Seeming engine knock heard right at startup until engine is revved up - L4060

troverman

Active member

Equipment
2019 L4060 HSTC; 2020 Kubota Z421KW-54 zero turn mower
Jun 9, 2015
989
94
43
NH
OK guys, it seems like the engine in my 2019 model year L4060 with somewhere around 400 hours on it is making a knocking sound right when I start it up. It will continue to lightly knock until I rev it up, or until maybe 30 seconds to a minute passes. (I don't rev it high when I rev it, just maybe to 1200RPMs).

I do my own oil changes at or around each 100 hour mark. The first two after factory fill were with Rotella T6 full synthetic 15w40. The last oil change there was a deal on T5 semi-synthetic, same weight. Oil level is full. The knock seemed to start right around the last oil change.

It definitely goes away when the engine is warm, or even just after a few minutes. I wouldn't expect to be hearing "fuel knock" from a modern common rail direct injection diesel. Plus, it never did it for the first few hundred hours.

Thoughts? I know the dealer will say its normal.
 

JerryMT

Active member

Equipment
Kubota M4500, NH TD95D,Ford 4610
Jun 17, 2017
306
40
28
The Palouse - North Idaho
OK guys, it seems like the engine in my 2019 model year L4060 with somewhere around 400 hours on it is making a knocking sound right when I start it up. It will continue to lightly knock until I rev it up, or until maybe 30 seconds to a minute passes. (I don't rev it high when I rev it, just maybe to 1200RPMs).

I do my own oil changes at or around each 100 hour mark. The first two after factory fill were with Rotella T6 full synthetic 15w40. The last oil change there was a deal on T5 semi-synthetic, same weight. Oil level is full. The knock seemed to start right around the last oil change.

It definitely goes away when the engine is warm, or even just after a few minutes. I wouldn't expect to be hearing "fuel knock" from a modern common rail direct injection diesel. Plus, it never did it for the first few hundred hours.

Thoughts? I know the dealer will say its normal.
Has it always done this? What are the ambient temperatures when this happens? Are you using a starting aid? (glow plugs and/or block heater)

Diesel's ignite fuel by the temperature generated in the compression process. During a cold start, the cold wall of the cylinder act as a deactivating surface for the chemical reactions in the combustion process. Further, on a cold day, the peak temperature during compression is less making it harder for the combustion process to start. Modern engine or not, these are the physical facts.

While it is certainly true that cold oil doesn't flow as well as warm oil, I presume you are using the lube oils the OEM has recommended. The residual oil film in the journal bearings provides lube while cranking until the oil pump can deliver oil.

None of our tractors are Tier IV compliant but they all make the typical combustion knock sound when starting in cold weather without the block heater being used for pre-start warming. Our 1979 M4500 Kubota is probably the worst. This clears up relatively quickly (<1 minute) and with a warm engine the knock does not occur on start up.

Based on your description of the problem I suspect what you are experiencing is just cold start knock.

A lot of Kubota owners on these forums use 5W40 full synthetic oil year around. If you are concerned that the knock you are experiencing is a lube oil issue, you might consider using the 5W40 synthetic oil and see if it makes any difference regarding starting knock. You will see a difference in the cranking speed due to the lower oil viscosity relative to 15W40.
 

troverman

Active member

Equipment
2019 L4060 HSTC; 2020 Kubota Z421KW-54 zero turn mower
Jun 9, 2015
989
94
43
NH
Thanks Jerry, it has not always done this, which is why I was somewhat concerned. I’m very familiar with diesels, having owned many diesel pickups and a few tractors. It has been doing this even in the summer, so nothing cold weather related. I don’t use a block heater, even in NH where we see below zero weather during the winter. These modern Kubota’s start as well as a modern diesel pickup without being plugged in.

I think I’ll monitor it and at my next oil change, switch back to T6 and see if anything changes. It could be fuel knock as you mention, although I’m not sure why it just started recently.
 

troverman

Active member

Equipment
2019 L4060 HSTC; 2020 Kubota Z421KW-54 zero turn mower
Jun 9, 2015
989
94
43
NH
I refuel out of a transfer tank in the bed of my pickup, which is equipped with a hydrosorb filter. Fuel always comes from the same location; I buy off road. Main fuel filter on the tractor was replaced this spring maybe 150 hours ago. No water in the separator/filter.
 

kubotafreak

Active member

Equipment
GRAND l6060, L3560, B6100, gr2100, tg 1860, g1800, g1900, g2160
Sep 20, 2018
533
134
43
Arkansas, US
Fuel would be my first suspect as mentioned previously. Check the water separator often. It is small and can fill up fast. You might try installing a new spin on fuel filter.
My l60 is the opposite. Mine seems to be quiet until about 5 min mark when you can actually hear it get louder, and the diesel clatter is more pronounced (seems the computer waits to provide full fueling). Raising the speed just drowns out any of this, in effect hiding the differences.
 

Dennis.D

Active member

Equipment
L6060, Erskine hydraulic snow blower, back hoe
Feb 16, 2018
110
39
28
Central, ME,USA
It might be worth taking it to your dealer and leave it over night and get their opinion on the noise at start up. You can always have the oil analyzed at a place like Blackstone Laboratories, it might give you peace of mind. My 6060 has always had a slight knocking noise at idle on start up. 1200 to 1500 RPM's it will go away and it's gone after 30 sec to a couple minutes depending on temperature.
 
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kubotafreak

Active member

Equipment
GRAND l6060, L3560, B6100, gr2100, tg 1860, g1800, g1900, g2160
Sep 20, 2018
533
134
43
Arkansas, US
OEM filter or aftermarket? Just curious. Not knocking non oem filters, but sometimes you will run across an incompatibility issue. If you don't figure it out, you may spin on an oem filter just to be sure. Wont cost you much in oil...
 

edritchey

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Lifetime Member

Equipment
Kubota SSV75, IHC 244, Ferris IS800Z
Jul 19, 2014
626
72
28
Wellsville, PA
I had a MX5800 that would do the same thing it didn't seem to harm anything I sold it because I needed a bigger machine it was a great little tractor IMO.
 

Blue316

New member

Equipment
2016 L4060, Ford flail mower, etc.
Sep 19, 2021
3
0
1
Vashon Wa
OK guys, it seems like the engine in my 2019 model year L4060 with somewhere around 400 hours on it is making a knocking sound right when I start it up. It will continue to lightly knock until I rev it up, or until maybe 30 seconds to a minute passes. (I don't rev it high when I rev it, just maybe to 1200RPMs).

I do my own oil changes at or around each 100 hour mark. The first two after factory fill were with Rotella T6 full synthetic 15w40. The last oil change there was a deal on T5 semi-synthetic, same weight. Oil level is full. The knock seemed to start right around the last oil change.

It definitely goes away when the engine is warm, or even just after a few minutes. I wouldn't expect to be hearing "fuel knock" from a modern common rail direct injection diesel. Plus, it never did it for the first few hundred hours.

Thoughts? I know the dealer will say its normal.

The only way to be sure would be to check your oil pressure. I would want to see it cranking, running, cold and warm.
 

troverman

Active member

Equipment
2019 L4060 HSTC; 2020 Kubota Z421KW-54 zero turn mower
Jun 9, 2015
989
94
43
NH
Well, the low oil pressure lamp goes out immediately when the engine starts, so it must be above whatever minimum Kubota established...
 

lynnmor

Active member

Equipment
B2601-1
May 3, 2021
207
103
43
Red Lion
I'll say this one more time, try a cetane booster, here is why:

The cetane number (CN) is an indicator of the ignitibility of diesel fuels. ... If the ignition delay is high, for example due to a low cetane number, most of the injected fuel burns explosively. This leads to the typical loud diesel combustion noise (“knocking”).
 
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troverman

Active member

Equipment
2019 L4060 HSTC; 2020 Kubota Z421KW-54 zero turn mower
Jun 9, 2015
989
94
43
NH
I'll say this one more time, try a cetane booster, here is why:

The cetane number (CN) is an indicator of the ignitibility of diesel fuels. ... If the ignition delay is high, for example due to a low cetane number, most of the injected fuel burns explosively. This leads to the typical loud diesel combustion noise (“knocking”).
Fair enough. I have some on hand, some from Ford and some from Archoil. My diesel truck doesn't knock and it comes from the same major refueling station, so I figured that might not be it. Won't hurt to try.
 

CGMKCM

Member

Equipment
RVT-1100C, ZD323, L4760
Jan 26, 2021
82
30
18
Randolph county N.C.
My 4760 Is a little loud at idle for the first 20 seconds or so after cold start up. I consider it to be normal and let it idle till noise goes away before accelerating.
 

m7060

Member
Lifetime Member
Jul 13, 2014
40
4
8
london, ky
OK guys, it seems like the engine in my 2019 model year L4060 with somewhere around 400 hours on it is making a knocking sound right when I start it up. It will continue to lightly knock until I rev it up, or until maybe 30 seconds to a minute passes. (I don't rev it high when I rev it, just maybe to 1200RPMs).

I do my own oil changes at or around each 100 hour mark. The first two after factory fill were with Rotella T6 full synthetic 15w40. The last oil change there was a deal on T5 semi-synthetic, same weight. Oil level is full. The knock seemed to start right around the last oil change.

It definitely goes away when the engine is warm, or even just after a few minutes. I wouldn't expect to be hearing "fuel knock" from a modern common rail direct injection diesel. Plus, it never did it for the first few hundred hours.

Thoughts? I know the dealer will say its normal.
If you changed the engine oil filter at the same time, you could possibly have gotten one with a defective anti drain back check valve. My 2014 M7060 has had initial startup knock since the first 100 hours. Last 3 to 6 seconds.
 
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