1998 ford 4.6 liter 4x4 Truck temp runs fine drive for 10 -15 minutes temp starts to increase .turn truck off temp goes back to normal . drive 2-5 minute gage increases to hot shut truck off again . motor hot radiator cool. replaced theromstat flushed rad. removed water pump checked impeller looked like new out of ideas

 

Checkout this thread 'possible headgasket.....'. Several members have gave some pretty good advice. I have a 98 with cooling system issues as well.
GL

 

After much analysis we replaced radiator replaced it with a 2 flute larger capasity and replaced rad cap. still went to over heating ran truck back to shop with cap off .thought for a few minutes took it for a nother test drive no problem only thing that we could come up with was air pocket around water pump .

 

You might want to put a scanner on your truck and read the ECT [ engine coolant temperature] sensor and make sure its ok. Also look at the CHT [ cylinder head temperature] sensor too!

 

problem came back after 8 miles temp gage goes up . shut truck off found motor hot and rad upper hose cold . Relieved pressure by opening cap and drove home.Removed thermostat drilled to holes in thermostat ring replaced no over temp .However truck to cold now.Has anyone had any dealing with fail safe thermostat?

 

This sounds right with the symptoms you are having. you have checked everything else. the holes you drilled in the ring sounds like it is letting it pass through without the thermostat being able to work. The thermostat actually allows the engine to warm otherwise it will stay in the cold if the coolant is able to pass right through to the engine. good luck hope you solve your problem soon I know your gut will probably hurt until it's fixed.

 

replaced thermostat with a new slant 195 deg. Same problem truck runs for 10 minunder normal driving temp goes up and rad is cold . I even checked thermostat in a pot of boiling water opened right @ 195 deg . I even went as far as to check the old part and once again it open @ 195 deg . Thats 2 thermostats larger radiator water pump empeller good and turning the correct way flushed system . What the hell! If any one has any idea please post completly out of ideas . Still leaning toward a blown head gasket but no signs that indicate the is the problem .

 

There is no evidence presented at this time that you have a head gasket problem.

All your signs are that you have one of the following faults:

1. Faulty water pump, regardless of how the impeller "looks"

2. A restriction in the system. This could be a clog in the engine's water jacket.

3. Thermostat installed backwards. Check orientation (spring towards block).

4. Lower radiator hose collapsed internally.

You'll likely find one of these to be the fault.

Steve

 

I would take out the thermostat just to see how good the water wasw flowing through the system. Also was thinking #4 from above post, a soft hose with rusted spring may be allow hose to collaspe cutting off water flow to the pump. I would think a bad head gasket would be pressurizing the system causing it to blow water out. Check it cold and see if it builds up pressure quickly, like first 2 or 3 minutes after start up. If it builds pressure that quick then you deffinetlly have head gasket issue.....

 

Well ,finally got to the root cause of overtemp problem . The root cause is a blown head gasket . It builds pressure in coolant before thermostat witch is more pressure than the thermostat can over come . thats why I can open Radiator cap and relieve pressure off the system and the thermostat will open allowing engine to cool in and instantly . Drilled a 1/16 hole in the ring of thermostat,That 1/16 hole allows pressurized fluid to pass by engine comes up to temp thermostat opens and never runns hot even under load . Engine never showed any signs of a head gasket problem like coolant in exhaust fumes or mixing in the oil or excessive bubbles in Radiator over flow.

 

Had the same problem with my 97 ford 150 4.6 litre engine. I found that I had a slight leak in the rad. Whenever the fluid level got about an inch below the cold fill level an air lock would develop and the engine would heat up. I replaced the rad and made sure the reservoir level is always filled to the correct level.

 

I have the same problem with the over heating on my 97 4.6 I am trying to decide if I should repair or replace motor. I have 191000 on motor.

 

heres what I did and evrything has been running good for 2 weeks 1st I removed the trickler valve on the thermostat so I could have equal pressure on both sides of the thermostat . Used a bottle of Moroso Cermaic block sealant run it for 24 hours drained and refilled with antifreeze .This is 4.6 with 206,000 miles 98 ford . The way I look at it for $30.00 it was worth a try and I believe it may have worked for how long ill have to see. Hope this helps.

SD