I'm not trying to track down a problem. Just trying to get some data points. I just assembled a little coolant pressure gauge to measure the coolant pressure when the truck is running. It tee's into the small line coming from the degauss bottle and then has a long hose that can be run back to the cab.

I went for a short (15 min or so) test ride from cold (~30 degrees) with a few short 3/4-full throttle bursts of a few seconds when I could. By the end of the drive the dash gauges were at operating temp and the degauss bottle went from min to max.

On the 0-15 psi gauge I found the needle never moved quickly (a good sign). Towards the end of my little test ride, the pressure peaked at about 4 psi. As I approached home on very flat ground I was down to around 2 PSI by the time I parked and shut down.

2 hours later the gauge was down to zero. I suspect that's normal too.

I also pumped it up to 10 psi and could not see the gauge move, but it was at about 9.5 psi after 3 or 4 minutes so I don't think the cap is limiting it to 4 psi.

My understanding is that they cooling system should operate under pressure. I always assumed that the the cap was what determined that pressure. Should the cooling system eventually get up to approx 16 psi and stay there? If yes, should it continue to gradually climb to that pressure or does it only reach that pressure over a longer drive cycle?

 

The OP is 0-16 PSIG. The cap is rated at 16 PSIG.

 

I guess I got confused because the coolant manufacturers specify the coolant boiling point at 15 PSI. At 3 psi the boiling point is significantly less.

Here's a chart:

 

Water under pressure raises its boiling temperature. That's the purpose of a pressurize coolant system.

Anti-Freeze is exactly that. Anti-Freeze. Lowers the temperature of when freezing will occur.

The Boil Over Protection is an additive which increases the surface tension of the mixture. That, coupled with pressure give a higher boiling point.

Boiling is the last thing you want in a closed system. The bubbles allow heat to burn through the jacket walls.

You're good to go. If it exceeds 16 PSIG it will begin to vent into the atmosphere. If your coolant tank is overfilled, it may displace some coolant as well.

The Pressure gauge needs the temperature gauge to take full advantage of monitoring it. If, that's what you're tiring to do.

 

Yes this is why i was asking about the low PSI. My understanding is that if a cap releases at a low pressure you should toss it. So I naturally assumed that the normal operating pressure was closer to 15 than zero.

I was out for about an hour and the pressure reached 7 1/4. The engine oil temp was 162 according to AE. I think the max oil temp reached was something like 172 going up a small hill. I have no way to get the coolant temp other than the dash gauge. So from that run, combined with the shorter run I assume that the coolant pressure builds very slowly over time.



I was really just trying to get a baseline to see how things worked when everything is operating correctly.

 

I'll guess your numbers are typical. Operating pressure is going to vary depending on temperatures, road and load conditions etc, not time.


I'd be curious to see it plotted over a longer run with varying conditions, especially vs oil temp.

 

The diesel shop that looked at my truck to see if there were combustion gasses in the coolant put a gauge on mine. They said it was never over 6PSI and took that as a sign that things were good.

 

Thinking out loud but the pressure comes from heat/expansion and since it's cold outside the radiator stays cold and the closed thermostat is keeping block warm.
Try blocking off grill and see if pressure goes up (single digits out tonight/tomorrow )

 

Yes, that makes sense to me. I had to make the truck work a little just to get the engine oil temp above 170 degrees after putting around for an hour.


I think all is well, I'll wait for a warm day to play around some more.