While visiting my car a few weeks ago, I had briefly run the car one afternoon, and had checked the radiator fluid level while the engine was warm. The next morning I noticed that the upper radiator hose had collapsed on itself. I popped the radiator cap and there was a sucking noise and the hose filled out.
I thought that the radiator cap had a vacuum relief valve. Is it likely that my cap is shot?
After this happened I filled the radiator up to about 1" from the top. I have since read in the service manual about the "cold fill" line and seen photos of radiators with a cold fill line about 3-4" from the top. Should I drain some of the fluid out?

 

P... It Al, just replaced the fuel pump last night but I finished late so I have not had time to test it, I will try to run it today and see if it still soaks my carburetor gasket,, as for your question do you have a over flow bottle? It is plug?

 

Peter, I can't remember if you installed a rad coolant overflow in your car or not. That should certainly take care of the issue of wondering how much fluid you have. It sounds a lot like you do have a defective rad cap though; likely the spring (which acts as a pressure relief valve) has failed.

 

Alan: I have an overflow tube, but if the cap is shot then will it drain excess fluid?
That is a new cap too

 

I agree with Alan, you probably have a defective cap. I would install an overflow bottle and run a lower pressure cap designed for it. Your problem should go away.

 

Peter, if the spring is stuck it might not allow even allow coolant to get to the overflow tube; and that's the way the pressure release is designed to work on all rad caps - even the ones with reservoir overflows. Most likely a defective spring in the cap. If it's new take it back and get a new one under warranty.

I'd definitely pull that cap and check it out right away - it could also lead to a blown rad hose in short order. Remember the pressure/volume equation? PV = nRT? In a closed system it will build higher pressure than designed if no relief valve operates. 1st point of failure should always be the weak links like the rad cap/reservoir, then the hoses.

Just a thought. I know you're meticulous about your car so please don't be offended by this next question. Have you got a properly rated cap??? The cooling system usually runs at or under 15 psi. If you have one rated for 20 psi or more that could be part of your problem.

 

Hey Alan: never any offense taken. I do not know what the rating is on the cap. I thought it was about 16psi. I cannot even remember where I got it now- when I say new - it was new last May, not original.
Luckily I have not driven the car since noticing the collapsed hose.
Thanks for the dire warning - I will get a new one from Napa before I even unlock the door.
Scary to think I drove 2500 miles accross country with that cap on there.
It seems like very time I turn around there is a new part that does not work as specified. I would gladly pay double to avoid dealing with parts that are defective.

Thanks again, Peter

 

The collapsed hose is not an issue as the engine heats up it expands again. It's physics.

 

My feeling is that if the cap is malfunctioning that way, then I cannot trust it to function in the pressure relief mode either. My peace of mind is worth a $5 part.

 

Absolutely.

How much is a new radiator, hose, water pump etc, and how much to have your car recovered if it lets go on the highway?.
More than a quality brand cap in all cases.

Roger.

 

Does the cap look OK? Id test it but I have a tester you may not. Old style cooling system caps w/o a recovery system do not act as a two way valve...they shouldnt. Yes when the engine cools to ambient there will be a slight vacuum but not enough to collapse a good hose. I wouldn't jump on the defective cap band wagon just yet as your cap is sealing as intended. Are you overflowing and or having to add coolant frequently? If your coolant level is to spec and its not overflowing when at op temp Id be inclined to investigate soft hoses first, wrong coolant level second. If the coolant level is too low and the hose is soft it will collapse so you could have a two fold problem. You didnt say if it was the upper or lower, but Ill assume its the upper because the lower should have the spring in it to prevent suction collapse from the pump at high RPM. Cheap chinesium hoses offered at all the big-box-houses-of-china parts outlets are notorious for collapsing. You get what you pay for. You certainly can try a new cap but invest in a non china high quality Stant same goes for hoses. I run 7PSI caps I don't see need to run 15lb caps never did. My bets on soft hoses and/or low coolant level.

 

And, originally, most hoses came with a spring inside to keep them from collapsing, especially the lower one!
I don't know if they can even be bought, anymore - never asked.

 

I bought the cap from Fusik (wanted correct) so it certainly wasn't a Walmart special.
I can find no other factory reference to a non recovery cap, but I understand from the service manual that the cap should have a vacuum releif valve (1970 Service Manual page 6K-1).
I believe the lower hose is the only one with a spring, and that functions to stop the pump from sucking it in during operation.
Thanks for the recommendation on Stant: Napa part 7031698.

Peter

 

According to my friends in the auto parts business springs are no longer used,,,nor needed. The new hoses are made thicker so no springs are necessary,,,for new fresh hoses. I do not know if this is true for repro hoses sold by vendors such as Fusick.
All caps do indeed have the one way valve/vacuum relief (which is the same valve used to recover fluids with a recovery cap which has an extra gasket the non recovery caps LACK), and have had the valve for as long as I can remember. My Chevys from the 50s had it. But anything that prevents air from getting to the cap will caue the radiator hose to collapse, like a kink in the overflow hose, or an obstruction such as a mud wasp nest. I would check everything before discarding your new repro cap.

 

Hey Mike: the reproduction hose I bought did not have a spring in it so we took one out of an old hose, cleaned it up and inserted it into the new hose. It was a nice tight fit and gave me confidence that that hose would not be collapsing. Certainly, while the top hose had collapsed the other day, the bottom hose looked fine.

Cheers, Peter

 

All caps do indeed have the one way valve/vacuum relief (which is the same valve used to recover fluids with a recovery cap which has an extra gasket the non recovery caps LACK), and have had the valve for as long as I can remember.

Humm Mike Ill have to look into that. I was unaware of this fact or I just forgot. Maybe the dual gasket thing is what I was forgetting. Im not afraid to be called wrong and enjoy being schooled if I am. I guess it makes some sense. Ive been around cooling systems as long as I can remember and I dont recall this. Again if true never too old to learn. thanks!

 

The oldest one close here is off my 67 Buick wagon, I imagine it is original. I wiped some Gibbs Lubricant on it hoping you would be able to read the stuff on top. As you can see compared to the new not yet installed replacement which has 2 rubber seals, old one has only one, both have one way valves. New not made nearly as nice as the original AC.
You can use a new one made for recovery in a non recovery situation, but an old one with one rubber gasket on a recovery system would likely loose the vacuum before recovering the fluid.

Have fun,
Mike

 

Well I can say for sure that when I replaced my hoses on the 72 in 1981 the OEM GM hoses (still on the car BTW) did NOT have springs in them. The hoses do have a fairly thick sidewall and are nylon reinforced. I don't know how they layer it or mold it, but the hose is very rigid. It's time to replace them now as they are starting to show bulges around the clamps, and the upper is starting to leak. Even at that, most of the sidewall is firm. I have never seen either of these hoses collapse on themselves. I know my rad cap works as designed - I've got the evidence in my coolant recovery tank.

Bought some brand new replacement hoses from Fusick last year. They are the same size and consistency as the OEMs although the markings aren't as good. They have NO springs in them at all. I seriously doubt they will collapse, especially since the GM ones didn't.

 

Just an update guys: I put a new Napa cap on, rated 16 pounds, about 5$.
I no longer have a collapsing upper hose.
As an experiment I put the old cap back on, ran the engine a bit, and then shut off. The next morning the upper hose was collapsed again.
Bottom line is, it was the cap that was not functioning correctly.
I might just buy another cap to keep as a spare.

 

Thanks for the update.
Another nugget of information for any of us with similar problems.

Roger.

 

So a relatively new "correct appearance" restoration part didn't function properly whereas an aftermarket replacement part did. I wonder what company made the resto part?

 

Older hoses have springs inside to prevent this. I would suggest replacing your upper radiator hose and MAW change the bottom one while you are at it. Although the new cap seemed to fix the problem, summer is here and you want your cooling system to be Happy, Happy, Happy

 

Hey Scot: My bottom hose has a spring. I do not believe the upper hose ever got one since during operation it is under pressure from the pump. The bottom hose is being sucked on, and that is why they put a spring in there.

Thanks for the Happy Wishes - never have enough of those!
Cheers, Peter