Quote:
Originally Posted by sleeeper
there are two small hoses, one between the upper part of the radiator filler neck and the side of the resevoir tank itself, and one that attaches to the side of the overflow resevoir filler neck that drains to the road. The first one only comes into play when the lower seal of the radiator cap is opened via pressure as in this picture: http://www.centuryperformance.com/images/tech/radcap.jpg . This has been the arrangement from both before and after this problem started. On my car the radiator and the resevoir both have caps and the radiator is an all metal replacement unit that was already installed when I bought the car. It has worked well in this configuration for at least the last 20k miles without causing the problems I am seeing now. |
Sounds like an air bubble. Expands when hot, forcing coolant into the reservoir tank. Reservoir cap bleeds pressure off to make room for coolant. Air bubble contracts when cool, but can't suck coolant from the reservoir due to its trapped negative pressure so a hose collapses instead. Open the radiator cap allows air into reservoir and radiator, equalizing pressures, then gravity brings the coolant back into the system.
That's only a theory. It should be easy to see if this is what's really happening. If it is, then one of the radiator hoses is probably collapsing until you open the rad cap. More likely to be one of the bigger ones, so should be easy to spot.
Disabling the rad cap's lower gasket will allow the coolant to flow back and forth freely, but won't get rid of the air bubble.
The system wouldn't have done this unless you had an air bubble in it, so maybe it didn't have one before but does now.