M-18 exhaust haze in engine compartment

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pcadkins

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Dec 27, 2019
3
Catalina C27 Olympia, WA
Hello all. new to the forum. I have done a search and guess I am the only one with this problem.

I have a C27, 1984 with a Universal M-18 engine. I have a exhaust leak somewhere on the engine as I can see a very slight haze of "smoke" with the engine compartment light off while using a flashlight.

Soapy water all over the engine and exhaust has yielded nothing, the water box is good and all connections to it are solid.

What I have found is a rather large amount of "air" coming out of the valve cover "breather outlet", the right elbow connector that is immediately forward to the oil cap on the top of the engine. If I place my finger over it to "plug" it, when I remove my finger it sounds like a air compressor releasing it's last 10 psi. Why would this breather vent have so much air or maybe its exhaust coming out?

The engine seems to run just fine without any issues. Cranks on the first 1 - 1 1.5 rotation no abnormalities at all. I was thinking, could the decompression lever not be fully releasing or could this be pressure coming from the crank below the pistons and I am having blowpass from weak rings and the crank case is somehow venting through this top "vent" as there does not seem to be any other vents on the engine.

Thanks a million and so glad I have joined this forum, as a first time sailboat owner in summer of 2019.
 
kloudie1

kloudie1

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Nov 6, 2006
9,894
Hunter 34 Mandeville Louisiana
Welcome to the group!
Couple of things.. First, it would be good to make sure that the crankcase oil is the correct viscosity and type.. next, watch the level carefully to see if it is increasing.. sometimes, fuel leaking into the crankcase oil from the injection pump can cause excessive blow-by .. What you are describing is crankcase blow-by .. gas being forced past the piston rings .. some of that is normal. The outlet of the crankcase breather hose should release the gas into the air intake of the engine so the gas gets burned instead of blowing out into the engine compartment.. There should be a clip or a fitting to hold the hose such that it discharges into the air inlet.. if not, you can put a hose fitting on the air cleaner housing to connect the hose so that the gas gets into the air cleaner housing behind the air cleaner.. It doesn't sound like excessive blow-by, since the engine starts so well.. Other stuff to check would be the breather packing and plates inside the valve cover .. (page 12-14 in attached file) If any of that stuff is missing or damaged, more gas could be allowed to escape than "normal"
 

Attachments

Richard19068

Richard19068

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Jun 11, 2004
1,633
Oday 31 Redondo Beach
I have the same engine and routed the blow-by to the air intake as in the examples in the post from Stu Jackson. I added an air oil separator I got from jegs.com inline between the breather outlet and the air intake

JEGS 52205: Air Oil & Water Separator [4 1/2 in. Height x 1 3/4 in. Diameter] - JEGS

air oil separator, oil separator, in line air oil separator, in-line air oil separator
www.jegs.com www.jegs.com

FWIW a K&N air filter that fits the intake on my M-18 and already has a hole in the top for a barbed fitting for the hose is
K&N RE-0240 Universal Clamp-On Air Filter

Amazon.com: K&N RE-0240 Universal Clamp-On Air Filter: Round Tapered; 1.5 in (38 mm) Flange ID; 3.5 in (89 mm) Height; 3 in (76 mm) Base; 3.5 in (89 mm) Top: Automotive

Buy K&N RE-0240 Universal Clamp-On Air Filter: Round Tapered; 1.5 in (38 mm) Flange ID; 3.5 in (89 mm) Height; 3 in (76 mm) Base; 3.5 in (89 mm) Top: Air Filters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com

Setting this up cleared all the haze from my engine compartment.


Maine Sail had a comment about the benefit of an air oil separator:


Re: K&N air filter breather hose
« Reply #14 on: November 22, 2016, 06:43:27 AM »

Please remember that we are on sailboats that heel when motor sailing. In order to avoid a run-away diesel or excess carbon, it's a good idea to put a "trap" in the PCV line before it hits the manifold or air filter. Even a cheap in-line filter for an air compressor will work to capture any oil before it gets to the manifold. These are often called "oil/air separators" or "oil catch cans".
« Last Edit: November 22, 2016, 06:49:03 AM by mainesail »
Logged
-Maine Sail
 
P

pcadkins

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Dec 27, 2019
3
Catalina C27 Olympia, WA
Thank you all for your detailed and thorough responses, off to the store and the sailboat, for this project, looking for a new cabin smell for 2020!!
 
jssailem

jssailem

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Oct 22, 2014
21,104
CAL 35 Cruiser #21 moored EVERETT WA
Just a possibility could the haze of smoke be something other than exhaust?

I had the water pump fail. The engine room was filled with the fine mist and steam of coolant escaping the water pump.
 
C

Capt jgw

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Feb 8, 2014
1,300
Columbia 36 Muskegon
I doubt it would be anything but blowby. All piston engines have some, but how much is too much is hard to judge. Checking a new or known good engine by putting your thumb across the breather hose and seeing how much pressure developed and then comparing to your own might give you an idea of the health of the rings and valves in your engine. A real compression test would be way more definative but a lot harder to do. A reduction in compression and accompanying increase in blowby can be detected long before running problems will be noticed.
 
MikeHoncho

MikeHoncho

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Dec 28, 2015
1,850
Laser, Hunter H30 Cherubini Tacoma
I’d be concerned with CO. Exhaust is exhaust no matter what orifice it is coming out of.
 
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pcadkins

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Dec 27, 2019
3
Catalina C27 Olympia, WA
I want to say thank you to all the experts that replied, sure enough it was the breather, vent hose attached to intake filter and problem solved, now to get the many years I am sure of ever so slight exhaust smell out of the cabin , think I might just have justification to replace all the 34 yr old mid 80's fabric cushions down below!

Again thank you to all that helped me resolve this issue, boat even feels like it sails better now!!
 
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RoyS

RoyS

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Jun 3, 2012
1,742
Hunter 33 Steamboat Wharf, Hull, MA
The blow-by you described seems excessive to me. On my engine if I put the breather hose end in a cup of water I get a slow stream of bubbles only. How is your engine at starting?
 
RoyS

RoyS

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Jun 3, 2012
1,742
Hunter 33 Steamboat Wharf, Hull, MA
While you are at it, suggest you check your valve lash.
 
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