So, I just picked up a 1994 Ranger XLT V6 4.0 4x4. 125k miles.

Everything ran pretty good. I took it to get smogged and it passed, and the mechanic told me there was a slight leak in the radiator, and recommended I flush the coolant and try some "stop leak" to try to plug the pin hole sized leak.

So, I flushed the system, and filled it with the correct 50/50 ratio, and after doing that, there is a knock coming from the engine when it's first started cold. Almost sounds like a "piston slap", and I'm afraid I'm going to throw a rod or something. Only thing is that it stops after about 3 or 4 minutes of running the engine. basically once it starts warming up, it stops the knock completely. I don't know what this could be. I'm usually good finding things that stick around, but I suck at intermittent mechanical problems.

Any help or advice would be greatly appreciated. Thanks in advance.

 

Since you just picked it up do you know how many miles it has been since the oil was changed???? If my ranger gets up around 3000mi or a little over it will develope a faint knock and I change it and it's gone, just a thought.

 

No, I do not... I've only driven it less than 50 miles, but the oil looks fresh. Still golden transparent. Haven't checked it since it started knocking yesterday though...

 

I've had similiar noises in my pushrod 4.0L over the years, caused by a number of different things.

The first was caused by wrist pins, so said the Dealers lead tech , over about a month it had come to sound more like a danged diesel, so Ford replaced the engine on my then new 99 4.0L. lol

The replacement engine developed a similiar sounding knock, that would go away after the engine warmed up some, that Ford named "marble noise", which they also said was "normal for this engine" & that high mileage tests showed it wouldn't adversly affect it's life, so engine replacement wasn't authorized!!!!!

They explained that it's caused be the piston wobbling in it's bore at the bottom of it's stroke, when the crank changes direction & pushes on the piston from the opposite side. This "wobble" in the cylinder, was caused by Ford boring, stroking & trimming the pistons skirt to shorten it, to increase engine displacement & lessen piston mass. It's kinda their explanation of "piston slap", I suppose.

The third knock source, was Combustion Chamber Deposit Interference (CCDI), this was caused by Ford letting engine part tolerance build up get away from them, such that there was too little clearance in the "squish zone", between the top of the piston & head, such that the piston could contact the head through the combustion chamber deposits on the piston crown & head, until things warm up & expanded to give some clearance, or until we do a "decarb treatment" to tidy things up inside.

The third thing was that I found on an oil change, if I didn't First drain the oil pan, then refill it without delay, then remove the old oil filter Last & without delay install a Completely filled new one, it would begin to "marble" about 30 seconds after restarting the engine after the oil change & sometimes it would marble knock for days, before quieting down, depending on how much of the unfilled oil filter air bubble was trapped. SO, if you've recently changed the oil & filter & didn't prefill the filter & or changed it first, you likely trapped an air bubble in an oiling system dead end gallery & it'll just have to work itself out over a few days running.

My marble noise was only heard at idle speed. Changing the oil & filter the way I outlined on the 4.0L pushrod engine, has cured that problem.

With your knock sound going away after a few minutes of running, it could be any of the last 3 things I outlined, so take your pick to see which one best fits. The marble knock on my replacement engine was caused by CCDI & my oil change routine, both of which I've found work arounds for.

A bunch of thoughts for pondering, Let us know what you find & how it goes.

 

Thanks for all of these possible scenerios. Ill look into those. I appreciate it.

 

Looked into above possibilites and it turns out its the lifters ticking. Don't know too much about this, so I'm going to dig into it a little more and its probably just going to need an adjustment.

 

Make sure your using 5w-30, Not 5W-20 & the FL-1A oil filter.

Can you see any sludge or varnish deposits on the dipstick, or around the oil fill hole in the valve cover????

 

No sludge. Oil was clean. Using 5w30. Going to look more into it tomorrow. No time today.

 

We have hydraulic self adjusting valves. You may have some sludge, gum, or varnish in a lifter thats causing mischief. Lots of cleaning oils out there that tout their cleaning abilities, several of SN Pennzoil recipies come to mind, along with a number of aftermarket pour-in's, like Marvel Oil, Auto-Rx, SeaFoam, ect, if your of a mind to try one of those that folks have reported good results with.

I've used Marvel Oil briefly on two occasions in the past, to fix intermittent sticky lifters on two of my Ford engines, with positive results.Did this just before an oil change & ran it just long enough to get positive results, then changed the oil & filter.

If you suspect lifter deposits, maybe consider pulling the valve cover on the noisy side & having a look inside for deposit type & load, before doing a treatment with a pour-in.

More thoughts for consideration.

 

Update: Did some sniffing around this morning, looking for leaky gaskets or anything in that nature, didn't find anything. I went about my day and came home decided to look again. Started her up with no knock. She was completely cold too...? Going to see what tomorrow morning brings, that's usually when it knocks the hardest.. So, maybe a fresh oil change was the answer all along. I'll let you know tomorrow.

 

Final Conclusion: Knock is completely gone. Started the truck this morning, no knock or tap at all.. Turns out all that was needed was a fresh oil change.

Thanks to everyone for their inputs.

 

Ok, good to hear all seems well after the oil change.