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I have a 2008 F250 Super duty and I seem to be losing coolant but when I remove the cap the system was still under pressure. I checked the oil and no signs of coolant in the oil
It's still possible to have a leak and the system hold pressure under certain conditions.
You can either add some UV dye to the cooling system or get a block tester and check for combustion gases in the cooling system. Probably reverse order of listed.
Lower levels when you check it cold? The levels must be checked cold.
Did you recently do or have someone do a cooling system service? Not unusual to have trapped air in the system, that's why I started using a vacum tester and filling system as I had been having issues with trapped air but this has eliminated the issue.
#1, perform either a pressure or vacum test of the cooling system. Pressure test will more likely show where a leak may be.
#2 replace the degas bottle cap, they get weak and you will lose coolant but it will still hold some pressure.
Couple things:
- The 6.4 was known to have radiators that could develop 'weeps,' that would lose coolant and you might never actually seen signs unless you pulled the radiator. If left alone long enough they would be come full-on leaks, usually around the tanks.
- It's not uncommon to have a degas bottle cap leak, especially on an older truck. The seal eventually breaks down and allows coolant to evaporate out over time. It will often still seal well enough to pressurize the system.
Couple things:
- The 6.4 was known to have radiators that could develop 'weeps,' that would lose coolant and you might never actually seen signs unless you pulled the radiator. If left alone long enough they would be come full-on leaks, usually around the tanks.
- It's not uncommon to have a degas bottle cap leak, especially on an older truck. The seal eventually breaks down and allows coolant to evaporate out over time. It will often still seal well enough to pressurize the system.
Agreed but the weeping radiator thing is common on virtually all plastic-tanked rads.
Coolant is kinda tricky 'cause it just sorta "vanishes" unless the leak is bad enough to find visible puddles/drips.
I'm not bashing plastic tanks -- they work surprisingly well in most situations. But I'd guess 60 to 70% of the vehicles on the road with over 100k miles are weeping a bit at the tank crimp connection. Usually it's mild enough drivers don't notice for a long time.
No issues with over heating, I had to replace the radiator and I put a vacuum test and it held the reading for 30 seconds then filled it with coolant, The lid on the degas reservoir is good. when I remove it a lot pressure is released, I also replaced all o rings on the hoses as well replacing the thermostat. I just don't get it.
