The needle on my gauge suddenly started swinging down under acceleration a couple nights ago. I noticed that once I hold RPMs steady or come to a stop, the needle will swing back up to the position it normally reads. I went to pull the radiator cap which is the lever-vent type from Stant. I lifted the lever but there was no pressure to be relieved. I didn't want to remove the cap for fear that coolant would blow everywhere. I thought then that the cap was bad so I replaced it but nothing changed. Today, after arriving home from work, I lifted the lever to relieve pressure but once again, there was no pressure relieved. The radiator and hoses are hot to the touch. I'm stumped. What's going on? Is my system not pressurizing?

 

The gauge problem is probably the sender or a bad connection they are not very reliable.

 

But why would there not be any pressure relief when I lift the lever on the radiator cap? I'm confused about that.

I'll check the sender connection tomorrow but it seems strange that it would so that only upon acceleration only.

 

Might be two seperate problems. Do you see coolant leaking anywhere?

 

Correct me if I'm wrong, but my experience is that the system is not necessarily pressurized at normal operating temps. It is just flowing hot liquid coolant, that,of course produces hydraulic pressure, not the gaseous type that you see when it is over heating. I would not open a radiator cap if the vehicle were hissing or cracking and popping or otherwise exhibiting signs of being hot...Mark

 

I don't have coolant leaking anywhere. That was the first thing I looked for.

I'd like to think there's pressure within the cooling system. In the past when I've lifted the lever on the radiator cap just a little, pressure was released. Plus, all radiator caps are rated to hold a certain pressure. Our cooling system is supposed to be 15-16lbs. Hydraulic pressure, that is, as you said Mark.

 

check the sender it could be leaking and evaporating as it leaks or check in side the cab re heater core no leaking outside just in side the cab good luck

 

I sure hope it's not the heater core. I suppose that won't be that difficult of a job. More time consuming than anything from what I've gathered.

 

Is the coolant level low? Do you have a pressure tester?

 

Buy a new cap.

Rule out the simplest problem first.

 

The system is pressurized to lower the boiling, that is why you can get to like 240 before it boils.

This graph shows it all, we are at 1 ATM(14.7 Psi), it you have a 10 psi cap then you will be at 24 psi overall which has a boiling point of 238F

 

That's a cool chart, Rick. Thanks for sharing!

I pulled the cap when things cooled off to check the level and it's just below the neck in the radiator. I don't have a pressure tester but I'm sure someone I know has one I could borrow.

 

I never get any pressure release when I open the rad cap on a vehicle that is at normal operating temp maybe it's the 100% antifreeze- no water to turn to steam...Mark

 

I assume that that is the boiling point of water, none in my radiators, so that chart would not apply to my vehicles...Mark

 

X2 Low pressure and no leaks usually means the cap is leaking pressure.