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I have a 525 hp ls3 crate engine. I have an aftermarket classic instruments temp gauge with the sender in the back of the passenger side head. My problem is is that the aftermarket gauge reads 20 degrees or so cooler than what the ecu reads. I have tested the gauge and it checks out. I have swapped out the aftermarket sender and same result. I have added another engine ground. Same result. Any ideas what may be going on? The only thing left I can think of is to swap out the ecu temp sensor in the front of the driver head. This engine has only a couple hundred miles on it.
verify temp readings after the vehicle has sat for awhile. Engine off/key on, compare aftermarket gauge reading, ECU temp and ambient temp reading. Im betting your temp sensor for the ECU is reading high.
this is exactly the case but how do i get them to read close to each other? My after market gauge doest start reading temp till 175 and my after market dakota digital fan controller doesn't start to read until 140. and at 140 the engine is reading 160 from the ecu
I have seen Gm factory sensors are generally within 2 degrees of nominal. If your dash reads wrong, warm the engine up fully then pull the needle and set it to what your obd2 scanner ready. Problem solved. Dash gages really suck for accuracy.
My Autometer temp gauge reads 15-20° off from my engine coolant temp sensor. It’s in the passenger side head. Hard for me to believe there’s a 20° difference
verify temp readings after the vehicle has sat for awhile. Engine off/key on, compare aftermarket gauge reading, ECU temp and ambient temp reading. Im betting your temp sensor for the ECU is reading high.
What he said. Get an infrared sensor and see which or both are wrong at room temperature. That way you know they should both read the same.
The reason it reads warmer at the front of the head is because that is where the coolant flows back into the block to the top ports of the water pump. The sender on the passenger side at the rear is seeing coolant that hasn’t had to cool off the entire head yet since both sides have the coolant outlet at the front. That’s probably why GM never put the ECT sensor at the back of the right side head.
FYI the coolant runs mostly in a loop from the water pump through the bottom holes in the water pump gaskets, through the block front to rear, up through the head gasket’s larger openings at the rear, through the head (rear to front), down through the large opening in the head gasket into the block and out the top opening in the water pump gasket. Obviously there are small openings between the block and head in the head gaskets, but the holes at the rear are larger to promote the circuit flow I described above.
From: Montgomery (Lake Conroe,) TX north of Houston
pdsq, I have my ECT sensor located in the rear of the passenger side head. You're saying that the actual coolant temperature will be higher at the front of the driver's side head because the coolant will have picked up additional heat from the heads, right?
This is why I couldn't run the ECT sensor in the front of the driver's side head, (LS376/480, Tremec T56 Magnum swapped, 1991 Foxbody coupe): I'm running a Fox power steering pump with ICT Billet front end accessory brackets. You can see the pump was right up against the ECT sensor.
pdsq, I have my ECT sensor located in the rear of the passenger side head. You're saying that the actual coolant temperature will be higher at the front of the driver's side head because the coolant will have picked up additional heat from the heads, right?
This is why I couldn't run the ECT sensor in the front of the driver's side head, (LS376/480, Tremec T56 Magnum swapped, 1991 Foxbody coupe): I'm running a Fox power steering pump with ICT Billet front end accessory brackets. You can see the pump was right up against the ECT sensor.
I would bet your actual outlet temp that the thermostat is seeing is 10-20* warmer than your gauge is showing. What’s your gauge usually sit at? 190*?
From: Montgomery (Lake Conroe,) TX north of Houston
Originally Posted by pdsq98gt
I would bet your actual outlet temp that the thermostat is seeing is 10-20* warmer than your gauge is showing. What’s your gauge usually sit at? 190*?
I drove the car 115 miles roundtrip to spend Christmas afternoon with my son and his family. I didn't use AC as the outside temperature was only about 70F. Temperature showed about 192F on my Holley 12.3 ProDash pretty much the whole drive. The PWM, OEM, C7 Corvette fan was off.
This past spring and into the first half of the summer, I didn't have the OEM airdam installed underneath the radiator support. The car struggled to stay cool driving down the road at 45-55mph with the fan programmed off at those speeds. I saw temperatures in the 215-217F range. Once I slowed down and the fan was commanded on, the coolant temp quickly dropped to below 210. All of this was with ambient temperatures in the low to mid 90s and the air conditioning on.
Someone online told me to install the airdam and boy what a difference that simple piece of plastic made! After I installed the airdam, I don't think that I ever saw a temperature above maybe 205-207F. This with the fan on or off and outside temperatures well into the 90s and air conditioning on.
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Temp difference between ecu and guage 
