Radiator cap lb rating info

[kketterling]

I want to replace my radiator cap on my coach but the lb rating is not on the cap, label’s missing. For my year coach with Cat C9 what lb rating should I get?

[kketterling]

Update: the Bar rating of 1.3 was stamped on the cap, which converts to 18.85PSI. So the question is this the correct rating for my coach as it's not the original cap that came with the coach?

[Happycarz]

Ken, my Cummins came with a 9lb cap. I would expect a 9-12 lb range for yours.

For each pound of pressure the boiling point is raised approximately 3° above the boiling point of 212° F.

9 x 3 = 27 212 + 27 = 239°, well above the engine derate point. So, my engine would derate before forcing any water out of the radiator pressure cap.

I assume your CAT would be similar, but don’t know what Monaco used as original equipment on your coach.

[kketterling]

Originally Posted by Happycarz

Ken, my Cummins came with a 9lb cap. I would expect a 9-12 lb range for yours.

For each pound of pressure the boiling point is raised approximately 3° above the boiling point of 212° F.

9 x 3 = 27 212 + 27 = 239°, well above the engine derate point. So, my engine would derate before forcing any water out of the radiator pressure cap.

I assume your CAT would be similar, but don’t know what Monaco used as original equipment on your coach.

After digging in the coach manual it appears from a photo that Beaver was putting 7lb caps on my Contessa Cat C9. To me 7 seems low and 18 that's on there now is high. So thinking maybe a 13. I could be wrong and am open to suggestions.

[96 Wideglide]

Pretty sure my coach with a Cummins ISL has a 13 or 14psi cap.

[windsorbill]

One of the problems with the higher rated cap, is as the plastic tanks age, they get brittle and are more likely to leaks or have a complete failure.

When mine started to leak, I replaced it with a stainless steel one from Source Engineering. It was plug and play.

[kketterling]

I agree about the plastic tank and changed over to a metal one awhile back.

[Happycarz]

I had local radiator shop make me an aluminum tank back in 2009. The original tank started leaking at the ultrasonically welded neck to tank.

I’m still running my 9lb cap.

The radiator cap does not make the pressure. It just keeps the pressure in the system when the rise of pressure exceeds the boiling point, 212°.

The engine/cooling system is what determines the coolant temp.

Automobile gas engines run hotter than our diesel powered motorhomes. We are used to our cars, and thereby associate that cooling system with our Diesel engine cooling system.

On some cars back in the 90's and 00's the electric radiator fan kicked on at 229°, if not running a/c. Some ran the fan at slow speed until 229°, then went to high speed. Still others had two fans the would turn on sequentially as temperature hit the set point.

If my motorhome even gets close to 220°, I am looking for reason. So far, my max is 216° on my SilverLeaf. And, I don’t like that!

Every two years I saturate my radiator, CAC, and condenser with simple green purple, from both the front and the rear. Then I flood it with medium pressure water hose. I disconnect the electronic motor controller and let the fan run full sped and set engine to fast idle, 1200rpm. All the water gets sucked out, and then I have the task to make the engine look pretty again.

Mind you, I have a side radiator.

Last year I was hitting 214°. I washed the radiator this spring. On 110°day pulling 6% grade, I only saw 205°.

I also use a long ¼” copper tube attached to my compressed air blower to get between the radiator and CAC at the bottom where somehow leaves find a way in. I do this before the washing.

I hope all the tidbits in this thread help other folks with both maintenance and heating issues.

[kketterling]

I get what your saying Harry which is why I’m going to drop the rating of the cap. I don’t want the cap to compensate for an engine that’s running hot. If engine’s hot it will derate and I monitor temp all the time when traveling. Also clean radiator out but just been spaying water thru it, haven’t tried the Simple green purple one that you’ve used.

[shootist]

Originally Posted by kketterling

I get what your saying Harry which is why I’m going to drop the rating of the cap. I don’t want the cap to compensate for an engine that’s running hot. If engine’s hot it will derate and I monitor temp all the time when traveling. Also clean radiator out but just been spaying water thru it, haven’t tried the Simple green purple one that you’ve used.

I was told the cap pressure is very important to engine cylinder cavitation. You run the cap cat says to run for your engine.

[kketterling]

I’ve been doing my calc all wrong. Been basing boiling point on plain water or 212 deg but based on 50/50 water and antifreeze mix boiling is 223 plus a 7 lb cap raises it another 21 degrees putting me at 244 degrees total.

My engine the warning light will come on at 225 and derate at 226. So I’m going to stick with the 7 lb cap recommended.

[96 Wideglide]

Originally Posted by Happycarz

Last year I was hitting 214°. I washed the radiator this spring. On 110°day pulling 6% grade, I only saw 205°.

I've never seen over 205F, and before I installed the Scangage, I would often change the screen to Alladin during long climbs, to watch temperatures!