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WillieH
Join Date: Feb 2003
Posts: 543 New England
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2006-03-18          126269

So here is the scenario...

1994 Ford V6 fuel injected gas engine.
Presently having 207,000 miles on it and runs GREAT!

No problems with fuel consumption, still delivers about 27-30 mpg on the highway.

No internal fluid leaks, ie: water in oil or vice versa

Recently decided to change t-stat, as I no longer had heat, and monitoring the temp gage, it (the needle) would wander up to "mid-normal" position, then moments later drop out, then slowly climb back up again. After its change, I still had the problems.

Then one horribly cold morning, I start the old girl up. As it is warming up, I notice a "wet" spot under the radiator. Long story short, I found that the topmost aluminum bracket had pulled away from the fins, causing a minor leak.

I drove the truck that day, watching the fluid level - no problem. The next day, after I arrived some 250 miles later, I decided to do some more checking. As I walk out of the garage, something catches my eye - the water pump let go, and I have fluid running everywhere.

OK I thought, time to start anew. I put in a new radiator, new water pump, new t-stat (again), new hoses, installed a flush kit. I purged the system and the vehicle runs great again, holding perfect fluid level and NO leaks.
.....But still no heat! (but at least the needle stays constant in the low range of normal)

Having the heater box open in the cab, I ran the engine until hot. I put my hand on the heater core, and she was blistering HOT ! EXCELLENT I thought. I turn on the blower, and within seconds, the heater was cooled off to the point, that no more heat was felt thru the core or the ducts. (!)

I took out my "zoo" gun, hooked it up to the heater hoses, and back flushed, forward flushed - you name it, I did it! (With the thinking that the heater was restricted, in some capacity)
Perfectly clear from the get-go. Hmmmm(?)

I removed the blower, with the idea that a "door" might be stuck open allowing cold outside fresh air into the blower plenum, causing the heater to "ice" over. Other than some tree debris, it was clear as well, and the door functions properly with the vacuum assist.

The vehicle runs great - no need to get rid of it, and yes I realize that spring is coming...eventually, and I won't need the heat, but....
I am stumped !

Anyone have any ideas?

- Willie H


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kwschumm
Join Date: Feb 2003
Posts: 5764 NW Oregon
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2006-03-18          126274

Just a guess. Plugged heater core? A constant flow of heat requires heat energy in to roughly equal heat energy out. If the heat energy can't get in as fast as the fan removes it then you get cold air. ....

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WillieH
Join Date: Feb 2003
Posts: 543 New England
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2006-03-18          126279

kw -
Nope...not a plugged heater core. As mentioned, I used my zoo gun and it checked out fine.
(Incase you are unfamiliar with a "zoo" gun, it is an inline water valve, that has an air blast assist. It gets placed in the heater hose circuit, then as the fluid flows, one can hit the trigger for a blast of compressed air besides. It is made by Kalamazoo Industries, hence the name "zoo" gun)

I had thought the possibility of the core as well, however, in the troubleshooting attempts that I have made, I disconnected the two heater hoses and installed a pony pump into a bucket of water, with the zoo gun inline. The return line went into another empty bucket.
As I turned on the pony, I had a strong constant output from the core circulation, without rusty or any other type of contaminates. Perfectly clean and strong flow.

I then, just for the heck of it , gave it a shot from the zoo gun, with no difference on the output, as it was clear and high flow coming out.

- Willie H ....

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kwschumm
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2006-03-18          126280

Wow, you've done a lot of troubleshooting. Never heard of a zoo gun before. Could the core be partially restricted but still flow enough water to pass your tests? It might be interesting to use an IR thermometer (or night vision in the dark) while the heater is running and see if some areas of the core fins are significantly cooler than others. If the water into the core is hot it seems to me that it either has to be a core problem or an easier path for the water to bypass the core. ....

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greg_g
Join Date: Jan 2004
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2006-03-18          126281

I tracked down an issue similar to this, but on the A/C side. '92 K2500, new radiator/hoses/thermostat/sending unit/condensor/compressor cranking out tons of cold stuff - but after about 15 minutes it stopped coming outa the vents. Vacuum switches that control the air flow in/out of the common airbox dryrotted (204k miles). Replaced with new vacuum line between switch and airbox, problem solved.

//greg// ....

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wingwiper
Join Date: Jun 2004
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2006-03-18          126282

Hey Willy

I am having the Exact same problem with a 98 Cherokee. I have flushed the core out several times and have plenty of water coming out with the pressure of a Garden Hose.
My Temp gauge reads 195 degrees and I put in a New Thermostat just to be safe. I have inspected my Radiator and it is fine, I checked the doors they open and close as they should. I felt the upper hose going into the firewall side of the core and it is HOT the bottom hose is only warm. Before I dismantale the whole dashboard to replace the core on a 98 Cherokee, I wanted to be sure that was my problem and I am NOT sure. I have taken note that the Water Pump Housing looks pretty new as compared to the rest of the engine. My thought is that the fins of the fan are NOT turning, which allows water to pass thru it from convection and is enough to keep a straight 6 on cool but not enough to give adequate pressure to speed up the flow of how water to do as KT said in his reply, pass it thr to keep it HOT long enough. My next step when we have a day above 50 degrees is to take a hose off and run the engine to see if there is any pressure at all which should fill a bucket up pretty fast. I too, am stumped. ....

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Peters
Join Date: Feb 2002
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2006-03-18          126292

I am also thinking a small vacuum leak. Is the heat valve vacuum controlled?
The cycling is typical of a vacuum leak. Air is sucked vacuum disappears heat is lost. Vacuum biulds until the material collapses and problem starts again. I had one similar, but could here the door opening and closing. It took for ever to determine where it was leaking. I think it was on one of the bellows.
In high vacuum work the moto is "Nature abhores a vacuum". A leak can take weeks to find. ....

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Andy_H
Join Date: Sep 2003
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2006-03-19          126318

You say the heater core cools down quikely when the blower is turned on, sounds like the core is restricting the flow of coolant. flushing the core doesn't always fix the problem of having been plugged, forcing water through a couple of good passages can fool you to think that it flows good throughout, plus you already have it torn apart. unless you have a restriction somewhere else in the heater hoses, I'd say it is the core. ....

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Murf
Join Date: Dec 1999
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2006-03-20          126354

Willie, we had a similar problem with a few of our Ford PSD pickups too.

It turns out Ford had a re-builder under contract here locally who had, let's say, a less than ideal QC program.

The re-man. water pumps were garbage, they had such a large tolerance that they couldn't develop any pressure to the flow, they barely exceeded the natural convection flow itself. As a result the small lines to the heater core saw barely any flow at all.

When we finally figured it out, because we replaced away from home and it worked like a champ, we raised heck with Ford here and they swapped us out our re-mans for brand new ones.

Best of luck. ....

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Iowafun
Join Date: Jul 2004
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2006-03-20          126370

I had a problem a good 6 years ago and it turned out to be a leak in the vacuum system. Im particular, the switch had a bad plastic weld on it. Not sure if that's your problem, but it's worth checking out. I can't tell you how to check it out. But after as many miles as you have, some parts in the vacuum system may be a bit old and leaky. ....

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oneace
Join Date: Mar 2004
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2006-03-20          126384

I would say a restriction in the core. Just because it flows good does not mean the volume that is need is there. ....

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WillieH
Join Date: Feb 2003
Posts: 543 New England
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2006-03-21          126411

I appreciate everyone's thoughts.

Wingwiper -
It must be our premium air up here! lol
Now that I have installed a tee in line of the radiator (basically to flush with), I have a means to check the pressure as well. I will be ptting a garden hose on the tee, and starting the engine with a return flow thru the radiator cap neck (to keep it from running dry)...just for that reason - to check for flow and pressure from the pump.

I do not believe that this is a vacuum issue because the only element that is vacuum controlled, is that of the MAX Air circuit (of which does work as it should), where all the heat controls are still mechanical in nature, ie cable.
(yes, the cable has been checked and rechecked, and is throwing and pulling in the correct distances and closure/opening operations)

The core, I do not believe to be the issue area either, as I have very good flow thru it - including heat. As mentioned, I put a small pony pump on it of which delivers comparable pressure to that of the water pump, and it flowed in and out without concern...especially at low pressure levels. I have also checked the hoses for collapse, however are ok (good).

Murf - That is an interesting point, as I put a "new" reman. water pump in. Not saying that is it perse, however certainly offers potential to check on. I would think, that if the pump had been manufactured outside of tolerance, that it would have a difficult time building pressures, and if it did build, it would not hold. (?)

When I run the vehicle, I get a strong pressure right from the beginning, and never faulters (I mean we are only talking 14-15 psi anyway)

The original t-stat, from Ford, had a ball check valve on the flange, to allow a release of any trapped air to escape prior to the t-stat opening under temperature control. The replacement did not have this. I was advised to drill a small (2-3mm) hole where the ball check would have been located, just to simulate the operation of pre-air release, if you will.
This infact did work for the trapped air aspect, however, as one could imagine, it now takes almost an hour for the engine to reach "normal" operating temp zone. So, I will replace the t-stat again, possibly with the check valve variety if I can find one.

What I am leaning towards, is possibly getting a higher temp t-stat. It had a 195 degree in it, with little heat that I can remember. I am starting to think, so long as every component is new and perfectly wide open, the likely hood of overheating will be slim, especially as I cannot get much heat to begin with. So why not put in a higher temp t-stat?
The present operating temp, is barely cracking into the "normal" range (WAY down on the low side).


- Willie H ....

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Murf
Join Date: Dec 1999
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2006-03-21          126419

Willie, you're missing one small point here.

In a coling system pressure is created by confining liquid and forcing it to a higher boil point.

The water pump only circulates the water.

If you have a 15 PSI rad. cap and the engine reaches operating temp. the system will have 15 PSI even without a water pump. In fact many Asian spec. machines don't even have a water pump, circulation is accomplished purely by convection.

The better test would be to put a pony pump in line between engine and heater core, get engine to temp, and check heat with pump off, then switch it on and see if you get dramatically more heat. I'm guessing you will.

The problem with the poor remans was the excessive clearance between the impellor and the housing. The impellor would let so much fluid by that between the resistance to flow in the heater core and the lack of flow, it was just easier for the water to take the path of least resistance and not go through the heater core.

Best of luck. ....

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WillieH
Join Date: Feb 2003
Posts: 543 New England
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2006-03-21          126430

Murf -
Yea you're right. I'll put the pony in line as see what develops....

Forget the truck for a moment, right now I am not firing on all cylinders - I am suffering of late (really in pain) as I find myself in and out of dental offices with emergency surguries. (rather wasted on meds, and trying to figure out this heating system at the same time...lol)
Do I know how to have fun or what?!

- Willie H ....

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WillieH
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2006-03-23          126589

Alright, now I am really scratching my head. Now the tekp gage does not even come up to the lowest point in the "normal" range....then it does then it dumps out all together.
So I am thinking air in the system at this point. I vacuum the system, check for any leaks (none are found), and refill the system slowly from the vacuum reservoir. Now I know that at least 99% of the air has been vacated.

I start it up again, let it run, and run, and run, and run, with revving and high speed running too. No read on gage and no heat.

T-stat gone now? Always a possibility that a new one is bad I guess.....

- Willie H ....

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Murf
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2006-03-24          126615

Willie, right back to what I said earlier, if the water pump isn't pumping, it won't displace any air trapped in the system either!!!

There's an old trick I've used before, CAREFULLY!!!!

When the engine is hot, and the system has a little pressure, carefully loosen the temp. sender. If there is air trapped it will hiss out past it, if not there will be coolant from the start.

If the temp. sender reads tiddly-squat (check it with a meter) when a thermometer tells you the coolant is say 175°, then you have a) air next to the sender, b) a bad sender, c) faulty wire leading to the meter, or d) your meter went south.

Best of luck. ....

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