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Unread 03-27-2012, 11:07 AM   #1
linuxbarista
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1995 ZJ 
 
Join Date: Oct 2010
Location: Belton, Texas
Posts: 28
95 ZJ Over cooling, bad temp sensor, or funky gauge..?

Recently got a used ZJ and I'm trying to figure out what quirks it has. I'm wondering if my t-stat is stuck open or gauge is just not reading correctly. Def don't want to burn up a water pump, so a couple of questions.

###

How long should it normally take for my engine to get up to temp (it's around 80 deg outside 70% humidity)...? Time/Miles?

Which sensor passes along the temp to the PCM for the gauge?

If I get an infrared thermo (this weekend) where should I be pointing to check temps vs what the gauge says?

###

Things I've checked, know, or plan to check.

Brand new idle air temp sensor (aka air charge sensor).

From what I've seen my gauge get's up to about 150 no higher after 20+ miles on the highway at 60-70mph.

Cabin heat gets pretty hot pretty quick.

Coolant hose going to t-stat is pretty hot to the touch (can't hold on to it for very long either) even after driving short distances 11-15 miles around 50mph. I've also got a new mopar 195 + gasket on standby too..

Coolant is 50/50 right under the full mark. Bright green shows no signs of corrosion or anything else.

No leaks or anything anywhere.

Doesn't burn oil that I've noticed yet...

No diag codes. Shows 55 when before I start it and 55 after it's run for a while. It did show 23 (air charge under/over voltage) and I checked from the PCM to the sensor 5v, so I replaced the sensor. Cleared codes drove for a week and doesn't show 23 anymore. I can read the temp via ohms on this sensor and it doesn't correlate with what the dash gauge says.

It's super difficult tot get to the temp sensor next to the t-stat so I haven't checked the ohm readings there yet.

Thanks in advance for any help!

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Unread 03-27-2012, 12:01 PM   #2
sebian
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1995 ZJ 
 
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It should take about 10 minutes to reach operating temp. There are 2 sensors that relay the coolant temp. Both are located next to the t-stat. The one to the right of the t-stat (2 wire harness) sends temp info to the PCM, the one to the left or the t-stat (1 wire harness) sends temp info to the dash gauge. Mine was a bit wonky last summer as well. Driving in the 100+ degree heat and it would show about 160* with a 195* t-stat installed. I tried an Autozone temp sensor, and it seemed to read about 20-30 degrees to high, swapped it out for a Napa one and now it reads between 190-215 degree. Since summer is fast approaching, also check your fan clutch to make sure it has not died on you. I have noticed the best results with the Napa Heavy Duty unit.

I have never used one of those IR temp guns, but I would assume you would want to point it at the coolant return hose going from the top of the block to the top of the radiator, or maybe near the base of the t-stat housing.
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Unread 03-27-2012, 12:38 PM   #3
speedbucket
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Quote:
Originally Posted by sebian View Post
I tried an Autozone temp sensor, and it seemed to read about 20-30 degrees to high, swapped it out for a Napa one and now it reads between 190-215 degree. Since summer is fast approaching, also check your fan clutch to make sure it has not died on you. I have noticed the best results with the Napa Heavy Duty unit.

I have never used one of those IR temp guns, but I would assume you would want to point it at the coolant return hose going from the top of the block to the top of the radiator, or maybe near the base of the t-stat housing.
same thing here with the napa one vs AZ

anywhere on the front top of the manifold will work
mine runs at 195* and it takes a while to warm up because my fan clutch locked up....on high....winter sucks
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Unread 03-27-2012, 08:46 PM   #4
linuxbarista
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Fan clutch has been replaced so I don't think it's that. I'll have to look into the temp sensors next, then onto the t-stat.
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Unread 03-28-2012, 10:45 AM   #5
linuxbarista
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Update... I'm now thinking fan clutch

Quote:
check your fan clutch to make sure it has not died on you. I have noticed the best results with the Napa Heavy Duty unit.
So I tested my (two year old; according to the receipt. I thought it was only a year old) fan clutch according to the Haynes manual and it states:

Quote:
With the engine cold push the fan blades and it should move freely. No more than five turns. Also check for any fluid leaking from the clutch.
Well with the engine cold and pushing the blades by hand there's a lot of resistance. I don't think I got even 1/32 of a turn if that. Seems that it requires constant pressure to turn even when cold which according to the manual denotes a dead clutch. I'm not even going to bother to check it when it's hot. Seems this may be the root to why it's taking so long to warm up the engine.

Anyone with a known good clutch wanna tune in and let me know I'm doing this right before I spend the $80 to get a new heavy duty one?

On another note if anyone could point me to where I can find the indexing marks on the belt tensioner assembly that'd be great... I feel that there's a little too much slack in the belt, but I can't find the darn index needle and marks anywhere (at least easily visible).
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