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  #1  
Old January 22nd, 2021, 00:39
Lost_Wrench Lost_Wrench is offline
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XJ Temp Sending Unit Shenanigans

Today I swapped out my old instrument cluster on my 96 XJ 4.0 which only had "idiot lights" and I put in a cluster with gauges but I ran into a few head banging issues that made the project take 5 times as long as it should have.

The rear Temp Sensor for the gauges near the back of the Valve Cover was a royal PITA!!! The first replacement sensor I picked up from Advance had a larger sized nut (9/16) than the OEM (13mm). With the threaded hole for the sensor being so close to the valve cover it simply wouldn't thread in. Stupid. Went to Oreilly this time and found one that was 13mm, but on this one the nut wasn't as "thick" or "deep" as the OEM so I could thread it in to a certain point but the socket would eventually bottom out on the edge of the valve cover. I literally had to get out the Dremel and cautiously grind off a section of my valve cover to allow the socket to fit all the way around the sensor. Prior to grinding I tried using a 13mm crows foot open-end wrench but it too would only get me so far before I needed more leverage and I was beginning to round out the nut on the sensor. This, I found out, was due to the hole for the sensor being drilled in at a slight angle for some reason. WTH seriously? Was this a mistake at the factory? By the time I finally snugged down the new sensor I noticed that it had the appearance of being badly cross-threaded. One side of the nut was contacting the metal on the block while the other side was higher by a few millimeters. Again, seems like a factory mistake to have that hole for the sensor drilled in at a slight angle. I backed out the sensor and checked the threads and they were all fine and not cross threaded at all. I put Teflon tape on and reinserted the sensor.

The new gauges all work but now that I can see my running temp for the first time it is at 160 or 170 degrees which seems way low, it should be around 200. Could it be the new sensor is faulty, or the new (used) cluster is off somehow? Thermostat maybe? Should I even worry about that? The Jeep runs great, heater blows hot, and she gets good gas mileage.

Last thought about this project. With the ease in which these instrument clusters can be swapped out (20 minutes) we should all be wary of mileage when buying older XJ's. I went from 150k on my old cluster - which was almost certainly not the original - to 144k on my "new" cluster. Since it's old enough for the Title of the vehicle to say "Mileage Exempt" there is really no repercussion to this type of fraud. Lots of lower mileage clusters are available online so this is an easy scam. Also, someone had removed the "Check Engine" bulb on my old cluster, haha. Oh and now my check engine light on my new cluster is on. :/

Thanks for reading. The End.
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  #2  
Old February 5th, 2021, 12:13
gmcchamp99 gmcchamp99 is offline
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Re: XJ Temp Sending Unit Shenanigans

I literally just did this last week on my 96 sport. I ended up removing the valve cover to gain the clearance i needed to get a deep socket in there. I was glad I did as I checked lash and torque on the rockers and 3 of them were at 15 ft lbs. Any who, my sensor did go in on an angle, also checked the threads and they were clean and no crossed so a little teflon tape did the trick with zero leaks. was running about 180 and wouldn't get past it, pulled the thermostat to find someone drilled a hole in it to burp the cooling system and no lie, it was about 1/2 diameter hole. Not sure how it never ended up destroying the thermostat but one I changed the thermostat out, flushed and refilled she rides around at a hair under 210.
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Old February 5th, 2021, 15:46
Lost_Wrench Lost_Wrench is offline
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Re: XJ Temp Sending Unit Shenanigans

Wow crazy about your Thermostat, someone actually drilled a hole in it? Seems like a lot of effort when they could have just replaced it while they already had it out... After removing the idiot light cluster and installing gauges I found that my running temp was about 160 or 170 so I replaced it with a stock 195 degree Thermostat and am now at 210 as well. What's with people wanting to run cold Thermostats on these? Won't that kill gas mileage?

So that's interesting, you had the same problem of not being able to get the socket on the temp sending unit and opted to remove the valve cover, which is probably smarter than grinding the side of the Valve Cover to allow for a socket like I did, but if I have to do it again in the future I don't want to have to keep removing the cover. Why the heck were those holes tapped so close to the Valve Covers? Peering into the hole when the sending unit was out it seemed like there was plenty of room to scoot that hole over 1/4 inch to allow more room for a socket.
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Old February 5th, 2021, 20:50
Unclewolverine Unclewolverine is offline
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Re: XJ Temp Sending Unit Shenanigans

It's always bugged me that people try to bandaid their over heating issues with a cold thermostat. It never let's the computer get past the warm up mode; so yes crappy gas mileage, and always running rich. Probably cause more problems down the line than not.
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Old February 6th, 2021, 10:15
gmcchamp99 gmcchamp99 is offline
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Re: XJ Temp Sending Unit Shenanigans

I dont think it was a band aid, they drilled the whole in the thermostat to release the pressure in the cooling system and burp the air out. Most thermostats like Stant & Motorad come with a valve that opens and allows pressure to bypass the stat to get the air out. This thermostat in the truck didnt have it so they drilled the hole and it was so close to the rubber seat of the valve that literally everything could blow past the spring.

There are many reasons to use an alt temp thermostat. It can impact gas mileage.

Im sure Snap On or another manufacture makes a thin wall socket that would work with the valve cover on but I have a slew of tools already. I wont buy more unless i know ill use it a good bit. Engineers look at everything on the screen or paper and if it looks good there, there's no problems with anything and its good to build.

Glad it worked out for us both.
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  #6  
Old February 6th, 2021, 10:41
lawsoncl lawsoncl is offline
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Re: XJ Temp Sending Unit Shenanigans

It's actually a good tip to add a 1/8" hole to the thermostat if it doesn't have one to help it burp air. Definitely not a 1/2" hole though.
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Old February 6th, 2021, 11:26
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techno1154 techno1154 is offline
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Re: XJ Temp Sending Unit Shenanigans

Way back in the 1980/s I have been drilling holes in thermostat,... 1/8 inch holes to allow water to by pass when the engine is cold. That was in the power boat industry working with Chevy, Ford and Chrysler V8 engines. A 1/2 inch hole is definitely too big. The genuine Chrysler thermostat have a hole in it with a jiggle valve in it so the end user do not have to drill a hole.

The part about the engine running cooler do not hold true with my XJ. I have been running a 180 degrees thermostat in my XJ since early summer 2020. On Florida highways cruising 70 MP my XJ consistently returns between 280 and 300 miles on 15 gls of 87 octane fuel. A low quality 87 octane fuel gives 15 to 20% less miles. highway temperature remains below 190 degrees.
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1996 XJ; 4.0L; AW4; NP231; SYE; D30 and D44; ECTED; 4.10 gears; 30X9.5 -15 BFG/AT/KO; 3" lift; Rusty's LCA; JKS ADJ UCA; Kevins ADJ Track bar; Drawtite Front Receiver; Dual Electric Fans; Dual Battaries.
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