Heat only when accelerating.

[sido]

Hi guys, i am having a problem with WJ jeep 1999 4.7

The car is heating only when i am accelerating.
If the car is standing still on the parking lot, heater blows cold air.
If i am revving the engine from 1000 to 2000 and back, or accelerating the heater starts working.
When driving, heating works-ish.

I checked the water pump. It looks normal, nothing broken or weird about it.
Flushed the heater core, about 4 times. I’ve also changed coolant. Every time I do this, I also bleed the system to get air out. Every time i flush it, heating works little bit better. After few days starts getting worse.

Is there anything else to check????
When I bought the car 8 months ago I had a leak, so I’ve used stop-leak product.
Which was a mistake, but I am new to this car repairing.

Topic

[college man]

Does the vehicle come up to operating temp?
Sounds like air is still trapped. usually when
you rev the engine and heat starts to be felt
and goes cold when at idle. Air is still trapped.

http://www.ericthecarguy.com/faq/what-to-do-when-your-engine-overheats#SolvingCoolingSystemProblems

[george gonzalez]

Find the highest spot in the cooling system, and bleed air out from there. Bubbles always go to the top, so you have to let the air out there, OR you have to rev the engine way up so the air gets pushed along to the radiator or overflow fill.

Also air will tend to work its way out over time if your overflow system is working properly. fill the overflow tank half full and put a crayon mark on the level. Drive the car a few days and you should see the level going down if the overflow system is working properly. For this to work right you need a new, well sealing radiator cap, not only keeping pressure in, but letting liquid in from the overflow tank as things cool. For this to work the overflow hose and its connections and O-rings have to be in perfect shape, otherwise it’s like trying to suck on a leaky straw.

[Erik]

Your heater core needs replaced and your blend air doors as well while your in there ive done like 6 this winter its pretty common on these you can check all the other stuff to but im almost positive you will need to put a heater core in it. The stop leak prob did help the situation.

[Tom]

I agree that it sounds very much like you need to bleed the system out, there is air trapped in it somewhere, and that is preventing your coolant from circulating properly. Fully bleed all the air out of it, and I think your heat will work 100%

[Matt Brandsema]

These are textbook symptoms of air in the cooling system. Bleed the system out. Eric has a video on how to do this.

[Kevin Criswell]

[quote=”Xyius” post=84227]These are textbook symptoms of air in the cooling system. Bleed the system out. Eric has a video on how to do this.[/quote]

Agree. Classic symptoms of air trapped in the system.

And it sometimes takes multiple bleedings to get all the air out.

[EricTheCarGuy]

I’m with the group, air in the cooling system. I cover it in more detail in this article.

http://www.ericthecarguy.com/faq/solving-automotive-hvac-problems

Keep us posted.

[Erik]

these engines are extremely easy to bleed if you look on the left side of the engine aka driver side you will see a bleed screw unscrew and fill with coolant once coolant comes out then you are bled I usually still use my fast fill funnel afterwards just to be safe then sorry, but if you get it bled and you still have the same issue im sticking with my original answer, also as a side note ive seen the water pump impellor be messed up as well, and on rare occasions electrolysis eating the timing cover.

[Jonathan Stiver]

Is it a Limited or Laredo? Blend doors are very common for this on the Limited with the auto climate system which has electronic blend doors. I converted mine to the manual (vacuum actuated) HVAC unit.

[Jonathan Gabriel]

Hey everyone, so I had this same issue the past year or so. I have an 05’ Honda Accord Ex 4cyl Auto. Back when a heating system issue occurred, I was told that the heater control valve plate, located at the firewall, rusted from the swivel mechanism and potentially got lodged in the fins of the heater core. After 2-3 reverse flushes it appeared that there was no extraction of that broken piece from within the heater core. So the heater control valve was replaced, along with the water pump, as that was initially what we believed the problem was, and the thermostat was replaced as well. For more background, I replaced my water pump 5 days ago, this time sue to a wobbly pulley, new coolant, did the whole air bleeding process, so no issues there. Fast forward to yesterday, its cold weather season again and I wasnt going to deal with this lack of heat anymore. Finally went to another guy to get this flush done correctly… A 2008 Honda Pilot pulls out of his garage and he directs me to pull into the garage, I quickly explain that I have heat when revving up the engine or driving at highway speeds, but not at idle. I assure him the temp guage stays at normal temp all the time, coolant levels proper, and water pump recently done. So he asks me to pop the hood in order to observe the heater control valve movement when switch from HOT to COLD and back a few times. Then he says “Wait a sec, let me tighten this valve, it looks loose”… and in that instant, the car blew out HOT air without revving it. I was amazed and annoyed at how simple that was, how easily overlooked it went, but also how convinced I was I needed a flush or new heater core when the problem lay with the looseness of the heater control valve. Turns out that the Pilot that left just before me had the exact same issue, go figure! Hope this helps someone experiencing this issue with their Honda.

[Author]

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