do I NEED pressure in my cooling system ?

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do I NEED pressure in my cooling system ?

Postby jethro » Sat May 07, 2016 12:03 am

I have been testing the fummins in the yard -
The daytime air temps here have gone from about 75 to about 93 lately.... only noticed that the water temp
comes up to equilibrium a little faster..... 15 min. vs about 5 min.
I have been running so far with the cap loose because early on i saw a couple of drops of oil in the water when it was
pressurising. I intend to do a head gasket re-torque after I had heat soaked it some (thats comming up soon when i do my
first on-road test drives) I put in A-1 head studs so im thinking retorques should be fine. (only back up to 115 ft-lbs which
was the nominal torque) I didnt want to risk pushing any water across the gasket untill it was fully compressed and heat cycled and retorqued.

I am wondering if it would be OK to run un-pressurised either for a little while or even for ever----- assuming I have lots of
"headroom" on mys radiators cooling capacity vs. engine heat production. (no plans to tow anything)

So far arround the yard - just barely getting into 3-rd gear ---seems like the 12 valve is capable of slinging the 8000 lb truck
around like a wet rag in an airplane prop-
Feels like i could go through all the gears and never get over 1000 rpm. i expect it will be even more so once I can get it on smooth pavement....

Put 235-85-16 coopers on factory steel wheels to help gas mileage (maybe) - cant wait to see what MPG looks like.....

Anyway- any thoughts on the water pressure question ? I should think it would be easier on the hoses if nothing else ....

Tim
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Re: do I NEED pressure in my cooling system ?

Postby DMan1198 » Sat May 07, 2016 7:44 am

The system is designed to be pressurized (usually about 7psi) this is done to raise the boiling point of the coolant (iirc it's 3 degrees higher for every 1psi of pressure) risking boiling your coolant to save something designed for that kind of pressure doesn't seem like a good idea to me. I know some people who've gone to higher pressure rad caps though.
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Re: do I NEED pressure in my cooling system ?

Postby jethro » Sat May 07, 2016 9:56 pm

Thanks D-Man-

The fummins is using the Ford reserve tank (plastic) - it diesnt have a cap of any kind on the radiator-
the only cap is in the reserve tank. And that cap is not the normal bayonet type-- its an all plastic one which
has screw threads. maybe I can find a new one as the one I have doesnt seem to have a pressure written on it---
i think I have seen regular caps up to 18 PSI- or the cap I have might even be bad.... (its a ford!)
maybe I can find a relatively low pressure new one.

Tim
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Re: do I NEED pressure in my cooling system ?

Postby Gots_a_sol » Sun May 08, 2016 9:57 am

That cap should have a pressure rating on it. I'd throw a new one on there just in case since they are cheap.
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Re: do I NEED pressure in my cooling system ?

Postby Richie O » Mon May 09, 2016 9:15 am

I have ran many with loose caps to get by just as long as it doesn't boil over it wouldn't worry me at all.
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Re: do I NEED pressure in my cooling system ?

Postby jethro » Tue May 10, 2016 9:56 pm

yeah Ritchie--- antique cars wernt pressurised ........ thats what I was thinking.......
especially if the Ford radiator is bigger than the dodge's was (or cools better) but i didnt have a dodge one to compare to......
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Re: do I NEED pressure in my cooling system ?

Postby Remps » Wed May 11, 2016 11:48 am

I've been running with my cap loose on my 96 for about a year now, no issues. It only gets up to about 85 Celsius, well below the boiling point of water. I keep the level 4-5" from the top. It actually seems to run a couple degrees cooler with the cap loose. I have no idea why.
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Re: do I NEED pressure in my cooling system ?

Postby jethro » Mon May 16, 2016 11:16 pm

Yes- i have noticed with the cap off- I can run it till it reaches thermal strady state- (till thermostat opens ?)
and I can stick my finger in the overflow bottle and hold it there..... (bath water temp)
not sure if that water is circulating on the ford.......
Only problem I noticed is that ford has the overflow bottle mounted sort of out on a cantalever-- and it is kind of not really
firm- more wiggly--
when I bo over bumps it throws the water in the bottle up into the underside of the cap and it runs out slowly- bump by bump.
Maybe I could drill the old cap for a small breather hose so it couldnt get out so easily. or maybe I can find a low pressure cap
maybe ( like 5 psi)
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Re: do I NEED pressure in my cooling system ?

Postby CumminsPower59 » Tue May 17, 2016 5:04 am

Tighten the cap. Seriously, you're going WAY too deep into this.

DMan1198 wrote:The system is designed to be pressurized (usually about 7psi) this is done to raise the boiling point of the coolant (iirc it's 3 degrees higher for every 1psi of pressure)


With my experience with super duty's, the degas tank cap (overflow tank cap) will let you know if its bad or not, they'll crown in the center. If it's flat, and the rest of the tank is in good shape, tighten the cap so the system can develop pressure, and you'll have no problems.
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