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Unread 03-20-2015, 07:50 AM   #1
rodney_bettis
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Heat goes cold while sitting at idle.

I take my daughter to school this morning and while sitting at a red light, I notice that the air temperature coming out of the vents has started getting cold. I checked the radiator fluid and it was fine. Has anyone had this problem before and if so could I get some advice.

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Unread 03-20-2015, 08:08 AM   #2
ronjenx
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Look at the bottom of the coolant overflow bottle and see if there is sludge there. Sludge in the coolant system can plug the heater core.

What is the engine temperature gauge doing when the heater goes cold? Is it still straight up?
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Unread 03-20-2015, 08:18 AM   #3
rodney_bettis
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Temp gauge is straight up and it does not appear to have sludge in the overflow bottle. When the rpm's go up, the air starts to warm up.
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Unread 03-20-2015, 08:30 AM   #4
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Originally Posted by rodney_bettis View Post
Temp gauge is straight up and it does not appear to have sludge in the overflow bottle. When the rpm's go up, the air starts to warm up.
Feel the hoses to the firewall.
If one is a lot cooler than the other, could be a restriction in the heater core.
If both hoses are cool, could be inadequate flow from the water pump.
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Unread 03-20-2015, 09:05 AM   #5
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Or the tstat opened while at the stop light... does it do it EVERY stop?
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Unread 03-20-2015, 09:28 AM   #6
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Perhaps what you were experiencing was actually normal and the inside cabin temp sensor was just doing its job. Ive had similar experiences with mine thinking that something was wrong but held my hand close to a vent and the air was still warm, just not max hot. These later model JKs will cook you in short order if not regulated somehow. Check how you have your settings, it could be as simple as that.
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Unread 03-20-2015, 01:14 PM   #7
ronjenx
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Originally Posted by 1222 View Post
Perhaps what you were experiencing was actually normal and the inside cabin temp sensor was just doing its job. Ive had similar experiences with mine thinking that something was wrong but held my hand close to a vent and the air was still warm, just not max hot. These later model JKs will cook you in short order if not regulated somehow. Check how you have your settings, it could be as simple as that.
Possible. He says it's rpm related, though.

Speaking of cabin temp control, back in the '70s my '53 Hudson Hornet had automatic cabin temperature control.
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Unread 03-20-2015, 02:27 PM   #8
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^^^ How, by regulating the window openings?

Not sure if you are joking or telling a fact. If fact then that is pretty cool and you must have been the envy of your friends and relatives too. Even just having that '53 Hudson Hornet by its self is enough for envy.
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Unread 03-20-2015, 02:36 PM   #9
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^^^ How, by regulating the window openings?
Nope - An adjustable knob controlled bi-metal thermo-controller that compared incoming air to cabin air - and turned the fan on or off... and moved the vent door. Starting in 39 - the first auto control and until computers probably the best for ease and reliability. (also in the Wasp).

His 53 was one year short of the Kelvinator - which is the backbone of every positive venting and climate system today.
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Unread 03-20-2015, 04:02 PM   #10
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^^^ How, by regulating the window openings?

Not sure if you are joking or telling a fact. If fact then that is pretty cool and you must have been the envy of your friends and relatives too. Even just having that '53 Hudson Hornet by its self is enough for envy.
Not kidding.
Wishing I hadn't brought it up, though.
Had to sell it to move back to Maine
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Unread 03-20-2015, 04:21 PM   #11
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Not kidding.
Wishing I hadn't brought it up, though.
Had to sell it to move back to Maine
I know how you feel abought selling your pride and joy because I sold my ’69 AMX street racer. I would line up with the small airplanes at Montgomery Field in San Diego (ran on aviation fuel) waiting for my turn for fuel. It probably looked a bit silly to see a car mixed in with the planes but I didn’t care at the time. Most likely I would never gotten into 4x4s had I still had it but that is another story all by itself.
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Unread 03-21-2015, 08:31 AM   #12
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I know how you feel abought selling your pride and joy because I sold my ’69 AMX street racer. I would line up with the small airplanes at Montgomery Field in San Diego (ran on aviation fuel) waiting for my turn for fuel. It probably looked a bit silly to see a car mixed in with the planes but I didn’t care at the time. Most likely I would never gotten into 4x4s had I still had it but that is another story all by itself.
Now thats a way back when - before they required an N number! I used the pumps at Gillespie for YEARS - even rented a hangar once (on the app I stated I was developing a flying car). They caught on when they saw us rolling the race car over to the speedway and did not renew the lease...

Im the stupid one - I let a 65 Polara 500 with poly head 318 go for 250 in 1980 (I owned it less than 6 months and came across a 72 chevelle SS for 500). Saw the Polara 5 years later at Pomona Car Show - the owner proudly displaying the one of 125 factory drag race authenticity plaque - I never noticed the aluminum bumper until then.

Price of being a dumb kid is growing old enough to see the stupidity...
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Unread 03-23-2015, 09:18 AM   #13
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I have the same issue with mine. While idle the temp coming from the vents goes down but heats right back up when the RPM's go up. Really only noticed it when we had some really cold days.
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Unread 03-23-2015, 09:46 AM   #14
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I have the same issue with mine. While idle the temp coming from the vents goes down but heats right back up when the RPM's go up. Really only noticed it when we had some really cold days.
That is low flow through the heater core. BUT if you have a climate system - try manual first - it could be "close" to cabin temp and dropping some heat. Consider doing a flush and refill... left alone it only goes downhill from here...
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Unread 03-23-2015, 01:51 PM   #15
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Originally Posted by rodney_bettis View Post
I take my daughter to school this morning and while sitting at a red light, I notice that the air temperature coming out of the vents has started getting cold. I checked the radiator fluid and it was fine. Has anyone had this problem before and if so could I get some advice.
Hey rodney_bettis,
Have you noticed a change in the blower speed? Also are you only experiencing this when your heat is activated?
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