Engine Overheating

I have a 1994 Ford Ranger XLT. The heat/cold guage stays on HOT (out of normal range) continuously. I have replaced the thermostat.I have flushed (4 times) out the radiator, coolant resevoir, and block. I have replaced
the coolant 4 times. I have checked all hoses and radiator for leaks. There are none. When i turn ON the a/c the radiator and resevoir boils over. If the a/c is OFF it doesn't boil over, but the guage shows HOT (out of normal range) and as far to the right as it will go. HELP
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Can you verify the operation of the cooling fan clutch? How did you flush the radiator? Can you verify that the water pump is actually moving water? A mechanic with an infrared temperature sensor would be of great help here. With the infrared sensor you can look at the temperature of the radiator and hoses and determine if they are actually working properly. Does the car overheat when moving, or just when stopped? Does it overheat very quickly, or does it take a while for it to heat up?
My first guess is that you have failed cooling fan clutch (assuming the truck uses a clutch fan). Second guess is a clogged radiator. Third guess is a water pump that is not actually moving water. These are just guesses. More information about the nature of the problem will improve the accuracy of the guesses.
Ed
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Thanks CE for your response. The cooling fan clutch is working properly. Flushing the system. First, I drained all the coolant out of the radiator. Second, I removed the radiator cap and the drain plug at the bottom. Using a hose and with the engine idling I let the clear water run thru the system. Third, I replaced the radiator cap and drain plug. With the engine running i let the clear water pump thru the system. I then turned the radiator cap to the first notch to release the pressure. Fourth, using the hose i flushed out the coolant resevoir, until i was getting nothing but clear water. Fifth, I filled the resevoir with 50/50 coolant to the "Cold Fill Mark". Then I filled the radiator with 50/50 coolant.
It did not resolve the problem. As soon as I started the engine, the gauge went to straight to HOT and remained there. I drove the truck about 10 miles at speed from 40-70 mph. I shut the engined off and waited til the engine cooled and drove back another 10 miles...Same problem...the heat guage stayed in the HOT zone.
Verifying the water pump is actually moving water. I removed the hose coming from the block and clean water came thru when I flushed the second time. The truck overheats as soon as I turn the ignition on and start the engine. At rest and when the engine has cooled the gauge does move up barely into the normal range on the Hot side of the guage. Now, SOMETIME, (and rarely) the needle will move up into the normal range on the high end of the HOT side.
It has never boiled over, UNLESS I turn the a/c on.
I think I have answered your questions and hope they will give you a better insight to my problem.
Again, thanks....
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I would remove the radiator and have it professionally cleaned. I'd also verify that the hoses are in good condition (ie not soft so that they can collaspe).
Rapid overheating is not a good sign. You might also have a professional mechanic check for exaust gas in the radiator.
Ed
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"acbran1" wrote: 1994 Ford Ranger XLT
Water temp gauge reads HOT (above normal range) continuously. I replaced the thermostat and flushed the radiator, reservoir, and block 4 times. There are no leaks in hoses or radiator. When I turn ON the AC the radiator and reservoir boils over. With AC off, it doesn't boil over, but the gauge shows HOT. _____________________________________________________
Some things to consider:
1.) Blast the dirt out of the cooling fins - spray hose or air gun. 2.) Install a larger-capacity radiator. 3.) Replace the fan with a higher-flow design. 4.) Replace a slipping fan clutch. 5.) Replace a cracked head (if unexplained coolant loss.) 6.) Replace intake maniforld gasket (if unexplained coolant loss.) 7.) Replace the water pump with a more efficient unit. 8.) Use a smaller diameter fan pulley or water pump pulley. 9.) Advance any retarded ignition timing.
Some persons will trim the fan shroud to expose more of the outer edge of the fan blades to increase centrifugal airflow. This has drawbacks; the unprotected fan blade tips will be hazardous to anyone working under the hood; and friends will jeer that the old restrictive fan shroud rim somehow provided better air flow.
Good luck,
Wendy & John. __________________________________________________
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Thanks Wendy & John, I have had 2 respnses to my problem with the overheating. Both have said almost the same thing. There is no unexplained coolant loss. The timing is right on. I think my next step is a trip to a mechanic....Thanks for your help....
AC
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I had a mysterious overheating problem; turns out the lower radiator hose looked normal, but the inner layers had separated, effectively plugging it off. -Tom

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of
flushed
replaced
leaks.
boils
HOT (out

There may be a TSB for this. I recall a field modification for the 3.0L. I'd change the water pump-there was an impeller change... Did this start all of a sudden?
Forget about trimming fan shrouds, etc.....
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Thanks Rick for your response. The engine is 4.0L. No,it did not start all of a sudden. At first, when i started the engine it would read HOT. After driving approx 8 mi, the heat gauge would read almost straight up, then drop up to HOT, but it would stay in the NORMAL range (hi-end). That's what told me to change the thermostat. But that didn't work. After changing the thermostat it acted the same way. Then after a very short period, when I started the engine it would go immediately to the HOT (completely out of needle range) zone and stay there. It never boils over UNLESS i turn the a/c on.
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start all

After
then
That's
short
over
\
If you haven't done this yet, disconnect the heater core hoses and backflush the heater core with a garden hose (engine dows not have to be running). Also, is there a vacuum operated valve in one of the heater core hoses? Turning the AC on would close that valve and also add extra heat load to the radiator.
You may also have an air pocket. Have you started it up cold with the radiator cap removed to insure you have flow through the radiator after the stat opens?.
I'll see if I can find the cooling system circuit diagram for a 4.0L Ranger when I get to work. I can't recall if it has an internal bypass. Did the original thermostat have a disk at the end of it?
I'll try to give you a better answer as soon as I can
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start all

After
then
That's
short
over
That water pump should have a cast iron impeller. Could be slipping on the shaft or eroded, but not all that common. The cycle you described above shows the stat is opening. Don't believe there were any head gasket problems but it's been a long long time...
Again. I'll try and find out more in a while...
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