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Old 12-30-2012, 09:03 PM   #1
Justin 3J
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Unhappy overheating this winter

Okay so I've had my newer 1994 ranger 4.0 since august and it has been very sound thus far. Recently my heater core sending hose went out and I thought nothing of it because the hoses are all original and the truck has over 160,000 on it.

About a week later driving on the highway the I noticed the temp. was higher than normal but nowhere near overheating. After I got off the highway the truck became very hot and I had to resort to turning the heater on full blast to keep it out of the red. Needless to say the first thing I did the next day was replace the thermostat, which in fact had failed and would not open fully.

The truck was running fine and no temp. issues until today, two days since the thermostat install, driving home from work, short trip, the temp. spiked again. I figured it was just passing a bubble, burping, but after letting it cool fully and running it to normal temp. with the cap off, I didn't get more than three miles down I-25 before I had the damn thing pushing red again, and this time the heater only blew ice cold.

I limped it back home and I think it's one one of two main components: the heater core and/or my water pump. Any suggestions or easy things to look for before I go crazy or the thing explodes on me!

Thanks
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Old 12-30-2012, 10:15 PM   #2
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You may have air in the coolant system, and since you replaced the heater hose there's probably air trapped in that hose as well causing issues. Take your lower heater hose off of the heater core, then warm the truck up to operating temperature, leave the hose off until coolant starts circulating through everything. Once you do that then put the lower hose back on and it should have purged the air out of the system.
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Old 12-31-2012, 01:41 PM   #3
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Heater blowing cold with warm engine means low coolant level.
Heater core can not cause overheating, it can leak and the loss of coolant can cause overheating, but a blocked heater core will not cause overheating, its part of a secondary system not related to engine cooling.

Could have been an air bubble.
But why was there an air bubble?
Refilling a cooling system and getting rid of air pockets can be a pain.
Most good T-stats have a "jiggle valve", its a small hole in the t-stat plate with a metal "jiggler" to prevent it from getting clogged, this hole allows air out when refilling cooling system, this hole should be install at the 12:00 position to get the best benefit.
I have drilled my own hole in the t-stat plate if they didn't come with "jiggle valve".

Quite often a heater hose is the high spot in the cooling system, I get a metal coupler and a couple of hose clamps and cut the heater hose going to the intake(near t-stat).
I then prop each end of that hose up as high as I can and fill the system, until full, then connect hose back together.

If system is filled properly then where does air pocket come from?
If flow or cooling is restricted then coolant reaching 240+deg can flash to steam in the head, this increases pressure in the system which forces coolant out into the overflow, which reduces cooling and more steam occurs, so overheating cycle.
Opening heater valve can help lower coolant temp below flash point, also raising rpm, without raising load on engine, can aid cooling.

I would first check the fan clutch, if this is going bad engine will not over heat until it is under a load, i.e. driving at higher speeds.
When engine is cold fan should spin easily.
With engine off but warm fan should not spin easily, it should be much tighter.
Fan clutch works from radiator heat so rad needs to be warm not just the engine.

Bad rad cap, rad cap allows cooling system to run with a higher pressure, the higher pressure means a high boiling point for the coolant, so instead of steam happening at 212deg, it won't happen until 240deg.
Cap and/or overflow tank can also prevent coolant that was pushed into the overflow tank from returning easily, floppy rubber gasket on the cap or debris in the overflow tank can do this.

Bad water pump or rad, hard to tell with these but checking the upper and lower hoses for temperature difference can be helpful.
With engine warm the upper and lower hose should be almost the same temp, lower hose is the return hose so will be 10-15degs cooler, if its a lot cooler then flow thru rad is restricted or water pump is not circulating very well.
Normal operating temp for an engine is 200-210deg, Fords use a 192-195deg t-stat to maintain that temp, that temp provides the best fuel efficiency and best lubrication, all motor oil is rated at 212deg.
If you remove the fan clutch and shroud, and then run the engine until warm you can feel the rad areas, it should be uniformly hot on one side(upper rad hose side) and get
cooler as you feel to the other side, or top to bottom depending on the style of rad, any cold areas right next to hot areas means a blocked tube or tubes at that spot.

Hard to tell about the flow provided by water pumps, if coolant isn't changed every few years(the green kind) then it can eat away at the pumps impellers, reducing the flow, but usually the seal in the pump will fail first showing up as a leak out of the pumps weep hole.



And the worst case scenario is a head gasket starting to give out.
You see this as white smoke when engine is first started.
Also starting engine cold with rad cap off and seeing coolant bubbling out is a sign of exhaust gas being forced into the cooling system from a bad head gasket.

Last edited by RonD; 12-31-2012 at 02:29 PM.
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Old 12-31-2012, 04:29 PM   #4
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^^^ Good write up. I'm going to save this thread for my personal info. IMO, if something similar isn't already, you should submit this to the tech library.

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Old 12-31-2012, 08:04 PM   #5
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Every time I read 94 4.0, I pay heed. Thanks for the reminder to check coolant I would treat for an air bound heater. If that doesnt fix overheat, replace pressure cap. You put new thermostat in right side up, right? Dont sweat the heater core . If it is full of air, then it isnt plugged. Did another old hose pop from over pressure?
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Old 01-04-2013, 12:08 PM   #6
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I have a 94 with a 4.0 and last winter i chased this same problem. temp guage would spike, then go down slow, no heat, rreplaced t-stat didnt help, replaced water pump, still the same, tried burping and it kept throwing out coolant! was told it was a head gasket! or rad plugged, replaced rad , still the same!! found out that when the t-stat is closed the engine uses the heater core as the bypass!! checked heater core flow PLUGGED!! replaced the heater core ( Very Easy Job on a 94 ) Problem solved!! no more overheating & Plenty of heat! .. Check your heater core!!!
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Old 01-04-2013, 03:01 PM   #7
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I have a 94 with a 4.0 and last winter i chased this same problem. temp guage would spike, then go down slow, no heat, rreplaced t-stat didnt help, replaced water pump, still the same, tried burping and it kept throwing out coolant! was told it was a head gasket! or rad plugged, replaced rad , still the same!! found out that when the t-stat is closed the engine uses the heater core as the bypass!! checked heater core flow PLUGGED!! replaced the heater core ( Very Easy Job on a 94 ) Problem solved!! no more overheating & Plenty of heat! .. Check your heater core!!!
If the heater core was use as the bypass, or part of the engine cooling system, then if the driver set Temp inside to Cold(summertime), shutting off the flow through the core, then engine would overheat.

On some Ford models they did use a Diverter(bypass valve) instead of a regular valve on the IN line to control coolant flow to the core.

The diverter allows coolant to pass between the two heater hoses(a bypass) when inside Temp control is set to Cold, as you increased the inside Temp control to Hot, coolant flow is diverted to the core.

If you had a Diverter and a blocked heater core and set the inside temp control to Hot then yes, you could experience loss of the bypass flow.
Setting inside temp control back to Cold would restore the bypass, if diverter was working correctly.
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Old 01-04-2013, 04:24 PM   #8
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if he has a 94 like he says the there is no valve .. coolent flows through the core all the time .. they use a blend door inside the heater box .. take alook at the cooling system on a 94 4.0 with a/c and you will see what i meen. after all the crap i went through with mine and money spent to chase this problem it was this simple. $35 for the heater core & about 20 minuts to put it in. just passing the info along
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Old 01-06-2013, 12:23 PM   #9
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if he has a 94 like he says the there is no valve .. coolent flows through the core all the time .. they use a blend door inside the heater box .. take alook at the cooling system on a 94 4.0 with a/c and you will see what i meen. after all the crap i went through with mine and money spent to chase this problem it was this simple. $35 for the heater core & about 20 minuts to put it in. just passing the info along
I just pulled the heater core on my '94............OMG!!!!
No valve or diverter, it is a straight IN/OUT from cooling system.

I stand corrected rags.

I plugged both lines and drove around, sure enough temp gauge went up and down, then did a restricted flow and same thing just not as pronounced.
Heater core is part of the cooling system............I assume the engineer who thought this up was fired, and is now a politician running the US ecomomy

Not enough failure points in a cooling system, let's add another one.

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Old 01-06-2013, 06:19 PM   #10
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All i can figure out is they did this so the heater core would get the warming coolent quickly so the windshield would defrost quickly. If there is no flow past the thermostat, it wont open quick enough, thus a temp guage spike. It took awhile to figure this out but after the new heater core everythings been perfect!!

Another thing i found to help burp the system was to cut the heater hose coming from the intake to the heater core and install a fitting from a flush kit with a screw on cap. Leave the cap off when filling the rad and most all the air will escape there, just screw on the cap and everything is sealed.
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