Hello everyone. I've recently noticed that my coolant practically empties itself if the car is parked overnight or for a few hours at work. However, if I fill it up again, I'm good to drive. I've let it run for a good half hour and no leaking at all during operation. Let it sit for a while, and it all comes out. I put the car on ramps and looked around. It seems to be dripping from above the front of the transmission, but I can't see the actual leak itself.

I did some research and found that there is a hose under the intake manifold which sometimes leaks into the vee of the engine, and from there towards the rear, which would explain the location of the puddles and the fact I can't see the actual leak.

So I was preparing to attempt to remove the intake manifold when I noticed coolant stains around what I believe is the thermostat housing (under the throttle body). If it is indeed the thermostat housing that has failed, is it conceivable that the leaking coolant could be flowing into the vee of the engine from there? What is the most likely culprit: the hose under the intake manifold or the thermostat housing?

My guess is the thermostat housing. If it were the hose, I can't imagine that a leak large enough to drain the coolant tank overnight would still allow me to drive the car normally, but if the plastic of the thermostat housing is contracting and expanding when the car is hot or cool, it may explain how the leak is cured when running.

I'm planning taking a closer look tonight. Any ideas or thoughts?

 

Have a look in the dark using a torch. Your eyes will be adjusted to darkness and if the torch light is reflected in a small amount of coolant, you'll see it more easily than in daylight when the torchlight gets overwhelmed. Coolant header tanks do crack and leak, as also does the pipe under the inlet manifold.

What year car, as the plastic thermostat housing is also a potential leak, and there is a company making replacements in aluminium

 

Its a 2005 non-supercharged.

I always snoop around with my torch in my dim garage. Always good advice. That's how I spotted the wetness around the thermostat housing.

I'm almost 100% certain that the expansion tank is fine. No wetness, stains, nothing in that area. I replaced the tank once in my old 2004 XJ because of leaks around the hoses and bleed nipple, so I have a fairly good idea of what to look for.