Hey guys, aside from my tranny problem (refer to other thread)
my car reads 2 different coolant temps, when it's around 225-230 on the
digital, the needle is almost at 260ish. What could 'cause this? In the fall we flushed the coolant and bled and burped the system. (1996 lt4 with lots of problems.) Thanks

 

The analog gauge is not a linear reading. As the needle moves up the scale, the values for the temp in degrees are spaced closer together. Look at the distance between the cold side of the gauge and the center value and from that center value to the highest value.

Each gauge has its own sending unit. The digital gauge gets a reading from the water pump while the analog gauge gets its reading from a sending unit in the side of the cylinder head. This can account for a few degrees difference in temp.

In any event, the temps you mentioned are pretty high. Did you clean debris from the radiator and the A/C condensor? Dirt and debris blocking the flow of air through the radiator is the biggest cause of overheating problems in C4's.

You can direct a stream of water from the fan side of the radiator to remove a lot of the junk that is trapped in the coils. Also look thru the shroud on the right side to see what sort of junk is in front of the radiator. You can even use a small shop vac hose to suck out garbage before using the water.

Car with very high mileage can also have radiators where the coolant tubes have become clogged due to poor maintenance or even worn thin due to the miles drive. Sometime a new radiator is the best solution.

Also, is the seconddary fan coming on? Once the temps reach about 238 degrees, the secondary fan will start and run until the coolant temps lower. You can test the secondary fan by simply running the A/C. Running the A/C forces the secondary fan to come on and it's a good way of cooling the engine down when temps get too warm.

 

Depending on the ambient temp and driving that was done the temp on the digital is not excessive.With the AC off the fans don't kick in till 235.The analog display is not accurate mine reads low your reads high but they are junk.The digital is from the same sensor that the ECM uses for engine management.The analog as stated above is in a different location.

 

[QUOTE=c4cruiser]
Also, is the seconddary fan coming on? Once the temps reach about 238 degrees, the secondary fan will start and run until the coolant temps lower. QUOTE]
LT4 cooling fans are either both off, both running low speed, or both running high speed......

Quote...Redeasy......AC off the fans don't kick in till 235.
Not true.......I am at work and don't have the correct numbers in front of me but on a LT4 they first come on low speed at maybe 210 and then high speed at 228.....



Update.....
Fans will come on low speed at 219 and off at 207.....Fans will jump to high speed at 228 and off at 214.........from my 1996 Service Manual page 6-639

 

I stand corrected Bud mine is an LT1 but his temp still is not excessive depending on the variables I mentioned.

 

The car is sitting when I experience these temps. With outside temp at around 50ish. When I drive the car around the block (around 30mph) the temps drop to around 210-215, so the high temps are only when it's sitting. Should I be worried? Or what can I do to lower temps that isn't too expensive. Thanks - Alex K.

 

Fans will come on low speed at 219 and off at 207.....Fans will jump to high speed at 228 and off at 214.........from my 1996 Service Manual page 6-639

Temp thresholds look right for the '94, but there isn't any low or high speed function - that's '96 only and incorporated into the a/c pressure switch signal. Speaking of which, that signal will turn on both fans on the '90 and up whenever a/c high side pressure exceeds 150 psi (about 1.5 volts from the switch). Otherwise, PCM grounds the fan relay(s) based on the CTS voltage with the main coming on around 219 and the secondary at 228. Verify that the fans are coming on within specs using a scanner. If not, you can start by troubleshooting the Coolant Temp Sensor. Buy another one for 9 Bucks and simply plug it into the harness (no need to install it). If it shows close to the same temp as the one installed after the engine has sat overnight (and that should be about the outside air temp), then your stock one is probably ok - if not, remove and replace. If you want test the accuracy of the analog gage, disconnect it - that should give you 0 on the display. Ground the harness and that should give you max. If it does, you might try a new sender. If not, there's high resistance in the wiring or the gage is whacked.

 

??????? He said he has an LT4.....ie 96........not a 94??????

 

Opps! Must be the wrong glasses or I need another prescription! Still, with it being a '96, the better way to check it out would be to scan it and monitor the CTS and A/C Pressure Switch Signals while observing the fans. You can disconnect and ground the analog harness to test it's accuracy.