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2.5L engine noise possibilities


fireguy12117

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Yes, another ubiquitous engine noise question...

Most of what I could find all pertained to 2.3L motors in this forum, so I'll take a shot a question or 10 about the 2.5L.

Lately i have notice a knock, or tap in the morning when starting up cold, that is gone by the time i get to work. The commute is a few miles city streets, couple lights, then 30 miles of 70mph freeway driving. By the time i pull into work i don't seem to notice the noise. As of today we have about 244,300 miles on the motor.

my question simply is: are these engines prone to any particular failure type at these higher mileages? Rods snapping, piston slap going outta control, internal rotating items that seem to just go poof after 250,000 miles?

I haven't gathered much info, but a trusted person has listened to the noise and cannot make up his mind what hes hearing. the best we can figure is piston slap, but its just not like what you normally hear everyone posting up for rod/piston noises.

i plan to do a compression check and try to get an actual oil pressure reading next week, and determine if i pursue a solution or start thinking about retiring this poor old truck.
 


RonD

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Rod and piston noises are usually associated with the cylinder firing.
If noise is persistent enough you can disable spark in one cylinder at a time and see if noise lessens or disappears when one specific cylinder isn't firing.

On 2.3l/2.5l Limas the exhaust side coil is the only coil active for startup, so you can unplug the intake side coil, start engine, then pull spark plug wires one at a time for test.


Also, just to take it off the table
Cold engine
Loosen fan belt, take it off crank
Start engine
Seeing if noise could be an accessory problem
yes unlikely but I have been tricked before :)

You can run a cold engine for 2 minutes or so without the water pump.
I often do this when listening for a noise or looking for vacuum leaks, not having the fan on and accessories turning makes for a less windy and much quieter engine bay
 
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fireguy12117

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Between fathers day and the work week I've had to drop the ball on this. I plan to try these things this weekend, so thanks for some ideas.

Are rod and pistons noises a function of the igniting the combustibles, creating forces against anything with slop on them? So, taking the combustion out of the picture will allow a sloppy component to just move freely, noise free...?

anyhow, it almost sounds like its a little diesel motor when the noise is present so i am hoping the rotating bits aren't the issue, but we shall see...
 

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"Sounds like a diesel" would be pre-detonation, pinging/knocking.
Diesel engines run on "self-ignition" of air/fuel mix, no spark plugs.
Gasoline can self-ignite under compression before spark plug fires, that noise, pinging, is the two or three wave fronts colliding in the cylinder

Run a tank of high octane fuel thru it, see if noise lessens as the lower octane is replaced by high octane.
Octane is the heat rating or self-ignition rating, the higher the octane the higher the self-ignition temperature is
 

tomw

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Also consider carbon deposits causing knocking, tapping, etc. They can form and also cause pre-ignition(pinging) if you don't cause them to leave. An "Italian Tune Up" helps at times.
Short list of things that can knock: wrist pin, connnecting rod bearing, piston slap, main bearing.

Wrist pin and connecting rod should quiet with spark removal.
Rod bearing also, but will also quiet with higher rpm.
Main bearing will be more 'thud' than 'rap'.
Cam followers will make noise if the 'supports' don't pump up or leak too much.

The Lima can go 300k without problem, and more likely valve/head problem than short block, for the most part. If maintained reasonably, it will easily reach that mark.
Get a length of heater hose or vacuum line and plug one end into a handy ear. Rove the other over the engine while running to (hopefully) locate the noise source area.
If you have kept good oil, changed reasonably, the bottom end should not be the source. If you live in cold climate where the engine needs a bit of warm-up before driving, or at least ginger driving until warmed up, you run more statistical likelihood of piston slap or collapsed piston.
You can have cam noise if the lobes get worn as the profile can change leading to tapping even if the lifters are working properly. Again, that would be a 'cold lube' type problem caused over time, for the most part, unless oil changes were un-performed.
tom
 

fireguy12117

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the good news is nothing conclusive, the bad news is, nothing conclusive.

i fired it up, made sure the noise was there, it was
pulled the fan belt, fired it up, noise was still present.

i did the spark plug wire trick, killing one coil pack and one at a time pulled the plugs. it was as if by the time i got to this, the noise died down, so that was frustrating. it seemed as though it was still there on each cylinder as i pulled the plug wires. i plan to repeat this test next chance i get on a fresh cool motor that i know i can hear the noise well on.

im also going to try a tank of premium. would a tank full be better than a can of snake oil octane boost?

ive had the truck 10 years. i got it with 80,000 miles and its seen regular maintenance the whole time ive had it. im not perfect, but im no slouch either. i go after things when they need repair but also dont go looking for trouble.

oh, and, i probed hopelessly with a harbor freight stethoscope, poking here, probing there. nothing outstanding, but there again the noise had died down and i simply didnt know what i was looking for. i heard what youd imagine hearing, rotating machinery with bearings purring away.
 
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tomw

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If the HF stethoscope was a 'touch' scope, having a rod or tip at the end, rather than open, you will hear telegraphed sounds from internal parts yammering to each other. An open ended(both ends...) piece of tubing can isolate the local sounds, from RIGHT THERE, and you will hear other, telegraphed from all over, sounds at a lower db level. I think.
I don't have a recording, but regularly my Lima will have a lifter(support) tap at first startup, but generally it will decrease in less than a minute. It is standard valve 'clatter' type sounds, as the cam is trying to push the follower down on the valve end of the follower, while the 'fixed' end is supported by the hydraulic 'lifter' or support. As oil pressure comes up, it extends the support to minimize the clearance of all three parts: valve stem, follower, cam lobe, given the follower is sitting on the support, and has zero clearance. If the supports are leaky, and the bits inside gummy, it will tap. You would be able to hear the taps better if you held tubing alongside the cam cover(rocker arm or valve cover). If that is the noise source, just ignore it until you do head work, unless you want to take followers off and pull the supports and clean them.
If that is not the noise source, moving down the engine, check if the noise is louder close to the head gasket level, or deeper/lower into the block. Piston slap or wrist pin would be closer to the gasket, rod knock further down. In most cases of all the noises, only piston slap would possibly disappear. Rod, wrist and main bearing noises get worse with temperature increase as the noise damping oil gets thinned with heat, and allows more noise for the most part. Piston slap due to a collapsed or worn piston will quiet a bit as the piston expands with temperature rise, and has less 'room' to flop around.
Maybe a sound recording, visual, with roving microphone...??
tom
 

fireguy12117

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whoa....nice. That's the exact tool. I've had good luck with it for other things so i drug it out. its funny the looks people give you when you have that thing out. anyhow, i have tons of tubing at work that i can grab a couple different chunks with and play around with exactly what you described. Intuitively it all makes sense. surfing you tube rod knock and piston slap videos, i dont have that sound, so i am leaning toward top end, witch, until i do isolate, everyone here seems to kinda agree is a good possibility.

Id still like to tap in someplace and get an oil pressure reading and do a compression test, as well as isolate this noise. i'd like to get the best idea i can if this thing will take me to 300k or not. i want it to!
 

tomw

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Tap the oil pressure on the side of the block, above and just a bit to the right of the oil filter. The sending unit, a basic switch, can be removed and a mechanical gauge fitted to determine actual pressures.
If you have access to a leakdown tester, that can give you a good idea of each cylinders condition. You can make on with a couple pressure gauges, tubing, hose, etc., but you need a compressor to operate it.
tom
 

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