I've started this thread in addition to my previous thread: 300 CU. In. Overheating, hoping to catch a new eye or two.
My 91 E 250 with a 300 6 has started to over heat at highway speeds.
I didn't have an overflow bottle, until, recently. The first thing I noticed was after driving a couple of miles to the store, I would come out after a while and notice anti-freeze on the ground. I don't go on the highyway for more than an exit or two very often, but, a couple of weeks ago I took a 25 mile, or so, trip and I noticed the gauge which normally, barely even moves due to the absence of a t-stat, started to climb past normal towards overheating.
My radiator is less than one year old, my water pump 2-3 years.
Yesterday I bought a block tester to look for exhaust gasses in the water and the test came up negative.
Today, I flushed out the system and installed a 195 degree t-stat. The water ran thru the engine when I stuck in the hose from all directions.
After buttoning it up, I idled it for a half hour and the gauge stayed right in the middle. I took it out on the highway, trying to maintain 65-75 mph. The gauge did not move for 25 miles!!!, but, then, gradually moved all the way over to Hot. I took an exit and while traveling 40-50 mph on secondary roads the gauge returned to where it had been. When I stopped, nothing had overflowed into the bottle. What could make it overheat after 25 miles?????
Lloyd

 

could be a blocked cooling line or raditator. also, did u install the t-stat the right way? not trying to question ur intelligence but those suckers are easy to mess up. also, is the water pump leaking outta the weep hole? also is ur clutch fan working properly?

 

optikal hit on some good points of interest. Serpentine belt on correctly? Make sure it's not turning the wrong direction. Just have to ask seein as I can't put my paws on it. Sounds like the block isn't getting moving fluid and short trips aren't enough to bring up the temp. What kind of climate are you in?

 

turn the heater on hot and run the fan, if its not blowing hot air you have a heater core plug. this will cause overheating due to no fluid flow.

ps: make sure the truck is warmed up

 

Sounds like classic fan clutch failure.

 

Hoses collapsing? Bad radiator cap? Only other things I could think of.

 

I did a second Block Gas test on what was released into the overflow bottle after taking it out on the highway and getting it to overheat. It was negative for CO. I replaced the pump, fan clutch and flushed water thru the entire system in both directions. After this, I took it out on the highway and after 12 miles or so, it climbed up to 230 degrees. A friend suggested I check the timing, which, I realize I should have done before. The timing was around 8-9 before. I moved it up to -12. I took it back out onto the highway and it took longer this time, but, it, gradually climbed to 230
A friend told me that sometimes an air bubble forms in the block, somehow breaking Bernouli's principle, and farma a hot spot. Is this likely and how do I get rid of it?

 

By design, the pointed or V shape portion of the T-stat should be pointing to the hose going to the radiator.

Replace your radiator cap, if the radiator cap is releasing pressure at lower PSI than the rated PSI of the radiator cap then the max boiling point of your coolant solution will get lower and so it will heat it faster. So, make sure that the radiator cap is good or just replace it if you have not replaced it in a long time.

What mixture of coolant do you have in your cooling system? I would suggest 70% coolant and 30% water. Not all cooling fluid is drained out of the engine when you drain the cooling system.

When you flush the cooling system, did you just drained out the cooling system fluid and top it off?

Proper flush would be to drain the cooling system fluid, fill it water, start the engine for 10 minutes and turn it off, drain the cooling system fluid, put a bottle of Cooling System Flush solution and top it it off with water, start the engine for 10 minutes and turn it off, drain the cooling system, fill it water and start the engine for 10 minuts and turn it off and drain the cooling system.
Check your manual, if your vehicle requires 6 gallons of coolant solution and it only takes 4.5 gallons to fill it up with water during flushing then we know it has 1.5 of water left in the engine.
70% of 6 = 4.2 gallons of coolant
30% of 6 = 1.8 gallons of water
Since we got 1.5 water left in the engine, then we just need to add 0.3 gallons of water to make it 30% water mixture and 4.2 gallons of coolant.

Probably it is just your coolant temperature sender that is gummed up and probably just needs cleaning or replacement.

 

just my two cents worth..but after driving on the highway and your noticing the gage going up..have you pulled over to see if anything is leaking...or does it sound like the antifreeze is boiling?....if its not..i use to have a mustang that the temp was reading really high..and it ended up be the temp sensor.....just my opinion, hope it helps

 

No leaks. Even when it gets up to 230, it has not overcome the 13lb cap and overflowed. New cap, new gauge with new pickup and what with taking the cooling system apart every few days to make these changes, I'm not about to add any anti-freeze untill the problem is solved.

 

your problem seems to be beyond me....only other thing i can think of, and i think this was already mentioned, seems like the problem your describing acts like a air pocket in the cooling system, since you have taken the cooling system apart numerous time, it may have a big pocket of air in it.....i know cars and trucks are diffrent but my mustand did the same thing, after changing the same parts you did, i let it go for a day or too, then to mkae sure i didnt have any leaks i did a pressure test on the entire system...not finding any leaks, i let it go for another day, checked the coolant, and it was low, added some more to it, and it was fine..temp gage never rose like it did...now by no means am i a mechanic..hope it helps

 

Did you pressure test your cooling system?

 

No, I did not pressure test the system as there is no evidence of leaking. I am not losing any fluid.

 

try this, with engine still cold remove the cap and start the truck. let it warm up to operating temp, even with water it will warm up enough to open the t-stat. watch down the hole to see if your pump is pumping and water is circulating inside the radiator. this could help you narrow it down, also help remove any air bubble if present. have the hose in stand-by to add water as nesessary. let it run like this for awhile. see what happens, can't hurt.

 

i agree with ssn randy..cant hurt to try it