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Discussion Starter #1
had a slight engine knock under accelleration that increased / decreased in speed along with acceleration / deceleration. had plenty of good oil in it. added 2 quarts and in the process realized my oil cap was almost completely off. continued driving with lighter intermittent knocking til i got home. not sure if fixed. last time this happened i realized i was low on oil as my drain plug had been leaking so when i changed the oil it stopped the knock. this was less than a month ago. any ideas?
 

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Until others more knowledgable respond, I would say a loose oil cap would not cause engine knock. A missing oil cap might allow you to hear more injector noise in the cab.

As you already discovered, running with low oil can result in a noisier engine but if you only required 2-quarts to get back in the hatch marks then it does not seem like the knock should continue.

How many miles since your last oil change? I see a month ago...what oil type?

I notice my engine gets noisier about the time I need an oil change. With full synthetic, that noise usually starts around 5,000 miles.
 
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Like Dan said - the oil cap will have no effect on the engine noise - other than you being able to hear the internals a bit better. Also, 2 quarts low on an engine that holds 15 quarts isn't going to make any significant difference. I think your oil worries are overshadowing whatever the real issue is. It could be fuel pressure-related - or even fuel quality given we're all running winter-grade right now.
 

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Discussion Starter #4
im using the rotela 15/40. should i be using synth? I agree the oil didnt seem low enough to be causing the issue nor did it immediately clear it up. I did drive about 5 miles around town last night and the issue only slightly popped up real briefly but thats just back street driving. really need to find out whats causing this knocking. oil pressure is fine according to guage. it doesnt knock at all under 1000 RPM or so. if I let off the gas it will continue to knock until it reaches just over 1000 RPM then it stops. very odd. 2 years in still relatively new to diesel. also i think my glow plugs are toast. how hard are they to change?
 

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Changing oil isn't going to change what is going on in the engine. If you have a knock you will have a knock.

It could even be something as simple as a injector.
 
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Discussion Starter #6
Still having issue and doesn't seem oil
Related. Plenty of oil. Got 3 trouble codes. One says communication failure between pcm and IDM. One is a speed sensor and one is a glow plug indicator circuit failure. I dont see any of that being related but.may explain why my fobs no longer work.
 

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I think the Rotella 15-40 is a popular oil for this 7.3 so no need to switch to a full synthetic unless you lived sonewhere real cold or wanted longer intervals between oil changes. I think the reason I asked was more to find out if a Quickie Lube kind of place changed your oil because the wrong oil could cause a noisier engine.

Maybe it would be a good idea to check your oil level weekly to make sure its not getting low again.
 
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Maybe clear your codes and see which ones come back again tomorrow.

Not sure about key fob. Maybe the battery inside the fob died...always start with the most simple...Haha
 

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Glow plugs are easy. It's getting the valve cover off that's the fun part. I have a 1/4 drive swivel socket that I use to get to the rear bolt. Nick sent it to me -it's been a lifesaver for that bolt. You can test your glow plugs at the 41 pin connector or at the valve cover.
 
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From what I know it is because of engineering quirk since there is a leak when there is no cap.
With the cap off, there's nothing that would cause a knock that wouldn't be there with the cap on. No "engineering quirk" involved.
 
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