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1990 Xj Coolant Temp Sensor VS 1991 Coolant Temp Sensor

randy57

NAXJA Forum User
Location
arizona
The 1990 renix coolant sensor is in the block reading coolant temp which would be hotter than the coolant at the thermostat housing.

The 1991 coolant sensor is in the thermostat housing reading coolant temp which would be cooler than the coolant in the block.

Question:
What Change on the 1991 computer to reflect the difference in temp readings due to the change in the placement of the coolant temp sensor from the block to the thermostat housing?
 
First, prove your premise. I haven't seen hardly any difference in the readings between the two sensors. The biggest reason for the two sensors was so the ECU could read the temp when a switch was used for an idiot light.

I measured the actual ohms readings which convert to the temp. I rarely saw more than 2 degrees difference when running and it wasn't even always the same direction.
 
There is more temp in the head due to the exhaust.
 
First, prove your premise. I haven't seen hardly any difference in the readings between the two sensors. The biggest reason for the two sensors was so the ECU could read the temp when a switch was used for an idiot light.

I cant prove it. It just seems logical that the temp in the block would be hotter (where the coolant sensor location), because that's where the heat is generated (cylinder head).

The coolant at the other side of the thermostat is cooled by the radiator.

Block side = hot [[thermostat]] sensor on radiator side = cold.
 
There is more temp in the head due to the exhaust.

So then the coolant sensor will read a lot cooler on the radiator side of the thermostat than it would if the sensor was in the block just below the head.

Because the 1990 renix was designed with the sensor in the block and if that spot is hotter than the radiator side of the thermostat than the sensor would read cooler if it were in the housing.

So they must have taken account for the relocation of the sensor in 1991 and re-programed the computer for the difference in temp readings.

Just guessing. cant prove my premise.
 
So then the coolant sensor will read a lot cooler on the radiator side of the thermostat than it would if the sensor was in the block just below the head.
There are a couple things wrong with that premise:

1) After passing through the radiator, the water pump forces the coolant from the front of the block to the rear of the block. From the rear of the block the coolant travels into the rear of the cylinder head, and exits the front of the cylinder head at the thermostat.

2) The sensor on the newer system is mounted in the coolant bypass to the heater core, isolated from the thermostat. If it were located "on the radiator side of the thermostat," it would be accurate only when the thermostat is open.
 
There are a couple things wrong with that premise:

1) After passing through the radiator, the water pump forces the coolant from the front of the block to the rear of the block. From the rear of the block the coolant travels into the rear of the cylinder head, and exits the front of the cylinder head at the thermostat.

2) The sensor on the newer system is mounted in the coolant bypass to the heater core, isolated from the thermostat. If it were located "on the radiator side of the thermostat," it would be accurate only when the thermostat is open.

That's not totally correct. The block and head have vertical ports at each cylinder that allows coolant flow into the head along it's entire length. That's the other reason why the OP is not thinking about this correctly.
P1080508_zpsmejh0ohh.jpg

P1080514_zpslz6n2eoi.jpg
 
That's not totally correct. The block and head have vertical ports at each cylinder that allows coolant flow into the head along it's entire length. That's the other reason why the OP is not thinking about this correctly.
Take a closer look at the gasket, those holes get blocked off:

attachment.php


I read (on an engine specific forum) that all those holes in the water jacket were put there to facilitate removing the sand used in the casting process.
 
Take a closer look at the gasket, those holes get blocked off:

attachment.php


I read (on an engine specific forum) that all those holes in the water jacket were put there to facilitate removing the sand used in the casting process.

See the six holes directly above the center of the bores.
 
So then the coolant sensor will read a lot cooler on the radiator side of the thermostat than it would if the sensor was in the block just below the head.

The temp sensor on a late model is on the head side of the t-stat so even when the thermostat is closed it's still seeing circulated fluid.
 
IMG]http://www.frontrange4x4.com/forums/attachment.php?attachmentid=49205&d=1566503910[/IMG]

Are you guys aware of the big hole on the left side just below the head bolt and it's function?
 
There's already to many hints in the photo's!
 
OK, I'll take a wild guess: Those holes are there to facilitate bleeding air from the cooling system.
 
I'm talking about the "big" hole on the left!!!!
 
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