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94 Radiator cooling fan - ECT

JeffC4

Member
Joined
Dec 12, 2005
Messages
9
Location
Woodbury, MN
Corvette
92 94
Recently purchased a 94 LT1. The coolant temp gauge climbed close to 260 in traffic while the electronic read out never went above 220. At the time I could not verify if the cooling fan came on (AC was off) but when I got the car up to speed the gauge returned to a normal operating range 210 and the electronic readout to 185. I have verified that the cooling fans come on with AC selected and the coolant will not run hot with the fans on. Can someone tell me an easy way to verify if the fans function with AC off? Also, is the ECT sensor in the water pump housing the only source of water temp information for the computer. Does the gauge and electronic readout get its information from the same source? How many relays are involed and what are there locations? Any help would be appreciated.
 

Toms007

Moderator
Joined
Sep 24, 2004
Messages
6,350
Location
Southwest Kansas
Corvette
2007 Atomic Orange Coupe
From what I understand, the digital gauge is more accurate than the analog, but I have no proof to verify this. Our cars are "bottom breathers" and when in slow moving (or not moving) traffic, the air flow nearly stops. As I grew up if the car was running hot, we always turned the AC off to reduce the load on the engine. With the C4, if you are running warm/hot you should turn the AC on to force the fans to run. The computer on our cars can be reprogramed to turn the fans on at a lower temp. I believe that the HyperTech reprogrammer can accomplish this, as well as a few other things. But if you have a program like TunerCat and a laptop with the correct interface cable you can do the same thing (plus more).

The secondary fan is programmed (I think) to come on at about 230* (some how 228* sticks in my mind)

Not sure if this answers your question or not, but hope it helps.
 

jmccloud

Well-known member
Joined
Feb 1, 2003
Messages
694
Location
Maryland
Corvette
1995 White Coupe LT-1 Auto
Cooling fan control

Search using the tab above to confirm this, my memory is vague.
The sensor in the water pump feeds the control circuit for the digital gauge and for the fan control. The sensor in the head feeds the analog gauge (which is much less accurate, not because it's analog but because it's a cheap gauge).
In stop-go town traffic with cars parallel parked or curbing nearby and the windows down (A/C off), I can easily hear the primary fan come on (215 or so) and the secondary fan is really loud (235+). The temp usually stabilizes at 194 F at cruising speed. The fan is programmed to shut off above 45mph.
Or park and let the engine idle until the primary fan comes on. It's easy to see and hear. The secondary may not activate unless the weather is warm.
Hope this helps.
 

JeffC4

Member
Joined
Dec 12, 2005
Messages
9
Location
Woodbury, MN
Corvette
92 94
Thanks for the help toms94 and jmccloud. I may just buy a ECT sensor in hopes the current one is a bit out of calibration. Otherwise will look into reprograming the computer to turn fan on a bit sooner.
 

Hot Rod Roy

Well-known member
Joined
Jul 6, 2005
Messages
317
Location
Mission Viejo CA
Corvette
Yellow '84 Coupe
If you're seeing 260 degrees, it's time to pull over and open the hood to see if the fan is working!! That's way too hot!! Your fan should come on at about 210 degrees or so.

My fan relay went out, and the temp went to 250, and the radiator cap started venting, with steam coming out of the overflow bottle. When this happens, don't remove the radiator cap!!! You need to keep the pressure in the radiator to prevent a violent guyser!! Turn off the engine and let it cool before removing the cap.

If you're in traffic, and the temperature starts climbing, it would be better to turn on the heater to get more heat out of the engine, rather than turning on the a/c. If you have to turn on the a/c to get the fan to work, you have a problem with your fan relay or the temp sensor that controls the relay. When you turn on the a/c, you are putting more heat into the engine.

:w S.T.W.
 

Hrtbeat1

Well-known member
Joined
Nov 24, 2002
Messages
923
Location
MS Gulf Coast
Corvette
'90 coupe (gone) '96 CE LT4 Z51
Sounds like normal operating temps to me. The fans are programed to come on at a really high temp IMHO. For my 96LT4 the stock settings were:
Fan 1 on (Low MPH) 104 C = 219 F
Fan 1 on (High MPH) 109 C = 228 F
Fan 2 on (Low MPH) 109 C = 228 F
Fan 2 on (High MPH) 113 C = 235 F

The fans can also be commanded to come on due to oil temps. The settings are kinda high but not as bad as the coolant temps.
Fan 1 on, oil temp (low RPM) 132 C = 269 F
Fan 1 on, oil temp (high RPM) 127 C = 260 F
Fan 2 on, oil temp (low RPM) 136 C = 276 F
Fan 2 on, oil temp (high RPM) 130 C = 266 F

These can be lowered with re-programming of the computer. The sensor in the water pump hsg controls the input to the PCM, which in turn displays the temp to the digital guage. This sensor typically reads a bit cooler. With the reverse cooling of the LTx motors the thermostat is the two way bypass to allow cool water in and hot water out of the engine. Water that doesn't enter the engine gets recycled back through the radiator, there for the sensor in the WP will read a bit cooler.

The analog guage is controlled by a sensor in the head, should be between #6 and #8 spark plugs. Its got a single wire to the sensor. The analog guage is not as accurate, plus the location tends to make it read higher.

In the old days before computer controls on cars you could turn the heater on to help reduce the coolant temp. With the computer controls though its just the opposite, turn the A/C on. The computer reads this as a higher load on the engine and commands both fans to run.

One other thing ... I do this at least annually ... take the front shroud off the radiator and clean all the leaves, pebbles, feathers, plastic, ect. out of the shroud. With these cars being bottom breathers you would not believe the stuff that gets sucked up.

:w
 

Hrtbeat1

Well-known member
Joined
Nov 24, 2002
Messages
923
Location
MS Gulf Coast
Corvette
'90 coupe (gone) '96 CE LT4 Z51
The relays for the fans are located near the drivers side headlight, on the side of the radiator shroud. If the fans are coming on with the A/C on then the relays are good.

:w
:pat
 

JeffC4

Member
Joined
Dec 12, 2005
Messages
9
Location
Woodbury, MN
Corvette
92 94
Thanks again everyone for the detailed info. I plan to have the computer programmed to kick the fans on a bit sooner. Piece of mind.
 

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