No Heat Puzzle?

[Preachdave]

We've got a 94 LS400 which the heater stopped blowing any hot air. First thought, thermostat. I've changed it twice---no change. Next, heater valve, or heater core. NOPE clean as a whistle through and through. Tried the valve manually in case it was broke, nothing again. Flushed and filled. Changed all the hoses. Nothing. Relays, fuses, OK, OK, OK. NO CODES SHOWING. Vent motor is working. I have had almost everything out and checked. ZIPPO. I'll take any ideas before I'm completely gray headed. Thanks!

[ROYT]

Did you top up the water inlet housing[ nut on top of thermostat housing ] with coolant first before the overflow tank?

the water valve lever is shown UP [presumably wide open] for this procedure.

Maybe this is to prevent an air lock?..just guessing but worth a try..

[Preachdave]

Did you top up the water inlet housing[ nut on top of thermostat housing ] with coolant first before the overflow tank?

the water valve lever is shown UP [presumably wide open] for this procedure.

Maybe this is to prevent an air lock?..just guessing but worth a try..

First of all, Thank you for responding. I'll try anything at this point. I didn't take it out, I tried like crazy to break it loose, but couldn't. I put some liquid wrench on it, and am going to try again tonight. Who knows maybe that might do it. Nothing else has. However, I am noticing a continous antifreeze smell when I get out of the car, but I have not leak. I've been working on this problem every day for almost 3 weeks now, and when I changed the thermostat the second time, the old hose cracked around the clamp and antifreeze leaked all over everything, so it just may be that. This is my daughters car, and I gave her mine to use while I TRY and fix hers. So I have to throw the car together each night so I have a way to get to work in the morning. Anyway, I'll give it a try. Thanks again.

[landar]

Dont grow another gray! Lets work this methodically. It shouldnt be that hard.

There are a lot of smart people on this board (excluding me of course ;) ).

Can you get to the heater hoses going into the firewall? Once the engine is up to temp and with the heater on max. heat,

feel the hoses. Are they hot or cold, lukewarm?

This is all presuming the engine comes up to temp and runs fine. It does come up to proper temp(~halfway on gauge), right?

If it does, that means your thermostat is good (and probably was good all along).

So, no heat in the hoses means air lock or blockage of some kind. And we go from there.

Heat in the hoses means something wrong with the core or a vent door/passage way.

Check those things and report back. We'll figure out where to go from there.

[Preachdave]

Thanks again. Sorry, my son plays football for the University of Tulsa and we went to the game yesterday. It was good to get away from the car for a day. Anyway, I checked out the heater core when I replaced the hoses, it looked great, but I blew it out anyway and it was clear as can be. The hoses all heat up fine. However something interesting did happen when I was refilling the radiator. I started getting some warm air, NOT HOT, but when I pushed the "auto" button I lost all warm air, and wasn't able to get it back no matter what I did. This happend when I replaced the Heater relay too, when I first started working on this problem. I started getting warm air, then boom, back to cold and couldn't get the warm air back again. Like I said before, I have replaced all hoses, thermostat, fuses, relays, blown out the system, cleaned the heater valve, flushed and refilled, have NO codes showing, and the circulations door is opening and closing just fine. I had another guy tell me he had this same problem and it turned out to be the control cable to the heater valve, so I have disconnected it and have the valve open all the time. I've tried opening it, closing it. halfway, all the way, nothing changes. It almost acts like something electrical, but everything appears to be working. Oh, I did get the bolt out of the water inlet and there was antifreeze clear to the top. That was before I made the BIG MESS with the antifreeze on the garage floor. OOPS! I am intersted in the small water line running from the water inlet to the manifold (I guess). I can't really see for sure where it goes until I take everything off. Anyway, still puzzelled. Thanks again and any suggestions still appreciated.

[eatingupblacktop]

Test the stat. Sounds like it could be wide open.

[Preachdave]

Test the stat. Sounds like it could be wide open.

I've change the thermostat twice thinking I might have got a bad one. I had that happen once with my chevelle. But it hasn't changed anything.

[landar]

Test the stat. Sounds like it could be wide open.

I've change the thermostat twice thinking I might have got a bad one. I had that happen once with my chevelle. But it hasn't changed anything.

The engine comes up to proper temp with gauge about half-way?

[dscabicky]

Test the stat. Sounds like it could be wide open.

I've change the thermostat twice thinking I might have got a bad one. I had that happen once with my chevelle. But it hasn't changed anything.

The engine comes up to proper temp with gauge about half-way?

Had the same problem. Replaced thermo, bypassed heat control valve...nada. Turned out all I needed was a new cap for the coolant overflow tank.

[Preachdave]

Test the stat. Sounds like it could be wide open.

I've change the thermostat twice thinking I might have got a bad one. I had that happen once with my chevelle. But it hasn't changed anything.

The engine comes up to proper temp with gauge about half-way?

Had the same problem. Replaced thermo, bypassed heat control valve...nada. Turned out all I needed was a new cap for the coolant overflow tank.

Yes, the engine comes up to temp. And I replaced the overflow cap a couple of weeks ago after reading a forum about that. I really thought that would do it. Anyway, I just came in from sticking a mirror up behind the controls to see if everything is working when I press the controls, and sure enough, everything is working like it should. I really, really, really, appreciate the suggestions. I figure someone will either hit on the problem, or has had it themselves. PLEASE keep any and alll suggestions coming!!!!!! THANKS AGAIN

[eatingupblacktop]

Ok, if your temp gauge shows normal temps, then stat's not the prob. Could be faulty cabin temp sensor.

[Preachdave]

Ok, if your temp gauge shows normal temps, then stat's not the prob. Could be faulty cabin temp sensor.

Thanks again. Where is it located?

[eatingupblacktop]

On my 91 it's on the lower panel just below and slightly to the right of the ign sw. There's also a solar sensor at the far right end of the windshield defroster, but that's for autoselecting the fresh/recirc mix and shouldn't affect your temp.

[landar]

Ok good, temp up to normal, stat is good (at least I hope your engine temp sensor is not lying to us...but probably not).

Next step, check the heater hoses again and try to see if they are hot, cold or lukewarm. Try to check right at the firewall (I am hoping there isnt

some kind of bypass valve inside the cabin itself). If the hoses are hot, then coolant is making it into the cabin and hopefully the heater core.

Check the hoses and let us know. I realize that you dont have a calibrated hand but you should be able to sense somewhat the temp. And be careful not

to get into any moving parts. (I know this is somewhat tedious. However, I am trying to get this narrowed and avoid the "shotgun" approach).

[Preachdave]

Ok good, temp up to normal, stat is good (at least I hope your engine temp sensor is not lying to us...but probably not).

Next step, check the heater hoses again and try to see if they are hot, cold or lukewarm. Try to check right at the firewall (I am hoping there isnt

some kind of bypass valve inside the cabin itself). If the hoses are hot, then coolant is making it into the cabin and hopefully the heater core.

Check the hoses and let us know. I realize that you dont have a calibrated hand but you should be able to sense somewhat the temp. And be careful not

to get into any moving parts. (I know this is somewhat tedious. However, I am trying to get this narrowed and avoid the "shotgun" approach).

I've finally got back to the car. I've checked the hoses repeatedly, and they both are extremely hot. I changed the cabin temp sensor, and still no heat. Lets see, I've replaced the thermostat twice, cleaned the heater valve twice, replaced all hoses (plus blew everything out), flushed the system and refilled twice (because I'm clumsy), burped the system I don't know how many times, removed, checked, and replaced all fuses and relays. changed the cabin temp sensor, checked for error codes, and still no heat. I've got the dash in shambles just checking wiring, from what I CAN see, everything on the controls seem to be working ok. SOOOOOOOOOOO I guess I'm going to have to send it in to have it diagnosed. It's snowing here today so driving with NO heat was a bit contrary to good sense. Maybe one day, the problem will be solved. Thanks again for ALL suggestions. Keep'em coming because I've got to wait until I've got the money to send it in, and with it being Christmas, that may be a while. Again, I really do appreciate any and all ideas. THANK YOU!

[eatingupblacktop]

After all the work you've done, my suspicion is a blocked heater core.

[PureDrifter]

Ok good, temp up to normal, stat is good (at least I hope your engine temp sensor is not lying to us...but probably not).

Next step, check the heater hoses again and try to see if they are hot, cold or lukewarm. Try to check right at the firewall (I am hoping there isnt

some kind of bypass valve inside the cabin itself). If the hoses are hot, then coolant is making it into the cabin and hopefully the heater core.

Check the hoses and let us know. I realize that you dont have a calibrated hand but you should be able to sense somewhat the temp. And be careful not

to get into any moving parts. (I know this is somewhat tedious. However, I am trying to get this narrowed and avoid the "shotgun" approach).

I've finally got back to the car. I've checked the hoses repeatedly, and they both are extremely hot. I changed the cabin temp sensor, and still no heat. Lets see, I've replaced the thermostat twice, cleaned the heater valve twice, replaced all hoses (plus blew everything out), flushed the system and refilled twice (because I'm clumsy), burped the system I don't know how many times, removed, checked, and replaced all fuses and relays. changed the cabin temp sensor, checked for error codes, and still no heat. I've got the dash in shambles just checking wiring, from what I CAN see, everything on the controls seem to be working ok. SOOOOOOOOOOO I guess I'm going to have to send it in to have it diagnosed. It's snowing here today so driving with NO heat was a bit contrary to good sense. Maybe one day, the problem will be solved. Thanks again for ALL suggestions. Keep'em coming because I've got to wait until I've got the money to send it in, and with it being Christmas, that may be a while. Again, I really do appreciate any and all ideas. THANK YOU!

put the temp on max, warm the car up, fan on max.

bring the RPM up to about 4000-4500 and hold it there.

hot air?

if so, you either have a bubble in the system, a leak somewhere (i had one that was TINY), a dead thermostat, or all of the above.

[yardbuzzard]

Ok good, temp up to normal, stat is good (at least I hope your engine temp sensor is not lying to us...but probably not).

Next step, check the heater hoses again and try to see if they are hot, cold or lukewarm. Try to check right at the firewall (I am hoping there isnt

some kind of bypass valve inside the cabin itself). If the hoses are hot, then coolant is making it into the cabin and hopefully the heater core.

Check the hoses and let us know. I realize that you dont have a calibrated hand but you should be able to sense somewhat the temp. And be careful not

to get into any moving parts. (I know this is somewhat tedious. However, I am trying to get this narrowed and avoid the "shotgun" approach).

I've finally got back to the car. I've checked the hoses repeatedly, and they both are extremely hot. I changed the cabin temp sensor, and still no heat. Lets see, I've replaced the thermostat twice, cleaned the heater valve twice, replaced all hoses (plus blew everything out), flushed the system and refilled twice (because I'm clumsy), burped the system I don't know how many times, removed, checked, and replaced all fuses and relays. changed the cabin temp sensor, checked for error codes, and still no heat. I've got the dash in shambles just checking wiring, from what I CAN see, everything on the controls seem to be working ok. SOOOOOOOOOOO I guess I'm going to have to send it in to have it diagnosed. It's snowing here today so driving with NO heat was a bit contrary to good sense. Maybe one day, the problem will be solved. Thanks again for ALL suggestions. Keep'em coming because I've got to wait until I've got the money to send it in, and with it being Christmas, that may be a while. Again, I really do appreciate any and all ideas. THANK YOU!

put the temp on max, warm the car up, fan on max.

Mine does the same thing. I have gone through the same diagnostics, new thermostat, cap, flush, burp, disconnected battery, Mine will get warm at higher revolutions but blows cold on idle. Sometimes it will quit heating at running speed. Sounds like climate control somewhere but I have yet to hear if anyone has fixed this problem with replacement of climate control...anyone out there? Thanks in advance. Closest dealership is 2 hours away and then how long to leave it, etc. Any help appreciated

bring the RPM up to about 4000-4500 and hold it there.

hot air?

if so, you either have a bubble in the system, a leak somewhere (i had one that was TINY), a dead thermostat, or all of the above.

[BillyShaft]

Wow man...with hot hoses up to the firewall, common sense engineering says there is either a valve preventing flow into the heat exchanger (I read where you said the valve was opening, but how do you know that? Just because the handle or operator moves does not imply the valve guts are actually turning.) or the heat exchanger is blocked.

Heater core or heat exchanger generally do not just up and clog completely...they will typically experience degraded performance producing warm but not hot air, or more commonly, leak all over the passenger side of the car and stink.

I will bet a frosty coke that the throttle valve that allows hot water into the heater core is not actually functioning. The operator may be moving, but I bet the valve itself is pooched.

Can't wait to hear what you find out...good luck!

~Brian

[cardona6569]

Hope, you can solve your problem soon. I tend to agree with the last post, you should get a valve and see what happens, or open the valve and see if it is not broken inside or really worn out. C

[oldskewel]

Maybe you could try to rig a tube/hose that bypasses the heater valve completely - as a test? I agree with others that say it sounds like the heater valve is not opening like it should. This test should determine in a very simple way whether that's true or not. If true, next step would be to figure out whether it is a bad valve, bad cable, bad control signal, bad sensor ... that is causing it not to open. (and until you figure that out, you could just leave the bypass hose in there if you can stand the heat)

Looking at the service records on my 91 LS400, the heater control valve was replaced at 96k miles due to leaking.

[yardbuzzard]

I went through everything like you did. Turned out it was a nearly clogged heater core. A determined mechanic spent 3 hours with solvents and air until it was clean. He said it was amazing at the amount of junk that came out of it. cost me a bunch but now it heats as new. And by the way, change your cabin filter if you have not done that in a while. Really helps the fan blow some serious air.

We've got a 94 LS400 which the heater stopped blowing any hot air. First thought, thermostat. I've changed it twice---no change. Next, heater valve, or heater core. NOPE clean as a whistle through and through. Tried the valve manually in case it was broke, nothing again. Flushed and filled. Changed all the hoses. Nothing. Relays, fuses, OK, OK, OK. NO CODES SHOWING. Vent motor is working. I have had almost everything out and checked. ZIPPO. I'll take any ideas before I'm completely gray headed. Thanks!

[roadkin98]

We've got a 94 LS400 which the heater stopped blowing any hot air. First thought, thermostat. I've changed it twice---no change. Next, heater valve, or heater core. NOPE clean as a whistle through and through. Tried the valve manually in case it was broke, nothing again. Flushed and filled. Changed all the hoses. Nothing. Relays, fuses, OK, OK, OK. NO CODES SHOWING. Vent motor is working. I have had almost everything out and checked. ZIPPO. I'll take any ideas before I'm completely gray headed. Thanks!

Not sure anyone is still looking at this thread but what did you ever find as the resolution to this heating issue

stu

[Ridgerez]

I went through everything like you did. Turned out it was a nearly clogged heater core. A determined mechanic spent 3 hours with solvents and air until it was clean. He said it was amazing at the amount of junk that came out of it. cost me a bunch but now it heats as new. And by the way, change your cabin filter if you have not done that in a while. Really helps the fan blow some serious air.

We've got a 94 LS400 which the heater stopped blowing any hot air. First thought, thermostat. I've changed it twice---no change. Next, heater valve, or heater core. NOPE clean as a whistle through and through. Tried the valve manually in case it was broke, nothing again. Flushed and filled. Changed all the hoses. Nothing. Relays, fuses, OK, OK, OK. NO CODES SHOWING. Vent motor is working. I have had almost everything out and checked. ZIPPO. I'll take any ideas before I'm completely gray headed. Thanks!

Where is the cabin filter?? Is it near the heater core?