Proper coolant recovery tank cap?

[tmw188]

Ok been looking but time to ask. Adding to my travel parts kit. My alum recovery tank has a 14# cap on it but doesn’t mean that’s what it should be.  It’s a 2002 ISC 8.3   

Edited August 14 by tmw188

[diplomat don]

I went thru this in April and couldn't find anything on 2 forums but Napa checked books and gave me a 16# cap. Found out somewhere later was right but 14# should also be fine.

[Ivan K]

Each 1 psi of pressure is raising coolant boiling temperature by about 3 degrees F above 223 usual coolant mix temp at no pressure. I get a stop light bellow 230F and could go with 7-9 psi cap if I found one. Easier on hoses and plastic reservoir.

[TomV48]

People tease me, but this thing is 19 yrs old so I try very hard to save wear and tear on rubber and other parts, and NEVER run above 200 degrees.   That puts me in the VERY SLOW TRUCKS lane occasionally, but we are not normally in a hurry anyway.

[Frank McElroy]

As long as your coolant temps are below 210 deg F, you are considered light duty and Cummins recommends a 7 PSI radiator cap.

I'm using a 7 PSI cap.

[tmw188]

Thanks Frank! Did you pull that from your Cummins Maintenance Manual? I didn’t see that anywhere in mine. It gave other info but not that specific info. I have a new 1yr old radiator with OAT coolant, I’ll have some mountain driving on an upcoming trip and now wonder if I should change the cap from the 14# down to a 7# or not?

Too low of a psi and too high of a psi are both problematic that many of us especially me may not understand correctly. So does this mean if it gets over 210F with a 7# it could boil over?

Edited August 14 by tmw188
Added content

[Frank McElroy]

Before you change the radiator cap, you need to know the max engine temp as you pull long grades at max HP RPM which will likely be in lower gear and lower MPH speed to get the engine RPM in the range of max HP.  I suspect your engine coolant temp will be below 210 deg F but you will need real world data to verify.  On my coach, I max out just above 200 deg F pulling long grades.

I pulled the page 8-61 picture out of the Cummins Troubleshooting and Repair Manual - ISC, ISCe, QSC8.3, ISL, ISLe3, ISLe4 and QSL9 Engines - Volume 2 manual.

[jacwjames]

My engine temps run 183F normally and will climb a little on hard pulls, I don't think I've seen it hit 190F.  I've set up data logging on my Silverleaf and reviewed it after my wife returned from her trip in July, she pulled some pretty good grades coming through the Appalachian mountains in KY & TN

The cap on my surge tank is 10psi, this is the original cap. 

[scottknight]

Last year i changed all engine radiator hoses and thermostate and went with OAT coolant for a mid-summer Family Texas gathering, hoses and thermostat original equipment .  I have a 2004 8.3 ISC rear radiator no clutch fan. I do not have any recording or monitoring equipment and have owned this Knight since new. I only have the transmission temp gauge somewhat agreeing with the engine temp gauge. I read somewhere that OAT may help run a few degrees cooler (marketing?) I looked at the radiator cap formulas from some of the cap manufactures fyi info and decided on 7 pounds and also considered mechanical stress and boiling point. I left Bullhead low elevation at 100 plus degrees, normal summer temps using as low as 4th gear when unable to climb with momentum for slow trucks ect. Extended climbs to 6400ish elevation caused no alarms yet........... Amarillo is nice right now. I have always had to be aware on engine temps.

Anyone else read or discovered when you turn on the headlight switch the gauges oil, temp, charging become a little deceiving with low voltage after all illuminating load on.  Battery compartment passenger rear and front driver bin for a lot of 12vdc distribution. Voltage drop = dash gauge changes. I am not a mecanic rv or diesel just a long-time owner \driver of this rig.

[Benjamin]

19 hours ago, tmw188 said:

...Too low of a psi and too high of a psi are both problematic that many of us especially me may not understand correctly. So does this mean if it gets over 210F with a 7# it could boil over?

It's all about the safety margin.  Using Ivan's numbers, the coolant won't boil till 223, and 7psi will add 21F so 244F boiling point AT SEA LEVEL.  But you want a healthy safety margin so the head doesn't get hot spots from bubbles, or cavitation in the liners etc.  Water is an excellent coolant (for reasons that also allow life on earth among other handy features), but the temperature differential get limited with high ambient temperatures, and heat off the engine with a rear radiator.  The engine itself doesn't care if it's 160F vs 190 vs 250, air cooled engines operate at much higher temps because the air doesn't boil and make hot spots.  The coolant boiling temp and the safety margin is what determines overheating temp for water cooled engines.  Pushing the temp differential up increases the cooling capacity, so the higher pressure you can safely run, the more cooling capacity you'll have, the downside of that is risking blowing hoses.  If you don't run the engine hot, then the 15PSI cap will not matter, the pressure is determined by the temperature. 

[diplomat don]

We are at the FMCA rally in Redmond right now. Talking to Jim of Source Engineering and looked at their metal recovery tank and it had a 17lb cap on it so sounds like it is all over the board. 

[Paul J A]

Used a 7# on a ISX 525 78k miles. No issues.  Same on the Aqua Hot.

[tmw188]

20 hours ago, scottknight said:

I do not have any recording or monitoring equipment and have owned this Knight since new. I only have the transmission temp gauge somewhat agreeing with the

Scott I would at a minimum suggest getting a ScanGaugeD for monitoring the parameters you mentioned, you would like having one. Look on AMZ for one. I normally have boost on the upper left display. You can change them and move them around.

Edited August 16 by tmw188
Punctuation

[scottknight]

Thanks, just downloaded 41-page pdf manual, take a looksee. On the road in Amarillo headed towards Dodge City? soon. Like to look at manuals over strong a.m. coffee and prefer to break things at home. Left bullhead first of august after new front air bag install, Interstate 40 under constant repair, things going well, wife and 2 Chiwawa's enjoying sites............... enjoy your travels be safe .

scan gauge 3 manual.pdf

[tmw188]

Not familiar with that version. Is it for Diesel? Try this one.

https://search.app/VCNLLpS8cyD6cfDT8

Edited August 16 by tmw188
Content

[GringoScot]

ScottKnight, we have a lot of similar stories......  I have a 2005 Knight, currently "docked" in San Antonio.  I have experienced many of the issues you have referenced.  My coach runs hotter than I would like and this has had me white knuckled at times.  Switching from a Cat C7 Safari (currently in remodel) to the Cummins ISC threw me for a loop the first trip or two.  I had the decreasing gauge reading/dimming illumination syndrome with the headlights on.  To counter this I isolated the gauge grounds behind the dash, that were previously ran in series.....now the gauges barely jump and no dimming with the head lights on.  Too, I changed out the (gauge) temperature sensor mounted on top of the ISC, adjacent to the thermostat (posted the photos on here previously) and connected the warning cable that the PO disconnected.  I purchased a Scan D gauge like tmw188 referenced and the temperature reading is just about exact with my new gauge temp sensor.  I have been on several July/August summer trips from SA to Kentucky, SA to Indiana, SA to Illinois, etc. and the first trip added 10 lbs. of grey hair!! The coolant overflow plastic container leaked, so JB Weld Marine epoxy around the neck solved the problem and is still doing the job (16# cap by the way).  Driving 55 mph the Scan D gauge reports about 188F, 65 mph averages 195F, 72 mph averages 205-211F.  The Scan D reads 215F every now and then and every time I am about to downshift from 6th to 5th, the RPMs increase and the temp drops about 10-12 degrees.  Lifting my foot from the accelerator pedal and letting the Pac brake activate raises the RPMs and drops the temps the same amount. Reconnecting the top mounted temp sensor #2 cable now gives me a faint temperature tone (sounds like fingernails across a chalkboard) when the temp is over 206F.  I always clean the radiator and fan with Simple Green Alum. from my garden sprayer (and watch the bubble factory) at least twice after I dock back in SA.  I did find that the reflective insulating material that lines the engine bay was peeling and collecting in the corners of the radiator where the frame rails end causing a little blockage.  I have added the breathable catch can mod to eliminate the slobber tube and I switched to the OAT two years ago.  This coach just runs hotter than my CAT C7.........and than I would like.  The Safari pulled a large SUV on a two axle race car trailer from Tennessee through the mountains to SA without so much as a sniffle, but I have yet to get my feet wet pulling anything behind the Knight.

Edited August 17 by GringoScot

[scottknight]

Your temp vs speed seems to match my experiances. The mh spent the first 14 years in the northwest having ambient temps in my favor. On my mh looking from the back doors the mh built structure on both sides blocks some of the radiator not allowing some airflow. I think if i needed to work the radiator, improvements there and added core could help. The 04 ISC with electronics and engine\transmission communicating produces a strong powerplant. I am comfortable driving at speeds 65 and under based on road conditions, there are so many ways to improve these nuances. I annually clean the radiator exterior and use an extension claw tool to remove foreign materials from shroud area. (tedious) small trap door under bed with body pillows reaching thru fan blades. I sure like your voltage drop gauge fixes and recommendation for good data from additional readout from both members, Information gives direction to improvements. Engines and trannies are expensive.

Rear bags systems and rear end fluid next on list. But right now, we are surrounded by farms in Liberal Kansas just looking up and around ....... Happy roaming to all. Thanks

[Bootlegger]

GringoScot, what is your radiator cleaning procedure where you get all the bubbles?  I just finished cleaning mine with Simple Green Pro and I did not get all the bubbles.

[GringoScot]

Bootlegger,  

I studied this procedure extensively for my C7 and my ISC diesels, asked many questions on many forums, talked to diesel mechanics, and came across this cleaning procedure in a forum (I did not note the origin of this procedure unfortunately).   This procedure, with the bubble factory addendum has been my default on both coaches.

A retired diesel mechanic, that specialized in diesel pusher school bus maintenance, pronounced the bubble factory method to me.  As he explained and I later noticed, when the bubbles first start to escape the radiator, dark debris are noticeable.  Once the bubbles start to trail off, the debris should trail off as well.  IF NOT, and the debris are still heavy, he stated to repeat this procedure.  As he explained, you want to see the debris totally evacuate from between the cooling fins......like a "white glove test" so to speak. 🙂

Tom C cleaning procedure (this soap mixture may give a little better results

"2 Quarts of Simple Green. If you want to use a gallon of Simple Green, then
that would be OK, but I would probably not put in more than three (3)
quarts.
8 - 16 Ounces (1/2 - 1 pint) of Wesley's Bleech White Tire cleaner (Auto
Zone or Walmart)
3 - 4 Ounces of Dawn (Blue) Dishwashing detergent.
Rest is water.
Wet down the radiator and knock off all the dirt. UNLESS you are well
versed in using a pressure washer, DON'T. The fins on the CAC are VERY
sensitive. Ordinarily a good garden hose sprayer nozzle and city water
pressure will work.
Spray the radiator and CAC from EVERY angle that you can get to. You need
to do it TWICE. The first time move the nozzle from left to right (or east
to west). THEN go back over it and move the nozzle up and down (or north to
south).
Let this sit for about 5 minutes. The Simple Green will remove most of the
dirt. However, the Wesley's is as close to Caustic Soda as you can get and
will really dissolve the grease and the grime. The Dawn acts like a
surfactant to keep the solution on the radiator and lets the chemicals work."
(GringoScot added bubble factory at this point: start motor and run at high 
idle for about 10-15 minutes, occasionally directing sprayer with distilled water at the radiator/fan) 
"NOW, rinse that sucker. Use every trick that you have been told and use the
same logic for the rinsing. Rinse it from east to west and then from north
to south. It NEVER hurts to rinse it again. The water will run off.
This will effectively clean most radiators and CAC's. If you have road tar
or other gunk on it, then it might take STEAM, but that is best left to a
PRO. By PRO, I mean a diesel shop that understands HOW to use Steam and how
to clean radiators without destroying them."

[Steve P]

Not to split hairs, but the multiple mentions of radiator cap has me confused. Are we referring to the cap on the coolant overflow TanK?  On my ISC 360 8.3L with rear radiator the radiator top is pretty buried and I can't even see how to tell if it has its own radiator cap.  Which are we talking about?  My overflow tank has a 14# cap, and it originally came with a 16# cap from the previous owner.

[Ivan K]

There should only be one pressure cap in the system, on the highest point, on an expansion tank. If you had an overflow tank, it would be past the cap and not pressurized.

[Steve P]

So apparently  my aluminum  expansion tank (from Source Engineering) has the only cap ... I'm still unsure what pressure the cap should be.

[Benjamin]

My 95 safari has a radiator cap on the radiator and one on the reservoir above the radiator, original as far as I can tell.  I'd imagine there are others that way as they transitioned to pressurized coolant tanks.  Anything between 5-15# is fine until you have a problem.

[scottknight]

Yesterday afternoon I I climbed the Raton Pass 7800 elv heavy head wind , Colorado \New Mexico border underconstruction NO Extra Lane Width fallowing semi, heavy pipe 35 mph. I have an 8.3 330hp cac \ radiator stacked no clutch fan 7 #cap on coolant overflow- fill, 3rd gear or 4th. I almost hit the red on gauge no alarms. That made the case for better visibility (electronic monitoring) for me. Read some interesting radiator cleaning methods here but on road roaming now would like to try\use when i get home soon...... thanks. When i parked for the night, I opened the trap door under bed closest to the radiator\serpentine belt to inspect recent new belt\ belt tensioner \idler as well as hoses\thermostate ect. Nothing found real concerning however black flakes from firewall rubber material flatten embedded on new idler pulley thought it could be new belt flakes, reflective foil on fire wall long gone over the years. I read post about black residue maybe some from oil flushed out just have-not seen that on my 05 knight with 6-gallon oil sump. However somewhere in the next couple of stops i will try to hose water flush fins looking for the firewall flakes contributing to cooling blockage(?) ......... considering refurbishing\ sealing firewall material to remove that threat!        

[wamcneil]

On 8/15/2024 at 11:28 AM, Benjamin said:

... If you don't run the engine hot, then the 15PSI cap will not matter, the pressure is determined by the temperature. 

Yeah. That's what I was thinking. At the temperatures these engines NORMALLY operate at, it shouldn't matter if it's a 7psi cap or a 14psi cap because the coolant should be making less than 7psi. 

If something happens and my coolant gets hotter than normal, I think I'd rather have it build pressure to 14psi before the cap starts letting it boil off.