loaded my 78 F150 with 460, pipe bumper, thick steel flatbed, etc, and put my tools in the back, and had a spare axle and the 35' boggers on the bed. I didn't cross a scale but probably hauling close to 10k all together.

Took this load out I-68, with all those hills. Ambient temps around 80 degrees. On the longest 2 hills my ECT reached around 223, and my EOT's maxed out at about 233. I was under the impression that I should not be venting coolant at these temperatures. I vented coolant last year on a relatively heavy tow (not this heavy) and replaced my degas cap and have not vented since then, even though I hauled 5500 lbs on the same 3000lb trailer along the same route I drove today a few months ago when it was cooler.

Even though it vented, judging from coolant level in degas I lost very little coolant (maybe less than half a quart, if that).

What do you guys think?

 

How full was the bottle? Do you use the new revised level?

 

well, it was suggested the last time it vented that it was just venting off the extra coolant because I had filled it to the MIN line.

i believe it was filled to right below the min line. Within an inch I'm not sure exactly where the revised line is. When cold like right now its probably 3-4 below the min line.

you thinking its just venting extra coolant? Is that how the degas system would work?

 

Water boils at 212* at sea level and for every pound of pressure the boiling point is raised 2*. so a 16 lb cap = 32*. 212 +32=244*. So your temps should not be the problem. I am having the same senario with my rig. And I think it is directly related to boost. When I get up in the 28 or higher pds. of boost I lose coolant. If I stay below that level I don't lose any. I think our head bolts are stretching under high boost and allowing compression to blow the coolant out...
I have my truck scheduled with a shop that specializes in the 6.0 diesel. But he is booked out for 2 weeks. I am going to have it studed, and he will also check the heads for flatness and cracks. I will see if that stops my problem, which will confirm my theory or fears....
I pulled a long hill with a light load for 15 min. but at 29 psi boost and temps were only 219 ect; 228 eot; ( or close to those figures) and I lost a gallon of fluid. Same hill at 24 psi. boost no loss of coolant..
Are you monitoring your boost? Might be the same issue.... just a thought..

 

If you don't have a pressure gauge to connect to your degas bottle, then I would try a new cap (if you haven't already).

 

flamebuster- thats what I'm afraid of. Boost pushing coolant means even if its only on long grades at high boost, its blowing past the headgaskets. That means its only a matter of time but I'd need headgaskets done. And thats definitely not in the budget anytime in the future.

bismic- as I said I replaced it a while ago and haven't vented since then, until now. It vented a couple times last year while towing heavy loads up long hills.

 

I have a pressure tester and I put it on the degas bottle pumped it up to 16 lbs and it held the pressure for over 14 hrs. I replaced the cap and thermostat, along with the FASS fan unit ( I thought it felt loose like a bad brg.)back in Sept of last year and still have the same issues... I havn't tried lightly sanding the lip of the degas bottle. But I don't think it will help much.. I have the FICM out right now and I am shipping it to ED today.So the truck is down for the week.
I hate spending this much money but it is cheaper than a brand new rig or a break down..

 

Before I'd go through any OTHER replacing of anything, I'd want to know the spread of the coolant vs oil temps.

 

Hasteranger; You can probably put off the inevitable by just not using full pedal pulling the hills. If you can read boost just keep it below 25 on long pulls. Which is easy to do and it will be no slower than a gasser or the semi's. I really won't know if I am correct till after I get studed..

 

In his first post it was ect 223; eot 233; while pulling hills, that is only 10 deg. so he is probably less on the flat unloaded..Totally agree on not throwing money without knowing the source of the problem...