Sorry to jump in on this thread like this, hoping for a quick answer and I will be off.

I always have a pool of coolant in the hex hole on that small black cap at the top of the thermostat housing assembly. At the front top of the engine. What's that all about, what is that AND whats the term for it? I want to replace it...

Yup - I been gone a while, struggling with a restoration on a 1990 XJS Convertible. Then school, then activism and a punch in the gut of a broken heart that took the wind out of me. WOMEN! Give me car problems any OL day. smh

I would appreciate any help, suggestion and directions. Thanks

 

No need - I've thrown you off the coolant hose thread onto a new one of your own.

That part is the Thermostat Housing Cap. A strange place for coolant to collect.

Are you losing any appreciable amount of coolant?

The plastic thermostat housing is such a regular issue that it's not worth replacing the cap alone. Far better to go for a complete replacement aftermarket aluminium thermostat housing.

Graham

 

I had exactly the same issue replaced cap problem solved
Jeremy

 

The resin has become porous and the cap is failing.

bob

 

LOL,,, appropriate name... I think I've lost my bearings... Been a long time since I have been tinkering... I found the part and ordered a new one.
It's not a lot of coolant, but enough. Overtime it adds up. I smell it sometimes. Too much

Thanks for the guidance. I'm on it!
swapping the engine in the spring! Can't wait!!!!