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Unread 10-21-2006, 10:52 PM   #31
j.love
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Join Date: Jun 2006
Location: 39 57′ 1″ N, 75 9′ 1″ W
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You would test the sensor by contacting one of the leads off the meter to ground. The botom of the sensor is grounded to the block and the resistance is from there. I dont know what kind of switch you would call it but I would guess a "ground resistance switch.." or something like that. but thats how it works.


I set up the meeter to the sensor and to an engine ground. Got an initial reading of 1,190 ohms. Then I took a series of readings at the start then in 30 sec. intervalls till it seemed to platue. I then switched to 1 min. intravals to keep from going crazy. The lowest reading I got was 314 ohms after 20 min. at idle. I also was keeping track of the temp of rad fluid at the rad. cap. but I had no way of keeping track of the temp at the sensor its self. I guess the only way to truely confirm its function is to do the removal and water test.



1,190 ohms- with no motor running and ignition on. water temp 60 deg.
ambiant outside air temp of 40 deg.

ohms/deg/time elapsed since last reading
start test.....

745/60/10 sec.
638/60/30
580/60/30
526/60/30
485/60/30
446/60/30
417/60/30
390/60/30
361/60/30
342/60/30
325/60/30
308/60/30
309/65/30
329/70/30
333/71/1 mim.
332/73/1
328/75/1
317/75/5 min.
315/78/5
314/79/5
314/100/ after 25 min of idle and a long trip around the block 10/15 miles.


This was the test after 25 min. +/- pluss drive time. I know that the readings on your graph are a direct corilation between ohms and tempature at the sensor but I figured that the rad temp would help point me in the direction of some sort of conclusion as to if the sensor is at fault.

I also dit a test on the dash gauge. to test that haynes says to conect the lead to groung and the guage should move all the way to full scale. I passed that test so if the coolant temp is in the corect range then the sensor is def. bad.

Here is what is throwing me. Why would the temp of the rad fluid bee so cool at the rad cap? the highest I read is 100 deg. and ambiant temp of 40 deg. This is after running at idle for 25 min and after taking a drive for a few miles also. When I got back and did a final reading on sensor and temp at cap and was still at 314 ohms/ 100 deg.

I seriously think that this can't be rite only 100 deg.? Even if I do swap out the gauge sensor and it then reads properly I would still think this still would be a problem.

I would also add that it has a new fan and clutch, suposidly new 180 thermostat and a build code of "NMCP- heavy duty engine cooling". I think thats a larger radiator?

Now I guess I need to test the other sensor in the morning and see if I can get a reading on that, Then I will pull the two of them and bench test them. ( or should I say kitchen test!)
besides testing the sensors and or changing them. I wouldnt know how to go further.




.

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David.
94 ZJ laredo 5.9 V8 swap D44a posi
Quote:
Originally Posted by ratmonkey View Post
I wouldn't drive down a driveway on that.
''If we do everything right, if we do it with absolute certainty, there's still a 30% chance we're going to get it wrong.''
Joe Biden
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Unread 10-21-2006, 11:01 PM   #32
j.love
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ok, think simple Dave, I guess I got two problems. faulty sensor and a open thermostat. and a radiator that cools realy well!




.
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David.
94 ZJ laredo 5.9 V8 swap D44a posi
Quote:
Originally Posted by ratmonkey View Post
I wouldn't drive down a driveway on that.
''If we do everything right, if we do it with absolute certainty, there's still a 30% chance we're going to get it wrong.''
Joe Biden
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Unread 10-21-2006, 11:14 PM   #33
-Joe-
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The manual I have has these for the temp gauge calibration..

100 F grad 1365 ohms
210 F grad 115 ohms
260 F grad 55.1 ohms
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242TC - Extreme Engineering 2" Front Lift/1.75" Rear Lift - ES9000 Shocks + JKS BPEs
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Unread 10-21-2006, 11:42 PM   #34
j.love
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Thanks joe.
Now I just need to find out how to create ohms resistance so I can test the gauge. Gee alls I need is a bigger bader test meter than the one I allready dont know how to use.

seriously where are you guys getting these factory service manuals and how do I get my greasy little hands on one?






.
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David.
94 ZJ laredo 5.9 V8 swap D44a posi
Quote:
Originally Posted by ratmonkey View Post
I wouldn't drive down a driveway on that.
''If we do everything right, if we do it with absolute certainty, there's still a 30% chance we're going to get it wrong.''
Joe Biden
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Unread 10-22-2006, 05:58 AM   #35
greasefingers
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Quote:
Originally Posted by -Joe-
The manual I have has these for the temp gauge calibration..

100 F grad 1365 ohms
210 F grad 115 ohms
260 F grad 55.1 ohms
And the above is what I graphed on my post numbers 23 & 25
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88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 10-22-2006, 07:46 AM   #36
greasefingers
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Sorry I forgot that you stated that you have a 180 degree F thermostat. Therefore from the graph the resistance of the dash board sensor should be around 425 ohms at 180 F
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Unread 10-22-2006, 08:46 AM   #37
j.love
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now I got a few questions.
If I read that graph corectly I would say that at 314 ohns would put me at around 185/190.
Now on the readings I was getting on the dash guage were down at the 127 mark. lets just say that the guage is out of calibration. Would I see a 90 deg drop across the radiator with a engine temp of 190 and a rad fluid cap temp of 100deg. ? That seems like too much.

I cant get to the second sensor for the computer with out pulling the ac pump. So I think I'm gona drain and pull the sensors and bench test them today.






.
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David.
94 ZJ laredo 5.9 V8 swap D44a posi
Quote:
Originally Posted by ratmonkey View Post
I wouldn't drive down a driveway on that.
''If we do everything right, if we do it with absolute certainty, there's still a 30% chance we're going to get it wrong.''
Joe Biden
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Unread 10-22-2006, 09:46 AM   #38
greasefingers
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Since the two different coolant temperature sensors yield different resistance outputs, we really need to clarify them. I will call the sensor at the thermostat the CTS. This is not what the dash board uses to display temperature ( this is true for the 4.0L engine) not sure about the 5.2L engine.

Therefore from the graph below the resistance for 180 F is 1190 ohms and for 195 F it would be 915 ohms.

The other coolant temperature sensor, for the dash board, I call CTD for coolant temp dashboard. At 180 F it will measure 425 ohms and at 195 F is will be 250 ohms.

If I understand the flow path of the coolant correctly? Then the CTS will always be cooler then the dash sensor.
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88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 10-22-2006, 09:49 AM   #39
greasefingers
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Quote:
Originally Posted by j.love
So I think I'm gona drain and pull the sensors and bench test them today
You do not have to drain the coolant to remove the sensors. The ports will weep a bit, so just remove them and place a rag next to the holes
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88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 10-22-2006, 07:09 PM   #40
Dr. Righteous
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Quote:
Originally Posted by greasefingers
The left side of the gage has different increments then the right side (past the 210 mark)

This is where it should be in a perfect world. Mine is just off the 182.5 mark, so I guess I run about 10 degrees colder then one would expect.

Identical to my wife's '95 ZJ v8 with 175K miles. New rad, pump, hoses, fan clutch, and 195* stat from NAPA (Its stainless steel)
All this after I had 3 thermostats IN A ROW fail prematurely and racked my brain tying to figure out why it runs to hot, and then runs too cold ect....
Avoid Chinese made thermostats.
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Unread 10-22-2006, 08:30 PM   #41
j.love
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I ran my tests today. You are corect we are talking about two diferent sensors, and this is the same for the 5,2 as well. One for the computer "cts" as per your post, and one for the dash guage "ctd". The cts is a two post sensor, witch reads a higher ohms value. where the ctd is a single post sensor, witch has a lesser ohms reading than the cts.

On the 5.2 it is extreamly dificult to try to remove the sensors with out pulling the alternator. Figured if I was gona solve this issue I should test the thermostat also. Ran the bench test on all three. Here are the results.

CTS (sensor for computer)
temp/ohms
160/1576
170/1319
180/1132
185/1030
190/1011
195/0895
200/0886
210/0713

CTD (sensor for dash guage)
temp/ohms
160/337
170/290
180/247
185/230
190/214
195/196
200/175
210/154

The first test was the cts and closely match the charts you have provided. The key measurements you gave for the cts were, 180/1190 and 195/915. My cts readings were 180/1132 and195/895.


The ctd had diferent results. 180/425 and 195/250 were what you posted. 180/247 and 195/196 were the results that I got. being that this is just a guage, and dose not effect the computer, I am not to concerend that it is off. More importiantly by how much. so I can adjust my readings at the dash.

The third test was the thermostat. It started to open up at 155 and was at full open at 160. I was shocked to see it open that soon. This was the "ghost in the machine" I was after. It makes perfect sence since the readings I was getting prior to bench test were a ctd of 314ohms. I made note of that when I bench tested and the temp was 165 deg.

With the motor running that cold I can understand now why I was only getting 100 deg at the rad fill cap. If the sensor was corect at 314 ohms it would put it at a temp of somewhere around 190 deg. witch we know know to be a false tempature.

I relpaced the thermostat with a standard 195 thermostat. I am running a jet chip that I belive requires a 180 thermostat. What I want to do rite now is exstablish some "normalcy" to this system. Then I can change out the thermostat for the 180 If I decide to keep the Jet chip in. On a side note I dont know how much this chip is helping or hurting my proformance.

With the new thermostat in I did not have the chance to make further ohms readings due to time constraints. and relighed on the dash guage for now knowing that it is off. I have to sit and calculate the amount that the gage is off.



.
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David.
94 ZJ laredo 5.9 V8 swap D44a posi
Quote:
Originally Posted by ratmonkey View Post
I wouldn't drive down a driveway on that.
''If we do everything right, if we do it with absolute certainty, there's still a 30% chance we're going to get it wrong.''
Joe Biden
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Unread 10-23-2006, 06:26 AM   #42
greasefingers
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Good work! If I understand things correctly, the engine might ping now with the hotter thermostat and the Jet-chip still in place. You may have to run premium fuel, as I believe the only thing that the Chip does is change the ignition timing?

I would calculate your fuel mileage, over a full tank of gas, as it is. Then I would remove the Jet-Chip and repeat. If you do not notice any decrease in performance, then choose which ever yields the best fuel economy.
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94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 11-18-2006, 10:56 AM   #43
Woody
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Well, I messed around a bit more trying to get to 195 and this is what's happened.

I closed off my radiator openings. At idle it gets up to 195 quicker, but it still cools down when I drive, not as bad, but it still happens. I checked the fan clutch and it seems okay, but for fun, I removed the shroud. It still drops off to about 182.5 when going down the highway, but it doesn't drop off as fast.

Next step is to remove the fan. I'm holding off until I can put an electric one in, I'd rather not overheat and get into big trouble.

Note it's -25 here and has been for the better part of two weeks straight. I think this has something to do with my current problem.
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Unread 11-18-2006, 02:12 PM   #44
greasefingers
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Yea it could just be normal given the climate. At -25 F the engine and everything else looses so much heat to the surroundings.

You just need a 210 F thermostat. Then I bet she would read closer to 195 F.
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94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 11-18-2006, 02:20 PM   #45
Woody
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Parts are another issue up here. Stores don't keep enough stock for us 4-wheelin' guys. You break your rig on the trail, trailer it home and spend a month waiting for parts to fix it.

That's why the D35 needs to be upgraded. I think I'm set on a solution, but need to sell a few things first to get me rolling.

I will keep my search going for a 210 though. Already found one for my 6.2L in the Burb, but Chevy parts are mucho cheaper and readily available than Chrysler crap.
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