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November 21, 2019, 06:58:42 PM

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Author Topic: Running hot/overheating  (Read 4589 times)
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RattleTrap55
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Posts: 597
84 CJ7
« Reply #15 on: July 22, 2019, 01:56:45 PM »

Sorry I am late to this discussion - how do I say this? The 4.0L is setup to run with a 195F thermostat with an operating temperature of 210F on engines with the sensor located at the back of the cylinder head (next to the firewall).

It would appear that you are off by a few degrees which can be the result of bad timing (not likely the ECU will compensate for this) or spark plugs out of the heat range for your application. Also a lean running engine will run hot, but once again not likely unless you have bad O2 sensor. Most likely a bad O2 sensor will "throw" an error code. Too hot of a plug can cause pre-ignition and increase cylinder temperature along with engine knock.

Question, have you had the plugs changed recently? Are they the correct heat range? There is no standard for spark plug heat range. So the 10 or so heat ranges of an NGK plug are different for say, a Champion plug.

I know a little out there but pull your plugs, look at the tips what do you have to lose?

« Last Edit: July 22, 2019, 02:31:34 PM by RattleTrap55 »

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4" Lift on 33's
4.2L w/HESCO MFI & Howard Cam
T-5 & Dana 300
Smittybilt 9,500 Winch
Spartan Locker

2018 JKU - box stock
2002 TJ Sahara w/Very Rusted Frame
sirjames186
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Member 2018 VA4WD
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Posts: 2500
05 LJ
« Reply #16 on: July 22, 2019, 02:02:43 PM »

Sounds like an air bubble or something in it. Maybe one of the lines has some gunk build up that is slowing coolant flow.

Might be worth flushing the system and putting in g05 coolant. On the TJs that's the factor spec, and I noticed a significant improvement when I switched from green universal to g-05.

Sent from my SM-G930V using Tapatalk



Even the hoses are new, so unlikely there's gunk in there.  But there might be something gunking up inside the block.
You can run a couple cycles of water through it to test for anything in the block. I blew a radiator hose then the radiator on my LJ about 9 months apart and got really good at flushing the system.

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"I'm no longer ashamed to wheel with you." - Jeremy
Onyx Dragon
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Posts: 436
« Reply #17 on: July 22, 2019, 02:06:43 PM »

Sorry I am late to this discussion - how do I say this? The 4.0L is setup to run with a 195F thermostat with an operating temperature of 210F on engines with the sensor located at the back of the cylinder head (next to the firewall).

This is my 4th 4.0.  It definitely has the sensor on the front in the thermostat housing just like the other 3, close to the radiator.

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Bill Staples
1999 XJ
2018 JL Unlimited
RattleTrap55
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Member 2019
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Posts: 597
84 CJ7
« Reply #18 on: July 22, 2019, 02:41:48 PM »

Sorry I am late to this discussion - how do I say this? The 4.0L is setup to run with a 195F thermostat with an operating temperature of 210F on engines with the sensor located at the back of the cylinder head (next to the firewall).

This is my 4th 4.0.  It definitely has the sensor on the front in the thermostat housing just like the other 3, close to the radiator.

Never mind

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4" Lift on 33's
4.2L w/HESCO MFI & Howard Cam
T-5 & Dana 300
Smittybilt 9,500 Winch
Spartan Locker

2018 JKU - box stock
2002 TJ Sahara w/Very Rusted Frame
Onyx Dragon
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Posts: 436
« Reply #19 on: July 22, 2019, 03:02:25 PM »

Sorry I am late to this discussion - how do I say this? The 4.0L is setup to run with a 195F thermostat with an operating temperature of 210F on engines with the sensor located at the back of the cylinder head (next to the firewall).

It would appear that you are off by a few degrees which can be the result of bad timing (not likely the ECU will compensate for this) or spark plugs out of the heat range for your application. Also a lean running engine will run hot, but once again not likely unless you have bad O2 sensor. Most likely a bad O2 sensor will "throw" an error code. Too hot of a plug can cause pre-ignition and increase cylinder temperature along with engine knock.

Question, have you had the plugs changed recently? Are they the correct heat range? There is no standard for spark plug heat range. So the 10 or so heat ranges of an NGK plug are different for say, a Champion plug.

I know a little out there but pull your plugs, look at the tips what do you have to lose?



Answered before your edit!  Plugs are new, but it was doing this before hand. 

There's no errors from the 02 sensor and it just passed an emissions test.  I was contemplating this as well, but saw no pending codes before the test.  I can easily hook the scanner back up to check and see if there are any pending codes now.

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Bill Staples
1999 XJ
2018 JL Unlimited
Onyx Dragon
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Posts: 436
« Reply #20 on: July 28, 2019, 12:05:13 PM »

Ok, so re-did the gasket, changed out the thermostat (which I found out, I wasn't the last person to do the thermostat.  The last person to do the thermostat put a 180F one in).  Drove it around without AC, it was fine.  Drove it around with AC and it started warming up.  Pulled back in the driveway, electric fan isn't working.  It was working before.  I thought it seemed to be turning kind of slow, but thought it was just me.  If the fan wasn't working as well as it should, or was intermittent, then that would explain part of the problem.  At least now I can drive around without the AC on if I want, and it runs at normal temps.

I'm going to order an electric fan today.  I'm also going to do the fan mod on it.  I like that extra bit of safety cushion better.

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Bill Staples
1999 XJ
2018 JL Unlimited
dave2002ti
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Member 2019
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Posts: 1118
« Reply #21 on: July 29, 2019, 03:03:50 PM »

Ok, so re-did the gasket, changed out the thermostat (which I found out, I wasn't the last person to do the thermostat.  The last person to do the thermostat put a 180F one in).  Drove it around without AC, it was fine.  Drove it around with AC and it started warming up.  Pulled back in the driveway, electric fan isn't working.  It was working before.  I thought it seemed to be turning kind of slow, but thought it was just me.  If the fan wasn't working as well as it should, or was intermittent, then that would explain part of the problem.  At least now I can drive around without the AC on if I want, and it runs at normal temps.

I'm going to order an electric fan today.  I'm also going to do the fan mod on it.  I like that extra bit of safety cushion better.

Just wait one day your JLU's thermostat will have rationality issues if you have the 3.6l V6.  Not a cheap fix. 

Dave Apker

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Onyx Dragon
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« Reply #22 on: July 29, 2019, 03:09:24 PM »

Ok, so re-did the gasket, changed out the thermostat (which I found out, I wasn't the last person to do the thermostat.  The last person to do the thermostat put a 180F one in).  Drove it around without AC, it was fine.  Drove it around with AC and it started warming up.  Pulled back in the driveway, electric fan isn't working.  It was working before.  I thought it seemed to be turning kind of slow, but thought it was just me.  If the fan wasn't working as well as it should, or was intermittent, then that would explain part of the problem.  At least now I can drive around without the AC on if I want, and it runs at normal temps.

I'm going to order an electric fan today.  I'm also going to do the fan mod on it.  I like that extra bit of safety cushion better.

Just wait one day your JLU's thermostat will have rationality issues if you have the 3.6l V6.  Not a cheap fix. 

Dave Apker

Yeah, not looking forward to that. 

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Bill Staples
1999 XJ
2018 JL Unlimited
Onyx Dragon
Offline
Forum User
Posts: 436
« Reply #23 on: August 02, 2019, 07:29:56 PM »

Got the fan replaced, and it's running at the right temp around town. 

Not at ALL impressed with the shops in my sister's area who did the work.  The radiator is just sitting in there, held in place by the airbox (where it pushes up against it...) and the upper part of the mounting frame.  front metal piece that does things like hold the middle hood pin down to the upper radiator mounting frame is missing 2 bolts, the other two aren't even all the way down, and seem to be cross threaded, so they just stopped.  That's in addition to the wrong thermostat having been put in it, them being unable to diagnose an running hot problem (while the AC was blowing warmer than it should and the car was running warmer than it should, and the electric fan wasn't spinning as fast as it should...).  Thankfully she has a warranty now.

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Bill Staples
1999 XJ
2018 JL Unlimited
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