No heat

My daughter has a 1998 GMC Jimmy. It has climate control. She is getting no heat even if the temp is turned all the way up. I check the coolant level
its fine. The engine temp gauge shows its up to operating temp. I felt the hose's to the heater core and one was warm but not hot the other was cool.
Is there some kind of a flow switch that controls the water to the core, or should I be looked at a blocked core. Core replacement sounds like difficult job.
I need to get it fixed soon we are in Michigan and its not going to get any warmer for a long time.
Thanks
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Temperature is controlled by the amount of air the system allows across the heater core. No control on the coolant side. Your temperature observations suggest low coolant flow through the heater core.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Tim & Linda wrote:

Not sure about the '98 Jimmy, but older GM cars had a vacuum operated flow control valve that was supposed to open when you "turned up the temp".
Good Luck, Mark
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Mark Sparge wrote:

--------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------- Second thoughts on my previous post -- if you find that your vehicle has a vacuum operated flow valve, check for the presence of vacuum before you change anything.
HTH, Mark
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
thanks for your ideas. I pulled the radiator cap today and found a slug on it and in the rediator. I took it to a repair shop and they said someone had put stop leak in. It was by the previous owner. Tomorrow it goes in for a flush hope that will fix it.

-------------------------------------------------------------------------------------------------------
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Well, the previous owner put the stop leak in there for a reason...to avoid fixing a leak, most likely. When you flush the radiator and engine, you may well find your leak is back.
I developed a slow leak in my van soon after I acquired it (used). Turned out it was corroded freeze plugs. When I pried the old ones out, found the block FULL of putty-like gum. Had to dig it out, flush it, etc until I got it clean, and replaced the bad freeze plugs with new ones.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

meaning, coolant is not flowing through the core. The heater core is just like the radiator, only in a mini-version. So, either there is a faulty control valve(the T-stat is the 'control' for the radiator) or the core is clogged with junk. I'd first suspect a faulty control in the flow system to/through the core, if there is one. If that isn't the case, then it's a problem with the core. Maybe you can 'back-flush' the core with a water hose. Remove the hoses, put a garden hose on the core hose connection that is the cold one. Turn on the hose.....at a slow rate of flow....if there is not a flow control valve involved, and the core isn't too badly clogged, water 'should' flow out of the connection that was the warm hose. I'd have a length of hose on the other core connection, to avoid getting the engine compartment wet if this flush method works. If the flush works with this hose connection, reverse them and make sure water flows both ways. Unfortunately, there can be some bad news with the core even with if you get flow through the core. If the core was clogged, whatever was stopping the flow, might also have cause a break/hole in the tubing of the core...meaning it's a leaker! A leaking core has only one fix.....replacment. Breathing the chemical-laden air in the cabin is bad for the lungs. The 'life' of a heater core is about 10yrs(give/take), depending on how well the cooling system was maintained and the quality of the water used.
Hope some of this helps.....
Dave S(Texas)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
You should be able to do the same thing from the firewall side where the hoses go in. No need to go near the core unless it is bad.
On Thu, 1 Dec 2005 08:42:25 -0600, snipped-for-privacy@webtv.net wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Sorry, I didn't catch the original message. Bear in mind that the control valves are all vacuum operated - my Impala A/C got stuck in one position; after a LOT of searching, I found a tiny vacuum line with a hole in it (some battery acid had apparently dripped onto it.) You should be able to hear/feel the airflow changing if you change the controls from floor to vent to defrost, etc. - if no change, likely a vacuum line.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Is it possible for me to get a good system flush? Or should I just spend the $60 and take it to the shop?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It sounds like it needs a good flush. Unfortunately, that flush is liable to expose the reason why the PO put stop leak in it. Maybe you'll get lucky.
Dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

flush it with a garden hose. I've done that a couple of times on different cars and it's worked well.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You can do a pretty fair job yourself. You might want to take off both radiator hoses, take out the thermostat, and flush with a garden hose. You can usually take off one end of the heater hose and flush through the core as well.
Then replace the radiator hoses and thermostat with new. (There is never a better or cheaper time to do it.)
Now, your original owner's leak may show up. It may be best to test the system with water alone until you are sure the heater is working and nothing is leaking. I hate to lose new antifreeze when I dont have to.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I should of taken it to the shop. I went out and got a flush thing made by Prestone to put in a heater hose. I got a new hose took the old one off and put this flush thing in it. Then I turned on the hose let it run for about 10 minutes then I started the truck and let it run for another 10 minutes. I got a bunch of junk out. Then we time to put it back together but I have to drain the water out so I can put antifreeze in. The drain plug is a real pain to get to. I found but just ended up taking the lower hose off. Filled it back up and started it. Let it run for a while and added coolant as needed. The heater only puts out heat when I accelerate while at idle its cool air. I will take it for a short drive and check the level again. Time spend about 5 hours, two bottles of coolant, and the flush thing. around $25.00. If a heater core is needed I will take it in to be fixed. All this and I was in the cold (25 F) and snow.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It was sort of a halfway job, the way you did it, Im afraid. But I agree, run it awhile and see what happens.
On things like this, you either fix them properly yourself or take it to the shop. Half measures avail nothing....
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
And I froze my butt off doing it. I wonder now if I have an air lock in the heater core. I cant remember how to get it out, its been a long time that I have done that.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I'll bet you did get a mite cold.
Airlock is claimed to be a non-uncommon problem. I dont know if there is an easier way (I hope so), but on those occasions I have suspected it, I just removed a heater hose and flushed directly through the core.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I second that. One thing that hasn't worked for me since early 90's vintage cars is simply allowing it to burp out. Just doesn't seem to do it anymore. I know GM dealers often pull a vacuum now on newer cars to evacuate any air. I should think HLS' idea would work just as well in this situation - it's worked for me.
--

-Mike-
snipped-for-privacy@alltel.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.