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Unread 08-26-2014, 08:25 PM   #1
Group_er
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1986 CJ7 
 
Join Date: Sep 2008
Location: Victoria BC
Posts: 235
4.2L Temp Sender Readings....?

hey Guys!

I've got some questions regarding the Ohm readings from my 4.2L's temp sender....

Bit of background:
Ill admit my bad... The last couple months I was driving my jeep, the temp gauge was not functioning at all..... :/ I know! I know! but the thing is just so dam reliable I took my chances... (fuel gauge wasn't working either so I suspect It burnt out, causing both gauges to not work) I was running a direct drive mechanical flex a light flex fan, and had been for a couple years.
Since then I've decided to upgrade to an electric fan. Why? Mostly because the flex fan was very very loud in my opinion. and a couple other insignificant reasons of my own.
Also, I'm running a regular style rad from a V8 jeep. The COMPLETE cooling system was replaced a couple years ago. EVERYTHING new at that time.

SO!

I suppose I did things a little backwords, But I was excited for the electric fan and just finished installing it! and testing out my wiring! It works great!
Thermo switch plumbed into Intake cooling jacket FYI.

But does it cool enough? I started to wonder...

The fan was the ONLY one available from flex-a-light that would fit for me. It was my Only choice, Even though Flex-a-light customer service suggested a slightly larger CFM fan.
http://www.flex-a-lite.com/electric-...ctric-fan.html

Well! I thought... until I get my gauges diagnosed and re installed(I was going to calibrate them both as well (fuel&temp))
I figured I could just throw my Voltmeter to Ohms, Hook it up to the temp sensor at the back of the head, and start er up! Lets see what happens!

So Heres the results!
The time in minutes don't mean much because my rpms and the outside temp and yada yada can all vary:

TIME OHMS
5:16 176 -Start motor.-motor was running earlier. cool but not "cold"
5:17 131
5:18 115
5:19 80
5:20 60
5:20.50 72 -thermostat opened???
5:21 60
5:22 55
5:23 47
5:24 42
5:25 38
5:26 37
5:26 37.9 -Manually turned fan on my self (Ill explain after)
5:27 41.9
5:28 45
5:29 48
5:30 50
5:31 52
5:32 54
5:33 56
5:34 56
5:35 56
5:36 52 -revved motor 6ish times pretty high.
5:37 55 -Shut motor off...
5:38 51
5:39 54
5:40 61
5:50 87

So........ Does 56 ohms sounds like the correct reading for my motors temp sender? Should I "calibrate" my Temp gauge to sit in the middle of the green at 56 omhs? Am I over heating? lol

Any info thoughts or comments are accepted with open arms!!

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Unread 08-27-2014, 09:57 AM   #2
Group_er
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1986 CJ7 
 
Join Date: Sep 2008
Location: Victoria BC
Posts: 235
Has nobody ever done this before?
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Unread 08-27-2014, 10:46 AM   #3
Mike Romain
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1986 CJ7 
 
Join Date: Nov 2007
Location: Off the Grid in Chester Grant, Nova Scotia, Canada
Posts: 13,591
Something wrong there. (No thermostat or a failed fail safe?) A CJ 4.2 engine reads room temp 200-400 ohms. C on the gauge or 130F reads 73 ohms, beginning of band, 171F, 36 ohms, top of band, 242F, 13 ohms and Hot 272F, 9 ohms. (From John Strenk's gauge diagnostic page)
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
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Unread 08-27-2014, 11:06 AM   #4
Group_er
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1986 CJ7 
 
Join Date: Sep 2008
Location: Victoria BC
Posts: 235
Quote:
Originally Posted by Mike Romain View Post
Something wrong there. (No thermostat or a failed fail safe?) A CJ 4.2 engine reads room temp 200-400 ohms. C on the gauge or 130F reads 73 ohms, beginning of band, 171F, 36 ohms, top of band, 242F, 13 ohms and Hot 272F, 9 ohms. (From John Strenk's gauge diagnostic page)
Thank for the reply, I just ran down stairs to take a reading of the sender after sitting in my garage all night, and it read 285ohm.

What do you mean by no thermostat or a failed fail safe?
I believe around 5:20 and 5:21 the thermostat opened when the resistance temporarily came up(as in got cooler) then continued to go down(got warmer)

What would your jeeps temp sender be reading in ohms while your jeeps idling and fully warmed up? I suppose that should have been my original post.
mine appeared to be 56 ohms....
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