sometimes knocks

My mom has a 98 expedition 5.4 triton v8. When she starts it it will knock pretty loud then all the sudden quit. Something seems to be stickin. I dont know if it does it pereodically or only at startup. Any ideas please DAVE

Hey Dave
Have you heard the noise yourself, does it sound like a hammer blow on iron, or more like a ticking noise like a lifter would make? Lately i have been getting a rash of vehicles with the same complaint. What i have found in almost every case, is that the inside of the engine is full of gum and varnish and the lifters are sticking. The lifters on most of the ohc engines arent real healthy to start with, and if they get varnished up, they can leak down and rattle on cold start till the oil pressure gets up. Most of this is caused by people switching to cheap oil because of the high prices, or just not changing it. And alot of it is people that have their oil "changed" at wal-mart or some of the other quick lube places where it doesnt actually get changed, they just wipe the filter and the filler cap off to make it look like it. We`ve caught several of the shops here doing that. What ive been doing with them is changing to a good quality oil and adding a quart of Marvel Mystery oil for a couple of oil changes, It will slowly dissolve the gum and varnish without making it break loose in big chunks and stopping up the pick up screen. In almost every case this has solved the problem.See what the inside of the engine looks like, if its dirty, Its worth a try. On the other hand it also sounds like it could be a main bearing, hard to tell without hearing it.

Thanks uncle it does sound more like a lifter actually once i had a loose plug sounds kinda like that but a whole lot louder. I know my dad puts mobil 1 in it always has but hes become lazy and only changes it once a year. Anyway its good to have an uncle on this forum...DAVE