP is definitely turning and it's definitely bled.

I guess the next step is checking continuity from the PCM to the sensor?
 

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Discussion Starter · #14 ·
Can't find my old sensor for some reason, but the new one measures correctly according to that chart. I tested the voltage at the connector too and got 5.02 VDC.
 

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Next check would be to make sure your cooling system is holding pressure. If there is even a slight leak, the coolant will start boiling before the temperature gets hot enough to turn on the fans. The coolant cap is a likely suspect.
 
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