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Unread 01-03-2014, 11:50 PM   #1
HiPoint
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Engine not getting up to operating temp and no heat inside.

1999 Sahara 4.0L, 3 spd. automatic.

Title pretty much says it all. Temp is barely above the 1st notch on the temp gauge (it was like this in the summer also) and there is no heat on any setting. I replaced the t-stat with a 195* thinking the PO had a 165* in it and no change. I bled the air from the system properly after t-stat replacement.

Anyone have a similar issue? I tried searching this forum and Google with no luck. Heater core clogged? Radiator clogged? Thanks in advance.

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Unread 01-04-2014, 04:57 AM   #2
ky-homelite
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Maybe a combination of things? Temp sending unit bad and the heater core plugged up?
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Unread 01-04-2014, 10:02 AM   #3
JFM626
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Check your actual temperature at the thermostat housing with an infra-red sensor. It will be correct within a couple of degrees. If it is around 200 to 210 after warming up, your thermostat is working fine. If the engine temperature is where it should be turn the heatrr on full blast and check the two hoses going into the heater core at the firewall, one should be at operating temperature -- about 200 the other about 10 - 15 degree cooler. If the cooler one is a lot cooler and no heat is present in the cab then you most likely have a blocked heater core and you will need to flush it. If both hoses are close to the operating temperature, you may have a problem with the blend door, or the heater core fins are plugged with duff.
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Unread 01-04-2014, 10:11 AM   #4
Stu Olson
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^^^ Agreed....pick up an infra-red temp sensor. I bought one years ago at the local Harbor Freight and it is still working. I use it to check everything...from my diff housing temps, brake temps, the heat pump in my house, electrical circuit breakers on my house, etc. They aren't that expensive and beats the heck out of guessing when trying to troubleshoot your Jeep!
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Unread 01-04-2014, 10:12 AM   #5
Jerry Bransford
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Are you by any chance running a "fail-safe" thermostat? That type of thermostat has a nasty habit of failing in the open position which would prevent the engine from warming up in a reasonable amount of time.
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Unread 01-04-2014, 10:37 AM   #6
HiPoint
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Quote:
Originally Posted by Jerry Bransford View Post
Are you by any chance running a "fail-safe" thermostat? That type of thermostat has a nasty habit of failing in the open position which would prevent the engine from warming up in a reasonable amount of time.
The t-stat I recently installed was a Murray 195* from O'Reilly.
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Unread 01-04-2014, 10:46 AM   #7
Jerry Bransford
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Quote:
Originally Posted by HiPoint View Post
The t-stat I recently installed was a Murray 195* from O'Reilly.
Ok, do you know if that is a fail-safe model or not? Some Murray thermostats are fail-safe designs which are notorious for failing in the open position.

Here's one thread on that... http://www.jeepforum.com/forum/f9/an...tchin-1066813/

I never (!) recommend a fail-safe thermostat, stick with a standard 195 degree thermostat like from Stant.
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Unread 01-04-2014, 02:56 PM   #8
HiPoint
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Quote:
Originally Posted by Jerry Bransford View Post
Ok, do you know if that is a fail-safe model or not? Some Murray thermostats are fail-safe designs which are notorious for failing in the open position.

Here's one thread on that... http://www.jeepforum.com/forum/f9/an...tchin-1066813/

I never (!) recommend a fail-safe thermostat, stick with a standard 195 degree thermostat like from Stant.
It is not a fail safe model.
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