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Camper_Jeff___K's avatar
Jun 09, 2026

No More 6.0 Liter Degas Coolant Boilovers

VIDEO: No More 6.0 Liter Degas Coolant Boilovers

After 150 miles of test driving, I was unable to make the engine blow coolant out the degas bottle. I never turned on the main engine fan using the blue wire switch modification. I am declaring my overheating and over pressure problems fixed. All testing was done with the 4000 pound Truck Camper on the F550. I am now able to comfortably drive up hills that would make my engine get hot and build pressure causing coolant to blow out of the degas bottle. Everything I had tried to correct the problem helped but completely fix the issue. This latest attempt to fix the problem with heat and pressure seems to have worked. I installed a Mishimoto Degas Bottle and larger hoses and fittings. The connections are also lower and closer to the water pump intake which helps. Combining the hoses closer to the water pump encourages coolant to be sucked into the pump. Being lower from the degas bottle increases downflow with help from gravity. Using larger hoses and fittings lowers pressure, back pressure, and increases flow. Where the heater and coolant filter hoses recombine into 1" hose is a recombination of the two circuits that were divided at the Tee by the alternator, half going to the heater core, and the other half going to the coolant filter and through the Hayden 1040 radiator in front behind the AC Condenser and in front of the Intercooler. Since half the circuit is cooled by the heater core, I decided the other half should be cooled by an equivalent auxiliary radiator. The degas bottle was restored to factory plumbing with the addition of the two Hayden 405 transmission coolers being used as radiators. The 3/8" degas hose from the top of the engine, originally meant for the EGR cooler, goes up to the two coolers and flows through them in series, then into the degas bottle input. The degas output goes to the top of the radiator connection. I did not connect the coolant filter return as many do into the degas to radiator hose. I decided to use the original IPR filter method and recombine with the heater core hose return under the degas bottle. I did not experience any benefit from using that connection earlier so left that hose factory untouched and recombined into the 3/4"x3/4"x1" Tee. That connection connects into the 1" SS Wye down from the Mishimoto aluminum degas bottle and immediately, about 4", into the water pump. This setup has resulted in a successfully functioning cooling system. With the new setup, I have not had to use the blue wire switch to turn on the main engine fan to full lockup. The cooling system is now able to achieve adequate cooling without the fans assistance. The Hayden 1500 CFM electric fan does turn on about 188 degrees but in all honesty, it's added ability to cool the engine is not that much. What it really does well is bring the AC temperatures down in the cab making hot summer days and trips south to Arizona etcetera, much cooler and more comfortable. There you have it, after throwing plenty of effort and a couple thousand dollars at it, I have a rock solid cooling system on my 2006 6.0 Liter PSD.

This picture shows all the important changes. Mishimoto Degas bottle at top and 1" hose coming down to 1" SS Wye. To the left of the master cylinder, you can see the PEX A 3/4x3/4x1" Tee and to the right, under the front brake line on the master cylinder, you can see the 3/4 90 degree PEX A elbow making the turn over to the TEE. The hoses combine lower than the factory Y hose does with larger fitting connections for better flow and less restriction. Personally, I attribute the success I'm enjoying to the larger hoses and fittings, not so much the degas bottle. So that's it, the overheating, coolant blowing problem is resolved. It wasn't head gaskets as so many has insisted. So far, the temperature hasn't gone over 192 degrees and coolant pressure above 14 PSI. I haven't even had to turn the fan on. Very happy with results.

9 Replies

  • Glad to hear all the supplemental mods appear to have helped. 
    You’ll actually find out how much when you do a serious pull in real summer temperatures or sit in traffic for an hour when it’s 100 deg outside with the AC blasting and not just a cruise down flat I5 in late spring. 
    The kicker is, all the recent improvements are to cooling circuits that shouldn’t need to be relied on to provide cooling, but only a method of transporting coolant for ancillary purposes. Like expansion tank and cab heat. 


    • Camper_Jeff___K's avatar
      Camper_Jeff___K
      Navigator

      All the cooling additions will continue to contribute to the engines cooling abilities. Each setup does have a purpose. The heater circuit goes through the heater core unless the AC is on MAX, then the vacuum valve will close the line off. The split to the coolant filter, would have gone through the heater core if not redirected so since it would have been cooled by the heater core, I figure it's natural and proper this half of the circuit should also be run through a cooler. I would imagine the heater core was thoughtfully engineered into the cooling system and having the other half about equally cooled is what should happen. As for the two coolers on top of the engine, they do functionally cool down coolant from the top of the engine. Originally it was where the EGR cooler deposited superheated water and siiteam to the degas bottle. These two coolers do a good job cooling that hot coolant and condensing the steam back ito liquid. I just don't have the urge to spend $ on a new truck. I now have both the 250 and 550 working just how I want them. Right now, I dont think Ill need to service either the trucks for a long while. Both are a pleasure to drive in thier own way. The 250 suspension is fully upgraded with a couple inches lift. It's ready for some rough roads. The 550 is highly capable and will be our home away from home with the little old but cozy S&S. With 800 solar, 400 lifepo, 320 amps alternator powering a 50 amp dc charger, we have all the power a nd storage we need. Starlink is about the only wishlist item left. 2 ebikes. Better stop. Alaska is probably out this year but exploring the North Cascades all the way to Montana may still happen.

       

      • Grit_dog's avatar
        Grit_dog
        Trailblazer

        I love that you got your rigs set up how you want. That is what it’s about!

        And I understand that all the ancillary stuff helps with cooling, by default. But it is not and should not be by design.  
        I’ve run demo derby cars just off the heater core and they make it 20-30 min lol. 
        If a super duper radiator, super water pump and fan don’t get it, that’s an issue. 
        And the pressure variation issue at low ish temps is an issue. 
        You haven’t had a “temperature “ issue per se. Any normal vehicle will get into the 220s-230 before blowing off. 
        All I’m saying is be careful. I don’t believe the problem is solved once you really work the cooling system. 
        it’ll be 100 deg in Vantage next week. 
        I think it’s worth your time to toodle out there next Wed, giver hell with the camper on, up the east side.  And if it’s good, turn around and flat pedal it back up the hill westbound at 80mph into the wind.  
        Thats the best local torture test route. 
        That will remove a whole bunch of speculation and worry before any big road trips if it passes that.  
        Just food for thought