No Heat but Engine Overheats

[ExploreMinnesota]

I've had a problem getting heat for some time now, and with the temp outside going below zero now, it's really becoming a problem. The engine temp has been running hotter and hotter and now has begun overheating.

What I have already done is, new t-stat, new heater-core, new radiator and cap, new hoses, new water pump, and of course flushed out the engine block as best I could when water pump was off. There seems to be no restrictions to water flow, when I use a water hose to flush it out, yet it appears that the water is not flowing through the system.

Changed the t-stat again, and yes, it is installed correctly, facing the right direction and the small bleeder hole is at the top. There seems to be no water flowing through the system. It should flow throug the heater core even if the t-stat is closed, but the heater never heats up and the hoses stay cold. I detatched the heater hose from the exit side of the heater core while the engin was running, and barely a trickle was coming out. I shut the engine off and using my hand as a seal around the hose, I blew into the hose. A full stream of water came gushing out of the heater core . . . water flows easily so it seems. That's when I decided to change the water pump . . . but that did not fix it.

As it stands now, water boils out of the overflow after driving 4 or 5 miles. The upper radiator hose is warm and under pressure, but not hot. Heater hoses are cold. I shut the engine off and felt the radiator . . . upper 4 or 5 inches is hot, below that feels cold . . . ice cold, but it is still bubbling out of the overflow . . . with most of the radiator feeling ice cold. The fluid level was as full as I could get it. It took over 2 gallons and I filled it with the upper radiator hose off until water was flowing out of it. Then I attached the hose and topped it off.

It seems like I've changed everything that could possibly be the problem, but the problem still exists. Anyone have any ideas?

 

[Howard]

It sounds like you have a blockage. Have you tested the valve going to the heater block? Did you reverse flush? Is it just air trapped inside?

 

[ExploreMinnesota]

There is no valve in the heater hose on the 91 through 94 models. I'm not sure when those were introduced, but they are not on the older models of the explorer. The hose goes directly from the top of the engine to the heater core, and the other one goes directly from the heater core to the water pump.

There doesn't seem to be a blockage since I can pour water through the entire system in either direction with no obvious resustance.

I just removed the thermostate and put it back together with no thermostat in it. I will try it like that to see if the overheating problem goes away . . . obviously I still won't have any heat. I will also boil the thermostat to see if it opens. I'll let you know how each test turns out.

 

[ExploreMinnesota]

Update: The new t-stat tests out good when boiled. I ran the engine with no t-stat installed and as expected the engine does not warm up . . . fluid stays relatively cold. However, it still "boiled" out through the overflow. Obviously not boiling, but certainly bubbling. My conclusion, something on the order of a blown head gasket or a cracked head or cylinder. No sign of coolant in the oil.

Right now the engine is disassembled to the point where I have the heads off. I know that most of the tourqe specifications for this engine are surprisingly low, but during disassembly there were a number of bolds that were not more than finger tight . . . litterally I loosened some with just me fingers. Not the head bolts, but even some of those were not as tight as I would expect. No obvious blow-outs in the head gaskets, but unmistakeable evidence of colant having been burned in several cylinders (unusually clean areas). The number 1 cylinder had coolant standing in it, and I don't think it came from the disassembly process.

I have cleaned the heads and there are no signs of cracks. The engine block also looks good. The plan . . . buy some good gaskets and reassemble. The Ford dealer says it will take 2 to 4 days to get the gaskets. I plan to go to the local Checker Auto and perhaps Napa to take a look at their gasket sets if they have any. If I find some that look good I will use them, otherwise I will order the Ford gaskets and wait for them.

I have confirmed that the old heater code was clogged, so that explains the original heat problem. What puzzles me is that the bubbling out of the overflow did not start until immediately after replacing the heater core. Obviously with large amounts of exhaust gases being forced into the cooling system and a closed thermostat, the flow was in the backward direction as the gasses proceeded to fins their way to the overflow line at the radiator filler neck. Up at the thermostat, it would quickly fill with the hot gasses which the temp gauge would eventually show, but with no water flowing to the heater core . . . still no heat. That makes sense, but the original problem (clogged heater core) and this problem do not appear to be related. Is it a coincedence that one happened just after fixing the other? That has me nervous, but the bubbling over definitely did not occur until just after installing the new heater core.

Any insight?

I'll post again when I know more.

 

[Howard]

I've had head gaskets go on a v6 before and there is not always any obvious evidence to show where the leak occurred. Sounds like you've found the problem.

 

[marragtop]

Since you have the heads off, you might need to replace the head bolts. On some engines they can only be torques once (due to stretching) and then need to be replaced. Not sure about the Ford 4.0. I'm sure someone can jump in with more info on this.

 

[Brain]

Yep, replace the head bolts. They are TTY (torque to yeild) type bolts which means that they are stretched past the point of springing back to their original length. Be sure to lube the bolts as the torque specs are for lubed/clean threads. Be sure to check for hairline fractures between the valves (most common), around the valve spring seats, and at the oil drainback passages. Cracked heads are pretty common for the '91 4L. Since you are going to be spending over $100 for gaskets and bolts than can only be used once, it would be a shame to miss a small crack and have to buy those things again.

 

[Eneurb]

But don't lube the bolts too much as to cause a hydraulic lock when tightening them... a light coating will do... and it is very often overlooked to lube the head of the bolt where it contacts the cylinder head to keep them from binding.

 

[ExploreMinnesota]

I cleaned up the heads and there are no cracks that I can see. I took them to a machinest and had them resurfaced today. He said one had a 6 thousands warp in it and the other had 4 thousands. I showed him the gaskets when I brought the heads in. He pointed out on the heads and the gaskets where the failures were (there were multiple). He machines a lot of heads. He said that other than the slight warp, the heads looked fine.

I bought a Fel Pro gasket set which came with the bolts. Like marragtop and Brain said, the head bolts on this engine can only be used once. It seems strange that they would use the TTY bolts on this engine (cast iron heads on a cast iron block), but they do.

I cleaned up the heads after getting them back from the machinest and they are back on the block now, but not fully torqued yet. They are touqued to the first step which is 44 lbs. (and yes, I oiled the threads and the heads on the bolts and finger tighten all of them to the point where they seated against the heads first to make sure there is no undwanted resistance that would affect the tourqe). I will finish cleaning the lower intake manifold in the morning and mount that onto the engine. Those bolts need to be tourqued to their first setting before I can tourque the head bolts to their next setting.

I should be driving the Explorer again sometime tomorrow. I sure hope the heater works when I'm done. The high temp for tomorrow is supposed to be -2 F. It is -7 right now heading for an overnight low of -12. Heat would be nice!

 

[Brain]

You are forgetting the sealant set time....it goes above and below the inside corners of the head gaskets and the intake manifold gasket (the ends are JUST sealant). I would get an extra tube of Permatex Super-Black and make sure they are sealed up good (and let alone the 24 hours to cure), or you might be looking at re-doing it again really soon. Just a heads-up.

 

[ExploreMinnesota]

Thanks Brian. You're right, the new gasket set comes with a small tube of RTV for the front and back ends under the lower intake manifold. The gaskets that I took out of it had cork ends that looked like they had a bit of RTV on each side to help it seal across where the heads meet the block. The new gasket set uses only RTV on the ends. I think the results with only the RTV is better anyway . . . but it means I won't be driving it until tomorrow. It is all back together now, but it took most of the day to do it. I'll let you know how the test drive goes.

 

[XplodeThis]

wow, That's EXACTLY what happened to me, Except I haven't replaced my heater core yet, ANyways My head gaskets were blown and I have cracked heads, in between the two valves in the combusion chamber in 4 out of the 6 cylinders. IN fact one of my plugs was melted and another appears to have been blown up cause the center electrode was just hanging there, but no evidence of damage or scoring in the cylinders or damage to the piston head so that's great. Im just waiting on a set of heads to get here, 321 shipped to my door, brand new ready to bolt on with valves and springs and everything. So how did the test drive go? The X running good now?

 

[ExploreMinnesota]

Merry Christmas to all of you!

Well, the explorer runs great. All of the coolant seems to be staying where it should be. It put out great heat . . . for a while. Somehow the heater has stopped again. The engine runs great and does not overheat, but the heater core appears to be clogged again. I don't understand how that could happen.

I still had the original heater core, so I took some time to check it out. Water did not flow well at all through it, which is what I suspected when I replaced it at the start of this ordeal. I back flushed it and got some crap out of it. Most went down the drain before I could see what it was, but the bits that I did capture fell apart like sand in my hand . . . not sure what it was. I flushed it out to where water ran through it freely and the entire heater core would change to hot or code instantly depending what temp water I ran through it. I swapped the old heater core back into the vehicle. The heater was working again . . . but only for a few hours. Then it was clogged again.

I now have the new one in there again after flushing it out, and it too lasted only a short time.

When I had the engine apart, I obviously drained the entire cooling system and I flushed it out as best I could again. I filled it up with new antifreeze and clean water, plus I added some Bars stop leak to it. Could the stop leak be clogging the heater cores? It has never clogged it before in this vehicle or any of my other vehicles. I con't believe it would do that. It would never be able to stay on the market if it did that.

Any clues as to what is going on? Like I said, other than the heater core getting clogged, the explorer appears to be running perfectly.

 

[Ira]

Personally, I have used leak stop, but don't really like to. I think it can lead to clogs in small passages. As for your heater core, is it possible that you are getting air pockets in there and they are stopping your heat? Usually when I drain coolant and replace, I will try to get all that I can in there plus put extra in the overflow. I will then run the engine long enough to build up heat and pressure. When this has happened, I will park on a hill with the front end up higher than the rear. There is a bank on the side of our driveway that is about 18" higher than the drive, and I will pull the front wheels up on that and park overnight. Do this for a couple of nights and it should help get the air out since air will seek the highest point (top of radiator). This will cause air to be pushed out of radiator when engine is shut off, and will pull coolant from overflow as it cools and will eventually displace the air.

A couple other possibilites...radiator cap defective or corrosion nearly blocking passages to/from heater core. Have you looked at the inside of your heater core when it clogged to see what kind of corrosion you have...tar, corrosion, etc.? Are you sure you don't have a hose that is pinching off and restricting flow after running?

 

[ExploreMinnesota]

Here is the latest . . . Something is definitely clogging the heater core. I am certain that the air is out of the system. When I remove the heater hoses, coolant drains out of both tubes of the heater core . . . no air space there. After not getting any heat from the heater for a couple of days I was certain that the heater core was clogged with something but I did not have the time to remove it and flush it out again. I decided to swap the heater core lines instead . . . run the coolant through the heater core in the opposite directon. Right away I started getting heat from the heater core again. It produced very good heat . . . but only for about 20 miles. On my way home that evening the heater quit producing heat again. Now it is clogged in the opposite direction. I will need to flush it out and capture the contaminates to find out what it is.

Ira, the heater core is new. Even so, I have flushed out both the old and the new heater cores and have swapped them a number of times after each flushing. The problem is not corrosion in the heater core (or at least not the new one). Either heater core works great after flushing and reinstalling. The radiator cap is brand new too. Everything is brand new . . . all of the coolant, the heater core, the radiator cap, the heater hoses, the water pump, the thermostat, radiator, the radiator hoses. I have flushed the engine out three times now during all of this including the heater hose connections at the manifold and the water pump. It makes no sense to me.

I will flush out the heater core again and capture the contaminates. I'll let you know what I find.

 

[Ira]

I don't really know what to tell you. Is it possible that there is a chunk of something that is circulating thru there and getting lodged in the opening of your heater core, and then blowing back into your block when you reverse it? As for having air in the core, you can have air in there and it will appear to be all coolant coming out. As the coolant level gets low, you would not know of an air pocket because the air wouldn't necessarily be visible. An air pocket would make sense because it would not allow the heat to be transferred into the truck. If you could possibly find a piece of clear plastic tubing in the right diameter and put it inline with your heater core, at least you could see what is going on and maybe get an answer to your problem. Another idea would be to remove your thermostat and back flush your complete cooling system and see what comes out.

It sounds like you have tried about everything else, and I don't really know what to tell you. I did have a carburetor that kept giving me problems a few years ago. One minute it ran fine, then it would cut out completely. After allowing it to sit a few mins, everything was fine. I ended up disassembling it and found a paper sticker that was floating around in the float bowl and shuting off the fuel supply. It nearly drove me crazy and I don't know how it ever passed thru the needle and seat to make it into the bowl, but it was there.

 

[ky85yota]

no heat

what kind of water are you using tap water or like a bottled water the reason i ask is if you have hard water you are probably getting sediment from the water when you heat it just a thought