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Let s play Stump the mechanic
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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Let s play Stump the mechanic
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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I appreciate everyone's thoughts.
Wingwiper -
It must be our premium air up here! 
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 -
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...)
Do I know how to have fun or what?!
- Willie H
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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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