DT466 Engine Knock / Rattle? Does this sound right?

A_Bus_Called_Quest · 05-02-2021, 07:34 PM

Hey Skoolie Fam!
Back with another question for the wizards - I've linked 2 videos below so you can hear my '95 3800 DT466 engine - there is a kind of rattle, or "knock" sound. I've never had an engine this big so not sure how it is supposed to sound, but to me it sounds a little rough?

Video 1
Video 2

Some you tube engine knock shows a bent rod / rod knock - but I have no idea what I'm talking about, or looking for.

I'll be making an appointment this week with a local diesel mechanic, but wanted to get the gang's input so I know what to expect / have a point of reference when the mechanic comes back at me.

As always, your input is much appreciated!

ewo1 · 05-02-2021, 08:04 PM

Wow....
since I’m not there and can’ r see much on the videos...
I would take the fan belt off and start the bus again.

Wild guess here....

If it still makes the sound, it the engine.
No sound then maybe your fan ...????

A_Bus_Called_Quest · 05-02-2021, 08:09 PM

haha is that wow a bad one? My first thought was the fan but I can't see anything that it would be hitting to cause the noise, like a super fast spin-the-wheel.

It sounds like it's coming from the front/center of the engine - but then again, it's so loud in there I can't really tell.

I can take additional video if a better angle is better for diagnostics.

bigskypc50 · 05-02-2021, 10:38 PM

When was the last time you had the valves adjusted? But ya pop off the belt fire it up for a few secs remember the water pump won’t be turning without the belt. and see if it’s still loud. How many miles on the engine?

A_Bus_Called_Quest · 05-02-2021, 11:15 PM

Quote:

Originally Posted by bigskypc50

When was the last time you had the valves adjusted? But ya pop off the belt fire it up for a few secs remember the water pump won’t be turning without the belt. and see if it’s still loud. How many miles on the engine?

Me and the bus just met about 3 weeks ago so I don't know the last time anything was adjusted

We noticed the sound right when we picked her up, but she drove fine the 260 mile trip back home.

I'll try the fan belt tomorrow and see what happens.

Oh - and 265k miles

ABBus · 05-02-2021, 11:33 PM

Sounds like a diesel engine to me ...

A_Bus_Called_Quest · 05-03-2021, 02:14 PM

Quote:

Originally Posted by ABBus

Sounds like a diesel engine to me ...

Sounds good to you?

I feel like it's right on the threshold of sounding totally normal, and maybe something weird?

Thanks for the input!

A_Bus_Called_Quest · 05-03-2021, 02:26 PM

Quote:

Originally Posted by ewo1

I would take the fan belt off and start the bus again.

So . . . lame question - which belt to take off?

Also - can you help me identify this part (photo 2) is this the AC compressor? It looks like there are 2 of them, but only 1 of them has the wire connected - there is a loose black wire and red wire, both with compatible connectors??

Really appreciate your help on this

Mr4btTahoe · 05-03-2021, 03:38 PM

Is it just me... or is it idling really low? How's oil pressure?

cadillackid · 05-03-2021, 04:27 PM

yep pull the serp belt. actually id pull the A/C belts too.. then id start it dead cold and get a metal rod and touch various places on the timing cover.. air compressor (brakes), near the injection pump.

you touch something wit hthe metal road and put your ear against it.. you find where the clatter gets louder and software.. that doesnt sound like a rod knock or such the cadence is way to fast.. more than one per every engine rev and a rod knock is usually one clank every 2 engine revs.. one A/C system probably failed so they unplugged the compressor.. perhaps it locked up or the freon got low etc..

A_Bus_Called_Quest · 05-03-2021, 04:52 PM

Quote:

Originally Posted by Mr4btTahoe

Is it just me... or is it idling really low? How's oil pressure?

I had it running yesterday after I refilled the coolant to get it up to temp - steady 50psi on the oil pressure. I've attached a photo of the dash while the bus was in idle yesterday.

ABBus · 05-03-2021, 08:49 PM

Quote:

Originally Posted by Bear Gerschafer

Sounds good to you?

I feel like it's right on the threshold of sounding totally normal, and maybe something weird?

Thanks for the input!

Yep. Not an expert, but I had a 466 and I would not worry.

bigskypc50 · 05-03-2021, 10:46 PM

Ya that’s ideling really low 400 rpm? That’s too low I think, don’t quote me but I think the sticker says 650rpm on the engine? mine will rattle a lot at less the 550. I like to keep mine around 700-800. I have a knob on my dash that I can turn to adjust my idle speed. You can turn it to adjust idle speed or push the red button and pull up or down to make huge adjustments. If you don’t have the knob hold your rpms around 650 and shoot a new video see if it quiets down

Mr4btTahoe · 05-04-2021, 08:02 AM

Quote:

Originally Posted by Bear Gerschafer

I had it running yesterday after I refilled the coolant to get it up to temp - steady 50psi on the oil pressure. I've attached a photo of the dash while the bus was in idle yesterday.

You need to increase idle speed. That is likely why the diesel rattle sounds so harsh. Start there. It is currently relying on rotating mass to keep it running as it's sub 500rpm. I think spec is in the 700 range. I'll have to look. (650-700rpm is what it should be).

musigenesis · 05-04-2021, 08:16 AM

Quote:

Originally Posted by Bear Gerschafer

I had it running yesterday after I refilled the coolant to get it up to temp - steady 50psi on the oil pressure. I've attached a photo of the dash while the bus was in idle yesterday.

That's maybe a bit odd. My DT466e is around 20 psi when idling and 50 psi when revved up. You shouldn't be at 50 while idling.

ABBus · 05-04-2021, 08:26 AM

Quote:

Originally Posted by musigenesis

That's maybe a bit odd. My DT466e is around 20 psi when idling and 50 psi when revved up. You shouldn't be at 50 while idling.

The engine was cold.

cadillackid · 05-04-2021, 09:24 AM

my DT idles cold at 50 PSI.. that was pretty normal.. once ny DT is warmed up it idles hot around 20 PSI and runs about 52 on the highway..

I have my winter idle speed set around 600, i run it about 750 in summer (better A/C performance)..

ABBus · 05-04-2021, 10:00 AM

Quote:

Originally Posted by cadillackid

my DT idles cold at 50 PSI.. that was pretty normal.. once ny DT is warmed up it idles hot around 20 PSI and runs about 52 on the highway..

I have my winter idle speed set around 600, i run it about 750 in summer (better A/C performance)..

You should keep 750 (or even more) in winter too. Helps the engine to build enough heat to allow proper combustion.

cadillackid · 05-04-2021, 10:47 AM

Quote:

Originally Posted by ABBus

You should keep 750 (or even more) in winter too. Helps the engine to build enough heat to allow proper combustion.

I run the webasto along with the engine if im driving around in town with all my heaters on, plus I have air shutters to help with keeping the heat.

ABBus · 05-04-2021, 12:44 PM

Quote:

Originally Posted by cadillackid

I run the webasto along with the engine if im driving around in town with all my heaters on, plus I have air shutters to help with keeping the heat.

Air shutters don't help when the thermostat is closed, and having all the heaters (...) on don't help the engine to warm up. Anyway, just my thoughts and your engine

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