That rings true to me. Prior to this latest incident and excluding a leak in a radiator hose my truck would lose 4 to 8 ounces of coolant on a regular basis. Because I don't drive it except to tow the 5er I don't have a good pattern but what you say is pretty close.

 

Update. Refilled the tank with 50/50 and drove the truck 600+ miles (no towing) and everything was quite normal. Yesterday I hooked the trailer and towed about 100 miles. Had a couple moderate climbs but no real stress on the truck. Everything was OK. No coolant loss.

Senix, I sanded the top of the degas tank. I assume the idea was to just remove any burrs and rough the seal up a bit. Anyway that's what I did. I also noticed a very small indent right on the sealing edge. It's small but noticeable. Could that be enough to break contain at 16 PSI. I think there is a newer version of the tank anyway, as soon as I find one I'll install it.

Only other thought I had was the defueling, when the tuner defuels the truck could that reduce the coolant flow and increase heat and pressure to the point it would puke. What think? I can adjust that defueling point. but it's near at 37 PSI boost, wonder what stock is on the truck.

Either way tomorrow is the real test as I get to cross the passes east bound. I'll know something by then.

 

Sanding the top is to help reduce any variations for the best seal. Should help, did with mine when it puked once.

41 psi is what the motor should handle stock with no defueling.

 

Is your tuner defueling the truck?

 

Well, now that you make me think, I'm not sure. The tuner is telling me: DEFUELING boost. I don't know for sure the tuner is doing it.

I'm in a state park in Montana and I barely have a signal, plus it's about a half mile to where I had to park my truck. But I'm gonna walk up there and see if I can figure it out. I'm pretty sure the boost defuel is a parameter that I can set, but I've not done so, just left it where it was from the factory. I do know that all three really hard climbs I have gotten the "defueling" message. But, like I said before, if I didn't have the tuner on the truck I would not have known it was defueling. I barely noticed the power loss.

 

Stan,
Our tuner can defuel a whole bunch of stuff, boost ,temp, egt, the list goes on. If you were getting the defuel message something is set.

 

Yep, boost was set for the tuner to defuel at 35 PSI. I turned it off and will go with stock. Of course I checked the owners manual and it says that running for long with the boost at the high numbers may cause engine damage.

I still don't know that the defueling contributed to the puke but it kind of makes sense that it could by slowing the movement of the coolant.

 

Now we just have to wait for the test. Hope that is a little piece of the puzzel.

 

I will run up long grades at full throttle and max boost...I mean the guage (which is pretty accurate) will be right at 40 psi. There would not be any engine damage at that psi.

 

I'm just gonna go for it. I've not had a problem before doing just what Senix said. Let you know tomorrow night.

 

Good news for me. hooked up at 0 dark thirty this morning and towed from Flat Head to Billings. A little over 400 miles. Had three very high passes and a couple moderate passes. After each climb and decent I stopped at the next rest area and checked the hood. Best I can tell I did not lose a drop of coolant. Truck ran great and I held 60 MPH or a little over to near the top. Coolant hit 224 a bunch of times and fan came on and cooled everything down. Tranny hit some pretty high temps (maybe). The tuner has two areas I can put the tranny temp in and they each give me a different result. They vary by 20 degrees. The one on the dash didn't even move. Given what I spent on it that tranny it should hold up on any hill.

Now if I just knew what corrected the puking. My first choice would be the cap. When I get a chance I'm going to test the old one. If it wasn't the cap it had to be the tuner. Those are the only changes I made. Tuner is now set on lowest tune at "stock" setting which according to my instructions is no HP and no TQ increases. All defuel settings are off. To tell the absolute truth I'm not sure what the tuner was set on when she puked. Truck was out of my control for a month and I did not reset the tuner when I got it back. (won't do that again) I do know the defuel setting for the boost was 35 PSI. Way too low and it was defueling. Don't know if that would cause the puke. Anyway, it ends well for now and I'm a happy camper. I feel like I just ducked a bullet. Thanks to all for your input and support.

 

Great news...I am holding out for a bad cap.

 

Good report Stan, happy camping.

 

Found a parts store today and pressure tested my cap. It failed, just as Senix said it would, couldn't get past about 13 lbs. Plus, the coolant is holding fine for over a week now and a bunch of very hard climbs. So, let's close this puppy out on this note: No matter what distractions the truck throws at you, check out the most obvious solution first. Had I not had the previous coolant problems and thought there was air in the system in the beginning the first thing to suspect would have been the cap. But I made the whole thing way more complicated than it was.

I now think I mis-read the first problem which I thought was air in the coolant system when in fact the cap probably failed between home and Nashville as I went up and over Mount Eagle TN. When I checked the next morning and saw the coolant way down I assumed a coolant leak. When I was able to refill over two days and have it hold I then assumed there had been air in the system.

So, when I noticed the second failure due to puking I again assumed some kind of internal failure. Part of my reluctance to blame it on the cap is that I just installed that cap last winter.

I'm now pretty sure that the cap was the cause of all the coolant loss on this trip.

The one thing I did do right was check that hood every day and once the problem surfaced I checked it every stop. Had I not done so this could have easily become a very big problem. Oh yeah, I also bought a spare cap and threw it in the tool box. Never can tell when I might need one.

 

I always check my coolant at every stop when towing. I most of the time will pull the dipstick too.

Although the oil will not give a read out..it will show there is oil and if the color is abnormal.

Always pop the hood during the refill on the road.

Don't shut it off right away though if towing, rather let it run while fill up.

That under the hood is a might hot place...only one other location hotter and you are standing on it.