Radiator hose collapse (top)

**Donald R.** · #1 (**permalink**) 07-07-2012, 10:58 AM

I have a 1986 spider with all the related coolant items less than 1000 miles and 1 year old. Car runs with temp gauge straight up and will drop about 5/10degrees when heater is on when car is hot. After I shut it off and it sits overnight the top radiator hose collapses almost completly but springs back to life with a whosh when the radiator cap is opened. Is this normal or or hint at something not to smile about? I use a 50/50 coolant mix.
Thanks in advance.

**jcslocum** · #2 (**permalink**) 07-07-2012, 11:15 AM

You rad cap or the overflow cap is bad. One of them should vent so that any fluid pushed into the overflow can be dsrawn back into the system. Have you bled the system fully to remove all air?? There is a bleeder on the intake manifold.

**Donald R.** · #3 (**permalink**) 07-07-2012, 04:01 PM

Jon,
Thanks for the tip. I will check them both. I am sure the bleeding was done correctly.
By the way , what do I look for on the over-flow tank cap? I never checked one of those.

**jcslocum** · #4 (**permalink**) 07-07-2012, 06:41 PM

Dunno, I will have to look at mine and see how it works. :-)

**Donald R.** · #5 (**permalink**) 07-07-2012, 07:09 PM

Hi,
I just finished removing both of the aforementioned caps . The expansion tank cap has a simple slit in the inside rubber cap to allow it to vent to atmosphere. I soaked the radiator cap in CLR and then reinstalled it . If I still have the same problem when I drive it Sunday I will take it someplace to test and see if it releases pressure at 10 lbs as it should. Happy to be at the point that this is all of my problems with the Alfa.

**Donald R.** · #6 (**permalink**) 07-08-2012, 02:41 PM

I have just about determined that it is probably? the radiator cap. But when I went out locally to try and locate one I found that my 2.0L Spider which is listed in the Alfa manual as requiring a 10lb cap, is only available in a 13lb cap in the auto parts stores computer (various stores). Only a small difference but does anyone know if it is significant or is the 13lb cap ok to use? Does anyone have experience for any period of time with one of the 13lb caps? Perhaps the 10lb was all they had back in the day "86".
Thanks for the assistance

Erik · #7 (**permalink**) 07-09-2012, 07:16 AM

For Euro Spider there are two types, 7 PSI (round with two ears for cars without exp. bottle) and 10 PSI (nearly square with four ears for cars with exp. bottle).
I've tried both on my 1970 with exp. bottle, it doesn't seem that they let the coolant back in the radiator when cooling down.
A 13 PSI cap will not help letting coolant back in the radiator, but i might prevent coolant escaping from the radiator to the exp. bottle, in the first place.
Erik

**jcslocum** · #8 (**permalink**) 07-09-2012, 06:21 PM

13 lbs. raises the pressure in the cooling system by 30%. That seems like a lot. I would get the right cap, knowing that the Alfa engineers must have a clue about what is best. Order one and some other stuff and get the right part.

The tank cat flows air both ways and the tube isn't blocked?

Forzaguy · #9 (**permalink**) 07-09-2012, 07:06 PM

Raising the pressure in the cooling system raises the boiling point of the coolant. BP of modern low emission vehicles under pressure can be 235F or even more.

**Donald R.** · #10 (**permalink**) 07-09-2012, 08:42 PM

Hi all,
Jon and Forzaguy make a very valid point.
I got the nearly square original Euro style with four ears @ 10lbs pressure setting today. I will try it out on Thursday (or sooner) and let everyone know if it cured my collapsing top hose problem.
Don

**Donald R.** · #11 (**permalink**) 07-13-2012, 11:05 AM

Hi all,
Thank you for the reply's on a seemingly simple item, a collapsing top water hose. I replaced the radiator cap with the "correct" 10 lb cap and not a 13 lb one that is commonly offered at the automotive stores. Drove the car with some other friends on a Alfa drive of 328 miles up and down the north coast on Sunday. No heating issues and the hose remained round and full as it should. Problem solved!!!
Jon's comment on how much this extra pressure would increase the operating temp is a very good point. I wonder if this could be a contribution to the cause during the last few years of head-gasket problems we have seen in our aluminum engines of the Alfa.
Thanks for the guidence,
Don

**papajam** · #12 (**permalink**) 07-13-2012, 11:37 AM

That's excellent news!! Thanks for the update.

To be clear on the following;

Quote:

Originally Posted by Donald R.

...extra pressure would increase the operating temp...

**Donald R.** · #13 (**permalink**) 07-13-2012, 05:44 PM

Now I am confused. If the increased pressure allows the boiling point temperature of the coolant to increase, It would seem this would allow an increase in the coolant temperature and if the coolant temperature goes up the surrounding metal containing the coolant would also increase due to the ambient temperature. Perhaps I coasted through Physics?
Any way, I am just happy with my Alfa now.
Also, thankful for a place to go for assistance and support.
Thanks again.

**ghnl** · #14 (**permalink**) 07-13-2012, 06:16 PM

What Papajam is trying to explain is that increasing the cooling system pressure (i.e. by using a cap with a higher PSI rating) doesn't increase the temperature at which the engine runs. That is controlled by the thermostat. Increased pressure on the cooling system increases the temperature at which the coolant will boil - raising the margin of safety & allowing the system to safely operate at higher temps.

**jcslocum** · #15 (**permalink**) 07-13-2012, 08:50 PM

I was referring to max operating pressure on the system. 30% increase in pressure (potentially) to the system of a car that has known head gasket weaknesses.

Glad it's fixed and that we could help in some way.