STRANGE SPORADIC HEATER PROBLEM 99 mercury villager

FIXED!!!--after five years of torture!. On the left side of the engine is that big 2 gallon what I thought was an "over heat and over flow tank"--turns out that tank must be clean with the small hole not clogged in the bottom--the engine suctions coolant from it as it runs or the heater gets sporadically AIR LOCKED unless high rpm overcomes it and forces bubbly water through the core. Mine was bone dry and 2 inches of hardened mud in the bottom--took it off broke up the stuff and got it out--rinsed it out good which the hole also had to be unplugged--put it on added 2 inches of coolant HEATER WORKS PERFECT--as a matter of fact it was blowing out warm air even before the needle started to register. Even at idle it blasts out hot air--did a full test drive plus idle--HALLELUYAH. Turns out the reason the problem developed gradually was that tank was drying up and clogging. I never had any idea you have to pour coolant in to keep the lower part filled !

odd timing, as my 95 villager just recently started doing the same thing (probably a week before you posted this)... and after reading your post i'm willing to bet that is the exact problem, because i know that plastic jug is dirty in mine too. hopefully i can get it out and clean it good tomorrow.

You will be well pleased!--try and report back if you can. Thanks I had that monkey on my back for FOUR YEARS! Also just agonized on a month long trip up to the great white north of Portland and no warming up or defrosting of the van. I was researching replacing the heater core which cant be done--exceeds the value of the van and a true nightmare. I would have gotten ZERO results after days of work if I had succeeded.

GuruZPVD2, When you say huge 2 gallon tank, do you mean the actual coolant tank? I am confused. Because we are having this exact problem with our 1999 Mercury Villager and there is clearly coolant in the tank. It's about half full. And it doesn't flow into any sort of small tank, it has a hose that directly goes into the radiator. If possible could you take a picture of what you are talking about? The only tank I see is the coolant tank on the left side. And it's not even close to 2 gallons. It's about 3 litres.

There is the tank of the radiator itself and that tank you are talking about over on the left--2 gallons or not. However an update--mine is correct level and working and I had the sporadic heat develop a few weeks ago beginning of cold weather. I took the cap off the radiator and was not fooled in the slightest by the fact that coolant came out showing it was overfull if anything since ive dealt with this problem before. I drove up behind albertsons not even 60 seconds away and put the front wheels on a VERY steep loading dock and took the cap off and put a rag around and over it and ran the engine and let it warm up a bit and burp out the air--which by the way takes a while after the thermostat opens and you can see a little steam as the water starts circulating. You dont have to let it get up to full temp at all--but maybe three minutes after the thermostat opens. Sure --rev the engine a bit a couple times--it wont make coolant shoot out. Then shut it off and add coolant and sure enough it took about a half gallon and problem is solved again. I knew about parking on an incline but had not had the problem in a year or so--so I didnt bother. But i knew if it acted up again to park on an incline A STEEP ONE and let any air come out--which it did. You can also squeeze the radiator hose to help like some youtube videos show but if you take the cap off with a rag to catch coolant and let it warm up and burp out the air and add coolant again your heater will instantly come back to life--actually when you get back in after doing this?--it will already be blowing out hot air even with the needle barely registering. They do make expensive funnel setups to do this exact procedure where the coolant can even go way up the funnel and air burp out and let only coolant back in--then you insert a plug device to pull the funnel off holding the overflow coolant so it dosent go all over the engine--YOU DONT NEED THAT.. Car MUST be parked on an incline. Anyway lot of verbage to make sure its clear. When you start thinking or hearing from friends and relatives--- "HEATER CORE CLOGGED!!--IS TAKING HIGH RPM PRESSURE TO GET THE HOT COOLANT THROUGH BECAUSE ITS ON ITS LAST LEGS!"--thats pure crap-- there is air in the system. Your welcome in advance--I absolutely guarantee instant results on your van--same as mine 99 WHEN DOING PROCEDURE TURN ON HEATER FULL BLAST OF COURSE..

Another sign of air in the system--when my issue first developed in Florida where it didnt matter about the heater--is that the heat will sometimes come on burning hot as if its melting the plastic and damaging the ductwork for the vents--IT IS--because the trapped air allows the coolant to stay in contact with the hot engine and superheat it--when you rev the engine a bit the way too hot coolant then comes through and overheats the heater for a bit. -->ANOTHER HINT--going down hills even on the highway such as coming down from a mountain pass even at good rpm?--and the heater starts blowing cold?--BECAUSE THE AIR IS NOW ALL INSIDE THE HEATER AND HOSES. You go up the next hill--and the heater mysteriously kicks in low rpm or not!--those are dead giveaways-air in the system

Hey Guru., It's 4AM and I'm in bed wondering how to fix a similar problem in my 2002 Mercy Villager. I had a nee AC compressor installed over the Summer and shortly thereafter the engine began overheating. I actually pinned the temp gauge at 12oClock a couple of times. I took it to a mechanic who burped and that worked for about a week before it began overheating again. I don't I've harmed the engine - yet. It still runs strong and there's no water in the crankcase Besides that, my heater has been sporadic for years I had to take my wife to the doctor and when I parked, I noticed lots of steam coming out of the engine bay. I raised the hood and since the engine was red hot I didn't take the radiator cap off. I did notice that the reservoir was bone dry and dirty. I was excited to see your narrative. If it wasn't 4AM I'd follow your advice ASAP. I'm praying it works. This my 2nd Villager. I had a 1997 that I drive 245000 before selling it. My 02 only has 145000 and I love the car. I'm 81, live on sock sec and I've been scared that this might be my last car. I use top shelf synthetic oil and am hoping that saved my engine when it overheated. I took it to Midas shop last week and was told that I needed a new thermostat and radiator and the bill would be $985. I declined and he wanted an $80 diagnostic fee. I talked him down to $40. I can't wait till morning so I can follow your directions.If it does, I'll be the happiest man in town. Thanks very, very much