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Old 02-07-2011, 08:14 AM   #1
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Default 4.0 Water Temp Sensors

I just got the new to me engine installed in my '96 XJ. The engine I pulled out had a spot in the rear of the head for a second water temp sensor and the new engine does not. This second sensor is for the temp gauge.

Is there another spot on the engine I can put the sensor or should I put a T in the thermostat housing sensor location to put both sensors in?
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Old 02-07-2011, 09:10 AM   #2
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How 'bout a pic of the sensor that screws into the back of the head? Thread size? NPT thread? Always best to have the tip of sensor in the coolant flow.......might not be able to do that with a "T". Depending on size of sensor, might be enough room to drill/tap into the t-stat housing.
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Old 02-07-2011, 09:19 AM   #3
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It is in the back upper part of the head by the driver side rear corner head bolt that has the ground strap.

I don't have any pictures handy.
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Old 02-07-2011, 10:16 AM   #4
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I was thinking a pic of the sensor (not screwed in) would help to determine size wise if it could be relocated to the t-stat housing.
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Old 02-07-2011, 10:18 AM   #5
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It is the same size as the one already in the thermostat housing.
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Old 02-07-2011, 10:35 AM   #6
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If memory serves me correct, the threads would be either 1/4" NPT or 3/8" NPT. Wonder if it could be mounted in that flat spot to the right of the mounting bolt? Might be a clearance issue with the rad fan.
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Old 02-07-2011, 10:37 AM   #7
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It is not 1/4", I would say more like 3/8" is correct.

Since the pump will always be flowing water, why wouldn't a T work there with the sensors in each end? The pump will fill that area with fluid since it is still lower than the upper radiator hose.
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Old 02-07-2011, 11:10 AM   #8
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i would go this route instead...no drilling/tapping required.

Use a 3/8" NPT Brass T-fitting

http://www.jeepforum.com/forum/f11/a...method-990168/
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Old 02-07-2011, 11:24 AM   #9
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Quote:
Originally Posted by dukie564 View Post
i would go this route instead...no drilling/tapping required.

Use a 3/8" NPT Brass T-fitting

http://www.jeepforum.com/forum/f11/a...method-990168/
That is what I was talking about. I don't see why it would have to be brass. Any 3/8" NPT T and nipple should work.

Click the image to open in full size.
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Old 02-07-2011, 11:41 AM   #10
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What year is the engine? My 94, 95 and 96 all had the sensor in the back of the head and the other in the t stat housing. The t connection on the t stat housing will work but bleed any air out of it when it warms up (crack the threads loose enough to get straight coolant mix out) or your readings will not be accurate. (rear smaller is temp sensor, front, bigger is aux fan switch). If I remember correctly, they are both metric threads.
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Old 02-07-2011, 11:46 AM   #11
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Quote:
Originally Posted by sv41878 View Post
What year is the engine? My 94, 95 and 96 all had the sensor in the back of the head and the other in the t stat housing. The t connection on the t stat housing will work but bleed any air out of it when it warms up (crack the threads loose enough to get straight coolant mix out) or your readings will not be accurate. (rear smaller is temp sensor, front, bigger is aux fan switch). If I remember correctly, they are both metric threads.
The engine I got came out of a Wrangler and not a XJ. My brother's '97 TJ doesn't have a rear sensor, just the one on the thermostat housing.

So the sensor on the t-stat housing is for the electric fan? Interesting.

I will bleed the air out, but shouldn't any air trapped in there go out through the radiator cap since the cap will be higher than the sensors?
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Old 02-07-2011, 12:13 PM   #12
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With that "T", the tip of the sensor(s) are in stagnant coolant, not flowing coolant, like the factory sensor(s) are located. I would think stagnant coolant flow would give a low or somewhat false reading, just like the gauge (in the link) is displaying (low). The temp gauge (in the link) displays 190 and the OP says while driving it displays 170......doesn't that seem a little low (false reading maybe)?
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Old 02-07-2011, 12:18 PM   #13
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It wouldn't be as stagnant as one might think. The coolant will heat up to the same temp as the rest of the coolant since it has contact with it. I don't see where it would be 20* difference, maybe 1-5*.

Is there any other spot on the block to put in a temp sensor? In my Chilton's manual it shows a block coolant drain plug, but I have not been able to find it.
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Old 02-07-2011, 12:20 PM   #14
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Quote:
Originally Posted by djb383 View Post
With that "T", the tip of the sensor(s) are in stagnant coolant, not flowing coolant, like the factory sensor(s) are located. I would think stagnant coolant flow would give a low or somewhat false reading, just like the gauge (in the link) is displaying (low). The temp gauge (in the link) displays 190 and the OP says while driving it displays 170......doesn't that seem a little low (false reading maybe)?
no mines about 170 if im drivin constantly and only gets higher if im goin slow and only usin 1st or 2nd gear on the highway it stays at about 170 for as long as i drive it
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Old 02-07-2011, 12:23 PM   #15
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you're correct it probably would, but i can't imagine it would be more than a few degrees off. Water (coolant) holds heat extremely well, and would transfer the heat to the coolant in the T with no problem IMO. As long as there isn't an air bubble i'd think he would be fine. Sure beats drilling and tapping the block/thermostat housing.

From what the poster said it sounds like it's pretty accurate. At 38* outside, he said 190* in driveway at idle, and 170* while driving. This sounds pretty normal at that outside air temp (approx what I see in the winter as well).
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Old 02-07-2011, 12:23 PM
 
 
 
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