So I was washing my car while it was running to burn off some bad gas it had according to a mechanics advice. I wasn't thinking I quess. Anyways all of a sudden I heard a pop and white smoke was coming from my engine compartment. I opened and noticed that it was coming from the back of my motor and not from, say a hose or radiator up front as I thought. I quickly turned it off and found that it had blown the hose off what looked like a small filler tank. I'm sure it has a name but I am as ignorant about this car as they come. After the car cooled I figured I could start it long enough to move it off my front lawn and into the driveway before it got hot. Well I was wrong I guess. As I gave it gas to move it it started knocking really bad. It sounds like it's something down deep in the engine and not like a valve. Any ideas or suggestions? It's more on the drivers side. My son's pal pulled the valve cover and it was shooting oil into valve area as it should I assume, then he pulled the head and didn't see any damage. Head is back on but not tight. Car will still start and still makes same noise. Help.

 

Welcome to the forums John,

To get the discussion started with the correct focus, please add Model and Year details. I assume from posting here it's an XK8 but Normally Aspirated or Supercharged and Year make a difference to the possibilities and the troubleshooting sequence.

Graham

 

I wonder how you can start the car with the head on not tight.
Hard to say what happened before the hose popped.
I suspect the diagnose of bad fuel was not correct.
It seems the headgasket was gone before that and the top of your engine was filled with air instead of coolant..
Having it idle probably caused the remaining coolant to not circulate at all, and overheating just pushed the hose off by boiling high pressure coolant.
Since you mention the knock comes from below, in that case the bottom end of the engine might have said goodbye due to too much heat retained.
I do not know why bottom ends of these engine go bad so easy after an overheat.

You have already pulled the head to inspect and I expect you have also checked valve clearance.
So a dropped valve seat has then been eliminated I suppose.
Even a slightly dropped (still in its recess) valve seat gives you a large valve clearance at least. Which makes the camshaft hit the buckets harder then should.
But that noise comes from the head, not bottom.

I hope I am wrong about the bottom end of your engine...
Good luck.

 

A picture of where the hose came off would be helpful but from the description it sounds like a hose to the coolant reservoir that came off. If so, then it is very likely coolant got down under the knock sensors which would cause engine knock. Letting it dry out would likely solve the issue. I would have gone this route before immediately tearing into the engine