Coolant ejecting on ground--bad cap seal?

[hans3]

Hello,

I tried searching the archives, but it doesn’t perform searches on 3-letter or fewer words. Anyone have issues with coolant ejecting out of their expansion tank “cap” when hot, such as at stoplights? It’s a circular problem in that an overheating car will intentionally trip the cap’s pressure release, but a cap that doesn’t seal properly will surely induce hot running.

With my (2800 CS, 5-blade stock fan) engine temp gauge between 2:30 and 3:00, I have been losing coolant out the expansion tank overflow, onto the ground. Despite the original fan, the car is not running hot at these times. Rented a system pressure checker and observed no system leak down when cold. The cap also holds pressure, well beyond its rating. At stoplights the temp will creep up, but the cause may be because of a bad cap seal.

It seems that my relatively new, OEM cap (rated at 1 Bar, or 14 psi) doesn’t quite make a solid seal with the expansion tank. I painted the cap’s seal with White Out to see where it was not making contact. A similar, used cap also failed to completely seal when cold. I think there may be material loss on the exp tank end of things.

I can think of several ways to build up the contact surface on the expansion tank, but was first wondering if this was a frequently observed issue?

Thanks, -H

 

[HB Chris]

The coolant gauge should read 3:30 and not above if everything is functioning properly. If you haven't done so, I would suspect the radiator needs cleaning, thermostat isn't functioning properly or the water pump/fan clutch. Not many original fan clutches still around after almost 40 years.

 

[deQuincey]

i am not sure of every detail you are writing but anyway I will try to give you my best advice considering I have been living a nightmare with the f... cooling system

the cooling system should be presurized when the car is hot, but all the same, when it is hot, you must be able to open the cap, and if everything works ok, water must be kept inside the reservoir and must not be going out from it

let me explain:
1-my engine is cold now, I open the cap and I fix the level of liquid in the vessel 3 cm below the top of the vessel, I close the cap

2-I start my car, it warms up until the needle is at 3:00, I let it run, I open the front hood, I touch the rubber tube that goes to the top of the radiator and it is hot and hard ("pressurized"), then i go to the expansion vessel cap, and I open it until the first stop with my hand covered in a cloth, the pressure goes out from the system, and the previously mentioned rubber tube is now weak, I realise that the liquid level has gone up.

I open the cap completely and the water is maintained inside the vessel while the engine is still running

if your case is not this you might have some problem in the cooling system, please tell us what happens

 

[61porsche]

Expansion tank cap

Have you tried "clocking" the cap 180 degrees? The principal of fastening doesn't use the full opening. The gasket should make up some tolerance on a slightly tweaked opening and if it's not too bad will pull up the side that's not in perfect plane.

Since you've tried a couple caps, it might be worth it to to try a relief lever cap just to see if a newer/ different design has a better seal. ( I know NOT OEM- but heh if it works......) You can always put the OEM cap back on for show and shine after you've let it cool a bit.

No, it's not a common issue. Yes, if atmosphere is introduced past warm up, the boiling point will rapidly increase.

Fix/ solve the cap issue , but bleed, bleed, bleed.