browningejm

started my car today....after this brutal winter....ran great,then started to over heat... the fans didnt kick on......hit the ac button, fans, kicked in..and temp dropped....
.so i know they work.....need help ,
where should i look?......

joe paco

overheated in NY in winter? should not need the fans. check the coolant level first. radiator air flow blocked? not likely the t'stat.

the instinct says that it has no coolant, or the gauge is reading wrong.

DanielRicany

Well, check your fuses first.

Check to see if you are getting power and ground the cooling fan. I don't have an LT car, but some cars use different fans, or they use two control wires. If it only has two wires, and that same fan comes on with the A/C on then the fan is good.

After that, you would be looking at the circuit for the CTS, and the CTS itself. If that checks out okay.

And this is pretty unlikely if the fan is controlled by the same wire for both A/C and cooling. But check to see if you are getting either power or ground from the computer when the CTS reaches the fan-on temp. It's best to get this information from the ECM by using a scan tool, rather than the dash data. It uses two different sensors, and one or the other could be inaccurate.

If you don't have power or ground from that wire, which ever one it is supposed to supply, then the next thing I would do is test continuity on that wire from the point where you probed it, to the pin on ECM connector. If that's good, then the ECM is bad and needs to be replaced.

If you received either power or ground from the ECM at the correct fan-on temperature, then the problem would be in the wiring between the ECM and the cooling fan. There would be a short or an open circuit.

And that's how you do it. All you have to do now is find yourself a wiring diagram!

browningejm

i know that...i think it is a sensor...but don't know where it is......not a clogged radiator, anyone know were the sensor is

joe paco

temp gage sensor, if that is what you ask, is on right pass side of head, between 6-8 cylinders, one green wire on 91, maybe same for Lt1.

STL94LT1

The coolant temp sensor (cts) is on the front of the waterpump.

What temps on the digital coolant temp readout did your car reach.?

browningejm

above 250....the fan didn't kick on....i put the a/c on high temp and the fans went on, and temp dropped right away

ccrazor

This for the second fan not coming on but it gives the drawings for both..

http://forums.corvetteforum.com/c4-t...t-come-on.html

DanielRicany

If you let it get above 250 you better pray that you don't have a head gasket failure. That is the no no zone

RollaMo-LT4

What did the "Digital" temp read out list?

You can't say above 250 and be looking at the digital temp gauge.
That digital gauge will give you a 3 digit readout.

Don't go by the analog gauge (the gauge with the dial needle).

Your cooling fans will not come on until the temps reach the 228°F range on the digital readout.
At that temp, your analog gauge will very well look like it is overheating.
That gauge does not have a linear scale, and is next to impossible to tell exactly what the temp reading is.

RollaMo-LT4

He said the fans come on when he turns on the A/C.
So, the fuses are fine.

If the fans run under any condition, the fuses and relays are all fine.

RollaMo-LT4

Although that is true, I very much doubt his temps were anywhere close to that.

Until he lists what the "Digital" temp gauge reads, we won't know how hot it was running.

biggercanoe

anyone know why my 1994 lt1 seems to stumble under a load around 50 to 60mph then will smooth out?

kimmer

Your hijacking, start your own thread.

browningejm

ok...today started her up again, and watched the digital gauge.....let her run op to 230, and the fans never kicked on....turned the ac on , fans on ,cooled off.... i have checked the 30 amp fuse, 40 amp fuse...all good I know the fans are good because they turn on...WHAT THE PROBLEM?...help me

don hall

Citing a quote from Hib Halverson in another forum:

A 96 has two fans. Both run at the same time. The fans have two speeds low and high. When low fans are commanded the fans are wired in series. When high fans are commanded they are wired in parallel. There are three fan relays which operate the fans and which are controlled by the ECM.

"Low fans" is commanded by the ECM when either: certain DTCs are set, ECT is above 219°F, engine oil temp is above 270°F or A/C head pressure is above 189 psi. Also, when engine speed is over 3500 rpm and oil temperature is over 261°F low fans will come on. The fans will go off once CT drops about 11°F. If A/C head pressure kicks the fans on, it must drop to 150psi before the ECM will shut them off. Min. on time is about 50 seconds

"High fans" is commanded by the ECM when either: certain DTCs are set, ECT is above 228°F, engine oil temp is above 277°F or A/C head pressure is above 225-psi. Also, when engine speed is over 3500 rpm and oil temp is over 266°F, the ECM will request high fans. The ECM will turn off high fans once coolant temp drops about 11° or A/C head pressure drops below 189 psi.

If you saw 260 on the digital display and the coolant boiled over, obviously the car was way overheating. If you ran the car like that for any length of time, engine damage is possible. Hopefully that's not the case.

I'd be looking for cooling system problems other than just the fans such as restricted air flow through the cooling stack. Also, overheating really stresses cooling system parts such as radiator hoses, heater hoses, belts, radiator caps and so forth. Considering the car is 15 years old, if those parts are original, I'd carefully inspect them for damage.

But, again, the best way to troubleshoot the cooling fans on a 90-96 is using the diagnostic table in the Service Manual.

browningejm

this all happened while idling in my driveway

don hall

[QUOTE=browningejm;1586454131]this all happened while idling in my driveway[/QUOTE]

The sensors, ECM, t-stat, coolant, fans, hoses, radiator, reservoirs, air dam don't know that the vette is just idling in the driveway.

Tom400CFI

The ECM certainly does "know" that the car is idling. As such, it should run the fans as outlined in your above post. If the car is moving down the road at >35 mph, the fans don't run.

The OP's problem seems to be the fans, triggered by the CTS. The use of AC activates the fans and the car runs O.K....according to post #1.

He needs to diagnose the CTS circuit, IMO.

browningejm

bought a new relay...no change....ran the temp up to 230(digital)...
...idling, no fans....turn on a/c...both fans kicked on low...then high...