No Heat in my 91 Ex!

Since I replaced the leaky radiator I have not been able to get any heat. It's an exact capacity OEM type replacement. I flushed out the entire system and ran the yard hose through the heater core to make sure it was clean and had full flow. I filled & flushed 2x with clear water and added 50/50 antifreeze. I had to install 3 thermostats (2 180º & 1 195º) before I got a 195º one that would not go up and down like a yo-yo every 15 seconds. The needle gets straight up between the RM, but the minute I turn on the heater fan the temp gauge goes down to N or less and comes up slowly to RM and back down again. I put in a 4th different brand 195º stat with the same results, no heat, just cool air. Both heater core hoses are hot! I changed the AC/Heat selector dash module with no change. The coolant is equally scalding hot in all heater and rad hoses. Before the rad change, for five years, I was forced to use a 170º in summer to use AC so it would not overheat, and a 195º in winter to get good heat and the gauge always stayed steady in the middle of the A and never overheated even though it did run hot. My early model 91 does not have a heater control valve, but according to other posts is that it helps only to keep hot water out of the core in summer so the AC runs more efficiently. (I plan to do that mod next summer.) Even though I have full flow through the heater core could it be bad? Is there something I did not change or check?

You mentioned that both heater core hoses are hot, but is the coolant circulating? You might have a bad water pump. Disconnect one hose at a time from the heater core, and crank the engine. If you see coolant spray out, then the pump is working. Did you physically check the position of the blend door?

The water pump is brand new and is working fine. I will have to check the blend door position. Does the blend door work off vacuum or how would I adjust the position?

This thread has some good information on the heater core, and the blend door: http://www.explorerforum.com/forums/showthread.php?t=143617

BrooklynBay said:

This thread has some good information on the heater core, and the blend door: http://www.explorerforum.com/forums/showthread.php?t=143617

Click to expand...

The info I posted in the other thread is for a 2nd Gen Explorer, but the 1st Gen is quite a bit different.

I would remove the cover from under the dash and see if the heater core itself is getting hot.

http://www.autozone.com/servlet/UiB..._us/0900823d/80/0b/9b/39/0900823d800b9b39.jsp

Thanks, I'll hopefully get to work on it tomorrow....

Besides the blend doors (vac and mechanical doors).....the control panel head itself.......and IF you got one, the heater control valve.

http://www.explorerforum.com/forums//showthread.php?t=169964

I guess you pretty much covered the flush,t-stat and water pump.....so, keep us informed w/ feedback/updates.

Aloha, Mark

Some Heat in My 91 Ex!

I noticed that even though there was hot clear flow through the heater core hoses the volume was low. I put some radiator flush in the core and let it sit overnight. I flushed out a bunch of brown crud and I have full volume flow through the heater core. I get fluctuating heat but it's not hot like before rad/pump repairs. One thing I could not find was the location of the vacuum control valve. The vac lines come off the dash control head, (I replaced that, too) and it looks like they run behind the speedo/gauges somewhere. Prior to rad/water pump change the temp gauge always stayed constant at A, but now the temp gauge goes up to M and then back down to N but not as frequently as before core flush. I changed the stat 4x, 170°, 180°, 195° & ended with a 198° installed with the same results, so it's not the stat. What did I miss?

Just a thought

vacuum to and from the vacuum reserve bottle, and to coolant bypass valve???

My early 91 doesn't have a a coolant bypass valve, but if I understand correctly from others on the site, if I install one it will keep the heat out of the core for better AC in the summer. I plan to install one in the spring. I'll have to check the vacuum to and from the vacuum reserve bottle, though...Thanks.....

man I'm in the same boat with you new waterpump new t-stat flushed and back flushed the h-core 3 times whole motor 2 twice I got heat for 10 miles and loss it top hose close to the motor is hot but coll from other side guess the h-core is is bad... but I amd getting the wild temps I can't get mine above the N in normal 195% t-stat and cardboard in front of raditor?
let me know what you find out Im trying a new h-core mine dosent have the bypass either...

Still No Resolve...

Update to Project92:

Have you had any resolution to your problem yet?

All my hoses are hot. I am getting very warm air but still have the continual N to A and back again readings on the temp gauge. I am going to change the 2 temp sensors as it's the only thing I haven't changed. It's been 20 degrees here in NY so I have not been able to do much as I'm working outside. This week should be warmer (40's). I plan to get under the dash and check the blender door for full functioning and if the heater core is getting hot. I can hear the door open when I move the selector switch so as far as I can tell it's working.

Attached are pictures of the inside of my heater core. Same symptoms no heat. My working theory is that the rubber on the inside of the radiator hoses broke down and circulated through the system. One had burst several months before I discovered no heat.

The point is that when feeling the hoses in and out they should both be scalding hot. In my case one was scalding hot, the other was just hot. This crap is probably also stuck in the radiator, but after a reverse flush it seems to work fine for the last seven months.

well I decide to replace the h-core check at oriley's 19.99 autozonewas 49.99
but I had already had a autozone h-core so it was free (it started leaking also) so when I pulled it (10 min job at work) it was clogged agian... when they gave me the new one it was diffent it was aluminum and looked like a mini raditor.. my old one like like the one pictured above.... installed it on the parking lot and I have HEAT!!!!!!!!! so I had a cel code had it checked and it came back heat sending unit bad ... so that may be your problem

sorry to bring up an old post but was this ever resolved? Ive got the same exact problem. to any who have had this, did the interior heat fluctuate with the temp gauge? for me, it takes awhile to warm up, and only really warms up when i get driving. tends to stay in between the "N" and the first line on the "normal" line with the occasional jump to M and A with an increase of Interior air heat.

as far as the hoses, the lower rad hose is hot while the others are scalding hot, namely the upper hose.

Is it dangerous to drive my EX like this? I haven't seen anything to say its overheating...

Still Working On It, No Resolve Yet

Bump

Still Working On It, No Resolve Yet

Funny I'm working on replacing the heater core this weekend. After doing all the the previously mentioned work the heat was a litle better but the fluctuation of the temperature is still there but less wild. I'm hoping to resolve the heat issue by replacing the heater core. A neighbor had the same problem and after replacing the heater core it was resolved. She had the same; very little heat problem and fluctuating temperature.... I have 203K miles and the core looks original it's got a Ford tag on it, I have it since 43K so I'm guessing it's original...
I'll keep you posted!

PCTechman said:

Funny I'm working on replacing the heater core this weekend. After doing all the the previously mentioned work the heat was a litle better but the fluctuation of the temperature is still there but less wild. I'm hoping to resolve the heat issue by replacing the heater core. A neighbor had the same problem and after replacing the heater core it was resolved. She had the same; very little heat problem and fluctuating temperature.... I have 203K miles and the core looks original it's got a Ford tag on it, I have it since 43K so I'm guessing it's original...
I'll keep you posted!

Click to expand...

lol, that actually a little funny cause I just this morning, someone put a bug in my ear to reroute the HC hoses together. I noticed on undoing the inlet hose there was a had alot of green coolant in it, and the outlet hose had a small stream of darker red/brown coolant... hmmm

and as yours did, the temp gauge isn't jumping around as much, Ive got a 180degree T-stat and it now stays between the first line on the "normal" gauge and "N" only, hasn't gone past that... but still fluctuates... still perplexed by this i drive the car and then checked under the hood. the upper hose and HC hose was scalding hot while the lower rad hose was cool enough to hold to without any discomfort... it wasn't cold, but it sure wasn't hot ether... maybe warm would describe it. my theory is that the rad is clogged so that its still flowing, but not freely, and is staying in the rad for too long and cooling off too much. my next plan of attack is the rad, which my friend works at Advance will probably help me get as soon as I can pony up the dough... (still like $86 that I dont have...)

check your rad if you get a chance... Ill let you know if i get anywhere as well, maybe we'll be of some use to someone here

Update to VG30

I replaced my rad a year ago for the same reason you have now...
I replaced the heater core today and I now have heat! It's much hotter now and consistent, b4 the new core it would get warm, then cold and back to warm again. The temp gauge is still fluctuating but at less of a range; it runs almost up to the N and then down to the \ line and back up again, but slowly. When I have the heater on it fluctuates slower still, but in a smaller range, almost to the N then down shy of a quarter inch. The old heater core was the original aluminum OEM unit and although it was flowing clear hot water through it there was no heat transfer to the outside of the core. My best guess is that it was evenly coated with corrosion around the inside of the tubes that didn't block flow but did not allow the heat to transfer. I'm thinking that the temp sender and/or sensor isn't working right, I think it has one of each, I'll have to look it up in the manual. I'm not familar with the sensor, m/b it's not sending the correct info to the computer? I'm not overheating with a 195º stat in it. I had to run without one or it would overheat even when I bypassed the heater core. What I don't understand is why would it overheat with a 180° and now it's not with a 195°? No AC was running, there was no blockage in the rad, water flowed hot through all hoses, and it would overheat even on the highway at speed with a 180° stat even in 30-40° weather! The only change I made since is the heater core today and it was 43-49° all day. FYI, I am running a Stant Safe-T-Vent rad cap (13psi) and I keep my coolant overflow container filled halfway, my Ex uses some coolant while running and then put a little more than halfway back into the container after shutdown, but overnight after cooling it's back at the halfway mark again, I believe that's the way it's supposed to work. I have always used 50/50 mix Prestone/Water for coolant in all my vehicles. Tomorrow I will be driving 50 highway miles to church & back, and about 30 mles local driving, I am hoping the heat stays hot at highway speeds and m/b the fluctuation will stop, if I change the temp sender that should correct the gauge fluctuation problem, if it still exists. My next question is "If I do change the temp sensor what change would I see if the old unit was not working correctly?"...I'll give you an update Monday after driving it around all day tomorrow...
Keep me posted, m/b we'll stumble onto something by accident or someone will read the post and give us advice/help...
Thanks,
PCTechman