98 Sable - No heat when moving

Hi have a '98 Sable, 3.0L, overhead valve engine. It's generally around 35 degrees F outside right now. If I start up my car and let it sit there in park, the engine heats up and the temperature gauge
goes up to the 1/3 point or so and stays there, seeming to indicate the thermostat is doing its job, and I get heat out of the registers in the passenger compartment. If I then go driving down the road at 40 MPH or so, the registers stop putting out heat and start putting out cold air. Any ideas on what would cause this? I thought that probably the heater core was partially blocked like it was a year or two ago (and maybe it is), but my mechanic just flushed it out last week with no noticeable change. I then thought that maybe the water pump was only marginally working since there were a lot of problems with the water pump, corrosion, etc, so I replaced that. The old one didn't look brand new, but didn't look terrible, either. No noticeable change. (It was not a complete waste; as part of the process, I found that the tensioner was stuck, so I replaced that). Any insight would be much appreciated. Thanks!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Checked/changed your thermostat?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Noozer wrote:

The thermostat would be my first guess too.
Just sitting there the only air moving past the radiator comes from the fan, so even if the thermostat is stuck open the engine might still get warm, however once you get moving down the road there is going to be a LOT more cold air flowing over the radiator.
You say the gauge shows about 1/3 when you are sitting, does it stay there when driving down the road and the heater quits or does it drop?
Jeff DeWitt
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
low coolant level these cars are known for rusted cooling lines and seeping coolant is the blower working correctly?
Jeff DeWitt wrote:

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

Low coolant would certainly do it!
I had a VERY unpleasant 70 mile drive years ago with a badly leaking coolant line. About every two miles had to stop and add water, and I knew when it was time to add water because the heater would stop working.
That was in a Ford Tempo, last road trip I ever took in that car.
Jeff DeWitt
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks for the ideas and the feedback. Unfortunately, unless I messed something up along the line (which is certainly possible), I think I have already eliminated most of the ideas. I guess I forgot to mention, but the thermostat was changed a couple weeks ago. That seems to be working fine. The coolant level is OK. The blower motor is OK; it is definitely moving air. The temperature gauge stays at the 1/3 mark regardless of whether the car is sitting there or moving. Jim suggested perhaps there is a vacuum leak in the system that controls the doors that regulate airflow. I have not really noticed anything strange about the operation of the system. It does not seem to be slow to respond, but I have not really been thinking about it, either. I will try to do some research on this. In the meantime, if anyone has ideas on how to definitively determine whether this system has a problem or not, I'd be glad to hear them. Thanks much! - Phil
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@winfordeng.com wrote:

1. Two very recent threads detail recent experiences with new thermostats that weren't working right. 2. Was air bled from the system properly? How?

I know you meant to say something else, because the way to determine whether there's a problem would be to drive 40MPH and see whether you have heat.
--
Angry American flags attack Hillary Clinton!

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I can not guarantee that air was properly bled from the system. I squeezed the upper radiator hose a number of times and got gurgling noises from the overflow tank, indicating that fluid was moving. I realize that that may not totally eliminate that possibility of an air bubble. Actually, I did not mean to say something else. When I said "system," I was referring to the system that controls the airflow doors. Obviously, there is a problem with the vehicle. I'm trying to figure out which system has the problem.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
New does not necessarily mean good:
I would let it idle, and see how high the temp gauge goes, before the cooling fan comes on. (That is if it has an electric cooling fan?)
If so, and the gauge does not move more than one third, before the fan comes on. You still have a bad thermostat. Or alternatively, you may have a head gasket just starting to leak combustion into the cooling system.
Air goes in the heater core if a head gasket is starting to fail, and no way for hot coolant to get into it.
Feel both hoses going to the heater core, it can also be a partially plugged heater core.
I hope this helps.
RK

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
i know i flush alot of these cars heater cores out
snipped-for-privacy@winfordeng.com wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
get a 190's thermostst.should get you going.
http://www.minibite.com/america/malone.htm
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@winfordeng.com wrote:

Could possibly be a vacuum leak in the system that control the doors that regulate airflow. Do the other controls work that direct the flow to different areas (defrost, vent, floor, etc). Do they work normally or are they slow to respond?. I assume you would have mentioned if the temp gauge also went cold when you start to drive.
-jim
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hey, I just wanted to let everyone know what the deal was on this. I took it in to my mechanic. Like I mentioned, he had already flushed the heater core recently, and he had always used a Prestone flush. When he did the flush, he wasn't getting anything out to speak of. Anyway, he did some research and found out about a product called Matilda or something like that, I guess, from NAPA. He used that, and he got a bunch of black junk out of there. Heater works great now, regardless of vehicle speed and blower speed.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It pays to flush out your cooling system every year. Adds life to the components.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

When that happens, does the temperature gauge drop down to the cold side ?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Shawn wrote:

--
Angry American flags attack Hillary Clinton!

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.