Montana sv6 no heat at idle

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Thread: Montana sv6 no heat at idle

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    Montana sv6 no heat at idle

    My 2007 montana sv6 has lots of heat blowing except when I come to a stop at a light for example , then it blows non heated air , but when I take off it starts to blow warm air again . Any thoughts ?

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    Re: Montana sv6 no heat at idle

    Quote Originally Posted by gregross1 View Post
    My 2007 montana sv6 has lots of heat blowing except when I come to a stop at a light for example , then it blows non heated air , but when I take off it starts to blow warm air again . Any thoughts ?


    You are low on coolant and have air in the system.

    Check your coolant level - not just in the jug, but remove your radiator cap (when cool......) and check the level in the radiator. You probably have a small leak and if the radiator cap is weak, it will not draw coolant from the jug as the engine cools down. If the coolant level is low, add coolant to the radiator and install a new radiator cap. Fill the overflow jug to the "hot" or "full" position, then watch the jug level over several days of driving to see if the coolant level continues to drop.

    If the vehicle is slow to warm-up, the thermostat may be stuck in the open position ( in addition to the low coolant). However, once the coolant is fully warmed from driving, the heat should not become cool at idle, such as when you stop for a traffic light, unless there is air in the system.

    Good luck - let us know what you determine.

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    Re: Montana sv6 no heat at idle

    Quote Originally Posted by 1999 White C5 Coupe View Post
    You are low on coolant and have air in the system.

    Check your coolant level - not just in the jug, but remove your radiator cap (when cool......) and check the level in the radiator. You probably have a small leak and if the radiator cap is weak, it will not draw coolant from the jug as the engine cools down. If the coolant level is low, add coolant to the radiator and install a new radiator cap. Fill the overflow jug to the "hot" or "full" position, then watch the jug level over several days of driving to see if the coolant level continues to drop.

    If the vehicle is slow to warm-up, the thermostat may be stuck in the open position ( in addition to the low coolant). However, once the coolant is fully warmed from driving, the heat should not become cool at idle, such as when you stop for a traffic light, unless there is air in the system.

    Good luck - let us know what you determine.
    That is exactly what I was thinking, too.

    I would also add to that if your van uses Dexcool (which I am pretty sure it does) I would recommend a flush and fill if it has never been done. I think that this will correct the problem if it is an air pocket, plus clean your entire cooling system helping to extend its life.

    My mom had an Astro Van that used Dexcool and that stuff can get nasty- it had pretty much turned to pudding in her van and once it did, it was impossible to permenantly correct the issue.

    If you do add coolant yourself, make sure that you know exactly the correct type that your van uses and do not mix with any other coolant. If your van uses Dexcool and you add a different coolant to it, it can cause some problems.

    Good luck!
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    Re: Montana sv6 no heat at idle

    I just thought of another possibility- I experienced this issue with my S-10.

    The doors that open and close to regulate where the air flows (vents, defroster, etc) are controlled by vacuum and there are typically small vacuum hoses that run from somewhere on the engine, to a plastic diaphragm and then from the plastic diaphragm to the firewall. I believe that the diaphragm on my S-10 was round, black and mounted on the underside of the hood.

    The small, rubber vacuum lines in this system on my S-10 had become old and brittle from the heat under the hood and developed vacuum leaks which caused the doors in the HVAC unit not to operate properly. I too experienced a similar loss of heat or air at low idle. When I discovered the hose issues and replaced them, the doors began to operate well again allowing the door in the HVAC unit to close fully in each position.

    Since your problem is occurring at low engine idle, this is definitely a possibility. At a stop or low idle, your engine is not producing as much vacuum and if you have a bad vacuum hose, it could be that there is not enough vacuum to overcome any vacuum hose issues (leaks or collapse). The next time you stop and the heat stops blowing from the vents, feel the defroster vent and floor vents and see if any hot air is being blown from either of them. If there is and you do not have you your heater set to defrost, floor or mix, I would say that a bad vacuum line from the engine to the diaphram or the diaphram to the selector switch in the HVAC controls is a likely culpret.

    I'd still check the coolant though, just to be safe.
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    Re: Montana sv6 no heat at idle

    ^^ your vacuum should be relatively high at idle and should go very low when accelerating.

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    Re: Montana sv6 no heat at idle

    Im going to say it probably has a plugged heater core. its probably partially plugged only allowing coolant to flow with higher engine speeds, lower rpm will create less flow. i would check the coolant level, make sure its full. then if thats good, check the condition of the coolant. its an 07 and if you havent flushed the coolant then dexcool over time will degrade and turn to gunk. should be changed every 30-50k. i would back flush the heater core, and use an acid flush to flush the system.
    An easy way to tell if the heater core is plugged is to get the vehicle to normal operating temp, then check the heater core hoses with an infrared pyrometer. both hoses should be close in temp. if one is substantially colder than the other, its plugged. you can also feel the hoses to the heater core and one will be cool and the other hot if its plugged. a properly functioning system should be close in temp on both hoses.
    You dont have a vacuum leak. the temp doors are electrically actuated on newer cars. vacuum is old school. plus if there was a vacuum leak, the ecm would see the fuel trims as lean and it would set a lean code. the temp door actuator and the temp door are not the problem.

    The only other option would be a blown headgasket or a bad water pump. but its not overheating so i would rule those out.
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    Re: Montana sv6 no heat at idle

    You were right, level was down so I got a flush and fill and all seems good now , lots of heat, not sure why it was down , there did not seem to be any leaks. thanks...

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    Re: Montana sv6 no heat at idle

    I am having this exact issue with my 2009 montana. The heat is enough that iit is uncomfortable blowing directly on your hand until you stop, then it cools right down. I have checked the coolant level, both in the overflow, and in the radiator itself. I have had this issue in my old truck and it was easy to just top it up, when I unscrew the cap on the montana, with the engine off, the coolant (dexcool) is right to the top. I am a little baffled. I am guessing that a flush and fill is my best bet?

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    Re: Montana sv6 no heat at idle

    1988GMChalfton, I see that you're seeking DIY advice but I wanted to let you know that I'm available via private message if you ever want me to schedule an appointment at your dealership for a diagnosis. I'm sorry that you've been experiencing these frustrations!

    Katie
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    Follow us @GMCustomerSvc on Twitter.

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    Re: Montana sv6 no heat at idle

    Quote Originally Posted by 1988GMChalfton View Post
    I am having this exact issue with my 2009 montana. The heat is enough that iit is uncomfortable blowing directly on your hand until you stop, then it cools right down. I have checked the coolant level, both in the overflow, and in the radiator itself. I have had this issue in my old truck and it was easy to just top it up, when I unscrew the cap on the montana, with the engine off, the coolant (dexcool) is right to the top. I am a little baffled. I am guessing that a flush and fill is my best bet?
    That's the easiest step, if that doesn't work it could also be a worn out water pump, which at lower engine speeds just doen't move enough water yet at higher engine speeds it does.
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    Re: Montana sv6 no heat at idle

    Quote Originally Posted by funkypunnk View Post
    That's the easiest step, if that doesn't work it could also be a worn out water pump, which at lower engine speeds just doen't move enough water yet at higher engine speeds it does.
    I've seen a couple like that but it isn't really wear... it is like the coolant has become acidic, and has completely dissolved the impeller of the water pump. I took one out of a Pontiac once and there was just the shaft and a sharp very thin piece of flat steel in there, like a small circular saw (the impeller "pells" were all completely gone...)

    just punch the gas when stopped and see what happens...

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    Re: Montana sv6 no heat at idle

    In park, if I rev the engine I get great heat, but I have to be over 2000 RPM's I would really hope it is not the water pump, but there is 131000 kms on it. I didn't put a water pump in my truck until about 250,000

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    Re: Montana sv6 no heat at idle

    Quote Originally Posted by Smaart Aas Saabr View Post
    ^^ your vacuum should be relatively high at idle and should go very low when accelerating.
    Not necessarily.

    First of all, in a generic sense, nope, or maybe but .... because it depends on where you draw the engine sourced vacuum from ie above or below the throttle plate. Ie does a system in question use manifold . intake manifold vacuum ( sourced from below the throttle plate ) or does it draw from above ? The two move in opposite directions for obvious reasons. Above the throttle plate is commonly referred in the 'States as 'ported' vacuum. It also referred to in other ways elsewhere, most of which I cannot remember at the moment - one informal term is 'throttle' or 'throttle plate' vacuum.

    Second, also in a generic sense, vacuum leaks can open and close or go somewhere in between depending on a lot of things - the effects of which can be multiplied by changing levels of available vacuum.

    Third, with plenty of interesting variations btw, what brian5o describes is a fairly well known and at this point relatively common occurrence for his S10. ( There are interesting variations for 4x4 equipped product up to and including sucking transfer case oil into the HVAC control system. There are also plenty of TSBs from GM on this as well and also very similar ones for other vehicles with vacuum operated systems and accessories.


    As to if it belongs on the list for the op's vehicle don't know in a specific sense but again, in a generic sense checking for both control and system operation of both blending and distributing is a good idea once the rest of brian5o's suggestions are followed thru on first, just like he said.

    In other words, once the basics of the cooling system are ascertained to be nominal and if not then corrected and then after that if the problem persists.

    **********

    Brian5o, decent job + on both your posts - thanks for posting.
    Last edited by AMERICA 123; 01-23-2013 at 08:24 PM.
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    Re: Montana sv6 no heat at idle

    Quote Originally Posted by 1988GMChalfton View Post
    In park, if I rev the engine I get great heat, but I have to be over 2000 RPM's I would really hope it is not the water pump, but there is 131000 kms on it. I didn't put a water pump in my truck until about 250,000
    did you check the H2O pump belt - and related ?

    Is the air flow from the blower ( regardless of what the temp. is doing ) nominal ie performing correctly ?

    Any fluctuation etc on the engine coolant temp / engine coolant temp gauge ?
    Last edited by AMERICA 123; 01-23-2013 at 08:31 PM.
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