05 4.0 Spor Trac Sudden Engine Noise

[lougar]

Greetings all. I just started the truck today and it sounds like there is no oil getting to the top of the engine. Was fine last night. I've read about timing chains and tensioners, but this sounds more like a rocker arm or lifter. Not a rattle of any kind, but a "clack, clack, clack" which coincides with engine rpm.
It's got 116k, and is always low on coolant. Have replaced the thermostat housing 3 times, but coolant still "disappears". I have to top off coolant about every 200 miles. It takes about a quart. Not sure if one thing has anything to do with the other, but engine is smooth even with this new noise (have not tried to move it. IT'S LOUD!). No milky oil, no back pressure in radiator, no excessive moisture in exhaust or steam.

I guess those are 2 different problems. The loud (diesel sounding) clacking is my main issue. Sounds like something is going to shoot through the valve cover! Any ideas?

 

[lougar]

Update:

Started it again last night and although it initially made the clacking, it was considerably less. I did the screwdriver test at various locations on both heads and the clacking turned into a very small ticking, and eventually went away altogether. I was only able to pick up some of it on the driver said toward the rear cylinder.
Drained the oil, and there were some metal shavings in it? Not sure what that means. Went ahead and changed the filter too and put replaced with 5-30 Motorcraft synthetic blend (as always).
Started great this morning. No issues. The shavings have me a bit worried. Something was grinding or sheering off. I guess I'll keep driving until I hear it again, then remove the valve covers and take a look.

 

[2000StreetRod]

coolant loss & knock

Coolant can be lost externally or internally. If there is coolant dripping down the rear of the block its likely due to a leaking thermostat housing. If there are no external coolant leaks and no signs of coolant in the oil then it's probably leaking into the combustion chamber. A large leak can often be detected by smelling the exhaust. Slower leaks can often be detected by examining the spark plugs. Performing a compression test while examining the plugs can detect a blown head gasket of a cracked head.

Shavings in the drained oil are not a good sign. I would have pulled the oil pan and checked for larger pieces before adding new oil and driving the vehicle. The driver side cassette is at the front of the engine. The SOHC V6 will sometimes throw a cam follower (rocker arm). That can potentially be detected by a compression test or misfire DTC and reliably detected by visual inspection after removing the valve cover. I prefer my metal valve covers compared to the later "plastic" valve covers because they don't break when a cam follower is thrown. A large hole in the valve cover will result in rapid loss of engine oil.

 

[lougar]

Thanks for the reply. I am going to remove the valve covers and check.
I was pretty sure the coolant leak was one of the two things you mentioned. And the timing chain cassette issue is likely to happen very soon.
I hate to say it, but as much as I enjoy the truck, it may be time to trade it in for something more reliable.
I just spent $700 last month on the transmission solenoid pack. The front differential pinion seal was just replaced, and now this... And it's only got 115k on it.
I have read much worse problems on here with this engine. So I am going to get rid of it while I still can.
Maybe find 07 limited with the 4.6 V8.