Why no heat at idle??

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G35TR
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Why no heat at idle??

Postby G35TR » Mon Dec 22, 2008 5:10 pm

Anyone know why I might be loosing hot air from the heater whenever I come to a complete stop (like at a red light) at idle? The air starts turning to cold, but as soon as I accelerate and the RPM's raise, the air goes back to normal hot air.

I took this in to the dealer as I had this problem 2 years ago. The work order said no problem found and the the cause was suspected as air pocket in the coolant line. Just mentioned that they topped the fluid off.
Also, I notice now that when I shut the truck off, I hear a a hiss that seems to last about 2 seconds as soon a the engine shuts off.

Any ideas?


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Captain
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Postby Captain » Mon Dec 22, 2008 6:26 pm


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blink32
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Postby blink32 » Tue Dec 23, 2008 7:32 am

Captain caveman wrote:Thermostat my friend
You posted that before and you're thinking too hard. Check the post below, if your thermo is stuck open it'd have to be 40 below out to never get heat. And in florida I doubt that happens much.

http://www.thenissanpath.com/viewtopic.php?t=1410

A stuck open thermostat would never cause a hissing sound. Although a pressure escaping from a coolant leak would.

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Postby Jerseyparts » Tue Dec 23, 2008 7:45 am

I have to agree with Blink, I would think that what you are describing, is caused by not enough coolant in the system.

I would take it back to the dealer, and demand that they fix it.

B

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Postby Captain » Tue Dec 23, 2008 8:20 am

Out of all the times Ive seen trucks not heating up or blowing cold out of the dashes in all types of weather from 50F to 10F the Thermostat is stuck open.

Engines today need the coolant to be 170-180F but with a stuck Thermostat the engine will show close to operating temp around 150 or so in any ambient temp above 40deg. With 140 or less coolant temp by the time the coolant makes it to the HVAC unit its about 100F and will feel cold threw the vents. When you give it gas the water pump pumps harder and forces hotter water into the HVAC but off the gas the engine cools down to fast.

As to were the engine had a good thermostat the coolant will be close to 170F going into the HVAC.

Try what you want but I would put a thermostat in.

G35TR
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Postby G35TR » Tue Dec 23, 2008 8:25 am

Interesting. Well I noticed the problem return in the past month or so (with the cooler weather), and I just drained and flushed the coolant this past weekend. This being said, the problem still exists. Also, the water temp is showing normal.

I'm guessing this (being a coolant system problem) should be covered under powertrain? I got 2300 miles until 60K, so I might as well bring her in.

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Postby Captain » Tue Dec 23, 2008 9:51 am

G35TR wrote:Interesting. Well I noticed the problem return in the past month or so (with the cooler weather), and I just drained and flushed the coolant this past weekend. This being said, the problem still exists. Also, the water temp is showing normal.

.
Not to be a dick but Whats normal? our Gauges on the PF do not show the temp on a digital gauge but on a analog non accurate gauge. Is somewere around the middle considered normal? Like I said the Coolant temp sensor reads right on the block were the most heat is generated. In the intake its not that temp.

I hate to see you do a coolant flush two times with out changing it thermo. [/b]

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myriad46
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Postby myriad46 » Tue Dec 23, 2008 9:54 am

Is there a separate valve to the heater core? Isn't it regulated by the temperature control knob, on the dash?

This same issue is happening with my 2005, which I just bought. If i run it in the driveway, the temp gauge comes up, but no heat out of the vents. If I start it up and drive it cold, it heats up (both gauge and air) in no time.

Perhaps with the added pressure from the water pump while driving is enough to overcome the faulty valve, but at idle, it's just not enough.

G35TR
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Postby G35TR » Tue Dec 23, 2008 10:22 am

Captain caveman wrote:
G35TR wrote:Interesting. Well I noticed the problem return in the past month or so (with the cooler weather), and I just drained and flushed the coolant this past weekend. This being said, the problem still exists. Also, the water temp is showing normal.

.
Not to be a dick but Whats normal? our Gauges on the PF do not show the temp on a digital gauge but on a analog non accurate gauge. Is somewere around the middle considered normal? Like I said the Coolant temp sensor reads right on the block were the most heat is generated. In the intake its not that temp.

I hate to see you do a coolant flush two times with out changing it thermo. [/b]
I can only consider normal as it is described by Nissan in the vehicle's "Owner's Manual", which would be the middle area of the coolant temp. gauge.

Also, I won't be doing a second flush. I'll let my dealership pickup the costs of that one if need be.

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Postby G35TR » Tue Dec 23, 2008 10:27 am

Blink, if it were in fact a leak which allowed air into the system, wouldn't coolant also be leaking out?

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Postby Captain » Tue Dec 23, 2008 10:34 am

yes a you would be loosing coolant as well. Some leaks come when the truck is cool and other after its hot an running. If you stop by a pep boys they rent a coolant pressure tester. pump the pressure up to 15lbs or so and let it sit for 15min and check for leak at the gauge and look around the floor.

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Postby blink32 » Tue Dec 23, 2008 11:02 am

G35TR wrote:Blink, if it were in fact a leak which allowed air into the system, wouldn't coolant also be leaking out?
Typically this would be a yes. But it doesn't have to be a large leak to let air in. There doesn't necessarily have to be a puddle on the floor. If you have air bubbles in your system you have a leak. Prior to just throwing $$$ at it (in this case you said so you are taking it to a dealer since it is under warranty so you aren't spending anything) and replacing parts like a thermostat the free route should be explored. Driving the front of a Pathy up on ramps, opening the radiator cap and running the car to full operating temp would/should purge any bubbles.

I would, however, not suggest this in your case. You have the hissing sounds which is abnormal and, if it is a leak, a competent dealership should be able to find the leak and fix the issue.

If you like have a search over at nissanhelp.com where there are actual Nissan Tech's that respond to these issue. You will see it's been covered several times there and appears to be a semi-common occurance.

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Pappy
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Postby Pappy » Tue Dec 23, 2008 1:14 pm

The first thing to consider is the themostat is stuck open, however in the olden days, all the vents, heater control "doors" inside the dash were vacuum operated. It was common to have loss of heat because the vehicle might have a small vacuum leak and at idle, the doors would shift.

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Postby KEVSTER » Tue Dec 23, 2008 7:08 pm

I would say the cheapest test would be replace the T stat with a quality brand, make it stainless steel. Also the problem could go deeper with a bad water pump, pump may not be circulating the water correctly.

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Postby blink32 » Tue Dec 23, 2008 7:13 pm

Cheapest test is the free one following the service manual. Raise the front end, open the system, bring it up to temp and burp the system. Exact steps can be found in the troubleshooting section.


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