I was doing some cleaning and maintanance on my truck today and noticed that I had a little bit of puking around my degas bottle, so I hooked the block tester up and there was no change in the color of the fluid. So I cleaned it off and that got me wondering if maybe I had overfilled it or if my heads might be getting lifted under boost.

After that I ended up running into town and got an air pressure gauge and an 8' length of 3/8" hose. I have the hose running between the Degas bottle and the intake blocked off because of my remote oil cooler and EGR delete so I hooked one end of the hose up to the degas bottle and ran it through the fire wall where I attached the Gauge. My thinking behind this was that if the heads were leaking under boost the pressure of the coolant system would rise under max boost.

So I ran the truck up to operating temperature and after about 20 minutes of running it down the highway the coolant system pressure was holding steady at 6 PSI. So I began pumping the pedal until I hit max boost and then I would let off and then I would do it again. After every bump at max boost the coolant pressure would rise about 1 PSI until I hit about 11psi and returned home.

Does anyone else think the rise of coolant system pressure at max boost may indicate that I have a problem with my heads lifting under boost?

Thanks in advance
Jeremy

 

Nope.

At max boost, you are also at high rpms, and high heat generated, which increase the pressure in the system up to the cap limit.

Normal.

 

Seems to me Hubler that for someone that doesn't have studs, and still has stock bolts this would be a way to keep a check on cyl pres . So when pres on gauge goes beyond factory specs then you my be lifting the heads . JMO

 

11 psi is max observed pressure.

That is still below factory spec for the cap, which is 16 psi, I think.

http://www.thedieselstop.com/forums/...essure-246450/

 

The thermostat holds the coolant temperature fairly constatnt. At fairly constant temperature, then the coolant vapor pressure (degas bottle pressure) will be essentially constant. You do get liquid expansion, but that also should be constant once your coolant reaches a stable temperature. So, unless you see the coolant getting quite a bit hotter when WOT, then there is something else going on that generates the pressure. I think that leaking head gaskets is a possibility. Hopefully you are running a proper 50/50 mix of water/coolant, because a weak mixture can cause more fluctuation in localized heating and maybe flash boiling of the fluid.

I do agree that more heat removed in the engine will get the coolant hotter in localized areas, but this will ONLY affect the volume in the degas bottle (not the coolant vapor pressure) because of PORTION of coolant in the engine that has become hotter and less dense. This volume affect will not be very significant. When you see the coolant pressure steady at 6 psig on the highway at 190 *F coolant temp, and then see it creep up in pressure, try stopping quickly and seeing what the degas level has done and how quickly the temp drops and if the level drops. It takes a pretty good level increase to raise the pressure 5 psig.

 

Also -
Even though Ford's spec is 16 psig, slightly leaking heads can slowly cause issues even if the 16 psig limit is typically not reached. The combustion gasses can react w/ the silicates in the gold coolant and slowly cause silicate drop out and plug up things.

 

We had tested this quite extensively in the past however it wasn't on a Ford but the concept is the same and we suspected gasses from another point, not the heads. Bottom line is that coolant pressure will rise as the coolant expands as we all know but if you have additional gasses entering the coolant system you will see exactly what you saw. See once the coolant reaches it operating temp you should see the PSI level out, any boosts after that are from additional factors such as gasses, but that's not the only factor. I'm leaving a lot of info out because the specifics belong to a previous employer but you're on the right track. So if you read between the lines, you'll see that we saw the same thing and it is pretty normal and the stuff we saw it on was far more heavy-duty.

In short: You're fine.

 

I personally think you are OK based on the info you gave. You might consider that you may have a weak cap and replace it. About 8 bucks.

 

That's actually a fairly important little hose as it takes accumulated gas bubbles out. I had a filter installed in mine and when the filter plugged it PUKED. Might be your problem or just coincidence, but I know that same thing happened to me.

 

The exhaust gas in coolant test will pick that up.


The big unknown (since I don't have the tools to peer inside while it is running) is cavitation.

That can raise volume at high RPM / coolant flows far more than thermal expansion.

We know very little about that impact on coolant levels measured at the degas bottle.

To know this... all I need is some real time X-Ray imaging... or a Gamma Ray scanner.

Cavitation can happen anywhere coolant flows, not just at the pump.

Think the DOE might let me check one out for a few weeks?

LOL

 

Lets reflect on the post. He has an EGR delete and he has puked some from the cap. He is now measuring steady pressure rise at each high engine power outputs.

We agree that it is not liquid thermal expanisn, so where are these gasses coming from if not combustion gasses? I do not see the pressure rise in my engine. I even operated w/ the cold fill level at the max point for awhile and did not puke (therefore leaving WAY less vapor volume to "absorb" the effects of the volume rise from expanding liquid). This is based on the basic principal that the pressure rise will be less as the vapor volume increase above a constant mass of thermally expanding liquid.

I also do not subscribe to the thought that the combustion monitor is 100% sure, and I doubt that he has any more cavitation issues than the rest of us that do not have minor puking. I do agree that the cap may be weak, but it held to 11 psig during hard accelerations.

Just my thoughts / opinions, so I am anxious for discussion.

 

When you did the block test... Was it before or after running it hard... It has been recommended to me ...that if you get a negative reading at idle and still have doubts take it for a hard run... Then pull over let the pressure out of the degas bottle and do your test... If your heads are lifting under boost you have a better chance of getting a More accurate reading...

Good luck

 

As for the your pressure test... If in fact it was heads I would think that the pressure would move up quick once the heads lift and a lot higher than 11 psi...

Also if it's a sealed system and the pressure doesn't exceed 16lbs why is the pressure dropping?..I would think the pressure would continue to increase with each pull that lifts the heads until it exceeded the cap release pressure and vent...

 

You can have minor head gasket leaks. It doesn't start catestrophically.

Also, his pressure rose and then stayed there until he returned home. At least that is how I read it - that the pressure did not drop.

 

Bis, we're actually agreeing on the topic and source of gasses, sorry my post was a little cryptic. What we're talking about is combustion gasses that are entering the system. Sorry my example must have been a bit ambiguous as I was referring to Caterpillar engines and a different source of gas incursion (a different gas too). However the concept is the same and from a rough estimate (scaling down from previous experiments on a far larger power plant) I think that the (scaled down) pressure the the OP is seeing is well within the "safety range" of the power-plant, which is why I think he's OK. However, as you noted his pressure increase is most likely from head gaskets allowing a little blow-by as the heads lift during an estimated 30lb boost event. In my Cat engine our gasses were being created by a type of inertial cavitation and that's all I feel safe talking about that but we saw the rise of coolant pres. which led us to the source of the problem (not the heads).