I have a 93 aerostar that up until a couple of days ago was putting out the heat just fine. Then, I blew the gasket out of the water pump and lost all of my fluid. I replaced the thermostat and had a new water pump and gasket put on, and I had heat for about 20 minuters of driving then no heat again. I thought maybe I needed to flush the radiator system because when the gasket was leaking I filled it with just water. But unfornuately after back flushing the system, after about 15-20 minutes, no heat again. I just replaced the heater core about two months ago, its got the proper amount of antifreeze, a new thermostat, and a brand new water pump and gasket. I'm stumped on what to check for now. Because all I can come up with, is to replace the heater core again, can anyone tell me what it could be, and possibly tell me what else I might be missing or what to look for????????

 

Sometime after the 91 model, they put in a by-pass valve that is vacuum operated. If that fails you might not get any heat.

Check the vacuum line on the by-pass. Is it broken or loose?

Have you checked the heater hoses to see if they are getting hot?

There is also the blend door that directs the airflow through or around the heater core. If the cable comes loose or breaks that will affect the amount of heat you get. However if you stopped getting heat without moving the **** I wouldn't think this is the problem.

Do you have rear heat? If you do, do you have hot air in the back?

Don't know if this helps but it may give you something to think about.

 

In both instances, you had heat then lost it. This sounds more like the thermostat sticking in the open position, overcooling the system. You can verify this by feeling the heater hoses. Water moves directly from the pump through the heater core at all times. As the engine warms up you should be able to feel a corresponding rise in the temperature of the either one of the heater hoses going to the heater core. They should feel toasty warm to hot to the touch after the engine has run 10 minutes. Feel the hose at that time and again right after you notice the loss of heat. If the heater hoses now feel noticeably cooler after heat loss, then the thermostat is failing/sticking in the open position and needs to be replaced. This can happen even with a new thermostat. Stant brand are known to have problems.

On the bypass valve Tom mentions, the default (no vacuum) is the open position. In other words, it requires an active vacuum to cause it to remain closed. Normally, this is only present when you have selected the MAX A/C position. At all other positions the valve will be open. Since you have heat intially then lose it, the valve appears to be operating correctly.

 

Thanks guys for the info about what to check out for my heat loss. My question now is..." Where is that by-pass valve located and what does it look like", so that I can track it down and see if its leaking or not operating correctly.What exactly is a blending door to? Thanks Tom
Aerocolorado I read some more articles here about the heater hose warming up after warming the engine and they are warming up "toasty" even after the second thermostat now and still nothing but maybe luke warm air out of the defroster at best. I get cool to almost cold air out of all of the other settings. So I guess my question to you is..."Should I try putting a third thermostat in..(and not a Stant) and see if that fixes my problem?" and also IS it possible that I might be running my antifreeze to strong? Thanks again for sharing your knowledge and you're straight forwardness on helping me with this problem.

thanks again!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!

 

Oh I forgot to add after the last post....I have A/C but I dont have a rear heater. I dont know if that makes a difference or not.

 

Open the hood. It should be way over at the left side by the finder. The heater hoses shoud come off of the engine (near the thermostat) and go over to this location.

Just before they go through the firewall there is a valve. Both hoses should connect to it. There should be two hoses that then go through the firewall. There should also be another small vacuum hose connected. This is the line that controls the by-pass valve.

I don't know if the valve is there on the 93 but I have one on both my 94 and 96 Aerostars. The vacuum line comes over from the heating/cooling control somewhere. Under some circumstances (Max Cooling I guess) the vacuum line will cause the by-pass switch to close and prevent flow through (thus by-passing) the heater core.

Aerocolorado checked and said that the default/normal position on the by-pass valve is to allow the flow. Either the valve would have to fail in some way that prevents the flow through the core or you have a vacuum on the line when you shouldn't.

I would give you the link to the discussion we had on this valve but the server is too busy to allow a search. When you get a chance use the search feature and see if you can find it. I think there is a picture of the valve there. Also sometimes there is a by-pass valve for sale on e-bay. I've seen it there about 3 times now using the same picture. It may be there now.

The blend door is next to the heater core. Which is behind the glove box. As you turn the temp **** from hot to cold there is a cable that moves this door back and forth. Full heat will direct all the air through the heater core. Cold will cause the air to by-pass the heater core. And of course in the middle will give you a mix of hot and cold air.

Turn the **** back and forth and see if you can feel any resistance. The cable can come off or even break. One time I had an ink pen fall down the defroster and lodge aginst the blend door preventing it from moving.

If you think there is a problem with the blend door, you can remove the cover to get at the heater core and see the blend door. Watch it while you turn the ****. I'm not sure how hard it is to get to the cable if that turns out to be the problem.

As far as the t-stat goes, it could be sticking open. If it does then the heater hoses would not be getting too hot. If the heater hoses are hot, it could be the by-pass valve or blend door. I don't know if you can get your hand on the heater hose on the other side of the by-pass valve to see if it is hot. Try and let us know what you find.

 

No, I wouldn't change the thermostat if heater hoses are staying hot to the touch after the interior air goes cold. Test those hoses near the firewall where they go into the core. At that point you are beyond the water control valve and if the hoses are hot there, the water valve is not the problem. If both are cooler at that point, then the valve may be at fault. Here's what you are looking for.

 

That's the picture I was talking about.

Aero.. are you the one trying to sell this on ebay?

 

Tom,
No, but I bought this one on ebay. I haven't seen an original one but this one is constructed of pretty thin plastic. For the time being it works but I have problems with leaks at the joints and I am afraid if I tighten the clamps any more....POW!

 

thank you guys for your input. I'll ll try and open the heater core compartment open and look for that blend door and the valve that you are talking about and use your suggestions. I'll let you know how it works out. Thanks again for sharing your knowledge.

 

If you couldnt tell, I'm not the most mechanically inclined person, but I was just looking at my Haynes Manual on my Aerostar and was wondering if the reason I dont have any heat could be caused by the temperature sending unit going out or is out??? :? Please let me know, cause I'm really not having much luck. Thanks!

 

You wouldn't be the first to wonder that. Actually, the temp. sending unit is just a thermometer of sorts that sends information to the temperature gauge or to the engine computer. It does affect heat production.

BTW, I would not recommend taking the heater core cover off if you are just testing for a broken blend door. You would have to remove the core itself to see the door. Just get someone to move the control lever back and forth while you listen for a soft "chunk" sound as the door reaches the limits of travel in both directions. If you can hear a definite sound at both limits, the door is operating properly. You can also try to reach the movement lever on the top of the heater core box with your hand and feel for movement that way. Space is tight so you need small hands to do this.

 

So which sensor is delivering temprature to the temp gauge in the dash? The ECT sensor by the thermostat housing, or the water temp sending unit one?

 

The sensor for the dash gauge has a single wire while the ECT sensor has two.

 

I have a 91 Aerostar and am having similar troubles. The hose going into the heater core is HOT and the return is noticeably cooler. I don't know if that is a product of the heat exchange process or of a clogged heater core. I've gone to the trouble of tearing into the dash and visibly checking the flapper- it is functioning normally. The air is lukewarm, not hot. I'm moving to Wisconsin and I really need a decent heater. The engine temp is running normal so I don't think it is the thermostat. I've read a lot of other postings with similar problems and no solutions. I'm wondering if it is possible that this is all the better of heat the Aerostar can push out? I am cosidering replacing the heater core but I am not confident that will help. I'd love any advice anyone might have.

Thanks