light thumping at idle

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alcyon

alcyon

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Kuala Lumpur ,Malaysia
http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3362756/Re:_Castrol_EDGE_0W-40__in_199#Post3362756
my mitsubishi engine makes a noise..a thump that is constant at idle. This noise started the last oil chamge with castrol edge 0w-40.
Oil analysis was done on that oil in the link above.
the engine is very smooth while accelerating and decelerating also smooth on the highway, exhaust is clean, engine isnt burning oil,fuel consumption is excellent at 31mpg mix of city and highway miles.
After i changed to amsoil 10w-40 the noise is muffled, but the thump is still noticable only on idle.
i will do another analysis in april on this amsoil.
What are your thoughts on the source of this noise as its driving me crazy. At first i thought it was a main bearing, but the sound should get worse at highway speeds.
 
Originally Posted By: michaelluscher
Wow. That's a grammar and spelling nightmare.
Please clarify on your problem or question



Take it easy in the fellow there shooter... Have you checked his location? I'd say he does better than some U.S. citizens on this board.

alcyon- have you tried to remove the accessory drive belt/belts to double check that the sound is from inside the engine? Also, does this engine have a timing belt or timing chain? If belt, have you investigated whether it's idler/tensioner bearing noise?
 
Thanks ! I will check those areas.
i will try to write better. I tend to be lazy to write when i use my mobile phone to post. I hate typing on the small screen so i take grammar shortcuts.
Its a timing belt engine from the 80s.
 
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I have a bad feeling that this thumping is caused by crankshaft bearing wear. I now remember that i changed my thermostat to 160f one last year while still on mobil 1. I surmise that when i am driving on the highway the temps must have dropped below optimal. If you guys look at the analysis in the 1st post, blackstone found lead and iron to be a tad high.
That coincides with driving about 10000kms with the 160f thermostat. Then i put an additional 8500km on this amsoil amo 10w40. Funny thing is if the temp were not optimal there should have been more water in my oil, from what i read. I just changed back my stat to 180f and will monitor wear. I think its probably too late, some wear has already set in judging by the thumping.
 
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Does the thump change whether the engine is hot or cold.
If it's consistent and temp doesn't affect it I'd start with the accessories then look at engine mounts,and anywhere something fastens to something else.
A 160f thermostat means that the oil was closer to optimal,since we've learned here that 150f is the ideal oil temp.
So I don't think the colder thermostat rid any harm. In fact I think it would lower oil sump temps and would actually be better for bearings to be honest.
Let us know what you find out if you don't mind.
 
Originally Posted By: HangFire
Thumping can also be a bad motor mount or even a bad belt. Hope it's not your main bearings.

i have decided not to do anything to the internals and just analyse the oil. Will then decide what to do.yeah i am keeping my fingers crossed ! I will have look at those. When you meant bad belt..is it the timing belt ?
 
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Originally Posted By: Clevy
Does the thump change whether the engine is hot or cold.
If it's consistent and temp doesn't affect it I'd start with the accessories then look at engine mounts,and anywhere something fastens to something else.
A 160f thermostat means that the oil was closer to optimal,since we've learned here that 150f is the ideal oil temp.
So I don't think the colder thermostat rid any harm. In fact I think it would lower oil sump temps and would actually be better for bearings to be honest.
Let us know what you find out if you don't mind.

thanks for the explanation. Do you have the links to those studies about oil temps. The sound is there no matter the engine temps.
I will have a check on the tensioner bearings for the alternator and a/c tommorow.
happy new year everyone !
 
Originally Posted By: alcyon
Originally Posted By: Clevy
Does the thump change whether the engine is hot or cold.
If it's consistent and temp doesn't affect it I'd start with the accessories then look at engine mounts,and anywhere something fastens to something else.
A 160f thermostat means that the oil was closer to optimal,since we've learned here that 150f is the ideal oil temp.
So I don't think the colder thermostat rid any harm. In fact I think it would lower oil sump temps and would actually be better for bearings to be honest.
Let us know what you find out if you don't mind.

thanks for the explanation. Do you have the links to those studies about oil temps. The sound is there no matter the engine temps.
I will have a check on the tensioner bearings for the alternator and a/c tommorow.
happy new year everyone !



You might try browsing this forum. 150* F seems a bit cool to me- it was my belief that 180-200 was "better", especially when it comes to burning moisture off. Either way, this forum should have the info for you to make an informed decision.

As far as your noise goes- bearing noises will get worse with increased engine/oil temps, as there is less cushion from the thinner, hotter oil.
 
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Serpentine belt tensioner? But...the fact that heavier oil seems to make it quieter does point to an internal engine condition causing the thump. If it is indeed quieter... Sometimes after doing something like using FI cleaner in the tank, I convince myself that the engine does run smoother simply because I'm expecting it to.
 
Originally Posted By: alcyon
Originally Posted By: HangFire
Thumping can also be a bad motor mount or even a bad belt. Hope it's not your main bearings.

i have decided not to do anything to the internals and just analyse the oil. Will then decide what to do.yeah i am keeping my fingers crossed ! I will have look at those. When you meant bad belt..is it the timing belt ?


Either one. Start with the easy one(s) first.
 
Ok, I finally removed the A/C and alternator waterpump belts yesterday.
The A/C V belt has cracked at several places, and the belts
tension seem too tight IMHO.
The A/C tensioner bearing looked fine, but I decided to oil it anyway. I installed new belts and tensioned it to grab the belts just enough without slipping. Feeling the resistance the water pump pulley and alternator pulley gives, it seems a super tight tension isn't needed. Only the A/C compressor needs to be tight as the load can be substantial when the clutch engages.
I am glad to report that I don't hear the thumping noise anymore, but there is a rattling noise at idle, which was there before. This must be caused by cheap aftermarket engine mounts.
So I am glad to report the problem is solved !
 
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