I am having to replace the thermostat housing cover/water outlet as the old one has disintegrated.
It has a small outlet next to the main top hose outlet from where a small hose runs to the top of the radiator. When I removed the housing…the small pipe outlet was gummed up and it also appears that the corresponding hole in the main thermostat housing has a metal (brass?) blanking plug…which may have a tiny hole in the middle…which seems to be blocked also.
Can anyone explain what this is and if it should blocked. It seems functional and once the thermostat is out…you can feel the opening behind this hole into the housing. So I am not sure whether this tiny hole should be unblocked (drilled out) or if it is as it should be?
I am thinking mine had a small bobber in it too act as a check valve – but in any case I felt it was too small to assure the head fully filled with coolant when starting from a drained system – so I drilled a small hole (1/8? 3/16?) in the thernostat to be sure it filled easily.
There has been some previous discussion on this and it looks to have been a vestigial/optional remnant of the earlier series’ header tank involvement in the cooling system. I still have mine in line but I can see the check-valve not doing much, pretty easily and pretty quickly and the hole in the T-stat is probably as functional if not more reliable.
It’s a jiggle valve that lets air escape from the manifold as the system fills with coolant. The idea is not to end up with a big pocket of air when you have added all the coolant it will take.
I wasn’t too successful relying on that (even after cleaning it and assuring it jiggled freely) so I did what most manufacturers did and drilled a hole in the thermostat, then positioned it with the hole at 12:00.
This hole is larger than what you need but I wanted to be very sure the air had a path to escape:
The valve in Monauk’s photo is complete and operable, or will be once the gunk is cleaned out.
The hole in Geo’s thermostat is far too large. All you need is a tiny hole to allow air to bleed out during fill. A hole that big is a leak.
The purpose of the jiggle valve is to allow air out of the block and head when the system is initially filled. Once that’s done, it serves no other purpose. The S2 E-Type is bizarrely unique in having a bleed valve that vents into the top of the radiator. Most manufacturers put this in the thermostat itself, or have an external bleed plug. The original thermostat was unvented, thus the weird arrangement. Read all about S2 thermostats here:
Mike, my S2 has 3.8 SU carbs on it, no jiggle valve and spigot blocked off on Rad header tank.
Last time I refilled coolant, let car idle to heat up… the T-stat opened and relieved air block head.
Lots of “uncomfortable” noises from head as the room temp coolant finally got into the head. Once the coolant level equalized, I refilled to normal level.
Is there anyway around that procedure short of removing the thermostat when replacing coolant to relieve the trapped air.
A trick I have heard of but not tried is to prop the thermostat open with an aspirin. The idea is that allows the air to move until the system is filled. Then the aspirin dissolves and the thermostat can close.
Guess that’s an approach if you find the process a bit of a headache.
Drill a 1/16" hole in the rim of the thermostat. When you install the thermostat, make sure the hole is at the top. Fill it, let the air slowly bleed out through the hole, and top it off. The other option is to buy one of the thermostats on my list that comes with a built in jiggle valve.
The old axiom of “don’t put cold water in a hot engine”? When the T-stat opened it sounded as if I violated that rule. Or a steam ship was sinking.
I was trying to save the gasket because I may not have one a spare. But I have the concept now. After Mike’s thermostat chronicles I vowed not to touch a known working example!
The bleeder may save a little time, but I’ve never found the need for one. Depending on the Porsche, there may be pockets that have individual bleed screws, and you can save some time and headache with a vacuum bleeder. The E-Type system has fewer air traps. The only place that air can really get hung up is at the thermostat, and if you have a thermostat with a jiggle valve or bleed hole, all you need is to give it a few minutes for the air to naturally bleed out.
