turbogrill Posted April 23, 2017 Report Share Posted April 23, 2017 Hi The L28 engine has two engine temp sensors. One measures the coolant temp (contact with water) and the other measures the block it self with no water connection. The first was is connected to the gauge the other one is used by the ecu for cold start. Why have two? Why is the driver interested in the water temp and the ecu in actual block temp. Sensors have identical range and response. I am curious which one to log using MS. Quote Link to comment Share on other sites More sharing options...
Ron_e Posted April 23, 2017 Report Share Posted April 23, 2017 Ford 5.0 has two water temp sensors as well. Same, one for ecu and one for the gauge. Quote Link to comment Share on other sites More sharing options...
Rodger Coan-Burningham Posted April 23, 2017 Report Share Posted April 23, 2017 Not uncommon, the Toyota 2JZ uses two sensors, one for the gauge (single wire) and one for the ecu (2 wire which grounds back to the same place as the ecu for same reference). Quote Link to comment Share on other sites More sharing options...
Bremsen Posted April 23, 2017 Report Share Posted April 23, 2017 Cylinder head temp sensor most likely. 1 Quote Link to comment Share on other sites More sharing options...
turbogrill Posted April 23, 2017 Author Report Share Posted April 23, 2017 Maybe the block sensor fluctuates more and the water sensor is more stable, like a lowpass filtered version. In that case it might make sense to show a more stable reading to the user. Just a theory. Quote Link to comment Share on other sites More sharing options...
mhr650 Posted April 23, 2017 Report Share Posted April 23, 2017 VW also uses 2 sensors, makes no sense to me. On my car the gage worked fine but it got to be hard to cold start, I hooked up to the OBD and sure enough the ECU was reading like 300 degrees water temp. Quote Link to comment Share on other sites More sharing options...
turbogrill Posted April 23, 2017 Author Report Share Posted April 23, 2017 On a second thought its hard to share one sensor with out complicating stuff. Specially for something that is 40years old. The Ecu would have to know about the voltage divider resistor inside the guage or vice versa. Quote Link to comment Share on other sites More sharing options...
tommytipover Posted April 24, 2017 Report Share Posted April 24, 2017 Yeah, the ECUs were not smart enough back then and if you think about it, a lot of early FI cars were cobbled together from former carb platforms. Nowadays they get by with one sensor. Quote Link to comment Share on other sites More sharing options...
Chiefidiot Posted April 24, 2017 Report Share Posted April 24, 2017 Water temp sensors don't read in air. When you run out of water, the sensor reads the warm air in the now empty hose/thermostat/wherever else, so nothing tells the engine to shut down. The cylinder head temp sensor rises fairly quickly without water so shuts the engine down for protection. 2 Quote Link to comment Share on other sites More sharing options...
turbogrill Posted April 25, 2017 Author Report Share Posted April 25, 2017 2 hours ago, Chiefidiot said: Water temp sensors don't read in air. When you run out of water, the sensor reads the warm air in the now empty hose/thermostat/wherever That happened to me as well, it sucks. 2 hours ago, Chiefidiot said: The cylinder head temp sensor rises fairly quickly without water so shuts the engine down for protection. Not mine 1 Quote Link to comment Share on other sites More sharing options...
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