ok folks heres a good one got a 97 f 150 4.6 has no coolant leaks or coolant loss . max coolant temp at the temp sensor after an hour and a half running is 187 degrees has a new t-stat and antifreeze . system will build no pressure but has never ran hot. have tryed a new cap , still no change. have never in 20 years as a mechanic seen this , if it were a bad water pump i.e bad impeller i thought i would have an over heating prob. but that has never happened. i'm stumped anyone have any ideas ? thanks in advance for any help:

 

ok folks heres a good one got a 97 f 150 4.6 has no coolant leaks or coolant loss . max coolant temp at the temp sensor after an hour and a half running is 187 degrees has a new t-stat and antifreeze . system will build no pressure but has never ran hot. have tryed a new cap , still no change. have never in 20 years as a mechanic seen this , if it were a bad water pump i.e bad impeller i thought i would have an over heating prob. but that has never happened. i'm stumped anyone have any ideas ? thanks in advance for any help:

 

Try another radiator cap. If it isn't leaking, it has to be the cap.

 

^^^

 

First thing is the thermostat is too low a temperature.
Should be 195.
.
I'm sure you know all this but review how a cooling system works.
All air must be purged from the system to prevent air blocks.
The thermostat is a matter of design requirement for engine working temperature because it affects fuel mileage, wear rate, heater operation etc..
As the system heats in a closed system, pressure builds against the pressure cap forcing any air left at that point out until the cap stops venting from the pressure build up. Many caps are two way operational.
After that point the pressure builds to a level below the caps blow down point.
This raises the boiling point of the coolant due to the pressure increase and has some limiting effect on the pressure peak.
At time of shut down the coolant pressure actually rises due to no circulation in a hot motor then begins to cool after a few minutes by conduction/ convection.
It's at this point the system pressure is at it's max. and can force out of a leak or even blow an old hard hose out.
As the coolant cools, a vacuum develops in the system.
The cap seals against this vacuum so air does not enter again.
.
Somewhere in this sequence is a problem but I'm not sure about how you are measuring system pressure unless with a test gage installed at some point.
I would get the correct thermostat in place, be sure the air is purges then run the truck a full hot cycle to see what it does.
Good luck.

 

thanks bluegrass yes it is a 195 t-stat, i used a snap -on coolant sys. pressure tester. at first i pressurized the sys. to 15 psi and started eng and after25 min. running and with constant monitoring the pressure never gained a single pound of pressure. this has me stumped. when cust. drove the truck to my shop the top hose had no pressure on it and when i removed the degauss cap there was nothing. i pressurized the sys. and had no loss of pressure after 20 min. any ideas .

 

tryed a new cap . even started eng with snap-on pressure tester installed and sys. never built a single pound after running eng for 20 min

 

Two threads merged. One per subject please, just causes too much confusion.

Thanks

 

What did you find was the issue? I'm having a similar problem with a vehicle.

 

I guess my previous message was sent directly to bill8177
my 97 expedition is doing the same thing no pressure on cooling system idling with a penny stuck in the throttle at 3,000 rpms
when I acquired the vehicle for 800 with 239,000 miles it would let fluid out under t hff e radiator cap so I replaced it with 1 from a Taurus and that seemed to fix that.
Then when you started it and waited for it to idle down and took off before operating temperature, before you get 3 miles the temperature gauge would peg to the H.
Bit if you warm it up to operating temperature you could drive for awhile before it would do that, sometimes it wouldn't do it at all.
The smell of gas fumes in the overflow tank with bubbles
I put a jug of bars leak in it last year and that stopped some of the bubbles, but some if that was thrown out under the overflow tank cap
Several days ago I drained it and flushed it with water and then put a jug of blue devil 3 in 1 cleaner and ran it for 90 minutes ( the last 10-15 minutes I stuck the penny in the throttle and revved it to 3000. Meanwhile still could remove the cap no pressure. The water in the overflow part of the tank just sits there and doesn't move.
I drained it and then put in a jug of blue devil pour n go 2x with well water but didn't read directions close enough and drained it [ was supposed to leave it in ].
So then
I went back and bought the 65 dollar bottle of blue devil head gasket sealer that your supposed to pour in slowly over a minute, but if I do that it'll just sit there in the overflow tank and not move [ there has been no thermostat in it this whole time using the blue devil and not much pressure on the upper radiator hose ]
should I jack up the driver side of the vehicle to try and get out trapped air? Or just pour in the jug of blue devil into the thermostat housing and then fill it up???
why is there no pressure!!!??? Improper water pump operation?
thanks