Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 13-07-2020, 15:35   #16
Registered User

Join Date: Sep 2007
Boat: GibSea 472
Posts: 520
Re: Blow by in a diesel engine. What is the cause and how to fix.

Some times, the blowby is caused by blown head gasket, ou more precisely a beguining of slight crack in this gasket. Things will get worst with time. The best way to findout, is to remove the valve cover, and run the engine: a valve bay be leaking, or the head gasket starting to loose it. It is not a big deal.
Elie is offline   Reply With Quote
Old 13-07-2020, 16:07   #17
Moderator Emeritus
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
Re: Blow by in a diesel engine. What is the cause and how to fix.

I’m trying to think of how a head gasket could cause blow by, and coming up with a blank.
Other than valve guides, there is no connection possible between the combustion chamber and the crankcase?
Oil galley maybe? But wouldn’t that burn oil like mad as it got blown in on the intake stroke?
a64pilot is offline   Reply With Quote
Old 13-07-2020, 16:12   #18
Registered User
 
Bill O's Avatar

Join Date: Jul 2015
Boat: Bruce Bingham Christina 49
Posts: 3,328
Re: Blow by in a diesel engine. What is the cause and how to fix.

Quote:
Originally Posted by a64pilot View Post
I’m trying to think of how a head gasket could cause blow by, and coming up with a blank.
Other than valve guides, there is no connection possible between the combustion chamber and the crankcase?
Oil galley maybe? But wouldn’t that burn oil like mad as it got blown in on the intake stroke?

Totally agree, it's not the head gasket.
__________________
Bill O.
KB3YMH
https://phoenixketch.blogspot.com/
Bill O is offline   Reply With Quote
Old 15-07-2020, 11:05   #19
Registered User

Join Date: Sep 2007
Boat: GibSea 472
Posts: 520
Re: Blow by in a diesel engine. What is the cause and how to fix.

If the head gasket is blown, and the exhaust gases will pass trough the valves pushrods, it will create an back pressure in the crankcase. It hapen long time ago when my previous boat's engine a Volvo MD17HD head gasket developped a leak and failed. In fact a blown head gasket may create many strange thing like mixing water wiith oil, blowing cooling water through the exhaust, and many other difficult to diagnostic problems.
Elie is offline   Reply With Quote
Old 24-12-2020, 07:43   #20
Registered User
 
wingssail's Avatar

Join Date: Jan 2010
Location: On Vessel WINGS, wherever there's an ocean, currently in Mexico
Boat: Serendipity 43
Posts: 5,508
Send a message via AIM to wingssail Send a message via Skype™ to wingssail
Re: Blow by in a diesel engine. What is the cause and how to fix.

What if the problem is opposite, or just slightly more complicated?

Yesterday, while briefly operating at higher than normal RPM, we had big clouds of oil smoke out the exhaust and loss of oil out the dipstick tube. Otherwise no symptoms.

Back at the dock I checked for excessive blow-by by removing the hose from the breather vent. I found it was clear and I found almost NO PRESSURE on the breather vent outlet even at 3000RPM.

Should my Yanmar 3JH with 6500 hours have some amount of blowby, especially considering the symptoms exhibited yesterday?
__________________
These lines upon my face tell you the story of who I am but these stories don't mean anything
when you've got no one to tell them to Fred Roswold Wings https://wingssail.blogspot.com/
wingssail is offline   Reply With Quote
Old 24-12-2020, 07:53   #21
Registered User
 
Scubaseas's Avatar

Join Date: Apr 2005
Location: Seabroook Texas or Southern Maine
Boat: Pearson 323, Tayana V42CC
Posts: 1,501
Images: 1
Re: Blow by in a diesel engine. What is the cause and how to fix.

Quote:
Originally Posted by wingssail View Post
What if the problem is opposite, or just slightly more complicated?

Yesterday, while briefly operating at higher than normal RPM, we had big clouds of oil smoke out the exhaust and loss of oil out the dipstick tube. Otherwise no symptoms.

Back at the dock I checked for excessive blow-by by removing the hose from the breather vent. I found it was clear and I found almost NO PRESSURE on the breather vent outlet even at 3000RPM.

Should my Yanmar 3JH with 6500 hours have some amount of blowby, especially considering the symptoms exhibited yesterday?
That sounds like a clogged breather baffle in the valve cover. There is a screen under the valve cover that stops gack from clogging up the breather hose from valve cover to air cleaner. Typically if your dipstick pukes only at high rpm it's something in the crankcase vent system.

https://www.atlantismarine.co.uk/Ima...ile/Tp5591.pdf
Group 5 part #52
Scubaseas is offline   Reply With Quote
Old 24-12-2020, 08:52   #22
Registered User

Join Date: Nov 2014
Posts: 1,613
Re: Blow by in a diesel engine. What is the cause and how to fix.

Quote:
Originally Posted by a64pilot View Post
I’m trying to think of how a head gasket could cause blow by, and coming up with a blank.
Other than valve guides, there is no connection possible between the combustion chamber and the crankcase?
Oil galley maybe? But wouldn’t that burn oil like mad as it got blown in on the intake stroke?
A leaking head gasket could easily pressurize a pushrod cavity or a cam chain cavity along side of or between cylinders, thereby causing excessive base pressure pressure and leakage out of the dipstick or crankcase breather.
DougR is offline   Reply With Quote
Old 24-12-2020, 09:11   #23
Registered User

Join Date: Nov 2014
Posts: 1,613
Re: Blow by in a diesel engine. What is the cause and how to fix.

Quote:
Originally Posted by wingssail View Post
What if the problem is opposite, or just slightly more complicated?

Yesterday, while briefly operating at higher than normal RPM, we had big clouds of oil smoke out the exhaust and loss of oil out the dipstick tube. Otherwise no symptoms.

Back at the dock I checked for excessive blow-by by removing the hose from the breather vent. I found it was clear and I found almost NO PRESSURE on the breather vent outlet even at 3000RPM.

Should my Yanmar 3JH with 6500 hours have some amount of blowby, especially considering the symptoms exhibited yesterday?
Yes, at 6500 hours there will be a degree of wear, and there will be some blow by.

When you ran the 3000 rpm test at the dock was the engine in neutral or in gear? If in neutral, there is almost no fuel being used to spin the engine up to that rpm, therefore very little combustion pressure to cause blow by. If the engine was in gear it would have required much more fuel to reach 3000 rpm, ( hence combustion pressure) and consequently more blow by.

I like to check blow-by with the oil fill cap removed instead of pulling off the breather tube. That eliminates the possibility of a restricted breather system.
DougR is offline   Reply With Quote
Old 24-12-2020, 10:37   #24
Registered User
 
Scubaseas's Avatar

Join Date: Apr 2005
Location: Seabroook Texas or Southern Maine
Boat: Pearson 323, Tayana V42CC
Posts: 1,501
Images: 1
Re: Blow by in a diesel engine. What is the cause and how to fix.

Quote:
Originally Posted by Cliffhanger View Post
One of the engines on my cat has developed a problem. (Volvo Penta MD2020.) Lots of fumes coming out of the filler cap and/or dipstick when open. But otherwise the engine runs perfectly. No smoke out of the exhaust, no lack of power, idles and runs smoothly. It has done about 1500 hrs and has overheated a couple of times - a problem that is now fixed. So, I'm not really sure what is wrong. I am guessing blow-by and perhaps carbon build-up on the compression rings but not sure.

So, any ideas what the problem is and what is the best way to fix it?
Take off the valve cover and clean out the screen and passages that is for the crank case vent system. The crank vents back into the intake manifold via the valve cover. The screen is in the center of the valve cover.

Best way to test rings (for blowby) is to do a cylinder leak down test. Most people have no idea how to do this and it requires an air source and a leak down tester that will work on your engine.

Best way to measure crank case pressure is with a manometer on the oil filler cap or on the breather hose, breather hose being the most common place to tap the system. The MD 2020 has the breather hose plugged off and vents crankcase pressure internally through the valve cover.

Yes a head gasket can cause excessive blowby but it's rare. More often the cooling system is effected but if you loose the compression ring seal on the head gasket and compression goes into an oil return or pushrod hole you will have ton of blowby. Very hard to imagine this on a MD2020.
Scubaseas is offline   Reply With Quote
Reply

Tags
diesel, engine

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Exhaust Riser: quick fix and permanent fix options wyb2 Engines and Propulsion Systems 23 09-12-2021 07:06
Lowering Main in a Blow w/o Engine theway Seamanship & Boat Handling 54 08-03-2015 13:09
Diesel smoke now considered to cause cancer sdowney717 Our Community 31 15-07-2012 22:40
Cavitation Cause and Remedy cat man do Propellers & Drive Systems 10 03-05-2012 04:41

Advertise Here


All times are GMT -7. The time now is 06:52.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.