BAC Forum
General Boards => Technical Support => Topic started by: Dave Atherton on May 09, 2016, 06:19:49 AM
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There seems to be many thoughts on how many pound pressure cap should be used on
engine cooling system. First of all the cooling system is designed to use a pressure cap
to prevent boiling of the coolant. Air in the coolant an result in the loss of coolant from
overflow when the aerated coolant is hot. The heated air expands, increasing the pressure
in the system, causing the pressure cap to open. Similarly, coolant can be displaced through
the overflow if the head gasket leaks compression gases to the coolant system. An incorrect
or malfunctioning cap can result in the loss of coolant and engine running hot. Radiator
Cap Pressure Test. Normal Duty Driving, system temperature 220 DEG F, Correct Cap ( 15 PSI ),
Light Duty Driving, system temperature 210 DEG F, Correct Cap ( 7 PSI )
Dave Atherton
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I have noticed that my cap allows leaking through the cap hose to the ground and my temperatures don't even approach 200 degrees. I suppose I need a new cap. Is there a napa part number or other descriptive info or are all radiator caps the same size and fit and they just go by lbs of pressure?
Mike
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Mike that is a good question I would suggest getting the pressure cap from a Cat Dealer.
I have found with auto part stores that sell, like kind parts in many cases do not meet the
call that Cat maintains. I find this real heavy in aftermarket electronic parts regulators and
sensors, filters etc. Good example last winter service call engine overheating found owner
bought engine thermostat at local parts store before leaving to come south. ( new thermostat
failed came apart ). Install correct Cat part. This is just my thoughts, Caterpillar to myself
Quailty parts and engine for the long haul. Many times cost and employees get into way and will
buying some place else. That is everyone's own choice. Dave Atherton Retired Cat Mechanic
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Mike,
If you have the Ford origin white plastic tank that Beaver used, it is a weak point. You can get a significantly longer life out of it by lowering the pressure using the 7lb cap. The Cat brand cap that Dave recommended would assure the quality. I think the 210F he referenced for the 7lb cap is a conservative max working temp given the boiling point is considerably higher. The actual boiling point would be about 230 degrees. Each pound of pressure raises the boiling point by about three degrees. If you fill the white tank even 1/3 full it will still force some onto the ground given that tank does not have enough volume for the normal expansion given the amount of antifreeze in the Marquis system. Many of us have added a second tank to the current system, piping the overflow hose to a second tank. Even with that I run the current original Ford tank about 1/2 full cold and with expansion the excess utilizes the extra tank but does not overflow. A search will show some of these installations.
Later Ed
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Are we talking the cap on the white plastic overflow tank or is there another cap somewhere?
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Adam,
That is the one. White tank in photo, also extra overflow tank arrangement on left. The main tank overflow hose from the cap area runs to the extra tank. the second tank has an overflow hose that drains to the ground.
Later Ed
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Mike,
I would not go out of my way to buy a Cat radiator cap if I were you. Your coach's cooling system was designed by SMC not Cat, and it never had a Cat radiator cap. The OEM radiator cap on your coach was a Ford cab since a Ford truck surge tank was used in the design. The only thing that I would do is to check the surge tank carefully for cracks if it is the original tank and if there are no cracks, install a good 7 PSI cap because the original 13 PSI cap caused many surge tank failures. If the tank has any cracks at all, replace it with a metal tank because the plastic tank is no longer made.
Gerald
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Gerald,
I'd have to agree with you on the NO CAT pressure cap simply because I am certainly turned off any anything CAT at this point. :)
But you make a great point and one that I was going to post and that is - Why would you use a CAT part on a Ford tank?
Anyway, on the '99 the location and thus the design of the system was a bit different than when the bedroom slide models came out in 2000. So the tank doesn't rest directly over the engine for one oriented right to left, and two we have a fan running all the time the engine is running to help keep that entire area cooler so that the tank isn't "baked" over the hot engine like in the ones 2000 onward with slides.
Our tanks in the '99s are bolted to the driver side of the compartment and oriented front to back because that location doesn't move as there is no slide. The tank looks great, though a bit yellowed over time. I have noticed in the past that when I attempt to fill it to the min line that the next time I stop I have antifreeze on the ground so I have limited what I put in it so that this doesn't happen but I pay careful attention to the engine temperature which stays typically in the 188-194 range.
I've never changed the cap, so I figure maybe its time to get another.
Mike
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Gentleman, Gerald has a very good point ( putting a cat part on a ford ). It is very interesting
Mfg & Builder change made to power plant to build a house over it. These little change over
time has caused many problems, location air intake for engine ( piping ), access to minor work
or work on engine, fuel system, connections and fastener etc. Same time reguardless of how
we feel about Cat we still need Cat. The great part of the Beaver members ( Knowledge ) about
owning and operation of motorhome, has corrected many ,many problems that Mfg & Builder
overlooked building the house. Passing experience foward by the forum membership taking
part, helping reduce cost on repairs. Trend it seems anymore we need to avoid getting ( hosed )
that happened in Mikes case. Again I agree people thoughts about Cat however this is not the
actions of all Cat Dealers and want to be clear with this thought. Dave Atherton retired Cat mechanic
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In the preceding post Dave referred to my experience with Peterson CAT in Portland. This morning I received a very nice email from Nick Smith of Peterson CAT here in Portland. He addressed my concerns and will refund a portion of the parts (extra parts originally ordered to craft a hydraulic hose) and some of the labor involved in the whole process. He also assured me that I have the "cat's meow" as far as a new fuel line and that made Margaret and myself very happy as well. He admitted that most of the time involved was spent scurrying about getting parts and initially they were hydraulic hose and parts and then a second time on the plastic hose and parts.
I just wanted to post that I am happy about our agreement and encourage anyone with a problem with any business to take your concerns politely to that business to seek a meeting of the minds. I just got off the phone with Mr. Smith and everybody is happy. I will cut and past this response to the other thread.
Mike
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I have the new BCS metal tank installed on my Beaver now. I've heard anything from 7PSI cap to 16 PSI cap now. I think I understand that the 7 PSI was to slow down or eliminate cracking of the plastic tanks. I filled with ELC last Friday (middle of sight glass on front.) When the transmission shop checked, it was not showing in sight glass. After test drive it was filling the sight glass again. This makes sense to my non mechanical brain because the fluid was expanded. I bought a NAPA universal surge tank and installed it to try to minimize fluid loss. So, my question, what is the ideal PSI cap for the cooling system on my C-12 with the metal tank? Thanks
Jerry
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Jerry,
It depends on what your temperature experience is with your coach. 7psi is less stressful as a pressure release point to overflow and is what I run. It has a lower boiling point then a 16 pound cap. The 7psi would not boil over until your engine reached about 230 degrees. If you are always 10 -15 degrees below that then you have a choice. It is not just the plastic tank, you have radiators cores, the transmission cooler, heater core, hoses etc that has to tolerate those working pressures as they age.
Later Ed
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Mike, just replaced Ford surge tank with an original from Ford dealer. They must be making them again because the first one I received had a small leak at fitting. Returned tank to Ford and had another one next day. Hope this helps in your decision for new tank. Price for tank was about $160.00. Thanks!!!
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Frank,
Do you have the Ford PN for that tank, be good to have that updated in case they changed it.
Laater Ed
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Mike, Ed, New PN for Ford surge tank is F6HZ-8A080-B, replaces old PN, F5HT-8A080-HA. Hope this helps. Frank B.
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Thanks Frank, good PN to have mentioned on the forum. I guess Ford changed the PN to confuse the innocent....
Later Ed
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...and I installed 2 new Ford tanks before I realised a steel tank from Beaver would have been a better way to go !!!
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...and I installed 2 new Ford tanks before I realised a steel tank from Beaver would have been a better way to go !!!
At $400+ very pricey but at least it won't break anytime soon!